Merge branch 'master' into access-tokens

72 files changed, 1163 insertions, 666 deletions

diff --git a/src/libexpr/common-eval-args.cc b/src/libexpr/common-eval-args.cc
index d71aa22f1..10c1a6975 100644
--- a/src/libexpr/common-eval-args.cc
+++ b/src/libexpr/common-eval-args.cc
@@ -76,7 +76,7 @@ Path lookupFileArg(EvalState & state, string s)
     if (isUri(s)) {
         return state.store->toRealPath(
             fetchers::downloadTarball(
-                state.store, resolveUri(s), Headers {}, "source", false).first.storePath);
+                state.store, resolveUri(s), "source", false).first.storePath);
     } else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
         Path p = s.substr(1, s.size() - 2);
         return state.findFile(p);
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 139067f20..883fc27a7 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -356,6 +356,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
     , sEpsilon(symbols.create(""))
     , repair(NoRepair)
     , store(store)
+    , regexCache(makeRegexCache())
     , baseEnv(allocEnv(128))
     , staticBaseEnv(false, 0)
 {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 80078d8a5..0e1f61baa 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -6,7 +6,6 @@
 #include "symbol-table.hh"
 #include "config.hh"
 
-#include <regex>
 #include <map>
 #include <optional>
 #include <unordered_map>
@@ -65,6 +64,11 @@ typedef std::list<SearchPathElem> SearchPath;
 void initGC();
 
 
+struct RegexCache;
+
+std::shared_ptr<RegexCache> makeRegexCache();
+
+
 class EvalState
 {
 public:
@@ -120,7 +124,7 @@ private:
     std::unordered_map<Path, Path> resolvedPaths;
 
     /* Cache used by prim_match(). */
-    std::unordered_map<std::string, std::regex> regexCache;
+    std::shared_ptr<RegexCache> regexCache;
 
 public:
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 01f464859..b4ede542c 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -48,17 +48,17 @@ static std::tuple<fetchers::Tree, FlakeRef, FlakeRef> fetchOrSubstituteTree(
                 resolvedRef = originalRef.resolve(state.store);
                 auto fetchedResolved = lookupInFlakeCache(flakeCache, originalRef);
                 if (!fetchedResolved) fetchedResolved.emplace(resolvedRef.fetchTree(state.store));
-                flakeCache.push_back({resolvedRef, fetchedResolved.value()});
-                fetched.emplace(fetchedResolved.value());
+                flakeCache.push_back({resolvedRef, *fetchedResolved});
+                fetched.emplace(*fetchedResolved);
             }
             else {
                 throw Error("'%s' is an indirect flake reference, but registry lookups are not allowed", originalRef);
             }
         }
-        flakeCache.push_back({originalRef, fetched.value()});
+        flakeCache.push_back({originalRef, *fetched});
     }
 
-    auto [tree, lockedRef] = fetched.value();
+    auto [tree, lockedRef] = *fetched;
 
     debug("got tree '%s' from '%s'",
         state.store->printStorePath(tree.storePath), lockedRef);
@@ -215,10 +215,9 @@ static Flake getFlake(
 
     if (auto outputs = vInfo.attrs->get(sOutputs)) {
         expectType(state, tLambda, *outputs->value, *outputs->pos);
-        flake.vOutputs = allocRootValue(outputs->value);
 
-        if ((*flake.vOutputs)->lambda.fun->matchAttrs) {
-            for (auto & formal : (*flake.vOutputs)->lambda.fun->formals->formals) {
+        if (outputs->value->lambda.fun->matchAttrs) {
+            for (auto & formal : outputs->value->lambda.fun->formals->formals) {
                 if (formal.name != state.sSelf)
                     flake.inputs.emplace(formal.name, FlakeInput {
                         .ref = parseFlakeRef(formal.name)
@@ -248,7 +247,7 @@ Flake getFlake(EvalState & state, const FlakeRef & originalRef, bool allowLookup
 }
 
 /* Compute an in-memory lock file for the specified top-level flake,
-   and optionally write it to file, it the flake is writable. */
+   and optionally write it to file, if the flake is writable. */
 LockedFlake lockFlake(
     EvalState & state,
     const FlakeRef & topRef,
@@ -367,7 +366,7 @@ LockedFlake lockFlake(
 
                 /* If we have an --update-input flag for an input
                    of this input, then we must fetch the flake to
-                   to update it. */
+                   update it. */
                 auto lb = lockFlags.inputUpdates.lower_bound(inputPath);
 
                 auto hasChildUpdate =
diff --git a/src/libexpr/flake/flake.hh b/src/libexpr/flake/flake.hh
index c2bb2888b..69c779af8 100644
--- a/src/libexpr/flake/flake.hh
+++ b/src/libexpr/flake/flake.hh
@@ -34,7 +34,6 @@ struct Flake
     std::optional<std::string> description;
     std::shared_ptr<const fetchers::Tree> sourceInfo;
     FlakeInputs inputs;
-    RootValue vOutputs;
     ~Flake();
 };
 
diff --git a/src/libexpr/flake/flakeref.cc b/src/libexpr/flake/flakeref.cc
index 6363446f6..d5c2ffe66 100644
--- a/src/libexpr/flake/flakeref.cc
+++ b/src/libexpr/flake/flakeref.cc
@@ -1,6 +1,7 @@
 #include "flakeref.hh"
 #include "store-api.hh"
 #include "url.hh"
+#include "url-parts.hh"
 #include "fetchers.hh"
 #include "registry.hh"
 
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index a74846944..78431f000 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -1,5 +1,6 @@
 #include "lockfile.hh"
 #include "store-api.hh"
+#include "url-parts.hh"
 
 #include <nlohmann/json.hpp>
 
diff --git a/src/libexpr/json-to-value.cc b/src/libexpr/json-to-value.cc
index 76e1a26bf..9ca5ac86d 100644
--- a/src/libexpr/json-to-value.cc
+++ b/src/libexpr/json-to-value.cc
@@ -115,6 +115,14 @@ public:
     {
         return handle_value<void(Value&, const char*)>(mkString, val.c_str());
     }
+#if NLOHMANN_JSON_VERSION_MAJOR >= 3 && NLOHMANN_JSON_VERSION_MINOR >= 8
+    bool binary(binary_t&)
+    {
+        // This function ought to be unreachable
+        assert(false);
+        return true;
+    }
+#endif
 
     bool start_object(std::size_t len)
     {
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index d84b150e0..687a8ccda 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -42,6 +42,6 @@ $(eval $(call install-file-in, $(d)/nix-expr.pc, $(prefix)/lib/pkgconfig, 0644))
 $(foreach i, $(wildcard src/libexpr/flake/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix/flake, 0644)))
 
-$(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh
+$(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh $(d)/primops/derivation.nix.gen.hh
 
 $(d)/flake/flake.cc: $(d)/flake/call-flake.nix.gen.hh
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 28e31f46b..a4c84c526 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -614,8 +614,7 @@ Path resolveExprPath(Path path)
         // Basic cycle/depth limit to avoid infinite loops.
         if (++followCount >= maxFollow)
             throw Error("too many symbolic links encountered while traversing the path '%s'", path);
-        if (lstat(path.c_str(), &st))
-            throw SysError("getting status of '%s'", path);
+        st = lstat(path);
         if (!S_ISLNK(st.st_mode)) break;
         path = absPath(readLink(path), dirOf(path));
     }
@@ -719,7 +718,7 @@ std::pair<bool, std::string> EvalState::resolveSearchPathElem(const SearchPathEl
     if (isUri(elem.second)) {
         try {
             res = { true, store->toRealPath(fetchers::downloadTarball(
-                        store, resolveUri(elem.second), Headers {}, "source", false).first.storePath) };
+                        store, resolveUri(elem.second), "source", false).first.storePath) };
         } catch (FileTransferError & e) {
             logWarning({
                 .name = "Entry download",
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index d0b0c57b2..2b304aab0 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2236,6 +2236,10 @@ static RegisterPrimOp primop_catAttrs({
 static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     state.forceValue(*args[0], pos);
+    if (args[0]->type == tPrimOpApp || args[0]->type == tPrimOp) {
+        state.mkAttrs(v, 0);
+        return;
+    }
     if (args[0]->type != tLambda)
         throw TypeError({
             .hint = hintfmt("'functionArgs' requires a function"),
@@ -3085,17 +3089,25 @@ static RegisterPrimOp primop_hashString({
     .fun = prim_hashString,
 });
 
-/* Match a regular expression against a string and return either
-   ‘null’ or a list containing substring matches. */
+struct RegexCache
+{
+    std::unordered_map<std::string, std::regex> cache;
+};
+
+std::shared_ptr<RegexCache> makeRegexCache()
+{
+    return std::make_shared<RegexCache>();
+}
+
 void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto re = state.forceStringNoCtx(*args[0], pos);
 
     try {
 
-        auto regex = state.regexCache.find(re);
-        if (regex == state.regexCache.end())
-            regex = state.regexCache.emplace(re, std::regex(re, std::regex::extended)).first;
+        auto regex = state.regexCache->cache.find(re);
+        if (regex == state.regexCache->cache.end())
+            regex = state.regexCache->cache.emplace(re, std::regex(re, std::regex::extended)).first;
 
         PathSet context;
         const std::string str = state.forceString(*args[1], context, pos);
@@ -3565,13 +3577,11 @@ void EvalState::createBaseEnv()
 
     /* Add a wrapper around the derivation primop that computes the
        `drvPath' and `outPath' attributes lazily. */
-    try {
-        string path = canonPath(settings.nixDataDir + "/nix/corepkgs/derivation.nix", true);
-        sDerivationNix = symbols.create(path);
-        evalFile(path, v);
-        addConstant("derivation", v);
-    } catch (SysError &) {
-    }
+    sDerivationNix = symbols.create("//builtin/derivation.nix");
+    eval(parse(
+        #include "primops/derivation.nix.gen.hh"
+        , foFile, sDerivationNix, "/", staticBaseEnv), v);
+    addConstant("derivation", v);
 
     /* Now that we've added all primops, sort the `builtins' set,
        because attribute lookups expect it to be sorted. */
diff --git a/src/libexpr/primops/derivation.nix b/src/libexpr/primops/derivation.nix
new file mode 100644
index 000000000..c0fbe8082
--- /dev/null
+++ b/src/libexpr/primops/derivation.nix
@@ -0,0 +1,27 @@
+/* This is the implementation of the ‘derivation’ builtin function.
+   It's actually a wrapper around the ‘derivationStrict’ primop. */
+
+drvAttrs @ { outputs ? [ "out" ], ... }:
+
+let
+
+  strict = derivationStrict drvAttrs;
+
+  commonAttrs = drvAttrs // (builtins.listToAttrs outputsList) //
+    { all = map (x: x.value) outputsList;
+      inherit drvAttrs;
+    };
+
+  outputToAttrListElement = outputName:
+    { name = outputName;
+      value = commonAttrs // {
+        outPath = builtins.getAttr outputName strict;
+        drvPath = strict.drvPath;
+        type = "derivation";
+        inherit outputName;
+      };
+    };
+
+  outputsList = map outputToAttrListElement outputs;
+
+in (builtins.head outputsList).value
diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index cef85cfef..1a064ed5c 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -3,8 +3,7 @@
 #include "store-api.hh"
 #include "fetchers.hh"
 #include "url.hh"
-
-#include <regex>
+#include "url-parts.hh"
 
 namespace nix {
 
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index 3001957b4..06e8304b8 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -201,8 +201,8 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
 
     auto storePath =
         unpack
-        ? fetchers::downloadTarball(state.store, *url, Headers {}, name, (bool) expectedHash).first.storePath
-        : fetchers::downloadFile(state.store, *url, Headers{}, name, (bool) expectedHash).storePath;
+        ? fetchers::downloadTarball(state.store, *url, name, (bool) expectedHash).first.storePath
+        : fetchers::downloadFile(state.store, *url, name, (bool) expectedHash).storePath;
 
     auto path = state.store->toRealPath(storePath);
 
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 62807e53b..36d44f6e1 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -73,7 +73,7 @@ public:
 
     StorePath computeStorePath(Store & store) const;
 
-    // Convience functions for common attributes.
+    // Convenience functions for common attributes.
     std::string getType() const;
     std::optional<Hash> getNarHash() const;
     std::optional<std::string> getRef() const;
@@ -118,15 +118,15 @@ struct DownloadFileResult
 DownloadFileResult downloadFile(
     ref<Store> store,
     const std::string & url,
-    const Headers & headers,
     const std::string & name,
-    bool immutable);
+    bool immutable,
+    const Headers & headers = {});
 
 std::pair<Tree, time_t> downloadTarball(
     ref<Store> store,
     const std::string & url,
-    const Headers & headers,
     const std::string & name,
-    bool immutable);
+    bool immutable,
+    const Headers & headers = {});
 
 }
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 5ca0f8521..ad7638d73 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -3,6 +3,7 @@
 #include "globals.hh"
 #include "tarfile.hh"
 #include "store-api.hh"
+#include "url-parts.hh"
 
 #include <sys/time.h>
 
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 443644639..142b8b87c 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -4,6 +4,7 @@
 #include "globals.hh"
 #include "store-api.hh"
 #include "types.hh"
+#include "url-parts.hh"
 
 #include <optional>
 #include <nlohmann/json.hpp>
@@ -19,9 +20,9 @@ struct DownloadUrl
         : url(url), headers(headers) { }
 };
 
-// A github or gitlab url
-const static std::string urlRegexS = "[a-zA-Z0-9.]*"; // FIXME: check
-std::regex urlRegex(urlRegexS, std::regex::ECMAScript);
+// A github or gitlab host
+const static std::string hostRegexS = "[a-zA-Z0-9.]*"; // FIXME: check
+std::regex hostRegex(hostRegexS, std::regex::ECMAScript);
 
 struct GitArchiveInputScheme : InputScheme
 {
@@ -64,7 +65,7 @@ struct GitArchiveInputScheme : InputScheme
                 ref = value;
             }
             else if (name == "host") {
-                if (!std::regex_match(value, urlRegex))
+                if (!std::regex_match(value, hostRegex))
                     throw BadURL("URL '%s' contains an invalid instance host", url.url);
                 host_url = value;
             }
@@ -204,7 +205,7 @@ struct GitArchiveInputScheme : InputScheme
 
         auto url = getDownloadUrl(input);
 
-        auto [tree, lastModified] = downloadTarball(store, url.url, url.headers, "source", true);
+        auto [tree, lastModified] = downloadTarball(store, url.url, "source", true, url.headers);
 
         input.attrs.insert_or_assign("lastModified", lastModified);
 
@@ -247,7 +248,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
         auto json = nlohmann::json::parse(
             readFile(
                 store->toRealPath(
-                    downloadFile(store, url, headers, "source", false).storePath)));
+                    downloadFile(store, url, "source", false, headers).storePath)));
         auto rev = Hash::parseAny(std::string { json["sha"] }, htSHA1);
         debug("HEAD revision for '%s' is %s", url, rev.gitRev());
         return rev;
@@ -310,7 +311,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         auto json = nlohmann::json::parse(
             readFile(
                 store->toRealPath(
-                    downloadFile(store, url, headers, "source", false).storePath)));
+                    downloadFile(store, url, "source", false, headers).storePath)));
         auto rev = Hash::parseAny(std::string(json[0]["id"]), htSHA1);
         debug("HEAD revision for '%s' is %s", url, rev.gitRev());
         return rev;
diff --git a/src/libfetchers/indirect.cc b/src/libfetchers/indirect.cc
index b981d4d8e..74332ae3d 100644
--- a/src/libfetchers/indirect.cc
+++ b/src/libfetchers/indirect.cc
@@ -1,4 +1,5 @@
 #include "fetchers.hh"
+#include "url-parts.hh"
 
 namespace nix::fetchers {
 
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 3e76ffc4d..d80c2ea7a 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -3,6 +3,7 @@
 #include "globals.hh"
 #include "tarfile.hh"
 #include "store-api.hh"
+#include "url-parts.hh"
 
