Merge branch 'master' of github.com:NixOS/nix into derivation-header-include-order

43 files changed, 548 insertions, 401 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c1a9af9b2..58066fa48 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -366,7 +366,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
 
             if (store->isInStore(r.second)) {
                 StorePathSet closure;
-                store->computeFSClosure(store->parseStorePath(store->toStorePath(r.second)), closure);
+                store->computeFSClosure(store->toStorePath(r.second).first, closure);
                 for (auto & path : closure)
                     allowedPaths->insert(store->printStorePath(path));
             } else
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index f9e03a09f..4bbfbd3f5 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -883,10 +883,10 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
             .hint = hintfmt("path '%1%' is not in the Nix store", path),
             .errPos = pos
         });
-    Path path2 = state.store->toStorePath(path);
+    auto path2 = state.store->toStorePath(path).first;
     if (!settings.readOnlyMode)
-        state.store->ensurePath(state.store->parseStorePath(path2));
-    context.insert(path2);
+        state.store->ensurePath(path2);
+    context.insert(state.store->printStorePath(path2));
     mkString(v, path, context);
 }
 
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 9f52ddafa..b791c125b 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -15,6 +15,7 @@
 #include <chrono>
 #include <future>
 #include <regex>
+#include <fstream>
 
 #include <nlohmann/json.hpp>
 
@@ -57,6 +58,13 @@ void BinaryCacheStore::init()
     }
 }
 
+void BinaryCacheStore::upsertFile(const std::string & path,
+    std::string && data,
+    const std::string & mimeType)
+{
+    upsertFile(path, std::make_shared<std::stringstream>(std::move(data)), mimeType);
+}
+
 void BinaryCacheStore::getFile(const std::string & path,
     Callback<std::shared_ptr<std::string>> callback) noexcept
 {
@@ -113,13 +121,74 @@ void BinaryCacheStore::writeNarInfo(ref<NarInfo> narInfo)
         diskCache->upsertNarInfo(getUri(), hashPart, std::shared_ptr<NarInfo>(narInfo));
 }
 
+AutoCloseFD openFile(const Path & path)
+{
+    auto fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
+    if (!fd)
+        throw SysError("opening file '%1%'", path);
+    return fd;
+}
+
+struct FileSource : FdSource
+{
+    AutoCloseFD fd2;
+
+    FileSource(const Path & path)
+        : fd2(openFile(path))
+    {
+        fd = fd2.get();
+    }
+};
+
 void BinaryCacheStore::addToStore(const ValidPathInfo & info, Source & narSource,
-    RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
+    RepairFlag repair, CheckSigsFlag checkSigs)
 {
-    // FIXME: See if we can use the original source to reduce memory usage.
-    auto nar = make_ref<std::string>(narSource.drain());
+    assert(info.narHash && info.narSize);
+
+    if (!repair && isValidPath(info.path)) {
+        // FIXME: copyNAR -> null sink
+        narSource.drain();
+        return;
+    }
+
+    auto [fdTemp, fnTemp] = createTempFile();
+
+    auto now1 = std::chrono::steady_clock::now();
+
+    /* Read the NAR simultaneously into a CompressionSink+FileSink (to
+       write the compressed NAR to disk), into a HashSink (to get the
+       NAR hash), and into a NarAccessor (to get the NAR listing). */
+    HashSink fileHashSink(htSHA256);
+    std::shared_ptr<FSAccessor> narAccessor;
+    {
+    FdSink fileSink(fdTemp.get());
+    TeeSink teeSink(fileSink, fileHashSink);
+    auto compressionSink = makeCompressionSink(compression, teeSink);
+    TeeSource teeSource(narSource, *compressionSink);
+    narAccessor = makeNarAccessor(teeSource);
+    compressionSink->finish();
+    }
+
+    auto now2 = std::chrono::steady_clock::now();
+
+    auto narInfo = make_ref<NarInfo>(info);
+    narInfo->narSize = info.narSize;
+    narInfo->narHash = info.narHash;
+    narInfo->compression = compression;
+    auto [fileHash, fileSize] = fileHashSink.finish();
+    narInfo->fileHash = fileHash;
+    narInfo->fileSize = fileSize;
+    narInfo->url = "nar/" + narInfo->fileHash.to_string(Base32, false) + ".nar"
+        + (compression == "xz" ? ".xz" :
+           compression == "bzip2" ? ".bz2" :
+           compression == "br" ? ".br" :
+           "");
 
-    if (!repair && isValidPath(info.path)) return;
+    auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1).count();
+    printMsg(lvlTalkative, "copying path '%1%' (%2% bytes, compressed %3$.1f%% in %4% ms) to binary cache",
+        printStorePath(narInfo->path), info.narSize,
+        ((1.0 - (double) fileSize / info.narSize) * 100.0),
+        duration);
 
     /* Verify that all references are valid. This may do some .narinfo
        reads, but typically they'll already be cached. */
@@ -132,23 +201,6 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, Source & narSource
                 printStorePath(info.path), printStorePath(ref));
         }
 
-    assert(nar->compare(0, narMagic.size(), narMagic) == 0);
-
-    auto narInfo = make_ref<NarInfo>(info);
-
-    narInfo->narSize = nar->size();
-    narInfo->narHash = hashString(htSHA256, *nar);
-
-    if (info.narHash && info.narHash != narInfo->narHash)
-        throw Error("refusing to copy corrupted path '%1%' to binary cache", printStorePath(info.path));
-
-    auto accessor_ = std::dynamic_pointer_cast<RemoteFSAccessor>(accessor);
-
-    auto narAccessor = makeNarAccessor(nar);
-
-    if (accessor_)
-        accessor_->addToCache(printStorePath(info.path), *nar, narAccessor);
-
     /* Optionally write a JSON file containing a listing of the
        contents of the NAR. */
     if (writeNARListing) {
@@ -160,33 +212,13 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, Source & narSource
 
             {
                 auto res = jsonRoot.placeholder("root");
-                listNar(res, narAccessor, "", true);
+                listNar(res, ref<FSAccessor>(narAccessor), "", true);
             }
         }
 
         upsertFile(std::string(info.path.to_string()) + ".ls", jsonOut.str(), "application/json");
     }
 
-    /* Compress the NAR. */
-    narInfo->compression = compression;
-    auto now1 = std::chrono::steady_clock::now();
-    auto narCompressed = compress(compression, *nar, parallelCompression);
-    auto now2 = std::chrono::steady_clock::now();
-    narInfo->fileHash = hashString(htSHA256, *narCompressed);
-    narInfo->fileSize = narCompressed->size();
-
-    auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1).count();
-    printMsg(lvlTalkative, "copying path '%1%' (%2% bytes, compressed %3$.1f%% in %4% ms) to binary cache",
-        printStorePath(narInfo->path), narInfo->narSize,
-        ((1.0 - (double) narCompressed->size() / nar->size()) * 100.0),
-        duration);
-
-    narInfo->url = "nar/" + narInfo->fileHash.to_string(Base32, false) + ".nar"
-        + (compression == "xz" ? ".xz" :
-           compression == "bzip2" ? ".bz2" :
-           compression == "br" ? ".br" :
-           "");
-
     /* Optionally maintain an index of DWARF debug info files
        consisting of JSON files named 'debuginfo/<build-id>' that
        specify the NAR file and member containing the debug info. */
@@ -247,12 +279,14 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, Source & narSource
     /* Atomically write the NAR file. */
     if (repair || !fileExists(narInfo->url)) {
         stats.narWrite++;
-        upsertFile(narInfo->url, *narCompressed, "application/x-nix-nar");
+        upsertFile(narInfo->url,
+            std::make_shared<std::fstream>(fnTemp, std::ios_base::in),
+            "application/x-nix-nar");
     } else
         stats.narWriteAverted++;
 