 #include <sys/time.h>
 
diff --git a/src/libfetchers/registry.cc b/src/libfetchers/registry.cc
index 551e7684a..4367ee810 100644
--- a/src/libfetchers/registry.cc
+++ b/src/libfetchers/registry.cc
@@ -145,7 +145,7 @@ static std::shared_ptr<Registry> getGlobalRegistry(ref<Store> store)
         auto path = settings.flakeRegistry.get();
 
         if (!hasPrefix(path, "/")) {
-            auto storePath = downloadFile(store, path, Headers {}, "flake-registry.json", false).storePath;
+            auto storePath = downloadFile(store, path, "flake-registry.json", false).storePath;
             if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
                 store2->addPermRoot(storePath, getCacheDir() + "/nix/flake-registry.json");
             path = store->toRealPath(storePath);
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index cf6d6e3d2..ca49482a9 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -12,9 +12,9 @@ namespace nix::fetchers {
 DownloadFileResult downloadFile(
     ref<Store> store,
     const std::string & url,
-    const Headers & headers,
     const std::string & name,
-    bool immutable)
+    bool immutable,
+    const Headers & headers)
 {
     // FIXME: check store
 
@@ -38,7 +38,8 @@ DownloadFileResult downloadFile(
     if (cached && !cached->expired)
         return useCached();
 
-    FileTransferRequest request(url, headers);
+    FileTransferRequest request(url);
+    request.headers = headers;
     if (cached)
         request.expectedETag = getStrAttr(cached->infoAttrs, "etag");
     FileTransferResult res;
@@ -112,9 +113,9 @@ DownloadFileResult downloadFile(
 std::pair<Tree, time_t> downloadTarball(
     ref<Store> store,
     const std::string & url,
-    const Headers & headers,
     const std::string & name,
-    bool immutable)
+    bool immutable,
+    const Headers & headers)
 {
     Attrs inAttrs({
         {"type", "tarball"},
@@ -130,7 +131,7 @@ std::pair<Tree, time_t> downloadTarball(
             getIntAttr(cached->infoAttrs, "lastModified")
         };
 
-    auto res = downloadFile(store, url, headers, name, immutable);
+    auto res = downloadFile(store, url, name, immutable, headers);
 
     std::optional<StorePath> unpackedStorePath;
     time_t lastModified;
@@ -225,7 +226,7 @@ struct TarballInputScheme : InputScheme
 
     std::pair<Tree, Input> fetch(ref<Store> store, const Input & input) override
     {
-        auto tree = downloadTarball(store, getStrAttr(input.attrs, "url"), Headers {}, "source", false).first;
+        auto tree = downloadTarball(store, getStrAttr(input.attrs, "url"), "source", false).first;
         return {std::move(tree), input};
     }
 };
diff --git a/src/libmain/progress-bar.cc b/src/libmain/progress-bar.cc
index be3c06a38..07b45b3b5 100644
--- a/src/libmain/progress-bar.cc
+++ b/src/libmain/progress-bar.cc
@@ -256,7 +256,7 @@ public:
         }
 
         else if (type == resBuildLogLine || type == resPostBuildLogLine) {
-            auto lastLine = trim(getS(fields, 0));
+            auto lastLine = chomp(getS(fields, 0));
             if (!lastLine.empty()) {
                 auto i = state->its.find(act);
                 assert(i != state->its.end());
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 34f844a18..ebc0bd6a4 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -11,6 +11,7 @@
 #include "nar-accessor.hh"
 #include "json.hh"
 #include "thread-pool.hh"
+#include "callback.hh"
 
 #include <chrono>
 #include <future>
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 6e55f83d5..0499273a4 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -17,6 +17,7 @@
 #include "daemon.hh"
 #include "worker-protocol.hh"
 #include "topo-sort.hh"
+#include "callback.hh"
 
 #include <algorithm>
 #include <iostream>
@@ -295,9 +296,21 @@ public:
     ~Worker();
 
     /* Make a goal (with caching). */
-    GoalPtr makeDerivationGoal(const StorePath & drvPath, const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
-    std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(const StorePath & drvPath,
-        const BasicDerivation & drv, BuildMode buildMode = bmNormal);
+
+    /* derivation goal */
+private:
+    std::shared_ptr<DerivationGoal> makeDerivationGoalCommon(
+        const StorePath & drvPath, const StringSet & wantedOutputs,
+        std::function<std::shared_ptr<DerivationGoal>()> mkDrvGoal);
+public:
+    std::shared_ptr<DerivationGoal> makeDerivationGoal(
+        const StorePath & drvPath,
+        const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
+    std::shared_ptr<DerivationGoal> makeBasicDerivationGoal(
+        const StorePath & drvPath, const BasicDerivation & drv,
+        const StringSet & wantedOutputs, BuildMode buildMode = bmNormal);
+
+    /* substitution goal */
     GoalPtr makeSubstitutionGoal(const StorePath & storePath, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);
 
     /* Remove a dead goal. */
@@ -948,10 +961,12 @@ private:
     friend struct RestrictedStore;
 
 public:
-    DerivationGoal(const StorePath & drvPath, const StringSet & wantedOutputs,
-        Worker & worker, BuildMode buildMode = bmNormal);
+    DerivationGoal(const StorePath & drvPath,
+        const StringSet & wantedOutputs, Worker & worker,
+        BuildMode buildMode = bmNormal);
     DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
-        Worker & worker, BuildMode buildMode = bmNormal);
+        const StringSet & wantedOutputs, Worker & worker,
+        BuildMode buildMode = bmNormal);
     ~DerivationGoal();
 
     /* Whether we need to perform hash rewriting if there are valid output paths. */
@@ -993,6 +1008,8 @@ private:
     void tryLocalBuild();
     void buildDone();
 
+    void resolvedFinished();
+
     /* Is the build hook willing to perform the build? */
     HookReply tryBuildHook();
 
@@ -1084,8 +1101,8 @@ private:
 const Path DerivationGoal::homeDir = "/homeless-shelter";
 
 
-DerivationGoal::DerivationGoal(const StorePath & drvPath, const StringSet & wantedOutputs,
-    Worker & worker, BuildMode buildMode)
+DerivationGoal::DerivationGoal(const StorePath & drvPath,
+    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
     : Goal(worker)
     , useDerivation(true)
     , drvPath(drvPath)
@@ -1093,7 +1110,9 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath, const StringSet & want
     , buildMode(buildMode)
 {
     state = &DerivationGoal::getDerivation;
-    name = fmt("building of '%s'", worker.store.printStorePath(this->drvPath));
+    name = fmt(
+        "building of '%s' from .drv file",
+        StorePathWithOutputs { drvPath, wantedOutputs }.to_string(worker.store));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -1102,15 +1121,18 @@ DerivationGoal::DerivationGoal(const StorePath & drvPath, const StringSet & want
 
 
 DerivationGoal::DerivationGoal(const StorePath & drvPath, const BasicDerivation & drv,
-    Worker & worker, BuildMode buildMode)
+    const StringSet & wantedOutputs, Worker & worker, BuildMode buildMode)
     : Goal(worker)
     , useDerivation(false)
     , drvPath(drvPath)
+    , wantedOutputs(wantedOutputs)
     , buildMode(buildMode)
 {
     this->drv = std::make_unique<BasicDerivation>(BasicDerivation(drv));
     state = &DerivationGoal::haveDerivation;
-    name = fmt("building of %s", StorePathWithOutputs { drvPath, drv.outputNames() }.to_string(worker.store));
+    name = fmt(
+        "building of '%s' from in-memory derivation",
+        StorePathWithOutputs { drvPath, drv.outputNames() }.to_string(worker.store));
     trace("created");
 
     mcExpectedBuilds = std::make_unique<MaintainCount<uint64_t>>(worker.expectedBuilds);
@@ -1463,8 +1485,40 @@ void DerivationGoal::inputsRealised()
     /* Determine the full set of input paths. */
 
     /* First, the input derivations. */
-    if (useDerivation)
-        for (auto & [depDrvPath, wantedDepOutputs] : dynamic_cast<Derivation *>(drv.get())->inputDrvs) {
+    if (useDerivation) {
+        auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
+
+        if (!fullDrv.inputDrvs.empty() && fullDrv.type() == DerivationType::CAFloating) {
+            /* We are be able to resolve this derivation based on the
+               now-known results of dependencies. If so, we become a stub goal
+               aliasing that resolved derivation goal */
+            std::optional attempt = fullDrv.tryResolve(worker.store);
+            assert(attempt);
+            Derivation drvResolved { *std::move(attempt) };
+
+            auto pathResolved = writeDerivation(worker.store, drvResolved);
+            /* Add to memotable to speed up downstream goal's queries with the
+               original derivation. */
+            drvPathResolutions.lock()->insert_or_assign(drvPath, pathResolved);
+
+            auto msg = fmt("Resolved derivation: '%s' -> '%s'",
+                worker.store.printStorePath(drvPath),
+                worker.store.printStorePath(pathResolved));
+            act = std::make_unique<Activity>(*logger, lvlInfo, actBuildWaiting, msg,
+                Logger::Fields {
+                       worker.store.printStorePath(drvPath),
+                       worker.store.printStorePath(pathResolved),
+                   });
+
+            auto resolvedGoal = worker.makeDerivationGoal(
+                pathResolved, wantedOutputs, buildMode);
+            addWaitee(resolvedGoal);
+
+            state = &DerivationGoal::resolvedFinished;
+            return;
+        }
+
+        for (auto & [depDrvPath, wantedDepOutputs] : fullDrv.inputDrvs) {
             /* Add the relevant output closures of the input derivation
                `i' as input paths.  Only add the closures of output paths
                that are specified as inputs. */
@@ -1484,6 +1538,7 @@ void DerivationGoal::inputsRealised()
                         worker.store.printStorePath(drvPath), j, worker.store.printStorePath(drvPath));
             }
         }
+    }
 
     /* Second, the input sources. */
     worker.store.computeFSClosure(drv->inputSrcs, inputPaths);
@@ -1611,6 +1666,13 @@ void DerivationGoal::tryToBuild()
 
     actLock.reset();
 
+    state = &DerivationGoal::tryLocalBuild;
+    worker.wakeUp(shared_from_this());
+}
+
+void DerivationGoal::tryLocalBuild() {
+    bool buildLocally = buildMode != bmNormal || parsedDrv->willBuildLocally(worker.store);
+
     /* Make sure that we are allowed to start a build.  If this
        derivation prefers to be done locally, do it even if
        maxBuildJobs is 0. */
@@ -1621,12 +1683,6 @@ void DerivationGoal::tryToBuild()
         return;
     }
 
-    state = &DerivationGoal::tryLocalBuild;
-    worker.wakeUp(shared_from_this());
-}
-
-void DerivationGoal::tryLocalBuild() {
-
     /* If `build-users-group' is not empty, then we have to build as
        one of the members of that group. */
     if (settings.buildUsersGroup != "" && getuid() == 0) {
@@ -1674,7 +1730,34 @@ void DerivationGoal::tryLocalBuild() {
 }
 
 
-void replaceValidPath(const Path & storePath, const Path tmpPath)
+static void chmod_(const Path & path, mode_t mode)
+{
+    if (chmod(path.c_str(), mode) == -1)
+        throw SysError("setting permissions on '%s'", path);
+}
+
+
+/* Move/rename path 'src' to 'dst'. Temporarily make 'src' writable if
+   it's a directory and we're not root (to be able to update the
+   directory's parent link ".."). */
+static void movePath(const Path & src, const Path & dst)
+{
+    auto st = lstat(src);
+
+    bool changePerm = (geteuid() && S_ISDIR(st.st_mode) && !(st.st_mode & S_IWUSR));
+
+    if (changePerm)
+        chmod_(src, st.st_mode | S_IWUSR);
+
+    if (rename(src.c_str(), dst.c_str()))
+        throw SysError("renaming '%1%' to '%2%'", src, dst);
+
+    if (changePerm)
+        chmod_(dst, st.st_mode);
+}
+
+
+void replaceValidPath(const Path & storePath, const Path & tmpPath)
 {
     /* We can't atomically replace storePath (the original) with
        tmpPath (the replacement), so we have to move it out of the
@@ -1682,11 +1765,20 @@ void replaceValidPath(const Path & storePath, const Path tmpPath)
        we're repairing (say) Glibc, we end up with a broken system. */
     Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % random()).str();
     if (pathExists(storePath))
-        rename(storePath.c_str(), oldPath.c_str());
-    if (rename(tmpPath.c_str(), storePath.c_str()) == -1) {
-        rename(oldPath.c_str(), storePath.c_str()); // attempt to recover
-        throw SysError("moving '%s' to '%s'", tmpPath, storePath);
+        movePath(storePath, oldPath);
+
+    try {
+        movePath(tmpPath, storePath);
+    } catch (...) {
+        try {
+            // attempt to recover
+            movePath(oldPath, storePath);
+        } catch (...) {
+            ignoreException();
+        }
+        throw;
     }
+
     deletePath(oldPath);
 }
 
@@ -1905,6 +1997,9 @@ void DerivationGoal::buildDone()
     done(BuildResult::Built);
 }
 
+void DerivationGoal::resolvedFinished() {
+    done(BuildResult::Built);
+}
 
 HookReply DerivationGoal::tryBuildHook()
 {
@@ -2004,13 +2099,6 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-static void chmod_(const Path & path, mode_t mode)
-{
-    if (chmod(path.c_str(), mode) == -1)
-        throw SysError("setting permissions on '%s'", path);
-}
-
-
 int childEntry(void * arg)
 {
     ((DerivationGoal *) arg)->runChild();
@@ -2366,10 +2454,7 @@ void DerivationGoal::startBuilder()
         for (auto & i : inputPaths) {
             auto p = worker.store.printStorePath(i);
             Path r = worker.store.toRealPath(p);
-            struct stat st;
-            if (lstat(r.c_str(), &st))
-                throw SysError("getting attributes of path '%s'", p);
-            if (S_ISDIR(st.st_mode))
+            if (S_ISDIR(lstat(r).st_mode))
                 dirsInChroot.insert_or_assign(p, r);
             else
                 linkOrCopy(r, chrootRootDir + p);
@@ -2949,14 +3034,6 @@ struct RestrictedStore : public LocalFSStore, public virtual RestrictedStoreConf
         goal.addDependency(info.path);
     }
 
-    StorePath addToStoreFromDump(Source & dump, const string & name,
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override
-    {
-        auto path = next->addToStoreFromDump(dump, name, method, hashAlgo, repair);
-        goal.addDependency(path);
-        return path;
-    }
-
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair = NoRepair) override
     {
@@ -3151,9 +3228,7 @@ void DerivationGoal::addDependency(const StorePath & path)
             if (pathExists(target))
                 throw Error("store path '%s' already exists in the sandbox", worker.store.printStorePath(path));
 
-            struct stat st;
-            if (lstat(source.c_str(), &st))
-                throw SysError("getting attributes of path '%s'", source);
+            auto st = lstat(source);
 
             if (S_ISDIR(st.st_mode)) {
 
@@ -3742,29 +3817,6 @@ void DerivationGoal::runChild()
 }
 
 
-static void moveCheckToStore(const Path & src, const Path & dst)
-{
-    /* For the rename of directory to succeed, we must be running as root or
-       the directory must be made temporarily writable (to update the
-       directory's parent link ".."). */
-    struct stat st;
-    if (lstat(src.c_str(), &st) == -1) {
-        throw SysError("getting attributes of path '%1%'", src);
-    }
-
-    bool changePerm = (geteuid() && S_ISDIR(st.st_mode) && !(st.st_mode & S_IWUSR));
-
-    if (changePerm)
-        chmod_(src, st.st_mode | S_IWUSR);
-
-    if (rename(src.c_str(), dst.c_str()))
-        throw SysError("renaming '%1%' to '%2%'", src, dst);
-
-    if (changePerm)
-        chmod_(dst, st.st_mode);
-}
-
-
 void DerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
@@ -3865,7 +3917,7 @@ void DerivationGoal::registerOutputs()
            something like that. */
         canonicalisePathMetaData(actualPath, buildUser ? buildUser->getUID() : -1, inodesSeen);
 
-        debug("scanning for references for output %1 in temp location '%1%'", outputName, actualPath);
+        debug("scanning for references for output '%s' in temp location '%s'", outputName, actualPath);
 
         /* Pass blank Sink as we are not ready to hash data at this stage. */
         NullSink blank;
@@ -3920,7 +3972,6 @@ void DerivationGoal::registerOutputs()
                 outputRewrites[std::string { scratchPath.hashPart() }] = std::string { finalStorePath.hashPart() };
         };
 
-        bool rewritten = false;
         std::optional<StorePathSet> referencesOpt = std::visit(overloaded {
             [&](AlreadyRegistered skippedFinalPath) -> std::optional<StorePathSet> {
                 finish(skippedFinalPath.path);
@@ -3951,7 +4002,9 @@ void DerivationGoal::registerOutputs()
                 StringSource source(*sink.s);
                 restorePath(actualPath, source);
 
-                rewritten = true;
+                /* FIXME: set proper permissions in restorePath() so
+                   we don't have to do another traversal. */
+                canonicalisePathMetaData(actualPath, -1, inodesSeen);
             }
         };
 
@@ -4034,7 +4087,7 @@ void DerivationGoal::registerOutputs()
             [&](DerivationOutputInputAddressed output) {
                 /* input-addressed case */
                 auto requiredFinalPath = output.path;
-                /* Preemtively add rewrite rule for final hash, as that is
+                /* Preemptively add rewrite rule for final hash, as that is
                    what the NAR hash will use rather than normalized-self references */
                 if (scratchPath != requiredFinalPath)
                     outputRewrites.insert_or_assign(
@@ -4108,44 +4161,21 @@ void DerivationGoal::registerOutputs()
                    else. No moving needed. */
                 assert(newInfo.ca);
             } else {
-                /* Temporarily add write perm so we can move, will be fixed
-                   later. */
-                {
-                    struct stat st;
-                    auto & mode = st.st_mode;
-                    if (lstat(actualPath.c_str(), &st))
-                        throw SysError("getting attributes of path '%1%'", actualPath);
-                    mode |= 0200;
-                    /* Try to change the perms, but only if the file isn't a
-                       symlink as symlinks permissions are mostly ignored and
-                       calling `chmod` on it will just forward the call to the
-                       target of the link. */
-                    if (!S_ISLNK(st.st_mode))
-                        if (chmod(actualPath.c_str(), mode) == -1)
-                            throw SysError("changing mode of '%1%' to %2$o", actualPath, mode);
-                }
-                if (rename(
-                        actualPath.c_str(),
-                        worker.store.toRealPath(finalDestPath).c_str()) == -1)
-                    throw SysError("moving build output '%1%' from it's temporary location to the Nix store", finalDestPath);
-                actualPath = worker.store.toRealPath(finalDestPath);
+                auto destPath = worker.store.toRealPath(finalDestPath);
+                movePath(actualPath, destPath);
+                actualPath = destPath;
             }
         }
 
-        /* Get rid of all weird permissions.  This also checks that
-           all files are owned by the build user, if applicable. */
-        canonicalisePathMetaData(actualPath,
-            buildUser && !rewritten ? buildUser->getUID() : -1, inodesSeen);
-
         if (buildMode == bmCheck) {
             if (!worker.store.isValidPath(newInfo.path)) continue;
             ValidPathInfo oldInfo(*worker.store.queryPathInfo(newInfo.path));
             if (newInfo.narHash != oldInfo.narHash) {
                 worker.checkMismatch = true;
                 if (settings.runDiffHook || settings.keepFailed) {
-                    Path dst = worker.store.toRealPath(finalDestPath + checkSuffix);
+                    auto dst = worker.store.toRealPath(finalDestPath + checkSuffix);
                     deletePath(dst);
-                    moveCheckToStore(actualPath, dst);
+                    movePath(actualPath, dst);
 
                     handleDiffHook(
                         buildUser ? buildUser->getUID() : getuid(),
@@ -4265,11 +4295,13 @@ void DerivationGoal::registerOutputs()
     /* Register each output path as valid, and register the sets of
        paths referenced by each of them.  If there are cycles in the
        outputs, this will fail. */
-    ValidPathInfos infos2;
-    for (auto & [outputName, newInfo] : infos) {
-        infos2.push_back(newInfo);
+    {
+        ValidPathInfos infos2;
+        for (auto & [outputName, newInfo] : infos) {
+            infos2.push_back(newInfo);
+        }
+        worker.store.registerValidPaths(infos2);
     }
-    worker.store.registerValidPaths(infos2);
 
     /* In case of a fixed-output derivation hash mismatch, throw an
        exception now that we have registered the output as valid. */
@@ -4281,12 +4313,21 @@ void DerivationGoal::registerOutputs()
        means it's safe to link the derivation to the output hash. We must do
        that for floating CA derivations, which otherwise couldn't be cached,
        but it's fine to do in all cases. */
-    for (auto & [outputName, newInfo] : infos) {
-        /* FIXME: we will want to track this mapping in the DB whether or
-           not we have a drv file. */
-        if (useDerivation)
-            worker.store.linkDeriverToPath(drvPath, outputName, newInfo.path);
+    bool isCaFloating = drv->type() == DerivationType::CAFloating;
+
+    auto drvPathResolved = drvPath;
+    if (!useDerivation && isCaFloating) {
+        /* Once a floating CA derivations reaches this point, it
+           must already be resolved, so we don't bother trying to
+           downcast drv to get would would just be an empty
+           inputDrvs field. */
+        Derivation drv2 { *drv };
+        drvPathResolved = writeDerivation(worker.store, drv2);
     }
+
+    if (useDerivation || isCaFloating)
+        for (auto & [outputName, newInfo] : infos)
+            worker.store.linkDeriverToPath(drvPathResolved, outputName, newInfo.path);
 }
 
 
@@ -4576,7 +4617,7 @@ void DerivationGoal::flushLine()
 
 std::map<std::string, std::optional<StorePath>> DerivationGoal::queryPartialDerivationOutputMap()
 {
-    if (drv->type() != DerivationType::CAFloating) {
+    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
         std::map<std::string, std::optional<StorePath>> res;
         for (auto & [name, output] : drv->outputs)
             res.insert_or_assign(name, output.path(worker.store, drv->name, name));
@@ -4588,7 +4629,7 @@ std::map<std::string, std::optional<StorePath>> DerivationGoal::queryPartialDeri
 
 OutputPathMap DerivationGoal::queryDerivationOutputMap()
 {
-    if (drv->type() != DerivationType::CAFloating) {
+    if (!useDerivation || drv->type() != DerivationType::CAFloating) {
         OutputPathMap res;
         for (auto & [name, output] : drv->outputsAndOptPaths(worker.store))
             res.insert_or_assign(name, *output.second);
@@ -5067,35 +5108,52 @@ Worker::~Worker()
 }
 
 
-GoalPtr Worker::makeDerivationGoal(const StorePath & path,
-    const StringSet & wantedOutputs, BuildMode buildMode)
+std::shared_ptr<DerivationGoal> Worker::makeDerivationGoalCommon(
+    const StorePath & drvPath,
+    const StringSet & wantedOutputs,
+    std::function<std::shared_ptr<DerivationGoal>()> mkDrvGoal)
 {
-    GoalPtr goal = derivationGoals[path].lock(); // FIXME
-    if (!goal) {
-        goal = std::make_shared<DerivationGoal>(path, wantedOutputs, *this, buildMode);
-        derivationGoals.insert_or_assign(path, goal);
+    WeakGoalPtr & abstract_goal_weak = derivationGoals[drvPath];
+    GoalPtr abstract_goal = abstract_goal_weak.lock(); // FIXME
+    std::shared_ptr<DerivationGoal> goal;
+    if (!abstract_goal) {
+        goal = mkDrvGoal();
+        abstract_goal_weak = goal;
         wakeUp(goal);
-    } else
-        (dynamic_cast<DerivationGoal *>(goal.get()))->addWantedOutputs(wantedOutputs);
+    } else {
+        goal = std::dynamic_pointer_cast<DerivationGoal>(abstract_goal);
+        assert(goal);
+        goal->addWantedOutputs(wantedOutputs);
+    }
     return goal;
 }
 
 
+std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drvPath,
+    const StringSet & wantedOutputs, BuildMode buildMode)
+{
+    return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() {
+        return std::make_shared<DerivationGoal>(drvPath, wantedOutputs, *this, buildMode);
+    });
+}
+
+
 std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath & drvPath,
-    const BasicDerivation & drv, BuildMode buildMode)
+    const BasicDerivation & drv, const StringSet & wantedOutputs, BuildMode buildMode)
 {
-    auto goal = std::make_shared<DerivationGoal>(drvPath, drv, *this, buildMode);
-    wakeUp(goal);
-    return goal;
+    return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() {
+        return std::make_shared<DerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode);
+    });
 }
 
 
 GoalPtr Worker::makeSubstitutionGoal(const StorePath & path, RepairFlag repair, std::optional<ContentAddress> ca)
 {
-    GoalPtr goal = substitutionGoals[path].lock(); // FIXME
+    WeakGoalPtr & goal_weak = substitutionGoals[path];
+    GoalPtr goal = goal_weak.lock(); // FIXME
     if (!goal) {
         goal = std::make_shared<SubstitutionGoal>(path, *this, repair, ca);
-        substitutionGoals.insert_or_assign(path, goal);
+        goal_weak = goal;
         wakeUp(goal);
     }
     return goal;
@@ -5526,7 +5584,7 @@ BuildResult LocalStore::buildDerivation(const StorePath & drvPath, const BasicDe
     BuildMode buildMode)
 {
     Worker worker(*this);
-    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, buildMode);
+    auto goal = worker.makeBasicDerivationGoal(drvPath, drv, {}, buildMode);
 
     BuildResult result;
 
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 0885c3d0e..90a3ad1f5 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -4,11 +4,13 @@
 
 namespace nix {
 
-std::string FixedOutputHash::printMethodAlgo() const {
+std::string FixedOutputHash::printMethodAlgo() const
+{
     return makeFileIngestionPrefix(method) + printHashType(hash.type);
 }
 
-std::string makeFileIngestionPrefix(const FileIngestionMethod m) {
+std::string makeFileIngestionPrefix(const FileIngestionMethod m)
+{
     switch (m) {
     case FileIngestionMethod::Flat:
         return "";
@@ -26,7 +28,8 @@ std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash)
         + hash.to_string(Base32, true);
 }
 
-std::string renderContentAddress(ContentAddress ca) {
+std::string renderContentAddress(ContentAddress ca)
+{
     return std::visit(overloaded {
         [](TextHash th) {
             return "text:" + th.hash.to_string(Base32, true);
@@ -37,54 +40,97 @@ std::string renderContentAddress(ContentAddress ca) {
     }, ca);
 }
 
-ContentAddress parseContentAddress(std::string_view rawCa) {
-    auto rest = rawCa;
+std::string renderContentAddressMethod(ContentAddressMethod cam)
+{
+    return std::visit(overloaded {
+        [](TextHashMethod &th) {
+            return std::string{"text:"} + printHashType(htSHA256);
+        },
+        [](FixedOutputHashMethod &fshm) {
+            return "fixed:" + makeFileIngestionPrefix(fshm.fileIngestionMethod) + printHashType(fshm.hashType);
+        }
+    }, cam);
+}
+
+/*
+  Parses content address strings up to the hash.
+ */
+static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & rest)
+{
+    std::string_view wholeInput { rest };
 
     std::string_view prefix;
     {
         auto optPrefix = splitPrefixTo(rest, ':');
         if (!optPrefix)
-            throw UsageError("not a content address because it is not in the form '<prefix>:<rest>': %s", rawCa);
+            throw UsageError("not a content address because it is not in the form '<prefix>:<rest>': %s", wholeInput);
         prefix = *optPrefix;
     }
 
     auto parseHashType_ = [&](){
         auto hashTypeRaw = splitPrefixTo(rest, ':');
         if (!hashTypeRaw)
-            throw UsageError("content address hash must be in form '<algo>:<hash>', but found: %s", rawCa);
+            throw UsageError("content address hash must be in form '<algo>:<hash>', but found: %s", wholeInput);
         HashType hashType = parseHashType(*hashTypeRaw);
         return std::move(hashType);
     };
 
     // Switch on prefix
     if (prefix == "text") {
-        // No parsing of the method, "text" only support flat.
+        // No parsing of the ingestion method, "text" only support flat.
         HashType hashType = parseHashType_();
         if (hashType != htSHA256)
             throw Error("text content address hash should use %s, but instead uses %s",
                 printHashType(htSHA256), printHashType(hashType));
-        return TextHash {
-            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
-        };
+        return TextHashMethod {};
     } else if (prefix == "fixed") {
         // Parse method
         auto method = FileIngestionMethod::Flat;
         if (splitPrefix(rest, "r:"))
             method = FileIngestionMethod::Recursive;
         HashType hashType = parseHashType_();
-        return FixedOutputHash {
-            .method = method,
-            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
+        return FixedOutputHashMethod {
+            .fileIngestionMethod = method,
+            .hashType = std::move(hashType),
         };
     } else
         throw UsageError("content address prefix '%s' is unrecognized. Recogonized prefixes are 'text' or 'fixed'", prefix);
-};
+}
 
-std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt) {
-    return rawCaOpt == "" ? std::optional<ContentAddress> {} : parseContentAddress(rawCaOpt);
+ContentAddress parseContentAddress(std::string_view rawCa) {
+    auto rest = rawCa;
+
+    ContentAddressMethod caMethod = parseContentAddressMethodPrefix(rest);
+
+    return std::visit(
+        overloaded {
+            [&](TextHashMethod thm) {
+                return ContentAddress(TextHash {
+                    .hash = Hash::parseNonSRIUnprefixed(rest, htSHA256)
+                });
+            },
+            [&](FixedOutputHashMethod fohMethod) {
+                return ContentAddress(FixedOutputHash {
+                    .method = fohMethod.fileIngestionMethod,
+                    .hash = Hash::parseNonSRIUnprefixed(rest, std::move(fohMethod.hashType)),
+                });
+            },
+        }, caMethod);
+}
+
+ContentAddressMethod parseContentAddressMethod(std::string_view caMethod)
+{
+    std::string_view asPrefix {std::string{caMethod} + ":"};
+    return parseContentAddressMethodPrefix(asPrefix);
+}
+
+std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt)
+{
+    return rawCaOpt == "" ? std::optional<ContentAddress>() : parseContentAddress(rawCaOpt);
 };
 