-    stats.narWriteBytes += nar->size();
-    stats.narWriteCompressedBytes += narCompressed->size();
+    stats.narWriteBytes += info.narSize;
+    stats.narWriteCompressedBytes += fileSize;
     stats.narWriteCompressionTimeMs += duration;
 
     /* Atomically write the NAR info file.*/
@@ -351,7 +385,7 @@ StorePath BinaryCacheStore::addToStore(const string & name, const Path & srcPath
     ValidPathInfo info(makeFixedOutputPath(method, h, name));
 
     auto source = StringSource { *sink.s };
-    addToStore(info, source, repair, CheckSigs, nullptr);
+    addToStore(info, source, repair, CheckSigs);
 
     return std::move(info.path);
 }
@@ -366,7 +400,7 @@ StorePath BinaryCacheStore::addTextToStore(const string & name, const string & s
         StringSink sink;
         dumpString(s, sink);
         auto source = StringSource { *sink.s };
-        addToStore(info, source, repair, CheckSigs, nullptr);
+        addToStore(info, source, repair, CheckSigs);
     }
 
     return std::move(info.path);
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 52ef8aa7a..9bcdf5901 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -36,9 +36,13 @@ public:
     virtual bool fileExists(const std::string & path) = 0;
 
     virtual void upsertFile(const std::string & path,
-        const std::string & data,
+        std::shared_ptr<std::basic_iostream<char>> istream,
         const std::string & mimeType) = 0;
 
+    void upsertFile(const std::string & path,
+        std::string && data,
+        const std::string & mimeType);
+
     /* Note: subclasses must implement at least one of the two
        following getFile() methods. */
 
@@ -75,8 +79,7 @@ public:
     { unsupported("queryPathFromHashPart"); }
 
     void addToStore(const ValidPathInfo & info, Source & narSource,
-        RepairFlag repair, CheckSigsFlag checkSigs,
-        std::shared_ptr<FSAccessor> accessor) override;
+        RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method, HashType hashAlgo,
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 347fe1b99..ac2e67574 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2041,7 +2041,10 @@ void DerivationGoal::startBuilder()
             if (!std::regex_match(fileName, regex))
                 throw Error("invalid file name '%s' in 'exportReferencesGraph'", fileName);
 
-            auto storePath = worker.store.parseStorePath(*i++);
+            auto storePathS = *i++;
+            if (!worker.store.isInStore(storePathS))
+                throw BuildError("'exportReferencesGraph' contains a non-store path '%1%'", storePathS);
+            auto storePath = worker.store.toStorePath(storePathS).first;
 
             /* Write closure info to <fileName>. */
             writeFile(tmpDir + "/" + fileName,
@@ -2080,7 +2083,7 @@ void DerivationGoal::startBuilder()
         for (auto & i : dirsInChroot)
             try {
                 if (worker.store.isInStore(i.second.source))
-                    worker.store.computeFSClosure(worker.store.parseStorePath(worker.store.toStorePath(i.second.source)), closure);
+                    worker.store.computeFSClosure(worker.store.toStorePath(i.second.source).first, closure);
             } catch (InvalidPath & e) {
             } catch (Error & e) {
                 throw Error("while processing 'sandbox-paths': %s", e.what());
@@ -2765,10 +2768,9 @@ struct RestrictedStore : public LocalFSStore
     { throw Error("addToStore"); }
 
     void addToStore(const ValidPathInfo & info, Source & narSource,
-        RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs,
-        std::shared_ptr<FSAccessor> accessor = 0) override
+        RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs) override
     {
-        next->addToStore(info, narSource, repair, checkSigs, accessor);
+        next->addToStore(info, narSource, repair, checkSigs);
         goal.addDependency(info.path);
     }
 
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 3d753836f..6cb69d0a9 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -82,4 +82,16 @@ std::string renderContentAddress(std::optional<ContentAddress> ca) {
     return ca ? renderContentAddress(*ca) : "";
 }
 
+Hash getContentAddressHash(const ContentAddress & ca)
+{
+    return std::visit(overloaded {
+        [](TextHash th) {
+            return th.hash;
+        },
+        [](FixedOutputHash fsh) {
+            return fsh.hash;
+        }
+    }, ca);
+}
+
 }
diff --git a/src/libstore/content-address.hh b/src/libstore/content-address.hh
index ba4797f5b..22a039242 100644
--- a/src/libstore/content-address.hh
+++ b/src/libstore/content-address.hh
@@ -53,4 +53,6 @@ ContentAddress parseContentAddress(std::string_view rawCa);
 
 std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt);
 
+Hash getContentAddressHash(const ContentAddress & ca);
+
 }
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index a8fb62e0a..db7139374 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -81,7 +81,7 @@ struct TunnelLogger : public Logger
         showErrorInfo(oss, ei, false);
 
         StringSink buf;
-        buf << STDERR_NEXT << oss.str() << "\n";
+        buf << STDERR_NEXT << oss.str();
         enqueueMsg(*buf.s);
     }
 
@@ -391,7 +391,8 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         }
         HashType hashAlgo = parseHashType(s);
 
-        TeeSource savedNAR(from);
+        StringSink savedNAR;
+        TeeSource savedNARSource(from, savedNAR);
         RetrieveRegularNARSink savedRegular;
 
         if (method == FileIngestionMethod::Recursive) {
@@ -399,7 +400,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                a string so that we can pass it to
                addToStoreFromDump(). */
             ParseSink sink; /* null sink; just parse the NAR */
-            parseDump(sink, savedNAR);
+            parseDump(sink, savedNARSource);
         } else
             parseDump(savedRegular, from);
 
@@ -407,7 +408,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (!savedRegular.regular) throw Error("regular file expected");
 
         auto path = store->addToStoreFromDump(
-            method == FileIngestionMethod::Recursive ? *savedNAR.data : savedRegular.s,
+            method == FileIngestionMethod::Recursive ? *savedNAR.s : savedRegular.s,
             baseName,
             method,
             hashAlgo);
@@ -442,7 +443,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
     case wopImportPaths: {
         logger->startWork();
         TunnelSource source(from, to);
-        auto paths = store->importPaths(source, nullptr,
+        auto paths = store->importPaths(source,
             trusted ? NoCheckSigs : CheckSigs);
         logger->stopWork();
         Strings paths2;
@@ -731,9 +732,9 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (GET_PROTOCOL_MINOR(clientVersion) >= 21)
             source = std::make_unique<TunnelSource>(from, to);
         else {
-            TeeSink tee(from);
+            TeeParseSink tee(from);
             parseDump(tee, tee.source);
-            saved = std::move(*tee.source.data);
+            saved = std::move(*tee.saved.s);
             source = std::make_unique<StringSource>(saved);
         }
 