-std::string renderContentAddress(std::optional<ContentAddress> ca) {
+std::string renderContentAddress(std::optional<ContentAddress> ca)
+{
     return ca ? renderContentAddress(*ca) : "";
 }
 
diff --git a/src/libstore/content-address.hh b/src/libstore/content-address.hh
index 22a039242..f6a6f5140 100644
--- a/src/libstore/content-address.hh
+++ b/src/libstore/content-address.hh
@@ -55,4 +55,23 @@ std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt);
 
 Hash getContentAddressHash(const ContentAddress & ca);
 
+/*
+  We only have one way to hash text with references, so this is single-value
+  type is only useful in std::variant.
+*/
+struct TextHashMethod { };
+struct FixedOutputHashMethod {
+  FileIngestionMethod fileIngestionMethod;
+  HashType hashType;
+};
+
+typedef std::variant<
+    TextHashMethod,
+    FixedOutputHashMethod
+  > ContentAddressMethod;
+
+ContentAddressMethod parseContentAddressMethod(std::string_view rawCaMethod);
+
+std::string renderContentAddressMethod(ContentAddressMethod caMethod);
+
 }
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 8adabf549..ec3391a6d 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -2,7 +2,6 @@
 #include "monitor-fd.hh"
 #include "worker-protocol.hh"
 #include "store-api.hh"
-#include "local-store.hh"
 #include "finally.hh"
 #include "affinity.hh"
 #include "archive.hh"
@@ -240,6 +239,23 @@ struct ClientSettings
     }
 };
 
+static void writeValidPathInfo(
+    ref<Store> store,
+    unsigned int clientVersion,
+    Sink & to,
+    std::shared_ptr<const ValidPathInfo> info)
+{
+    to << (info->deriver ? store->printStorePath(*info->deriver) : "")
+       << info->narHash.to_string(Base16, false);
+    writeStorePaths(*store, to, info->references);
+    to << info->registrationTime << info->narSize;
+    if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
+        to << info->ultimate
+           << info->sigs
+           << renderContentAddress(info->ca);
+    }
+}
+
 static void performOp(TunnelLogger * logger, ref<Store> store,
     TrustedFlag trusted, RecursiveFlag recursive, unsigned int clientVersion,
     Source & from, BufferedSink & to, unsigned int op)
@@ -350,47 +366,83 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     }
 
     case wopAddToStore: {
-        HashType hashAlgo;
-        std::string baseName;
-        FileIngestionMethod method;
-        {
-            bool fixed;
-            uint8_t recursive;
-            std::string hashAlgoRaw;
-            from >> baseName >> fixed /* obsolete */ >> recursive >> hashAlgoRaw;
-            if (recursive > (uint8_t) FileIngestionMethod::Recursive)
-                throw Error("unsupported FileIngestionMethod with value of %i; you may need to upgrade nix-daemon", recursive);
-            method = FileIngestionMethod { recursive };
-            /* Compatibility hack. */
-            if (!fixed) {
-                hashAlgoRaw = "sha256";
-                method = FileIngestionMethod::Recursive;
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 25) {
+            auto name = readString(from);
+            auto camStr = readString(from);
+            auto refs = readStorePaths<StorePathSet>(*store, from);
+            bool repairBool;
+            from >> repairBool;
+            auto repair = RepairFlag{repairBool};
+
+            logger->startWork();
+            auto pathInfo = [&]() {
+                // NB: FramedSource must be out of scope before logger->stopWork();
+                ContentAddressMethod contentAddressMethod = parseContentAddressMethod(camStr);
+                FramedSource source(from);
+                // TODO this is essentially RemoteStore::addCAToStore. Move it up to Store.
+                return std::visit(overloaded {
+                    [&](TextHashMethod &_) {
+                        // We could stream this by changing Store
+                        std::string contents = source.drain();
+                        auto path = store->addTextToStore(name, contents, refs, repair);
+                        return store->queryPathInfo(path);
+                    },
+                    [&](FixedOutputHashMethod &fohm) {
+                        if (!refs.empty())
+                            throw UnimplementedError("cannot yet have refs with flat or nar-hashed data");
+                        auto path = store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType, repair);
+                        return store->queryPathInfo(path);
+                    },
+                }, contentAddressMethod);
+            }();
+            logger->stopWork();
+
+            to << store->printStorePath(pathInfo->path);
+            writeValidPathInfo(store, clientVersion, to, pathInfo);
+
+        } else {
+            HashType hashAlgo;
+            std::string baseName;
+            FileIngestionMethod method;
+            {
+                bool fixed;
+                uint8_t recursive;
+                std::string hashAlgoRaw;
+                from >> baseName >> fixed /* obsolete */ >> recursive >> hashAlgoRaw;
+                if (recursive > (uint8_t) FileIngestionMethod::Recursive)
+                    throw Error("unsupported FileIngestionMethod with value of %i; you may need to upgrade nix-daemon", recursive);
+                method = FileIngestionMethod { recursive };
+                /* Compatibility hack. */
+                if (!fixed) {
+                    hashAlgoRaw = "sha256";
+                    method = FileIngestionMethod::Recursive;
+                }
+                hashAlgo = parseHashType(hashAlgoRaw);
             }
-            hashAlgo = parseHashType(hashAlgoRaw);
-        }
 
-        StringSink saved;
-        TeeSource savedNARSource(from, saved);
-        RetrieveRegularNARSink savedRegular { saved };
+            StringSink saved;
+            TeeSource savedNARSource(from, saved);
+            RetrieveRegularNARSink savedRegular { saved };
 
-        if (method == FileIngestionMethod::Recursive) {
-            /* Get the entire NAR dump from the client and save it to
-               a string so that we can pass it to
-               addToStoreFromDump(). */
-            ParseSink sink; /* null sink; just parse the NAR */
-            parseDump(sink, savedNARSource);
-        } else
-            parseDump(savedRegular, from);
+            if (method == FileIngestionMethod::Recursive) {
+                /* Get the entire NAR dump from the client and save it to
+                  a string so that we can pass it to
+                  addToStoreFromDump(). */
+                ParseSink sink; /* null sink; just parse the NAR */
+                parseDump(sink, savedNARSource);
+            } else
+                parseDump(savedRegular, from);
 
-        logger->startWork();
-        if (!savedRegular.regular) throw Error("regular file expected");
+            logger->startWork();
+            if (!savedRegular.regular) throw Error("regular file expected");
 
-        // FIXME: try to stream directly from `from`.
-        StringSource dumpSource { *saved.s };
-        auto path = store->addToStoreFromDump(dumpSource, baseName, method, hashAlgo);
-        logger->stopWork();
+            // FIXME: try to stream directly from `from`.
+            StringSource dumpSource { *saved.s };
+            auto path = store->addToStoreFromDump(dumpSource, baseName, method, hashAlgo);
+            logger->stopWork();
 
-        to << store->printStorePath(path);
+            to << store->printStorePath(path);
+        }
         break;
     }
 
@@ -494,6 +546,20 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
            are in fact content-addressed if we don't trust them. */
         assert(derivationIsCA(drv.type()) || trusted);
 
+        /* Recompute the derivation path when we cannot trust the original. */
+        if (!trusted) {
+            /* Recomputing the derivation path for input-address derivations
+               makes it harder to audit them after the fact, since we need the
+               original not-necessarily-resolved derivation to verify the drv
+               derivation as adequate claim to the input-addressed output
+               paths. */
+            assert(derivationIsCA(drv.type()));
+
+            Derivation drv2;
+            static_cast<BasicDerivation &>(drv2) = drv;
+            drvPath = writeDerivation(*store, Derivation { drv2 });
+        }
+
         auto res = store->buildDerivation(drvPath, drv, buildMode);
         logger->stopWork();
         to << res.status << res.errorMsg;
@@ -675,15 +741,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (info) {
             if (GET_PROTOCOL_MINOR(clientVersion) >= 17)
                 to << 1;
-            to << (info->deriver ? store->printStorePath(*info->deriver) : "")
-               << info->narHash.to_string(Base16, false);
-            writeStorePaths(*store, to, info->references);
-            to << info->registrationTime << info->narSize;
-            if (GET_PROTOCOL_MINOR(clientVersion) >= 16) {
-                to << info->ultimate
-                   << info->sigs
-                   << renderContentAddress(info->ca);
-            }
+            writeValidPathInfo(store, clientVersion, to, info);
         } else {
             assert(GET_PROTOCOL_MINOR(clientVersion) >= 17);
             to << 0;
@@ -749,59 +807,12 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             info.ultimate = false;
 
         if (GET_PROTOCOL_MINOR(clientVersion) >= 23) {
-
-            struct FramedSource : Source
-            {
-                Source & from;
-                bool eof = false;
-                std::vector<unsigned char> pending;
-                size_t pos = 0;
-
-                FramedSource(Source & from) : from(from)
-                { }
-
-                ~FramedSource()
-                {
-                    if (!eof) {
-                        while (true) {
-                            auto n = readInt(from);
-                            if (!n) break;
-                            std::vector<unsigned char> data(n);
-                            from(data.data(), n);
-                        }
-                    }
-                }
-
-                size_t read(unsigned char * data, size_t len) override
-                {
-                    if (eof) throw EndOfFile("reached end of FramedSource");
-
-                    if (pos >= pending.size()) {
-                        size_t len = readInt(from);
-                        if (!len) {
-                            eof = true;
-                            return 0;
-                        }
-                        pending = std::vector<unsigned char>(len);
-                        pos = 0;
-                        from(pending.data(), len);
-                    }
-
-                    auto n = std::min(len, pending.size() - pos);
-                    memcpy(data, pending.data() + pos, n);
-                    pos += n;
-                    return n;
-                }
-            };
-
             logger->startWork();
-
             {
                 FramedSource source(from);
                 store->addToStore(info, source, (RepairFlag) repair,
                     dontCheckSigs ? NoCheckSigs : CheckSigs);
             }
-
             logger->stopWork();
         }
 
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index 9d8ce5e36..2612f1ff7 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -69,7 +69,7 @@ bool BasicDerivation::isBuiltin() const
 
 
 StorePath writeDerivation(Store & store,
-    const Derivation & drv, RepairFlag repair)
+    const Derivation & drv, RepairFlag repair, bool readOnly)
 {
     auto references = drv.inputSrcs;
     for (auto & i : drv.inputDrvs)
@@ -79,7 +79,7 @@ StorePath writeDerivation(Store & store,
        held during a garbage collection). */
     auto suffix = std::string(drv.name) + drvExtension;
     auto contents = drv.unparse(store, false);
-    return settings.readOnlyMode
+    return readOnly || settings.readOnlyMode
         ? store.computeStorePathForText(suffix, contents, references)
         : store.addTextToStore(suffix, contents, references, repair);
 }
@@ -644,4 +644,57 @@ std::string downstreamPlaceholder(const Store & store, const StorePath & drvPath
     return "/" + hashString(htSHA256, clearText).to_string(Base32, false);
 }
 
+
+// N.B. Outputs are left unchanged
+static void rewriteDerivation(Store & store, BasicDerivation & drv, const StringMap & rewrites) {
+
+    debug("Rewriting the derivation");
+
+    for (auto &rewrite: rewrites) {
+        debug("rewriting %s as %s", rewrite.first, rewrite.second);
+    }
+
+    drv.builder = rewriteStrings(drv.builder, rewrites);
+    for (auto & arg: drv.args) {
+        arg = rewriteStrings(arg, rewrites);
+    }
+
+    StringPairs newEnv;
+    for (auto & envVar: drv.env) {
+        auto envName = rewriteStrings(envVar.first, rewrites);
+        auto envValue = rewriteStrings(envVar.second, rewrites);
+        newEnv.emplace(envName, envValue);
+    }
+    drv.env = newEnv;
+}
+
+
+Sync<DrvPathResolutions> drvPathResolutions;
+
+std::optional<BasicDerivation> Derivation::tryResolve(Store & store) {
+    BasicDerivation resolved { *this };
+
+    // Input paths that we'll want to rewrite in the derivation
+    StringMap inputRewrites;
+
+    for (auto & input : inputDrvs) {
+        auto inputDrvOutputs = store.queryPartialDerivationOutputMap(input.first);
+        StringSet newOutputNames;
+        for (auto & outputName : input.second) {
+            auto actualPathOpt = inputDrvOutputs.at(outputName);
+            if (!actualPathOpt)
+                return std::nullopt;
+            auto actualPath = *actualPathOpt;
+            inputRewrites.emplace(
+                downstreamPlaceholder(store, input.first, outputName),
+                store.printStorePath(actualPath));
+            resolved.inputSrcs.insert(std::move(actualPath));
+        }
+    }
+
+    rewriteDerivation(store, resolved, inputRewrites);
+
+    return resolved;
+}
+
 }
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 0b5652685..d48266774 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -4,6 +4,7 @@
 #include "types.hh"
 #include "hash.hh"
 #include "content-address.hh"
+#include "sync.hh"
 
 #include <map>
 #include <variant>
@@ -100,7 +101,7 @@ struct BasicDerivation
     StringPairs env;
     std::string name;
 
-    BasicDerivation() { }
+    BasicDerivation() = default;
     virtual ~BasicDerivation() { };
 
     bool isBuiltin() const;
@@ -127,7 +128,17 @@ struct Derivation : BasicDerivation
     std::string unparse(const Store & store, bool maskOutputs,
         std::map<std::string, StringSet> * actualInputs = nullptr) const;
 
-    Derivation() { }
+    /* Return the underlying basic derivation but with these changes:
+
+	   1. Input drvs are emptied, but the outputs of them that were used are
+	      added directly to input sources.
+
+       2. Input placeholders are replaced with realized input store paths. */
+    std::optional<BasicDerivation> tryResolve(Store & store);
+
+    Derivation() = default;
+    Derivation(const BasicDerivation & bd) : BasicDerivation(bd) { }
+    Derivation(BasicDerivation && bd) : BasicDerivation(std::move(bd)) { }
 };
 
 
@@ -137,7 +148,9 @@ enum RepairFlag : bool { NoRepair = false, Repair = true };
 
 /* Write a derivation to the Nix store, and return its path. */
 StorePath writeDerivation(Store & store,
-    const Derivation & drv, RepairFlag repair = NoRepair);
+    const Derivation & drv,
+    RepairFlag repair = NoRepair,
+    bool readOnly = false);
 
 /* Read a derivation from a file. */
 Derivation parseDerivation(const Store & store, std::string && s, std::string_view name);
@@ -191,6 +204,16 @@ typedef std::map<StorePath, DrvHashModulo> DrvHashes;
 
 extern DrvHashes drvHashes; // FIXME: global, not thread-safe
 
+/* Memoisation of `readDerivation(..).resove()`. */
+typedef std::map<
+    StorePath,
+    std::optional<StorePath>
+> DrvPathResolutions;
+
+// FIXME: global, though at least thread-safe.
+// FIXME: arguably overlaps with hashDerivationModulo memo table.
+extern Sync<DrvPathResolutions> drvPathResolutions;
+
 bool wantOutput(const string & output, const std::set<string> & wanted);
 
 struct Source;
diff --git a/src/libstore/dummy-store.cc b/src/libstore/dummy-store.cc
index 128832e60..49641c2ac 100644
--- a/src/libstore/dummy-store.cc
+++ b/src/libstore/dummy-store.cc
@@ -1,4 +1,5 @@
 #include "store-api.hh"
+#include "callback.hh"
 
 namespace nix {
 
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 13ed429fa..cd619672f 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -5,6 +5,7 @@
 #include "s3.hh"
 #include "compression.hh"
 #include "finally.hh"
+#include "callback.hh"
 