@@ -741,7 +742,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
         // FIXME: race if addToStore doesn't read source?
         store->addToStore(info, *source, (RepairFlag) repair,
-            dontCheckSigs ? NoCheckSigs : CheckSigs, nullptr);
+            dontCheckSigs ? NoCheckSigs : CheckSigs);
 
         logger->stopWork();
         break;
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index f0f5c95bf..67565a704 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -3,7 +3,7 @@
 #include "globals.hh"
 #include "util.hh"
 #include "worker-protocol.hh"
-#include "istringstream_nocopy.hh"
+#include "fs-accessor.hh"
 
 namespace nix {
 
@@ -100,7 +100,7 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 }
 
 
-static DerivationOutput parseDerivationOutput(const Store & store, istringstream_nocopy & str)
+static DerivationOutput parseDerivationOutput(const Store & store, std::istringstream & str)
 {
     expect(str, ","); auto path = store.parseStorePath(parsePath(str));
     expect(str, ","); auto hashAlgo = parseString(str);
@@ -128,10 +128,10 @@ static DerivationOutput parseDerivationOutput(const Store & store, istringstream
 }
 
 
-Derivation parseDerivation(const Store & store, const string & s)
+Derivation parseDerivation(const Store & store, std::string && s)
 {
     Derivation drv;
-    istringstream_nocopy str(s);
+    std::istringstream str(std::move(s));
     expect(str, "Derive([");
 
     /* Parse the list of outputs. */
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 6a195d314..d32793b6a 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -76,7 +76,7 @@ StorePath writeDerivation(ref<Store> store,
     const Derivation & drv, std::string_view name, RepairFlag repair = NoRepair);
 
 /* Read a derivation from a file. */
-Derivation parseDerivation(const Store & store, const string & s);
+Derivation parseDerivation(const Store & store, string && s);
 
 // FIXME: remove
 bool isDerivation(const string & fileName);
diff --git a/src/libstore/export-import.cc b/src/libstore/export-import.cc
index 57b7e9590..082d0f1d1 100644
--- a/src/libstore/export-import.cc
+++ b/src/libstore/export-import.cc
@@ -7,24 +7,6 @@
 
 namespace nix {
 
-struct HashAndWriteSink : Sink
-{
-    Sink & writeSink;
-    HashSink hashSink;
-    HashAndWriteSink(Sink & writeSink) : writeSink(writeSink), hashSink(htSHA256)
-    {
-    }
-    virtual void operator () (const unsigned char * data, size_t len)
-    {
-        writeSink(data, len);
-        hashSink(data, len);
-    }
-    Hash currentHash()
-    {
-        return hashSink.currentHash().first;
-    }
-};
-
 void Store::exportPaths(const StorePathSet & paths, Sink & sink)
 {
     auto sorted = topoSortPaths(paths);
@@ -47,28 +29,29 @@ void Store::exportPath(const StorePath & path, Sink & sink)
 {
     auto info = queryPathInfo(path);
 
-    HashAndWriteSink hashAndWriteSink(sink);
+    HashSink hashSink(htSHA256);
+    TeeSink teeSink(sink, hashSink);
 
-    narFromPath(path, hashAndWriteSink);
+    narFromPath(path, teeSink);
 
     /* Refuse to export paths that have changed.  This prevents
        filesystem corruption from spreading to other machines.
        Don't complain if the stored hash is zero (unknown). */
-    Hash hash = hashAndWriteSink.currentHash();
+    Hash hash = hashSink.currentHash().first;
     if (hash != info->narHash && info->narHash != Hash(*info->narHash.type))
         throw Error("hash of path '%s' has changed from '%s' to '%s'!",
             printStorePath(path), info->narHash.to_string(Base32, true), hash.to_string(Base32, true));
 
-    hashAndWriteSink
+    teeSink
         << exportMagic
         << printStorePath(path);
-    writeStorePaths(*this, hashAndWriteSink, info->references);
-    hashAndWriteSink
+    writeStorePaths(*this, teeSink, info->references);
+    teeSink
         << (info->deriver ? printStorePath(*info->deriver) : "")
         << 0;
 }
 
-StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> accessor, CheckSigsFlag checkSigs)
+StorePaths Store::importPaths(Source & source, CheckSigsFlag checkSigs)
 {
     StorePaths res;
     while (true) {
@@ -77,7 +60,7 @@ StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> acces
         if (n != 1) throw Error("input doesn't look like something created by 'nix-store --export'");
 
         /* Extract the NAR from the source. */
-        TeeSink tee(source);
+        TeeParseSink tee(source);
         parseDump(tee, tee.source);
 
         uint32_t magic = readInt(source);
@@ -94,16 +77,16 @@ StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> acces
         if (deriver != "")
             info.deriver = parseStorePath(deriver);
 
-        info.narHash = hashString(htSHA256, *tee.source.data);
-        info.narSize = tee.source.data->size();
+        info.narHash = hashString(htSHA256, *tee.saved.s);
+        info.narSize = tee.saved.s->size();
 
         // Ignore optional legacy signature.
         if (readInt(source) == 1)
             readString(source);
 
         // Can't use underlying source, which would have been exhausted
-        auto source = StringSource { *tee.source.data };
-        addToStore(info, source, NoRepair, checkSigs, accessor);
+        auto source = StringSource { *tee.saved.s };
+        addToStore(info, source, NoRepair, checkSigs);
 
         res.push_back(info.path);
     }
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 57fb20845..aaed5c218 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -262,11 +262,13 @@ void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
 void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 {
     auto foundRoot = [&](const Path & path, const Path & target) {
-        auto storePath = maybeParseStorePath(toStorePath(target));
-        if (storePath && isValidPath(*storePath))
-            roots[std::move(*storePath)].emplace(path);
-        else
-            printInfo("skipping invalid root from '%1%' to '%2%'", path, target);
+        try {
+            auto storePath = toStorePath(target).first;
+            if (isValidPath(storePath))
+                roots[std::move(storePath)].emplace(path);
+            else
+                printInfo("skipping invalid root from '%1%' to '%2%'", path, target);
+        } catch (BadStorePath &) { }
     };
 
     try {
@@ -472,15 +474,15 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 
     for (auto & [target, links] : unchecked) {
         if (!isInStore(target)) continue;
-        Path pathS = toStorePath(target);
-        if (!isStorePath(pathS)) continue;
-        auto path = parseStorePath(pathS);
-        if (!isValidPath(path)) continue;
-        debug("got additional root '%1%'", pathS);
-        if (censor)
-            roots[path].insert(censored);
-        else
-            roots[path].insert(links.begin(), links.end());
+        try {
+            auto path = toStorePath(target).first;
+            if (!isValidPath(path)) continue;
+            debug("got additional root '%1%'", printStorePath(path));
+            if (censor)
+                roots[path].insert(censored);
+            else
+                roots[path].insert(links.begin(), links.end());
+        } catch (BadStorePath &) { }
     }
 }
 