 #ifdef ENABLE_S3
 #include <aws/core/client/ClientConfiguration.h>
diff --git a/src/libstore/filetransfer.hh b/src/libstore/filetransfer.hh
index 7e302ff39..c89c51a21 100644
--- a/src/libstore/filetransfer.hh
+++ b/src/libstore/filetransfer.hh
@@ -66,9 +66,6 @@ struct FileTransferRequest
     FileTransferRequest(const std::string & uri)
         : uri(uri), parentAct(getCurActivity()) { }
 
-    FileTransferRequest(const std::string & uri, Headers headers)
-        : uri(uri), headers(headers) { }
-
     std::string verb()
     {
         return data ? "upload" : "download";
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index e6cbc525d..518a357ef 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -574,9 +574,12 @@ bool LocalStore::canReachRoot(GCState & state, StorePathSet & visited, const Sto
     /* If keep-derivations is set and this is a derivation, then
        don't delete the derivation if any of the outputs are alive. */
     if (state.gcKeepDerivations && path.isDerivation()) {
-        for (auto & i : queryDerivationOutputs(path))
-            if (isValidPath(i) && queryPathInfo(i)->deriver == path)
-                incoming.insert(i);
+        for (auto & [name, maybeOutPath] : queryPartialDerivationOutputMap(path))
+            if (maybeOutPath &&
+                isValidPath(*maybeOutPath) &&
+                queryPathInfo(*maybeOutPath)->deriver == path
+                )
+                incoming.insert(*maybeOutPath);
     }
 
     /* If keep-outputs is set, then don't delete this path if there
@@ -660,9 +663,7 @@ void LocalStore::removeUnusedLinks(const GCState & state)
         if (name == "." || name == "..") continue;
         Path path = linksDir + "/" + name;
 
-        struct stat st;
-        if (lstat(path.c_str(), &st) == -1)
-            throw SysError("statting '%1%'", path);
+        auto st = lstat(path);
 
         if (st.st_nlink != 1) {
             actualSize += st.st_size;
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 491c664db..c5734852d 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -2,6 +2,7 @@
 #include "util.hh"
 #include "archive.hh"
 #include "args.hh"
+#include "abstract-setting-to-json.hh"
 
 #include <algorithm>
 #include <map>
@@ -41,6 +42,7 @@ Settings::Settings()
 {
     buildUsersGroup = getuid() == 0 ? "nixbld" : "";
     lockCPU = getEnv("NIX_AFFINITY_HACK") == "1";
+    allowSymlinkedStore = getEnv("NIX_IGNORE_SYMLINK_STORE") == "1";
 
     caFile = getEnv("NIX_SSL_CERT_FILE").value_or(getEnv("SSL_CERT_FILE").value_or(""));
     if (caFile == "") {
@@ -146,6 +148,12 @@ bool Settings::isWSL1()
 
 const string nixVersion = PACKAGE_VERSION;
 
+NLOHMANN_JSON_SERIALIZE_ENUM(SandboxMode, {
+    {SandboxMode::smEnabled, true},
+    {SandboxMode::smRelaxed, "relaxed"},
+    {SandboxMode::smDisabled, false},
+});
+
 template<> void BaseSetting<SandboxMode>::set(const std::string & str)
 {
     if (str == "true") value = smEnabled;
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index bd36ffc17..3b8ccadf3 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -2,7 +2,6 @@
 
 #include "types.hh"
 #include "config.hh"
-#include "abstractsettingtojson.hh"
 #include "util.hh"
 
 #include <map>
@@ -930,6 +929,19 @@ public:
 
     Setting<std::string> flakeRegistry{this, "https://github.com/NixOS/flake-registry/raw/master/flake-registry.json", "flake-registry",
         "Path or URI of the global flake registry."};
+
+    Setting<bool> allowSymlinkedStore{
+        this, false, "allow-symlinked-store",
+        R"(
+          If set to `true`, Nix will stop complaining if the store directory
+          (typically /nix/store) contains symlink components.
+
+          This risks making some builds "impure" because builders sometimes
+          "canonicalise" paths by resolving all symlink components. Problems
+          occur if those builds are then deployed to machines where /nix/store
+          resolves to a different location from that of the build machine. You
+          can enable this setting if you are sure you're not going to do that.
+        )"};
 };
 
 
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index f4ab15a10..86be7c006 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -2,6 +2,7 @@
 #include "filetransfer.hh"
 #include "globals.hh"
 #include "nar-info-disk-cache.hh"
+#include "callback.hh"
 
 namespace nix {
 
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index e9478c1d5..5af75669a 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -6,6 +6,7 @@
 #include "worker-protocol.hh"
 #include "ssh.hh"
 #include "derivations.hh"
+#include "callback.hh"
 
 namespace nix {
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index c618203f0..d29236a9c 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -6,6 +6,7 @@
 #include "derivations.hh"
 #include "nar-info.hh"
 #include "references.hh"
+#include "callback.hh"
 
 #include <iostream>
 #include <algorithm>
@@ -109,12 +110,11 @@ LocalStore::LocalStore(const Params & params)
     }
 
     /* Ensure that the store and its parents are not symlinks. */
-    if (getEnv("NIX_IGNORE_SYMLINK_STORE") != "1") {
+    if (!settings.allowSymlinkedStore) {
         Path path = realStoreDir;
         struct stat st;
         while (path != "/") {
-            if (lstat(path.c_str(), &st))
-                throw SysError("getting status of '%1%'", path);
+            st = lstat(path);
             if (S_ISLNK(st.st_mode))
                 throw Error(
                         "the path '%1%' is a symlink; "
@@ -418,10 +418,7 @@ static void canonicaliseTimestampAndPermissions(const Path & path, const struct
 
 void canonicaliseTimestampAndPermissions(const Path & path)
 {
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
-    canonicaliseTimestampAndPermissions(path, st);
+    canonicaliseTimestampAndPermissions(path, lstat(path));
 }
 
 
@@ -439,9 +436,7 @@ static void canonicalisePathMetaData_(const Path & path, uid_t fromUid, InodesSe
     }
 #endif
 
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
+    auto st = lstat(path);
 
     /* Really make sure that the path is of a supported type. */
     if (!(S_ISREG(st.st_mode) || S_ISDIR(st.st_mode) || S_ISLNK(st.st_mode)))
@@ -477,8 +472,7 @@ static void canonicalisePathMetaData_(const Path & path, uid_t fromUid, InodesSe
        ensure that we don't fail on hard links within the same build
        (i.e. "touch $out/foo; ln $out/foo $out/bar"). */
     if (fromUid != (uid_t) -1 && st.st_uid != fromUid) {
-        assert(!S_ISDIR(st.st_mode));
-        if (inodesSeen.find(Inode(st.st_dev, st.st_ino)) == inodesSeen.end())
+        if (S_ISDIR(st.st_mode) || !inodesSeen.count(Inode(st.st_dev, st.st_ino)))
             throw BuildError("invalid ownership on file '%1%'", path);
         mode_t mode = st.st_mode & ~S_IFMT;
         assert(S_ISLNK(st.st_mode) || (st.st_uid == geteuid() && (mode == 0444 || mode == 0555) && st.st_mtime == mtimeStore));
@@ -521,9 +515,7 @@ void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & ino
 
     /* On platforms that don't have lchown(), the top-level path can't
        be a symlink, since we can't change its ownership. */
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
+    auto st = lstat(path);
 
     if (st.st_uid != geteuid()) {
         assert(S_ISLNK(st.st_mode));
@@ -729,7 +721,7 @@ uint64_t LocalStore::queryValidPathId(State & state, const StorePath & path)
 {
     auto use(state.stmtQueryPathInfo.use()(printStorePath(path)));
     if (!use.next())
-        throw Error("path '%s' is not valid", printStorePath(path));
+        throw InvalidPath("path '%s' is not valid", printStorePath(path));
     return use.getInt(0);
 }
 
@@ -804,18 +796,58 @@ StorePathSet LocalStore::queryValidDerivers(const StorePath & path)
 }
 
 
-std::map<std::string, std::optional<StorePath>> LocalStore::queryPartialDerivationOutputMap(const StorePath & path)
+std::map<std::string, std::optional<StorePath>> LocalStore::queryPartialDerivationOutputMap(const StorePath & path_)
 {
+    auto path = path_;
     std::map<std::string, std::optional<StorePath>> outputs;
-    BasicDerivation drv = readDerivation(path);
+    Derivation drv = readDerivation(path);
     for (auto & [outName, _] : drv.outputs) {
         outputs.insert_or_assign(outName, std::nullopt);
     }
+    bool haveCached = false;
+    {
+        auto resolutions = drvPathResolutions.lock();
+        auto resolvedPathOptIter = resolutions->find(path);
+        if (resolvedPathOptIter != resolutions->end()) {
+            auto & [_, resolvedPathOpt] = *resolvedPathOptIter;
+            if (resolvedPathOpt)
+                path = *resolvedPathOpt;
+            haveCached = true;
+        }
+    }
+    /* can't just use else-if instead of `!haveCached` because we need to unlock
+       `drvPathResolutions` before it is locked in `Derivation::resolve`. */
+    if (!haveCached && drv.type() == DerivationType::CAFloating) {
+        /* Try resolve drv and use that path instead. */
+        auto attempt = drv.tryResolve(*this);
+        if (!attempt)
+            /* If we cannot resolve the derivation, we cannot have any path
+               assigned so we return the map of all std::nullopts. */
+            return outputs;
+        /* Just compute store path */
+        auto pathResolved = writeDerivation(*this, *std::move(attempt), NoRepair, true);
+        /* Store in memo table. */
+        /* FIXME: memo logic should not be local-store specific, should have
+           wrapper-method instead. */
+        drvPathResolutions.lock()->insert_or_assign(path, pathResolved);
+        path = std::move(pathResolved);
+    }
     return retrySQLite<std::map<std::string, std::optional<StorePath>>>([&]() {
         auto state(_state.lock());
 
-        auto useQueryDerivationOutputs(state->stmtQueryDerivationOutputs.use()
-            (queryValidPathId(*state, path)));
+        uint64_t drvId;
+        try {
+            drvId = queryValidPathId(*state, path);
+        } catch (InvalidPath &) {
+            /* FIXME? if the derivation doesn't exist, we cannot have a mapping
+               for it. */
+            return outputs;
+        }
+
+        auto useQueryDerivationOutputs {
+            state->stmtQueryDerivationOutputs.use()
+            (drvId)
+        };
 
         while (useQueryDerivationOutputs.next())
             outputs.insert_or_assign(
@@ -1454,7 +1486,7 @@ static void makeMutable(const Path & path)
 {
     checkInterrupt();
 
-    struct stat st = lstat(path);
+    auto st = lstat(path);
 
     if (!S_ISDIR(st.st_mode) && !S_ISREG(st.st_mode)) return;
 
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index da3981696..ad4dccef9 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -5,7 +5,7 @@
 #include "store-api.hh"
 #include "thread-pool.hh"
 #include "topo-sort.hh"
-
+#include "callback.hh"
 
 namespace nix {
 
diff --git a/src/libstore/names.cc b/src/libstore/names.cc
index d1c8a6101..41e28dc99 100644
--- a/src/libstore/names.cc
+++ b/src/libstore/names.cc
@@ -1,10 +1,18 @@
 #include "names.hh"
 #include "util.hh"
 
+#include <regex>
+
 
 namespace nix {
 
 
+struct Regex
+{
+    std::regex regex;
+};
+
+
 DrvName::DrvName()
 {
     name = "";
@@ -30,11 +38,18 @@ DrvName::DrvName(std::string_view s) : hits(0)
 }
 
 
+DrvName::~DrvName()
+{ }
+
+
 bool DrvName::matches(DrvName & n)
 {
     if (name != "*") {
-        if (!regex) regex = std::unique_ptr<std::regex>(new std::regex(name, std::regex::extended));
-        if (!std::regex_match(n.name, *regex)) return false;
+        if (!regex) {
+            regex = std::make_unique<Regex>();
+            regex->regex = std::regex(name, std::regex::extended);
+        }
+        if (!std::regex_match(n.name, regex->regex)) return false;
     }
     if (version != "" && version != n.version) return false;
     return true;
@@ -99,7 +114,7 @@ DrvNames drvNamesFromArgs(const Strings & opArgs)
 {
     DrvNames result;
     for (auto & i : opArgs)
-        result.push_back(DrvName(i));
+        result.emplace_back(i);
     return result;
 }
 
diff --git a/src/libstore/names.hh b/src/libstore/names.hh
index 00e14b8c7..bc62aac93 100644
--- a/src/libstore/names.hh
+++ b/src/libstore/names.hh
@@ -3,10 +3,11 @@
 #include <memory>
 
 #include "types.hh"
-#include <regex>
 
 namespace nix {
 
+struct Regex;
+
 struct DrvName
 {
     string fullName;
@@ -16,10 +17,12 @@ struct DrvName
 
     DrvName();
     DrvName(std::string_view s);
+    ~DrvName();
+
     bool matches(DrvName & n);
 
 private:
-    std::unique_ptr<std::regex> regex;
+    std::unique_ptr<Regex> regex;
 };
 
 typedef list<DrvName> DrvNames;
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
index e4b4b6213..c032a5e22 100644
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -17,9 +17,7 @@ namespace nix {
 
 static void makeWritable(const Path & path)
 {
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
+    auto st = lstat(path);
     if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
         throw SysError("changing writability of '%1%'", path);
 }
@@ -94,9 +92,7 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
 {
     checkInterrupt();
 
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
+    auto st = lstat(path);
 
 #if __APPLE__
     /* HFS/macOS has some undocumented security feature disabling hardlinking for
@@ -187,9 +183,7 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
 
     /* Yes!  We've seen a file with the same contents.  Replace the
        current file with a hard link to that file. */
-    struct stat stLink;
-    if (lstat(linkPath.c_str(), &stLink))
-        throw SysError("getting attributes of path '%1%'", linkPath);
+    auto stLink = lstat(linkPath);
 
     if (st.st_ino == stLink.st_ino) {
         debug(format("'%1%' is already linked to '%2%'") % path % linkPath);
diff --git a/src/libstore/profiles.cc b/src/libstore/profiles.cc
index c20386e2b..c3809bad7 100644
--- a/src/libstore/profiles.cc
+++ b/src/libstore/profiles.cc
@@ -39,13 +39,10 @@ std::pair<Generations, std::optional<GenerationNumber>> findGenerations(Path pro
     for (auto & i : readDirectory(profileDir)) {
         if (auto n = parseName(profileName, i.name)) {
             auto path = profileDir + "/" + i.name;
-            struct stat st;
-            if (lstat(path.c_str(), &st) != 0)
-                throw SysError("statting '%1%'", path);
             gens.push_back({
                 .number = *n,
                 .path = path,
-                .creationTime = st.st_mtime
+                .creationTime = lstat(path).st_mtime
             });
         }
     }
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 1abe236f7..be5eb4736 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -10,6 +10,7 @@
 #include "pool.hh"
 #include "finally.hh"
 #include "logging.hh"
+#include "callback.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -97,7 +98,16 @@ RemoteStore::RemoteStore(const Params & params)
     , RemoteStoreConfig(params)
     , connections(make_ref<Pool<Connection>>(
             std::max(1, (int) maxConnections),
-            [this]() { return openConnectionWrapper(); },
+            [this]() {
+                auto conn = openConnectionWrapper();
+                try {
+                    initConnection(*conn);
+                } catch (...) {
+                    failed = true;
+                    throw;
+                }
+                return conn;
+            },
             [this](const ref<Connection> & r) {
                 return
                     r->to.good()
@@ -182,8 +192,6 @@ ref<RemoteStore::Connection> UDSRemoteStore::openConnection()
 
     conn->startTime = std::chrono::steady_clock::now();
 
-    initConnection(*conn);
-
     return conn;
 }
 
@@ -299,6 +307,8 @@ struct ConnectionHandle
             std::rethrow_exception(ex);
         }
     }
+
+    void withFramedSink(std::function<void(Sink & sink)> fun);
 };
 
 
@@ -412,11 +422,28 @@ void RemoteStore::querySubstitutablePathInfos(const StorePathCAMap & pathsMap, S
 }
 
 
+ref<const ValidPathInfo> RemoteStore::readValidPathInfo(ConnectionHandle & conn, const StorePath & path)
+{
+    auto deriver = readString(conn->from);
+    auto narHash = Hash::parseAny(readString(conn->from), htSHA256);
+    auto info = make_ref<ValidPathInfo>(path, narHash);
+    if (deriver != "") info->deriver = parseStorePath(deriver);
+    info->references = readStorePaths<StorePathSet>(*this, conn->from);
+    conn->from >> info->registrationTime >> info->narSize;
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
+        conn->from >> info->ultimate;
+        info->sigs = readStrings<StringSet>(conn->from);
+        info->ca = parseContentAddressOpt(readString(conn->from));
+    }
+    return info;
+}
+
+
 void RemoteStore::queryPathInfoUncached(const StorePath & path,
     Callback<std::shared_ptr<const ValidPathInfo>> callback) noexcept
 {
     try {
-        std::shared_ptr<ValidPathInfo> info;
+        std::shared_ptr<const ValidPathInfo> info;
         {
             auto conn(getConnection());
             conn->to << wopQueryPathInfo << printStorePath(path);
@@ -432,17 +459,7 @@ void RemoteStore::queryPathInfoUncached(const StorePath & path,
                 bool valid; conn->from >> valid;
                 if (!valid) throw InvalidPath("path '%s' is not valid", printStorePath(path));
             }
-            auto deriver = readString(conn->from);
-            auto narHash = Hash::parseAny(readString(conn->from), htSHA256);
-            info = std::make_shared<ValidPathInfo>(path, narHash);
-            if (deriver != "") info->deriver = parseStorePath(deriver);
-            info->references = readStorePaths<StorePathSet>(*this, conn->from);
-            conn->from >> info->registrationTime >> info->narSize;
-            if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 16) {
-                conn->from >> info->ultimate;
-                info->sigs = readStrings<StringSet>(conn->from);
-                info->ca = parseContentAddressOpt(readString(conn->from));
-            }
+            info = readValidPathInfo(conn, path);
         }
         callback(std::move(info));
     } catch (...) { callback.rethrow(); }
@@ -517,6 +534,93 @@ std::optional<StorePath> RemoteStore::queryPathFromHashPart(const std::string &
 }
 
 
+ref<const ValidPathInfo> RemoteStore::addCAToStore(
+    Source & dump,
+    const string & name,
+    ContentAddressMethod caMethod,
+    const StorePathSet & references,
+    RepairFlag repair)
+{
+    std::optional<ConnectionHandle> conn_(getConnection());
+    auto & conn = *conn_;
+
+    if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 25) {
+
+        conn->to
+            << wopAddToStore
+            << name
+            << renderContentAddressMethod(caMethod);
+        writeStorePaths(*this, conn->to, references);
+        conn->to << repair;
+
+        conn.withFramedSink([&](Sink & sink) {
+            dump.drainInto(sink);
+        });
+
+        auto path = parseStorePath(readString(conn->from));
+        return readValidPathInfo(conn, path);
+    }
+    else {
+        if (repair) throw Error("repairing is not supported when building through the Nix daemon protocol < 1.25");
+
+        std::visit(overloaded {
+            [&](TextHashMethod thm) -> void {
+                std::string s = dump.drain();
+                conn->to << wopAddTextToStore << name << s;
+                writeStorePaths(*this, conn->to, references);
+                conn.processStderr();
+            },
+            [&](FixedOutputHashMethod fohm) -> void {
+                conn->to
+                    << wopAddToStore
+                    << name
+                    << ((fohm.hashType == htSHA256 && fohm.fileIngestionMethod == FileIngestionMethod::Recursive) ? 0 : 1) /* backwards compatibility hack */
+                    << (fohm.fileIngestionMethod == FileIngestionMethod::Recursive ? 1 : 0)
+                    << printHashType(fohm.hashType);
+
+                try {
+                    conn->to.written = 0;
+                    conn->to.warn = true;
+                    connections->incCapacity();
+                    {
+                        Finally cleanup([&]() { connections->decCapacity(); });
+                        if (fohm.fileIngestionMethod == FileIngestionMethod::Recursive) {
+                            dump.drainInto(conn->to);
+                        } else {
+                            std::string contents = dump.drain();
+                            dumpString(contents, conn->to);
+                        }
+                    }
+                    conn->to.warn = false;
+                    conn.processStderr();
+                } catch (SysError & e) {
+                    /* Daemon closed while we were sending the path. Probably OOM
+                      or I/O error. */
+                    if (e.errNo == EPIPE)
+                        try {
+                            conn.processStderr();
+                        } catch (EndOfFile & e) { }
+                    throw;
+                }
+
+            }
+        }, caMethod);
+        auto path = parseStorePath(readString(conn->from));
+        // Release our connection to prevent a deadlock in queryPathInfo().
+        conn_.reset();
+        return queryPathInfo(path);
+    }
+}
+
+
+StorePath RemoteStore::addToStoreFromDump(Source & dump, const string & name,
+        FileIngestionMethod method, HashType hashType, RepairFlag repair)
+{
+    StorePathSet references;
+    return addCAToStore(dump, name, FixedOutputHashMethod{ .fileIngestionMethod = method, .hashType = hashType }, references, repair)->path;
+}
+
+
 void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
     RepairFlag repair, CheckSigsFlag checkSigs)
 {
@@ -557,78 +661,9 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
                  << repair << !checkSigs;
 
         if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 23) {
-
-            conn->to.flush();
-
-            std::exception_ptr ex;
-
-            struct FramedSink : BufferedSink
-            {
-                ConnectionHandle & conn;
-                std::exception_ptr & ex;
-
-                FramedSink(ConnectionHandle & conn, std::exception_ptr & ex) : conn(conn), ex(ex)
-                { }
-
-                ~FramedSink()
-                {
-                    try {
-                        conn->to << 0;
-                        conn->to.flush();
-                    } catch (...) {
-                        ignoreException();
-                    }
-                }
-
-                void write(const unsigned char * data, size_t len) override
-                {
-                    /* Don't send more data if the remote has
-                       encountered an error. */
-                    if (ex) {
-                        auto ex2 = ex;
-                        ex = nullptr;
-                        std::rethrow_exception(ex2);
-                    }
-                    conn->to << len;
-                    conn->to(data, len);
-                };
-            };
-
-            /* Handle log messages / exceptions from the remote on a
-               separate thread. */
-            std::thread stderrThread([&]()
-            {
-                try {
-                    conn.processStderr(nullptr, nullptr, false);
-                } catch (...) {
-                    ex = std::current_exception();
-                }
-            });
-
-            Finally joinStderrThread([&]()
-            {
-                if (stderrThread.joinable()) {
-                    stderrThread.join();
-                    if (ex) {
-                        try {
-                            std::rethrow_exception(ex);
-                        } catch (...) {
-                            ignoreException();
-                        }
-                    }
-                }
-            });
-
-            {
-                FramedSink sink(conn, ex);
+            conn.withFramedSink([&](Sink & sink) {
                 copyNAR(source, sink);
-                sink.flush();
-            }
-
-            stderrThread.join();
-            if (ex)
-                std::rethrow_exception(ex);
-
+            });
         } else if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 21) {
             conn.processStderr(0, &source);
         } else {
@@ -639,57 +674,11 @@ void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
 }
 
 
-StorePath RemoteStore::addToStore(const string & name, const Path & _srcPath,
-    FileIngestionMethod method, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
-{
-    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
-
-    auto conn(getConnection());
-
-    Path srcPath(absPath(_srcPath));
-
-    conn->to
-        << wopAddToStore
-        << name
-        << ((hashAlgo == htSHA256 && method == FileIngestionMethod::Recursive) ? 0 : 1) /* backwards compatibility hack */
-        << (method == FileIngestionMethod::Recursive ? 1 : 0)
-        << printHashType(hashAlgo);
-
-    try {
-        conn->to.written = 0;
-        conn->to.warn = true;
-        connections->incCapacity();
-        {
-            Finally cleanup([&]() { connections->decCapacity(); });
-            dumpPath(srcPath, conn->to, filter);
-        }
-        conn->to.warn = false;
-        conn.processStderr();
-    } catch (SysError & e) {
-        /* Daemon closed while we were sending the path. Probably OOM
-           or I/O error. */
-        if (e.errNo == EPIPE)
-            try {
-                conn.processStderr();
-            } catch (EndOfFile & e) { }
-        throw;
-    }
-
-    return parseStorePath(readString(conn->from));
-}
-
-
 StorePath RemoteStore::addTextToStore(const string & name, const string & s,
     const StorePathSet & references, RepairFlag repair)
 {
-    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
-
-    auto conn(getConnection());
-    conn->to << wopAddTextToStore << name << s;
-    writeStorePaths(*this, conn->to, references);
-
-    conn.processStderr();
-    return parseStorePath(readString(conn->from));
+    StringSource source(s);
+    return addCAToStore(source, name, TextHashMethod{}, references, repair)->path;
 }
 
 
@@ -985,6 +974,49 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
     return nullptr;
 }
 
+void ConnectionHandle::withFramedSink(std::function<void(Sink &sink)> fun)
+{
+    (*this)->to.flush();
+
+    std::exception_ptr ex;
+
+    /* Handle log messages / exceptions from the remote on a
+        separate thread. */
+    std::thread stderrThread([&]()
+    {
+        try {
+            processStderr(nullptr, nullptr, false);
+        } catch (...) {
+            ex = std::current_exception();
+        }
+    });
+
+    Finally joinStderrThread([&]()
+    {
+        if (stderrThread.joinable()) {
+            stderrThread.join();
+            if (ex) {
+                try {
+                    std::rethrow_exception(ex);
+                } catch (...) {
+                    ignoreException();
+                }
+            }
+        }
+    });
+
+    {
+        FramedSink sink((*this)->to, ex);
+        fun(sink);
+        sink.flush();
+    }
+
+    stderrThread.join();
+    if (ex)
+        std::rethrow_exception(ex);
+
+}
+
 static RegisterStoreImplementation<UDSRemoteStore, UDSRemoteStoreConfig> regStore;
 
 }
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index a23690830..ec04be985 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -63,13 +63,21 @@ public:
     void querySubstitutablePathInfos(const StorePathCAMap & paths,
         SubstitutablePathInfos & infos) override;
 
+    /* Add a content-addressable store path. `dump` will be drained. */
+    ref<const ValidPathInfo> addCAToStore(
+        Source & dump,
+        const string & name,
+        ContentAddressMethod caMethod,
+        const StorePathSet & references,
+        RepairFlag repair);
+
+    /* Add a content-addressable store path. Does not support references. `dump` will be drained. */
+    StorePath addToStoreFromDump(Source & dump, const string & name,
+        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair) override;
+
     void addToStore(const ValidPathInfo & info, Source & nar,
         RepairFlag repair, CheckSigsFlag checkSigs) override;
 
-    StorePath addToStore(const string & name, const Path & srcPath,
-        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
-        PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) override;
-
     StorePath addTextToStore(const string & name, const string & s,
         const StorePathSet & references, RepairFlag repair) override;
 
@@ -106,8 +114,6 @@ public:
 
     void flushBadConnections();
 
-protected:
-
     struct Connection
     {
         AutoCloseFD fd;
@@ -123,6 +129,8 @@ protected:
 
     ref<Connection> openConnectionWrapper();
 
+protected:
+
     virtual ref<Connection> openConnection() = 0;
 
     void initConnection(Connection & conn);
@@ -139,6 +147,8 @@ protected:
 
     virtual void narFromPath(const StorePath & path, Sink & sink) override;
 
+    ref<const ValidPathInfo> readValidPathInfo(ConnectionHandle & conn, const StorePath & path);
+
 private:
 
     std::atomic_bool failed{false};
diff --git a/src/libstore/ssh-store.cc b/src/libstore/ssh-store.cc
index 8b6e48fb0..6d6eca98d 100644
--- a/src/libstore/ssh-store.cc
+++ b/src/libstore/ssh-store.cc
@@ -80,7 +80,6 @@ ref<RemoteStore::Connection> SSHStore::openConnection()
         + (remoteStore.get() == "" ? "" : " --store " + shellEscape(remoteStore.get())));
     conn->to = FdSink(conn->sshConn->in.get());
     conn->from = FdSource(conn->sshConn->out.get());
-    initConnection(*conn);
     return conn;
 }
 
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 76cbc0605..1bbc74db8 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -8,9 +8,7 @@
 #include "json.hh"
 #include "url.hh"
 #include "archive.hh"
-
-#include <future>
-
+#include "callback.hh"
 
 namespace nix {
 
@@ -1040,38 +1038,26 @@ static bool isNonUriPath(const std::string & spec) {
         && spec.find("/") != std::string::npos;
 }
 
-StoreType getStoreType(const std::string & uri, const std::string & stateDir)
+std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Params & params)
 {
-    if (uri == "daemon") {
-        return tDaemon;
-    } else if (uri == "local" || isNonUriPath(uri)) {
-        return tLocal;
-    } else if (uri == "" || uri == "auto") {
+    if (uri == "" || uri == "auto") {
+        auto stateDir = get(params, "state").value_or(settings.nixStateDir);
         if (access(stateDir.c_str(), R_OK | W_OK) == 0)
-            return tLocal;
+            return std::make_shared<LocalStore>(params);
         else if (pathExists(settings.nixDaemonSocketFile))
-            return tDaemon;
+            return std::make_shared<UDSRemoteStore>(params);
         else
-            return tLocal;
+            return std::make_shared<LocalStore>(params);
+    } else if (uri == "daemon") {
+        return std::make_shared<UDSRemoteStore>(params);
+    } else if (uri == "local") {
+        return std::make_shared<LocalStore>(params);
+    } else if (isNonUriPath(uri)) {
+        Store::Params params2 = params;
+        params2["root"] = absPath(uri);
+        return std::make_shared<LocalStore>(params2);
     } else {
-        return tOther;
-    }
-}
-
-std::shared_ptr<Store> openFromNonUri(const std::string & uri, const Store::Params & params)
-{
-    switch (getStoreType(uri, get(params, "state").value_or(settings.nixStateDir))) {
-        case tDaemon:
-            return std::shared_ptr<Store>(std::make_shared<UDSRemoteStore>(params));
-        case tLocal: {
-            Store::Params params2 = params;
-            if (isNonUriPath(uri)) {
-                params2["root"] = absPath(uri);
-            }
-            return std::shared_ptr<Store>(std::make_shared<LocalStore>(params2));
-        }
-        default:
-            return nullptr;
+        return nullptr;
     }
 }
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 1bea4837b..3ccee4f75 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -449,7 +449,8 @@ public:
     /* Like addToStore(), but the contents of the path are contained
        in `dump', which is either a NAR serialisation (if recursive ==
        true) or simply the contents of a regular file (if recursive ==
-       false). */
+       false).
+       `dump` may be drained */
     // FIXME: remove?
     virtual StorePath addToStoreFromDump(Source & dump, const string & name,
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair)
@@ -478,8 +479,38 @@ public:
         BuildMode buildMode = bmNormal);
 