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 58cf08763..4d5eec7bf 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -365,6 +365,9 @@ public:
 
     Setting<bool> warnDirty{this, true, "warn-dirty",
         "Whether to warn about dirty Git/Mercurial trees."};
+
+    Setting<size_t> narBufferSize{this, 32 * 1024 * 1024, "nar-buffer-size",
+        "Maximum size of NARs before spilling them to disk."};
 };
 
 
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 451a64785..c1ceb08cf 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -100,11 +100,11 @@ protected:
     }
 
     void upsertFile(const std::string & path,
-        const std::string & data,
+        std::shared_ptr<std::basic_iostream<char>> istream,
         const std::string & mimeType) override
     {
         auto req = FileTransferRequest(cacheUri + "/" + path);
-        req.data = std::make_shared<string>(data); // FIXME: inefficient
+        req.data = std::make_shared<string>(StreamToSourceAdapter(istream).drain());
         req.mimeType = mimeType;
         try {
             getFileTransfer()->upload(req);
diff --git a/src/libstore/legacy-ssh-store.cc b/src/libstore/legacy-ssh-store.cc
index 5657aa593..a8bd8a972 100644
--- a/src/libstore/legacy-ssh-store.cc
+++ b/src/libstore/legacy-ssh-store.cc
@@ -126,8 +126,7 @@ struct LegacySSHStore : public Store
     }
 
     void addToStore(const ValidPathInfo & info, Source & source,
-        RepairFlag repair, CheckSigsFlag checkSigs,
-        std::shared_ptr<FSAccessor> accessor) override
+        RepairFlag repair, CheckSigsFlag checkSigs) override
     {
         debug("adding path '%s' to remote host '%s'", printStorePath(info.path), host);
 
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index 48aca478c..87d8334d7 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -31,8 +31,18 @@ protected:
     bool fileExists(const std::string & path) override;
 
     void upsertFile(const std::string & path,
-        const std::string & data,
-        const std::string & mimeType) override;
+        std::shared_ptr<std::basic_iostream<char>> istream,
+        const std::string & mimeType) override
+    {
+        auto path2 = binaryCacheDir + "/" + path;
+        Path tmp = path2 + ".tmp." + std::to_string(getpid());
+        AutoDelete del(tmp, false);
+        StreamToSourceAdapter source(istream);
+        writeFile(tmp, source);
+        if (rename(tmp.c_str(), path2.c_str()))
+            throw SysError("renaming '%1%' to '%2%'", tmp, path2);
+        del.cancel();
+    }
 
     void getFile(const std::string & path, Sink & sink) override
     {
@@ -52,7 +62,9 @@ protected:
             if (entry.name.size() != 40 ||
                 !hasSuffix(entry.name, ".narinfo"))
                 continue;
-            paths.insert(parseStorePath(storeDir + "/" + entry.name.substr(0, entry.name.size() - 8)));
+            paths.insert(parseStorePath(
+                    storeDir + "/" + entry.name.substr(0, entry.name.size() - 8)
+                    + "-" + MissingName));
         }
 
         return paths;
@@ -68,28 +80,11 @@ void LocalBinaryCacheStore::init()
     BinaryCacheStore::init();
 }
 
-static void atomicWrite(const Path & path, const std::string & s)
-{
-    Path tmp = path + ".tmp." + std::to_string(getpid());
-    AutoDelete del(tmp, false);
-    writeFile(tmp, s);
-    if (rename(tmp.c_str(), path.c_str()))
-        throw SysError("renaming '%1%' to '%2%'", tmp, path);
-    del.cancel();
-}
-
 bool LocalBinaryCacheStore::fileExists(const std::string & path)
 {
     return pathExists(binaryCacheDir + "/" + path);
 }
 
-void LocalBinaryCacheStore::upsertFile(const std::string & path,
-    const std::string & data,
-    const std::string & mimeType)
-{
-    atomicWrite(binaryCacheDir + "/" + path, data);
-}
-
 static RegisterStoreImplementation regStore([](
     const std::string & uri, const Store::Params & params)
     -> std::shared_ptr<Store>
diff --git a/src/libstore/local-fs-store.cc b/src/libstore/local-fs-store.cc
index dd96d2578..2f1d9663a 100644
--- a/src/libstore/local-fs-store.cc
+++ b/src/libstore/local-fs-store.cc
@@ -20,9 +20,9 @@ struct LocalStoreAccessor : public FSAccessor
 
     Path toRealPath(const Path & path)
     {
-        Path storePath = store->toStorePath(path);
-        if (!store->isValidPath(store->parseStorePath(storePath)))
-            throw InvalidPath("path '%1%' is not a valid store path", storePath);
+        auto storePath = store->toStorePath(path).first;
+        if (!store->isValidPath(storePath))
+            throw InvalidPath("path '%1%' is not a valid store path", store->printStorePath(storePath));
         return store->getRealStoreDir() + std::string(path, store->storeDir.size());
     }
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index eed225349..b3f4b3f7d 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -962,7 +962,7 @@ const PublicKeys & LocalStore::getPublicKeys()
 
 
 void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
-    RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
+    RepairFlag repair, CheckSigsFlag checkSigs)
 {
     if (!info.narHash)
         throw Error("cannot add path '%s' because it lacks a hash", printStorePath(info.path));
@@ -976,7 +976,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
 
         PathLocks outputLock;
 
-        Path realPath = realStoreDir + "/" + std::string(info.path.to_string());
+        auto realPath = Store::toRealPath(info.path);
 
         /* Lock the output path.  But don't lock if we're being called
            from a build hook (whose parent process already acquired a
@@ -1047,8 +1047,7 @@ StorePath LocalStore::addToStoreFromDump(const string & dump, const string & nam
         /* The first check above is an optimisation to prevent
            unnecessary lock acquisition. */
 
-        Path realPath = realStoreDir + "/";
-        realPath += dstPath.to_string();
+        auto realPath = Store::toRealPath(dstPath);
 
         PathLocks outputLock({realPath});
 
@@ -1098,16 +1097,119 @@ StorePath LocalStore::addToStore(const string & name, const Path & _srcPath,
 {
     Path srcPath(absPath(_srcPath));
 
-    /* Read the whole path into memory. This is not a very scalable
-       method for very large paths, but `copyPath' is mainly used for
-       small files. */
-    StringSink sink;
-    if (method == FileIngestionMethod::Recursive)
-        dumpPath(srcPath, sink, filter);
-    else
-        sink.s = make_ref<std::string>(readFile(srcPath));
+    if (method != FileIngestionMethod::Recursive)
+        return addToStoreFromDump(readFile(srcPath), name, method, hashAlgo, repair);
+
+    /* For computing the NAR hash. */
+    auto sha256Sink = std::make_unique<HashSink>(htSHA256);
+
+    /* For computing the store path. In recursive SHA-256 mode, this
+       is the same as the NAR hash, so no need to do it again. */
+    std::unique_ptr<HashSink> hashSink =
+        hashAlgo == htSHA256
+        ? nullptr
+        : std::make_unique<HashSink>(hashAlgo);
+
+    /* Read the source path into memory, but only if it's up to
+       narBufferSize bytes. If it's larger, write it to a temporary
+       location in the Nix store. If the subsequently computed
+       destination store path is already valid, we just delete the
+       temporary path. Otherwise, we move it to the destination store
+       path. */
+    bool inMemory = true;
+    std::string nar;
+
+    auto source = sinkToSource([&](Sink & sink) {
+
+        LambdaSink sink2([&](const unsigned char * buf, size_t len) {
+            (*sha256Sink)(buf, len);
+            if (hashSink) (*hashSink)(buf, len);
+
+            if (inMemory) {
+                if (nar.size() + len > settings.narBufferSize) {
+                    inMemory = false;
+                    sink << 1;
+                    sink((const unsigned char *) nar.data(), nar.size());
+                    nar.clear();
+                } else {
+                    nar.append((const char *) buf, len);
+                }
+            }
+
+            if (!inMemory) sink(buf, len);
+        });
+
+        dumpPath(srcPath, sink2, filter);
+    });
+
+    std::unique_ptr<AutoDelete> delTempDir;
+    Path tempPath;
+
+    try {
+        /* Wait for the source coroutine to give us some dummy
+           data. This is so that we don't create the temporary
+           directory if the NAR fits in memory. */
+        readInt(*source);
+
+        auto tempDir = createTempDir(realStoreDir, "add");
+        delTempDir = std::make_unique<AutoDelete>(tempDir);
+        tempPath = tempDir + "/x";
+
+        restorePath(tempPath, *source);
+
+    } catch (EndOfFile &) {
+        if (!inMemory) throw;
+        /* The NAR fits in memory, so we didn't do restorePath(). */
+    }
+
+    auto sha256 = sha256Sink->finish();
+
+    Hash hash = hashSink ? hashSink->finish().first : sha256.first;
+
+    auto dstPath = makeFixedOutputPath(method, hash, name);
+
+    addTempRoot(dstPath);
+
+    if (repair || !isValidPath(dstPath)) {
+
+        /* The first check above is an optimisation to prevent
+           unnecessary lock acquisition. */
 
-    return addToStoreFromDump(*sink.s, name, method, hashAlgo, repair);
+        auto realPath = Store::toRealPath(dstPath);
+
+        PathLocks outputLock({realPath});
+
+        if (repair || !isValidPath(dstPath)) {
+
+            deletePath(realPath);
+
+            autoGC();
+
+            if (inMemory) {
+                /* Restore from the NAR in memory. */
+                StringSource source(nar);
+                restorePath(realPath, source);
+            } else {
+                /* Move the temporary path we restored above. */
+                if (rename(tempPath.c_str(), realPath.c_str()))
+                    throw Error("renaming '%s' to '%s'", tempPath, realPath);
+            }
+
+            canonicalisePathMetaData(realPath, -1); // FIXME: merge into restorePath
+
+            optimisePath(realPath);
+
+            ValidPathInfo info(dstPath);
+            info.narHash = sha256.first;
+            info.narSize = sha256.second;
+            info.ca = FixedOutputHash { .method = method, .hash = hash };
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
 }
 
 
@@ -1121,8 +1223,7 @@ StorePath LocalStore::addTextToStore(const string & name, const string & s,
 
     if (repair || !isValidPath(dstPath)) {
 
-        Path realPath = realStoreDir + "/";
-        realPath += dstPath.to_string();
+        auto realPath = Store::toRealPath(dstPath);
 
         PathLocks outputLock({realPath});
 
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index 03837bc5f..05f342902 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -140,8 +140,7 @@ public:
         SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & source,
-        RepairFlag repair, CheckSigsFlag checkSigs,
-        std::shared_ptr<FSAccessor> accessor) override;
+        RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method, HashType hashAlgo,
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index ca663d837..d884a131e 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -18,7 +18,7 @@ struct NarMember
 
     /* If this is a regular file, position of the contents of this
        file in the NAR. */
-    size_t start = 0, size = 0;
+    uint64_t start = 0, size = 0;
 
     std::string target;
 
@@ -34,17 +34,19 @@ struct NarAccessor : public FSAccessor
 
     NarMember root;
 
-    struct NarIndexer : ParseSink, StringSource
+    struct NarIndexer : ParseSink, Source
     {
         NarAccessor & acc;
+        Source & source;
 
         std::stack<NarMember *> parents;
 
-        std::string currentStart;
         bool isExec = false;
 
-        NarIndexer(NarAccessor & acc, const std::string & nar)
-            : StringSource(nar), acc(acc)
+        uint64_t pos = 0;
+
+        NarIndexer(NarAccessor & acc, Source & source)
+            : acc(acc), source(source)
         { }
 
         void createMember(const Path & path, NarMember member) {
@@ -79,31 +81,38 @@ struct NarAccessor : public FSAccessor
 
         void preallocateContents(unsigned long long size) override
         {
-            currentStart = string(s, pos, 16);
-            assert(size <= std::numeric_limits<size_t>::max());
-            parents.top()->size = (size_t)size;
+            assert(size <= std::numeric_limits<uint64_t>::max());
+            parents.top()->size = (uint64_t) size;
             parents.top()->start = pos;
         }
 
         void receiveContents(unsigned char * data, unsigned int len) override
-        {
-            // Sanity check
-            if (!currentStart.empty()) {
-                assert(len < 16 || currentStart == string((char *) data, 16));
-                currentStart.clear();
-            }
-        }
+        { }
 
         void createSymlink(const Path & path, const string & target) override
         {
             createMember(path,
                 NarMember{FSAccessor::Type::tSymlink, false, 0, 0, target});
         }
+
+        size_t read(unsigned char * data, size_t len) override
+        {
+            auto n = source.read(data, len);
+            pos += n;
+            return n;
+        }
     };
 
     NarAccessor(ref<const std::string> nar) : nar(nar)
     {
-        NarIndexer indexer(*this, *nar);
+        StringSource source(*nar);
+        NarIndexer indexer(*this, source);
+        parseDump(indexer, indexer);
+    }
+
+    NarAccessor(Source & source)
+    {
+        NarIndexer indexer(*this, source);
         parseDump(indexer, indexer);
     }
 
@@ -219,6 +228,11 @@ ref<FSAccessor> makeNarAccessor(ref<const std::string> nar)
     return make_ref<NarAccessor>(nar);
 }
 
+ref<FSAccessor> makeNarAccessor(Source & source)
+{
+    return make_ref<NarAccessor>(source);
+}
+
 ref<FSAccessor> makeLazyNarAccessor(const std::string & listing,
     GetNarBytes getNarBytes)
 {
diff --git a/src/libstore/nar-accessor.hh b/src/libstore/nar-accessor.hh
index 2871199de..8af1272f6 100644
--- a/src/libstore/nar-accessor.hh
+++ b/src/libstore/nar-accessor.hh
@@ -6,10 +6,14 @@
 
 namespace nix {
 
+struct Source;
+
 /* Return an object that provides access to the contents of a NAR
    file. */
 ref<FSAccessor> makeNarAccessor(ref<const std::string> nar);
 