     /* Build a single non-materialized derivation (i.e. not from an
-       on-disk .drv file). Note that ‘drvPath’ is only used for
-       informational purposes. */
+       on-disk .drv file).
+
+       ‘drvPath’ is used to deduplicate worker goals so it is imperative that
+       is correct. That said, it doesn't literally need to be store path that
+       would be calculated from writing this derivation to the store: it is OK
+       if it instead is that of a Derivation which would resolve to this (by
+       taking the outputs of it's input derivations and adding them as input
+       sources) such that the build time referenceable-paths are the same.
+
+       In the input-addressed case, we usually *do* use an "original"
+       unresolved derivations's path, as that is what will be used in the
+       `buildPaths` case. Also, the input-addressed output paths are verified
+       only by that contents of that specific unresolved derivation, so it is
+       nice to keep that information around so if the original derivation is
+       ever obtained later, it can be verified whether the trusted user in fact
+       used the proper output path.
+
+       In the content-addressed case, we want to always use the
+       resolved drv path calculated from the provided derivation. This serves
+       two purposes:
+
+         - It keeps the operation trustless, by ruling out a maliciously
+           invalid drv path corresponding to a non-resolution-equivalent
+           derivation.
+
+         - For the floating case in particular, it ensures that the derivation
+           to output mapping respects the resolution equivalence relation, so
+           one cannot choose different resolution-equivalent derivations to
+           subvert dependency coherence (i.e. the property that one doesn't end
+           up with multiple different versions of dependencies without
+           explicitly choosing to allow it).
+    */
     virtual BuildResult buildDerivation(const StorePath & drvPath, const BasicDerivation & drv,
         BuildMode buildMode = bmNormal) = 0;
 
@@ -516,7 +547,7 @@ public:
        - The collector isn't running, or it's just started but hasn't
          acquired the GC lock yet.  In that case we get and release
          the lock right away, then exit.  The collector scans the
-         permanent root and sees our's.
+         permanent root and sees ours.
 
        In either case the permanent root is seen by the collector. */
     virtual void syncWithGC() { };
@@ -791,16 +822,6 @@ ref<Store> openStore(const std::string & uri = settings.storeUri.get(),
     const Store::Params & extraParams = Store::Params());
 
 
-enum StoreType {
-    tDaemon,
-    tLocal,
-    tOther
-};
-
-
-StoreType getStoreType(const std::string & uri = settings.storeUri.get(),
-    const std::string & stateDir = settings.nixStateDir);
-
 /* Return the default substituter stores, defined by the
    ‘substituters’ option and various legacy options. */
 std::list<ref<Store>> getDefaultSubstituters();
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
index 13cf8d4ab..b100d1550 100644
--- a/src/libstore/worker-protocol.hh
+++ b/src/libstore/worker-protocol.hh
@@ -6,7 +6,7 @@ namespace nix {
 #define WORKER_MAGIC_1 0x6e697863
 #define WORKER_MAGIC_2 0x6478696f
 
-#define PROTOCOL_VERSION 0x118
+#define PROTOCOL_VERSION 0x119
 #define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
 #define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
 
@@ -18,7 +18,7 @@ typedef enum {
     wopQueryReferences = 5, // obsolete
     wopQueryReferrers = 6,
     wopAddToStore = 7,
-    wopAddTextToStore = 8,
+    wopAddTextToStore = 8, // obsolete since 1.25, Nix 3.0. Use wopAddToStore
     wopBuildPaths = 9,
     wopEnsurePath = 10,
     wopAddTempRoot = 11,
diff --git a/src/libutil/abstractsettingtojson.hh b/src/libutil/abstract-setting-to-json.hh
index b3fbc84f7..b3fbc84f7 100644
--- a/src/libutil/abstractsettingtojson.hh
+++ b/src/libutil/abstract-setting-to-json.hh
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 14399dea3..6ad9fa238 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -27,6 +27,8 @@ struct ArchiveSettings : Config
         #endif
         "use-case-hack",
         "Whether to enable a Darwin-specific hack for dealing with file name collisions."};
+    Setting<bool> preallocateContents{this, true, "preallocate-contents",
+        "Whether to preallocate files when writing objects with known size."};
 };
 
 static ArchiveSettings archiveSettings;
@@ -66,9 +68,7 @@ static void dump(const Path & path, Sink & sink, PathFilter & filter)
 {
     checkInterrupt();
 
-    struct stat st;
-    if (lstat(path.c_str(), &st))
-        throw SysError("getting attributes of path '%1%'", path);
+    auto st = lstat(path);
 
     sink << "(";
 
@@ -325,6 +325,9 @@ struct RestoreSink : ParseSink
 
     void preallocateContents(uint64_t len)
     {
+        if (!archiveSettings.preallocateContents)
+            return;
+
 #if HAVE_POSIX_FALLOCATE
         if (len) {
             errno = posix_fallocate(fd.get(), 0, len);
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 3c1f87f7e..f41242e17 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -192,7 +192,7 @@ public:
     {
         expectArgs({
             .label = label,
-            .optional = true,
+            .optional = optional,
             .handler = {dest}
         });
     }
diff --git a/src/libutil/callback.hh b/src/libutil/callback.hh
new file mode 100644
index 000000000..ef31794be
--- /dev/null
+++ b/src/libutil/callback.hh
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <future>
+#include <functional>
+
+namespace nix {
+
+/* A callback is a wrapper around a lambda that accepts a valid of
+   type T or an exception. (We abuse std::future<T> to pass the value or
+   exception.) */
+template<typename T>
+class Callback
+{
+    std::function<void(std::future<T>)> fun;
+    std::atomic_flag done = ATOMIC_FLAG_INIT;
+
+public:
+
+    Callback(std::function<void(std::future<T>)> fun) : fun(fun) { }
+
+    Callback(Callback && callback) : fun(std::move(callback.fun))
+    {
+        auto prev = callback.done.test_and_set();
+        if (prev) done.test_and_set();
+    }
+
+    void operator()(T && t) noexcept
+    {
+        auto prev = done.test_and_set();
+        assert(!prev);
+        std::promise<T> promise;
+        promise.set_value(std::move(t));
+        fun(promise.get_future());
+    }
+
+    void rethrow(const std::exception_ptr & exc = std::current_exception()) noexcept
+    {
+        auto prev = done.test_and_set();
+        assert(!prev);
+        std::promise<T> promise;
+        promise.set_exception(exc);
+        fun(promise.get_future());
+    }
+};
+
+}
diff --git a/src/libutil/config.cc b/src/libutil/config.cc
index b14feb10d..521733025 100644
--- a/src/libutil/config.cc
+++ b/src/libutil/config.cc
@@ -1,6 +1,6 @@
 #include "config.hh"
 #include "args.hh"
-#include "abstractsettingtojson.hh"
+#include "abstract-setting-to-json.hh"
 
 #include <nlohmann/json.hpp>
 
diff --git a/src/libutil/fmt.hh b/src/libutil/fmt.hh
index a39de041f..6e69bdce2 100644
--- a/src/libutil/fmt.hh
+++ b/src/libutil/fmt.hh
@@ -1,7 +1,6 @@
 #pragma once
 
 #include <boost/format.hpp>
-#include <boost/algorithm/string/replace.hpp>
 #include <string>
 #include "ansicolor.hh"
 
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 00c945113..a469a1e73 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -93,7 +93,7 @@ void Source::operator () (unsigned char * data, size_t len)
 }
 
 
-std::string Source::drain()
+void Source::drainInto(Sink & sink)
 {
     std::string s;
     std::vector<unsigned char> buf(8192);
@@ -101,12 +101,19 @@ std::string Source::drain()
         size_t n;
         try {
             n = read(buf.data(), buf.size());
-            s.append((char *) buf.data(), n);
+            sink(buf.data(), n);
         } catch (EndOfFile &) {
             break;
         }
     }
-    return s;
+}
+
+
+std::string Source::drain()
+{
+    StringSink s;
+    drainInto(s);
+    return *s.s;
 }
 
 
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 6f4f4c855..b41e58f33 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -69,6 +69,8 @@ struct Source
 
     virtual bool good() { return true; }
 
+    void drainInto(Sink & sink);
+
     std::string drain();
 };
 
@@ -340,7 +342,7 @@ T readNum(Source & source)
         ((uint64_t) buf[6] << 48) |
         ((uint64_t) buf[7] << 56);
 
-    if (n > std::numeric_limits<T>::max())
+    if (n > (uint64_t)std::numeric_limits<T>::max())
         throw SerialisationError("serialised integer %d is too large for type '%s'", n, typeid(T).name());
 
     return (T) n;
@@ -404,4 +406,93 @@ struct StreamToSourceAdapter : Source
 };
 
 
+/* A source that reads a distinct format of concatenated chunks back into its
+   logical form, in order to guarantee a known state to the original stream,
+   even in the event of errors.
+
+   Use with FramedSink, which also allows the logical stream to be terminated
+   in the event of an exception.
+*/
+struct FramedSource : Source
+{
+    Source & from;
+    bool eof = false;
+    std::vector<unsigned char> pending;
+    size_t pos = 0;
+
+    FramedSource(Source & from) : from(from)
+    { }
+
+    ~FramedSource()
+    {
+        if (!eof) {
+            while (true) {
+                auto n = readInt(from);
+                if (!n) break;
+                std::vector<unsigned char> data(n);
+                from(data.data(), n);
+            }
+        }
+    }
+
+    size_t read(unsigned char * data, size_t len) override
+    {
+        if (eof) throw EndOfFile("reached end of FramedSource");
+
+        if (pos >= pending.size()) {
+            size_t len = readInt(from);
+            if (!len) {
+                eof = true;
+                return 0;
+            }
+            pending = std::vector<unsigned char>(len);
+            pos = 0;
+            from(pending.data(), len);
+        }
+
+        auto n = std::min(len, pending.size() - pos);
+        memcpy(data, pending.data() + pos, n);
+        pos += n;
+        return n;
+    }
+};
+
+/* Write as chunks in the format expected by FramedSource.
+
+   The exception_ptr reference can be used to terminate the stream when you
+   detect that an error has occurred on the remote end.
+*/
+struct FramedSink : nix::BufferedSink
+{
+    BufferedSink & to;
+    std::exception_ptr & ex;
+
+    FramedSink(BufferedSink & to, std::exception_ptr & ex) : to(to), ex(ex)
+    { }
+
+    ~FramedSink()
+    {
+        try {
+            to << 0;
+            to.flush();
+        } catch (...) {
+            ignoreException();
+        }
+    }
+
+    void write(const unsigned char * data, size_t len) override
+    {
+        /* Don't send more data if the remote has
+            encountered an error. */
+        if (ex) {
+            auto ex2 = ex;
+            ex = nullptr;
+            std::rethrow_exception(ex2);
+        }
+        to << len;
+        to(data, len);
+    };
+};
+
+
 }
diff --git a/src/libutil/split.hh b/src/libutil/split.hh
index d19d7d8ed..87a23b13e 100644
--- a/src/libutil/split.hh
+++ b/src/libutil/split.hh
@@ -9,7 +9,7 @@ namespace nix {
 
 // If `separator` is found, we return the portion of the string before the
 // separator, and modify the string argument to contain only the part after the
-// separator. Otherwise, wer return `std::nullopt`, and we leave the argument
+// separator. Otherwise, we return `std::nullopt`, and we leave the argument
 // string alone.
 static inline std::optional<std::string_view> splitPrefixTo(std::string_view & string, char separator) {
     auto sepInstance = string.find(separator);
diff --git a/src/libutil/url-parts.hh b/src/libutil/url-parts.hh
new file mode 100644
index 000000000..64e06cfbc
--- /dev/null
+++ b/src/libutil/url-parts.hh
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <string>
+#include <regex>
+
+namespace nix {
+
+// URI stuff.
+const static std::string pctEncoded = "(?:%[0-9a-fA-F][0-9a-fA-F])";
+const static std::string schemeRegex = "(?:[a-z+.-]+)";
+const static std::string ipv6AddressRegex = "(?:\\[[0-9a-fA-F:]+\\])";
+const static std::string unreservedRegex = "(?:[a-zA-Z0-9-._~])";
+const static std::string subdelimsRegex = "(?:[!$&'\"()*+,;=])";
+const static std::string hostnameRegex = "(?:(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + ")*)";
+const static std::string hostRegex = "(?:" + ipv6AddressRegex + "|" + hostnameRegex + ")";
+const static std::string userRegex = "(?:(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + "|:)*)";
+const static std::string authorityRegex = "(?:" + userRegex + "@)?" + hostRegex + "(?::[0-9]+)?";
+const static std::string pcharRegex = "(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + "|[:@])";
+const static std::string queryRegex = "(?:" + pcharRegex + "|[/? \"])*";
+const static std::string segmentRegex = "(?:" + pcharRegex + "+)";
+const static std::string absPathRegex = "(?:(?:/" + segmentRegex + ")*/?)";
+const static std::string pathRegex = "(?:" + segmentRegex + "(?:/" + segmentRegex + ")*/?)";
+
+// A Git ref (i.e. branch or tag name).
+const static std::string refRegexS = "[a-zA-Z0-9][a-zA-Z0-9_.-]*"; // FIXME: check
+extern std::regex refRegex;
+
+// Instead of defining what a good Git Ref is, we define what a bad Git Ref is
+// This is because of the definition of a ref in refs.c in https://github.com/git/git
+// See tests/fetchGitRefs.sh for the full definition
+const static std::string badGitRefRegexS = "//|^[./]|/\\.|\\.\\.|[[:cntrl:][:space:]:?^~\[]|\\\\|\\*|\\.lock$|\\.lock/|@\\{|[/.]$|^@$|^$";
+extern std::regex badGitRefRegex;
+
+// A Git revision (a SHA-1 commit hash).
+const static std::string revRegexS = "[0-9a-fA-F]{40}";
+extern std::regex revRegex;
+
+// A ref or revision, or a ref followed by a revision.
+const static std::string refAndOrRevRegex = "(?:(" + revRegexS + ")|(?:(" + refRegexS + ")(?:/(" + revRegexS + "))?))";
+
+const static std::string flakeIdRegexS = "[a-zA-Z][a-zA-Z0-9_-]*";
+extern std::regex flakeIdRegex;
+
+}
diff --git a/src/libutil/url.cc b/src/libutil/url.cc
index 88c09eef9..c1bab866c 100644
--- a/src/libutil/url.cc
+++ b/src/libutil/url.cc
@@ -1,4 +1,5 @@
 #include "url.hh"
+#include "url-parts.hh"
 #include "util.hh"
 
 namespace nix {
diff --git a/src/libutil/url.hh b/src/libutil/url.hh
index 1f716ba10..6e77142e3 100644
--- a/src/libutil/url.hh
+++ b/src/libutil/url.hh
@@ -2,8 +2,6 @@
 
 #include "error.hh"
 