+ref<FSAccessor> makeNarAccessor(Source & source);
+
 /* Create a NAR accessor from a NAR listing (in the format produced by
    listNar()). The callback getNarBytes(offset, length) is used by the
    readFile() method of the accessor to get the contents of files
diff --git a/src/libstore/path.cc b/src/libstore/path.cc
index b3d8ce95c..dc9dc3897 100644
--- a/src/libstore/path.cc
+++ b/src/libstore/path.cc
@@ -2,8 +2,6 @@
 
 namespace nix {
 
-MakeError(BadStorePath, Error);
-
 static void checkName(std::string_view path, std::string_view name)
 {
     if (name.empty())
diff --git a/src/libstore/remote-fs-accessor.cc b/src/libstore/remote-fs-accessor.cc
index bd698d781..2d02a181b 100644
--- a/src/libstore/remote-fs-accessor.cc
+++ b/src/libstore/remote-fs-accessor.cc
@@ -16,26 +16,26 @@ RemoteFSAccessor::RemoteFSAccessor(ref<Store> store, const Path & cacheDir)
         createDirs(cacheDir);
 }
 
-Path RemoteFSAccessor::makeCacheFile(const Path & storePath, const std::string & ext)
+Path RemoteFSAccessor::makeCacheFile(std::string_view hashPart, const std::string & ext)
 {
     assert(cacheDir != "");
-    return fmt("%s/%s.%s", cacheDir, store->parseStorePath(storePath).hashPart(), ext);
+    return fmt("%s/%s.%s", cacheDir, hashPart, ext);
 }
 
-void RemoteFSAccessor::addToCache(const Path & storePath, const std::string & nar,
+void RemoteFSAccessor::addToCache(std::string_view hashPart, const std::string & nar,
     ref<FSAccessor> narAccessor)
 {
-    nars.emplace(storePath, narAccessor);
+    nars.emplace(hashPart, narAccessor);
 
     if (cacheDir != "") {
         try {
             std::ostringstream str;
             JSONPlaceholder jsonRoot(str);
             listNar(jsonRoot, narAccessor, "", true);
-            writeFile(makeCacheFile(storePath, "ls"), str.str());
+            writeFile(makeCacheFile(hashPart, "ls"), str.str());
 
             /* FIXME: do this asynchronously. */
-            writeFile(makeCacheFile(storePath, "nar"), nar);
+            writeFile(makeCacheFile(hashPart, "nar"), nar);
 
         } catch (...) {
             ignoreException();
@@ -47,23 +47,22 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
 {
     auto path = canonPath(path_);
 
-    auto storePath = store->toStorePath(path);
-    std::string restPath = std::string(path, storePath.size());
+    auto [storePath, restPath] = store->toStorePath(path);
 
-    if (!store->isValidPath(store->parseStorePath(storePath)))
-        throw InvalidPath("path '%1%' is not a valid store path", storePath);
+    if (!store->isValidPath(storePath))
+        throw InvalidPath("path '%1%' is not a valid store path", store->printStorePath(storePath));
 
-    auto i = nars.find(storePath);
+    auto i = nars.find(std::string(storePath.hashPart()));
     if (i != nars.end()) return {i->second, restPath};
 
     StringSink sink;
     std::string listing;
     Path cacheFile;
 
-    if (cacheDir != "" && pathExists(cacheFile = makeCacheFile(storePath, "nar"))) {
+    if (cacheDir != "" && pathExists(cacheFile = makeCacheFile(storePath.hashPart(), "nar"))) {
 
         try {
-            listing = nix::readFile(makeCacheFile(storePath, "ls"));
+            listing = nix::readFile(makeCacheFile(storePath.hashPart(), "ls"));
 
             auto narAccessor = makeLazyNarAccessor(listing,
                 [cacheFile](uint64_t offset, uint64_t length) {
@@ -81,7 +80,7 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
                     return buf;
                 });
 
-            nars.emplace(storePath, narAccessor);
+            nars.emplace(storePath.hashPart(), narAccessor);
             return {narAccessor, restPath};
 
         } catch (SysError &) { }
@@ -90,15 +89,15 @@ std::pair<ref<FSAccessor>, Path> RemoteFSAccessor::fetch(const Path & path_)
             *sink.s = nix::readFile(cacheFile);
 
             auto narAccessor = makeNarAccessor(sink.s);
-            nars.emplace(storePath, narAccessor);
+            nars.emplace(storePath.hashPart(), narAccessor);
             return {narAccessor, restPath};
 
         } catch (SysError &) { }
     }
 
-    store->narFromPath(store->parseStorePath(storePath), sink);
+    store->narFromPath(storePath, sink);
     auto narAccessor = makeNarAccessor(sink.s);
-    addToCache(storePath, *sink.s, narAccessor);
+    addToCache(storePath.hashPart(), *sink.s, narAccessor);
     return {narAccessor, restPath};
 }
 
diff --git a/src/libstore/remote-fs-accessor.hh b/src/libstore/remote-fs-accessor.hh
index 4afb3be95..347cf5764 100644
--- a/src/libstore/remote-fs-accessor.hh
+++ b/src/libstore/remote-fs-accessor.hh
@@ -10,7 +10,7 @@ class RemoteFSAccessor : public FSAccessor
 {
     ref<Store> store;
 
-    std::map<Path, ref<FSAccessor>> nars;
+    std::map<std::string, ref<FSAccessor>> nars;
 
     Path cacheDir;
 
@@ -18,9 +18,9 @@ class RemoteFSAccessor : public FSAccessor
 
     friend class BinaryCacheStore;
 
-    Path makeCacheFile(const Path & storePath, const std::string & ext);
+    Path makeCacheFile(std::string_view hashPart, const std::string & ext);
 
-    void addToCache(const Path & storePath, const std::string & nar,
+    void addToCache(std::string_view hashPart, const std::string & nar,
         ref<FSAccessor> narAccessor);
 
 public:
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 118aadf7e..9af4364b7 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -466,7 +466,7 @@ std::optional<StorePath> RemoteStore::queryPathFromHashPart(const std::string &
 
 
 void RemoteStore::addToStore(const ValidPathInfo & info, Source & source,
-    RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
+    RepairFlag repair, CheckSigsFlag checkSigs)
 {
     auto conn(getConnection());
 
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
index fb2052752..3c1b78b6a 100644
--- a/src/libstore/remote-store.hh
+++ b/src/libstore/remote-store.hh
@@ -60,8 +60,7 @@ public:
         SubstitutablePathInfos & infos) override;
 
     void addToStore(const ValidPathInfo & info, Source & nar,
-        RepairFlag repair, CheckSigsFlag checkSigs,
-        std::shared_ptr<FSAccessor> accessor) override;
+        RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 427dd48ce..1b7dff085 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -7,7 +7,6 @@
 #include "globals.hh"
 #include "compression.hh"
 #include "filetransfer.hh"
-#include "istringstream_nocopy.hh"
 
 #include <aws/core/Aws.h>
 #include <aws/core/VersionConfig.h>
@@ -262,12 +261,11 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
     std::shared_ptr<TransferManager> transferManager;
     std::once_flag transferManagerCreated;
 
-    void uploadFile(const std::string & path, const std::string & data,
+    void uploadFile(const std::string & path,
+        std::shared_ptr<std::basic_iostream<char>> istream,
         const std::string & mimeType,
         const std::string & contentEncoding)
     {
-        auto stream = std::make_shared<istringstream_nocopy>(data);
-
         auto maxThreads = std::thread::hardware_concurrency();
 
         static std::shared_ptr<Aws::Utils::Threading::PooledThreadExecutor>
@@ -307,7 +305,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
 
             std::shared_ptr<TransferHandle> transferHandle =
                 transferManager->UploadFile(
-                    stream, bucketName, path, mimeType,
+                    istream, bucketName, path, mimeType,
                     Aws::Map<Aws::String, Aws::String>(),
                     nullptr /*, contentEncoding */);
 
@@ -333,9 +331,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             if (contentEncoding != "")
                 request.SetContentEncoding(contentEncoding);
 
-            auto stream = std::make_shared<istringstream_nocopy>(data);
-
-            request.SetBody(stream);
+            request.SetBody(istream);
 
             auto result = checkAws(fmt("AWS error uploading '%s'", path),
                 s3Helper.client->PutObject(request));
@@ -347,25 +343,34 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1)
                 .count();
 
-        printInfo(format("uploaded 's3://%1%/%2%' (%3% bytes) in %4% ms") %
-                  bucketName % path % data.size() % duration);
+        auto size = istream->tellg();
+
+        printInfo("uploaded 's3://%s/%s' (%d bytes) in %d ms",
+            bucketName, path, size, duration);
 
         stats.putTimeMs += duration;
-        stats.putBytes += data.size();
+        stats.putBytes += size;
         stats.put++;
     }
 
-    void upsertFile(const std::string & path, const std::string & data,
+    void upsertFile(const std::string & path,
+        std::shared_ptr<std::basic_iostream<char>> istream,
         const std::string & mimeType) override
     {
+        auto compress = [&](std::string compression)
+        {
+            auto compressed = nix::compress(compression, StreamToSourceAdapter(istream).drain());
+            return std::make_shared<std::stringstream>(std::move(*compressed));
+        };
+
         if (narinfoCompression != "" && hasSuffix(path, ".narinfo"))
-            uploadFile(path, *compress(narinfoCompression, data), mimeType, narinfoCompression);
+            uploadFile(path, compress(narinfoCompression), mimeType, narinfoCompression);
         else if (lsCompression != "" && hasSuffix(path, ".ls"))
-            uploadFile(path, *compress(lsCompression, data), mimeType, lsCompression);
+            uploadFile(path, compress(lsCompression), mimeType, lsCompression);
         else if (logCompression != "" && hasPrefix(path, "log/"))
-            uploadFile(path, *compress(logCompression, data), mimeType, logCompression);
+            uploadFile(path, compress(logCompression), mimeType, logCompression);
         else
-            uploadFile(path, data, mimeType, "");
+            uploadFile(path, istream, mimeType, "");
     }
 
     void getFile(const std::string & path, Sink & sink) override
@@ -410,7 +415,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             for (auto object : contents) {
                 auto & key = object.GetKey();
                 if (key.size() != 40 || !hasSuffix(key, ".narinfo")) continue;
-                paths.insert(parseStorePath(storeDir + "/" + key.substr(0, key.size() - 8) + "-unknown"));
+                paths.insert(parseStorePath(storeDir + "/" + key.substr(0, key.size() - 8) + "-" + MissingName));
             }
 
             marker = res.GetNextMarker();
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 3cb3bae4f..5b0b33046 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -7,6 +7,7 @@
 #include "thread-pool.hh"
 #include "json.hh"
 #include "url.hh"
+#include "archive.hh"
 
 #include <future>
 
@@ -20,15 +21,15 @@ bool Store::isInStore(const Path & path) const
 }
 
 
-Path Store::toStorePath(const Path & path) const
+std::pair<StorePath, Path> Store::toStorePath(const Path & path) const
 {
     if (!isInStore(path))
         throw Error("path '%1%' is not in the Nix store", path);
     Path::size_type slash = path.find('/', storeDir.size() + 1);
     if (slash == Path::npos)
-        return path;
+        return {parseStorePath(path), ""};
     else
-        return Path(path, 0, slash);
+        return {parseStorePath(std::string_view(path).substr(0, slash)), path.substr(slash)};
 }
 
 
@@ -41,14 +42,14 @@ Path Store::followLinksToStore(std::string_view _path) const
         path = absPath(target, dirOf(path));
     }
     if (!isInStore(path))
-        throw NotInStore("path '%1%' is not in the Nix store", path);
+        throw BadStorePath("path '%1%' is not in the Nix store", path);
     return path;
 }
 
 
 StorePath Store::followLinksToStorePath(std::string_view path) const
 {
-    return parseStorePath(toStorePath(followLinksToStore(path)));
+    return toStorePath(followLinksToStore(path)).first;
 }
 
 
@@ -221,6 +222,40 @@ StorePath Store::computeStorePathForText(const string & name, const string & s,
 }
 
 
+ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
+    FileIngestionMethod method, HashType hashAlgo,
+    std::optional<Hash> expectedCAHash)
+{
+    /* FIXME: inefficient: we're reading/hashing 'tmpFile' three
+       times. */
+
+    auto [narHash, narSize] = hashPath(htSHA256, srcPath);
+
+    auto hash = method == FileIngestionMethod::Recursive
+        ? hashAlgo == htSHA256
+          ? narHash
+          : hashPath(hashAlgo, srcPath).first
+        : hashFile(hashAlgo, srcPath);
+
+    if (expectedCAHash && expectedCAHash != hash)
+        throw Error("hash mismatch for '%s'", srcPath);
+
+    ValidPathInfo info(makeFixedOutputPath(method, hash, name));
+    info.narHash = narHash;
+    info.narSize = narSize;
+    info.ca = FixedOutputHash { .method = method, .hash = hash };
+
+    if (!isValidPath(info.path)) {
+        auto source = sinkToSource([&](Sink & sink) {
+            dumpPath(srcPath, sink);
+        });
+        addToStore(info, *source);
+    }
+
+    return info;
+}
+
+
 Store::Store(const Params & params)
     : Config(params)
     , state({(size_t) pathInfoCacheSize})
@@ -316,6 +351,14 @@ ref<const ValidPathInfo> Store::queryPathInfo(const StorePath & storePath)
 }
 