-#include <regex>
-
 namespace nix {
 
 struct ParsedURL
@@ -29,40 +27,4 @@ std::map<std::string, std::string> decodeQuery(const std::string & query);
 
 ParsedURL parseURL(const std::string & url);
 
-// URI stuff.
-const static std::string pctEncoded = "(?:%[0-9a-fA-F][0-9a-fA-F])";
-const static std::string schemeRegex = "(?:[a-z+.-]+)";
-const static std::string ipv6AddressRegex = "(?:\\[[0-9a-fA-F:]+\\])";
-const static std::string unreservedRegex = "(?:[a-zA-Z0-9-._~])";
-const static std::string subdelimsRegex = "(?:[!$&'\"()*+,;=])";
-const static std::string hostnameRegex = "(?:(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + ")*)";
-const static std::string hostRegex = "(?:" + ipv6AddressRegex + "|" + hostnameRegex + ")";
-const static std::string userRegex = "(?:(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + "|:)*)";
-const static std::string authorityRegex = "(?:" + userRegex + "@)?" + hostRegex + "(?::[0-9]+)?";
-const static std::string pcharRegex = "(?:" + unreservedRegex + "|" + pctEncoded + "|" + subdelimsRegex + "|[:@])";
-const static std::string queryRegex = "(?:" + pcharRegex + "|[/? \"])*";
-const static std::string segmentRegex = "(?:" + pcharRegex + "+)";
-const static std::string absPathRegex = "(?:(?:/" + segmentRegex + ")*/?)";
-const static std::string pathRegex = "(?:" + segmentRegex + "(?:/" + segmentRegex + ")*/?)";
-
-// A Git ref (i.e. branch or tag name).
-const static std::string refRegexS = "[a-zA-Z0-9][a-zA-Z0-9_.-]*"; // FIXME: check
-extern std::regex refRegex;
-
-// Instead of defining what a good Git Ref is, we define what a bad Git Ref is
-// This is because of the definition of a ref in refs.c in https://github.com/git/git
-// See tests/fetchGitRefs.sh for the full definition
-const static std::string badGitRefRegexS = "//|^[./]|/\\.|\\.\\.|[[:cntrl:][:space:]:?^~\[]|\\\\|\\*|\\.lock$|\\.lock/|@\\{|[/.]$|^@$|^$";
-extern std::regex badGitRefRegex;
-
-// A Git revision (a SHA-1 commit hash).
-const static std::string revRegexS = "[0-9a-fA-F]{40}";
-extern std::regex revRegex;
-
-// A ref or revision, or a ref followed by a revision.
-const static std::string refAndOrRevRegex = "(?:(" + revRegexS + ")|(?:(" + refRegexS + ")(?:/(" + revRegexS + "))?))";
-
-const static std::string flakeIdRegexS = "[a-zA-Z][a-zA-Z0-9_-]*";
-extern std::regex flakeIdRegex;
-
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 082e26375..b8e201203 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -12,13 +12,9 @@
 #include <signal.h>
 
 #include <functional>
-#include <limits>
-#include <cstdio>
 #include <map>
 #include <sstream>
 #include <optional>
-#include <future>
-#include <iterator>
 
 #ifndef HAVE_STRUCT_DIRENT_D_TYPE
 #define DT_UNKNOWN 0
@@ -480,43 +476,8 @@ std::optional<typename T::mapped_type> get(const T & map, const typename T::key_
 }
 
 
-/* A callback is a wrapper around a lambda that accepts a valid of
-   type T or an exception. (We abuse std::future<T> to pass the value or
-   exception.) */
 template<typename T>
-class Callback
-{
-    std::function<void(std::future<T>)> fun;
-    std::atomic_flag done = ATOMIC_FLAG_INIT;
-
-public:
-
-    Callback(std::function<void(std::future<T>)> fun) : fun(fun) { }
-
-    Callback(Callback && callback) : fun(std::move(callback.fun))
-    {
-        auto prev = callback.done.test_and_set();
-        if (prev) done.test_and_set();
-    }
-
-    void operator()(T && t) noexcept
-    {
-        auto prev = done.test_and_set();
-        assert(!prev);
-        std::promise<T> promise;
-        promise.set_value(std::move(t));
-        fun(promise.get_future());
-    }
-
-    void rethrow(const std::exception_ptr & exc = std::current_exception()) noexcept
-    {
-        auto prev = done.test_and_set();
-        assert(!prev);
-        std::promise<T> promise;
-        promise.set_exception(exc);
-        fun(promise.get_future());
-    }
-};
+class Callback;
 
 
 /* Start a thread that handles various signals. Also block those signals
diff --git a/src/nix-channel/nix-channel.cc b/src/nix-channel/nix-channel.cc
index 94d33a75c..e48f7af9a 100755
--- a/src/nix-channel/nix-channel.cc
+++ b/src/nix-channel/nix-channel.cc
@@ -76,6 +76,13 @@ static void update(const StringSet & channelNames)
 
     auto store = openStore();
 
+    auto [fd, unpackChannelPath] = createTempFile();
+    writeFull(fd.get(),
+        #include "unpack-channel.nix.gen.hh"
+        );
+    fd = -1;
+    AutoDelete del(unpackChannelPath, false);
+
     // Download each channel.
     Strings exprs;
     for (const auto & channel : channels) {
@@ -87,7 +94,7 @@ static void update(const StringSet & channelNames)
         // We want to download the url to a file to see if it's a tarball while also checking if we
         // got redirected in the process, so that we can grab the various parts of a nix channel
         // definition from a consistent location if the redirect changes mid-download.
-        auto result = fetchers::downloadFile(store, url, Headers {}, std::string(baseNameOf(url)), false);
+        auto result = fetchers::downloadFile(store, url, std::string(baseNameOf(url)), false);
         auto filename = store->toRealPath(result.storePath);
         url = result.effectiveUrl;
 
@@ -104,7 +111,7 @@ static void update(const StringSet & channelNames)
 
         bool unpacked = false;
         if (std::regex_search(filename, std::regex("\\.tar\\.(gz|bz2|xz)$"))) {
-            runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import <nix/unpack-channel.nix> "
+            runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
                         "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
             unpacked = true;
         }
@@ -112,9 +119,9 @@ static void update(const StringSet & channelNames)
         if (!unpacked) {
             // Download the channel tarball.
             try {
-                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.xz", Headers {}, "nixexprs.tar.xz", false).storePath);
+                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.xz", "nixexprs.tar.xz", false).storePath);
             } catch (FileTransferError & e) {
-                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.bz2", Headers {}, "nixexprs.tar.bz2", false).storePath);
+                filename = store->toRealPath(fetchers::downloadFile(store, url + "/nixexprs.tar.bz2", "nixexprs.tar.bz2", false).storePath);
             }
         }
 
@@ -125,7 +132,7 @@ static void update(const StringSet & channelNames)
     // Unpack the channel tarballs into the Nix store and install them
     // into the channels profile.
     std::cerr << "unpacking channels...\n";
-    Strings envArgs{ "--profile", profile, "--file", "<nix/unpack-channel.nix>", "--install", "--from-expression" };
+    Strings envArgs{ "--profile", profile, "--file", unpackChannelPath, "--install", "--from-expression" };
     for (auto & expr : exprs)
         envArgs.push_back(std::move(expr));
     envArgs.push_back("--quiet");
diff --git a/src/nix-channel/unpack-channel.nix b/src/nix-channel/unpack-channel.nix
new file mode 100644
index 000000000..10515bc8b
--- /dev/null
+++ b/src/nix-channel/unpack-channel.nix
@@ -0,0 +1,12 @@
+{ name, channelName, src }:
+
+derivation {
+  builder = "builtin:unpack-channel";
+
+  system = "builtin";
+
+  inherit name channelName src;
+
+  # No point in doing this remotely.
+  preferLocalBuild = true;
+}
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index cfa634a44..6e652ccbf 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -1,5 +1,6 @@
 #include "shared.hh"
 #include "local-store.hh"
+#include "remote-store.hh"
 #include "util.hh"
 #include "serialise.hh"
 #include "archive.hh"
@@ -285,44 +286,28 @@ static int _main(int argc, char * * argv)
         initPlugins();
 
         if (stdio) {
-            if (getStoreType() == tDaemon) {
-                //  Forward on this connection to the real daemon
-                auto socketPath = settings.nixDaemonSocketFile;
-                auto s = socket(PF_UNIX, SOCK_STREAM, 0);
-                if (s == -1)
-                    throw SysError("creating Unix domain socket");
-
-                auto socketDir = dirOf(socketPath);
-                if (chdir(socketDir.c_str()) == -1)
-                    throw SysError("changing to socket directory '%1%'", socketDir);
-
-                auto socketName = std::string(baseNameOf(socketPath));
-                auto addr = sockaddr_un{};
-                addr.sun_family = AF_UNIX;
-                if (socketName.size() + 1 >= sizeof(addr.sun_path))
-                    throw Error("socket name %1% is too long", socketName);
-                strcpy(addr.sun_path, socketName.c_str());
-
-                if (connect(s, (struct sockaddr *) &addr, sizeof(addr)) == -1)
-                    throw SysError("cannot connect to daemon at %1%", socketPath);
-
-                auto nfds = (s > STDIN_FILENO ? s : STDIN_FILENO) + 1;
+            if (auto store = openUncachedStore().dynamic_pointer_cast<RemoteStore>()) {
+                auto conn = store->openConnectionWrapper();
+                int from = conn->from.fd;
+                int to = conn->to.fd;
+
+                auto nfds = std::max(from, STDIN_FILENO) + 1;
                 while (true) {
                     fd_set fds;
                     FD_ZERO(&fds);
-                    FD_SET(s, &fds);
+                    FD_SET(from, &fds);
                     FD_SET(STDIN_FILENO, &fds);
                     if (select(nfds, &fds, nullptr, nullptr, nullptr) == -1)
                         throw SysError("waiting for data from client or server");
-                    if (FD_ISSET(s, &fds)) {
-                        auto res = splice(s, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
+                    if (FD_ISSET(from, &fds)) {
+                        auto res = splice(from, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
                         if (res == -1)
                             throw SysError("splicing data from daemon socket to stdout");
                         else if (res == 0)
                             throw EndOfFile("unexpected EOF from daemon socket");
                     }
                     if (FD_ISSET(STDIN_FILENO, &fds)) {
-                        auto res = splice(STDIN_FILENO, nullptr, s, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
+                        auto res = splice(STDIN_FILENO, nullptr, to, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
                         if (res == -1)
                             throw SysError("splicing data from stdin to daemon socket");
                         else if (res == 0)
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index e5a433ac0..3e7c453fb 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -230,7 +230,7 @@ static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
 {
     DrvNames selectors = drvNamesFromArgs(args);
     if (selectors.empty())
-        selectors.push_back(DrvName("*"));
+        selectors.emplace_back("*");
 
     DrvInfos elems;
     set<unsigned int> done;
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index 1001f27af..377ae03a8 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -57,6 +57,7 @@ static int _main(int argc, char * * argv)
         bool fromExpr = false;
         string attrPath;
         bool unpack = false;
+        bool executable = false;
         string name;
 
         struct MyArgs : LegacyArgs, MixEvalArgs
@@ -81,6 +82,8 @@ static int _main(int argc, char * * argv)
             }
             else if (*arg == "--unpack")
                 unpack = true;
+            else if (*arg == "--executable")
+                executable = true;
             else if (*arg == "--name")
                 name = getArg(*arg, arg, end);
             else if (*arg != "" && arg->at(0) == '-')
@@ -175,7 +178,11 @@ static int _main(int argc, char * * argv)
 
             /* Download the file. */
             {
-                AutoCloseFD fd = open(tmpFile.c_str(), O_WRONLY | O_CREAT | O_EXCL, 0600);
+                auto mode = 0600;
+                if (executable)
+                    mode = 0700;
+
+                AutoCloseFD fd = open(tmpFile.c_str(), O_WRONLY | O_CREAT | O_EXCL, mode);
                 if (!fd) throw SysError("creating temporary file '%s'", tmpFile);
 
                 FdSink sink(fd.get());
@@ -201,7 +208,7 @@ static int _main(int argc, char * * argv)
                     tmpFile = unpacked;
             }
 
-            const auto method = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
+            const auto method = unpack || executable ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
 
             auto info = store->addToStoreSlow(name, tmpFile, method, ht, expectedHash);
             storePath = info.path;
diff --git a/src/nix/bundle.cc b/src/nix/bundle.cc
index 241c8699b..fc41da9e4 100644
--- a/src/nix/bundle.cc
+++ b/src/nix/bundle.cc
@@ -98,14 +98,14 @@ struct CmdBundle : InstallableCommand
         if (!evalState->isDerivation(*vRes))
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
-        auto attr1 = vRes->attrs->find(evalState->sDrvPath);
+        auto attr1 = vRes->attrs->get(evalState->sDrvPath);
         if (!attr1)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
         PathSet context2;
         StorePath drvPath = store->parseStorePath(evalState->coerceToPath(*attr1->pos, *attr1->value, context2));
 
-        auto attr2 = vRes->attrs->find(evalState->sOutPath);
+        auto attr2 = vRes->attrs->get(evalState->sOutPath);
         if (!attr2)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
diff --git a/src/nix/doctor.cc b/src/nix/doctor.cc
index 82e92cdd0..683e91446 100644
--- a/src/nix/doctor.cc
+++ b/src/nix/doctor.cc
@@ -49,9 +49,7 @@ struct CmdDoctor : StoreCommand
     {
         logger->log("Running checks against store uri: " + store->getUri());
 
-        auto type = getStoreType();
-
-        if (type < tOther) {
+        if (store.dynamic_pointer_cast<LocalFSStore>()) {
             success &= checkNixInPath();
             success &= checkProfileRoots(store);
         }
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 0eca4f8ea..494f00a20 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -44,6 +44,7 @@ struct CmdHash : Command
         switch (mode) {
         case FileIngestionMethod::Flat:
             d = "print cryptographic hash of a regular file";
+            break;
         case FileIngestionMethod::Recursive:
             d = "print cryptographic hash of the NAR serialisation of a path";
         };
diff --git a/src/nix/local.mk b/src/nix/local.mk
index e96200685..ab4e9121b 100644
--- a/src/nix/local.mk
+++ b/src/nix/local.mk
@@ -29,3 +29,5 @@ $(eval $(call install-symlink, $(bindir)/nix, $(libexecdir)/nix/build-remote))
 src/nix-env/user-env.cc: src/nix-env/buildenv.nix.gen.hh
 
 src/nix/develop.cc: src/nix/get-env.sh.gen.hh
+
+src/nix-channel/nix-channel.cc: src/nix-channel/unpack-channel.nix.gen.hh
diff --git a/src/resolve-system-dependencies/resolve-system-dependencies.cc b/src/resolve-system-dependencies/resolve-system-dependencies.cc
index 434ad80a6..d30227e4e 100644
--- a/src/resolve-system-dependencies/resolve-system-dependencies.cc
+++ b/src/resolve-system-dependencies/resolve-system-dependencies.cc
@@ -111,11 +111,7 @@ std::set<std::string> runResolver(const Path & filename)
 
 bool isSymlink(const Path & path)
 {
-    struct stat st;
-    if (lstat(path.c_str(), &st) == -1)
-        throw SysError("getting attributes of path '%1%'", path);
-
-    return S_ISLNK(st.st_mode);
+    return S_ISLNK(lstat(path).st_mode);
 }
 
 Path resolveSymlink(const Path & path)