 
+static bool goodStorePath(const StorePath & expected, const StorePath & actual)
+{
+    return
+        expected.hashPart() == actual.hashPart()
+        && (expected.name() == Store::MissingName || expected.name() == actual.name());
+}
+
+
 void Store::queryPathInfo(const StorePath & storePath,
     Callback<ref<const ValidPathInfo>> callback) noexcept
 {
@@ -343,7 +386,7 @@ void Store::queryPathInfo(const StorePath & storePath,
                     state_->pathInfoCache.upsert(hashPart,
                         res.first == NarInfoDiskCache::oInvalid ? PathInfoCacheValue{} : PathInfoCacheValue{ .value = res.second });
                     if (res.first == NarInfoDiskCache::oInvalid ||
-                        res.second->path != storePath)
+                        !goodStorePath(storePath, res.second->path))
                         throw InvalidPath("path '%s' is not valid", printStorePath(storePath));
                 }
                 return callback(ref<const ValidPathInfo>(res.second));
@@ -355,7 +398,7 @@ void Store::queryPathInfo(const StorePath & storePath,
     auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
 
     queryPathInfoUncached(storePath,
-        {[this, storePath{printStorePath(storePath)}, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
+        {[this, storePathS{printStorePath(storePath)}, hashPart, callbackPtr](std::future<std::shared_ptr<const ValidPathInfo>> fut) {
 
             try {
                 auto info = fut.get();
@@ -368,9 +411,11 @@ void Store::queryPathInfo(const StorePath & storePath,
                     state_->pathInfoCache.upsert(hashPart, PathInfoCacheValue { .value = info });
                 }
 
-                if (!info || info->path != parseStorePath(storePath)) {
+                auto storePath = parseStorePath(storePathS);
+
+                if (!info || !goodStorePath(storePath, info->path)) {
                     stats.narInfoMissing++;
-                    throw InvalidPath("path '%s' is not valid", storePath);
+                    throw InvalidPath("path '%s' is not valid", storePathS);
                 }
 
                 (*callbackPtr)(ref<const ValidPathInfo>(info));
@@ -515,7 +560,7 @@ void Store::pathInfoToJSON(JSONPlaceholder & jsonOut, const StorePathSet & store
                     if (!narInfo->url.empty())
                         jsonPath.attr("url", narInfo->url);
                     if (narInfo->fileHash)
-                        jsonPath.attr("downloadHash", narInfo->fileHash.to_string(Base32, true));
+                        jsonPath.attr("downloadHash", narInfo->fileHash.to_string(hashBase, true));
                     if (narInfo->fileSize)
                         jsonPath.attr("downloadSize", narInfo->fileSize);
                     if (showClosureSize)
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index b122e05d6..a4be0411e 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -31,7 +31,7 @@ MakeError(InvalidPath, Error);
 MakeError(Unsupported, Error);
 MakeError(SubstituteGone, Error);
 MakeError(SubstituterDisabled, Error);
-MakeError(NotInStore, Error);
+MakeError(BadStorePath, Error);
 
 
 class FSAccessor;
@@ -317,9 +317,9 @@ public:
        the Nix store. */
     bool isStorePath(std::string_view path) const;
 
-    /* Chop off the parts after the top-level store name, e.g.,
-       /nix/store/abcd-foo/bar => /nix/store/abcd-foo. */
-    Path toStorePath(const Path & path) const;
+    /* Split a path like /nix/store/<hash>-<name>/<bla> into
+       /nix/store/<hash>-<name> and /<bla>. */
+    std::pair<StorePath, Path> toStorePath(const Path & path) const;
 
     /* Follow symlinks until we end up with a path in the Nix store. */
     Path followLinksToStore(std::string_view path) const;
@@ -384,13 +384,16 @@ public:
         SubstituteFlag maybeSubstitute = NoSubstitute);
 
     /* Query the set of all valid paths. Note that for some store
-       backends, the name part of store paths may be omitted
-       (i.e. you'll get /nix/store/<hash> rather than
+       backends, the name part of store paths may be replaced by 'x'
+       (i.e. you'll get /nix/store/<hash>-x rather than
        /nix/store/<hash>-<name>). Use queryPathInfo() to obtain the
-       full store path. */
+       full store path. FIXME: should return a set of
+       std::variant<StorePath, HashPart> to get rid of this hack. */
     virtual StorePathSet queryAllValidPaths()
     { unsupported("queryAllValidPaths"); }
 
+    constexpr static const char * MissingName = "x";
+
     /* Query information about a valid path. It is permitted to omit
        the name part of the store path. */
     ref<const ValidPathInfo> queryPathInfo(const StorePath & path);
@@ -439,8 +442,7 @@ public:
 
     /* Import a path into the store. */
     virtual void addToStore(const ValidPathInfo & info, Source & narSource,
-        RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs,
-        std::shared_ptr<FSAccessor> accessor = 0) = 0;
+        RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs) = 0;
 
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.
@@ -450,6 +452,13 @@ public:
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
         PathFilter & filter = defaultPathFilter, RepairFlag repair = NoRepair) = 0;
 
+    /* Copy the contents of a path to the store and register the
+       validity the resulting path, using a constant amount of
+       memory. */
+    ValidPathInfo addToStoreSlow(std::string_view name, const Path & srcPath,
+        FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256,
+        std::optional<Hash> expectedCAHash = {});
+
     // FIXME: remove?
     virtual StorePath addToStoreFromDump(const string & dump, const string & name,
         FileIngestionMethod method = FileIngestionMethod::Recursive, HashType hashAlgo = htSHA256, RepairFlag repair = NoRepair)
@@ -616,8 +625,7 @@ public:
        the Nix store. Optionally, the contents of the NARs are
        preloaded into the specified FS accessor to speed up subsequent
        access. */
-    StorePaths importPaths(Source & source, std::shared_ptr<FSAccessor> accessor,
-        CheckSigsFlag checkSigs = CheckSigs);
+    StorePaths importPaths(Source & source, CheckSigsFlag checkSigs = CheckSigs);
 
     struct Stats
     {
diff --git a/src/libutil/ansicolor.hh b/src/libutil/ansicolor.hh
index a38c2d798..ae741f867 100644
--- a/src/libutil/ansicolor.hh
+++ b/src/libutil/ansicolor.hh
@@ -11,7 +11,7 @@ namespace nix {
 #define ANSI_GREEN "\e[32;1m"
 #define ANSI_YELLOW "\e[33;1m"
 #define ANSI_BLUE "\e[34;1m"
-#define ANSI_MAGENTA "\e[35m;1m"
-#define ANSI_CYAN "\e[36m;1m"
+#define ANSI_MAGENTA "\e[35;1m"
+#define ANSI_CYAN "\e[36;1m"
 
 }
diff --git a/src/libutil/archive.hh b/src/libutil/archive.hh
index 768fe2536..302b1bb18 100644
--- a/src/libutil/archive.hh
+++ b/src/libutil/archive.hh
@@ -63,11 +63,12 @@ struct ParseSink
     virtual void createSymlink(const Path & path, const string & target) { };
 };
 
-struct TeeSink : ParseSink
+struct TeeParseSink : ParseSink
 {
+    StringSink saved;
     TeeSource source;
 
-    TeeSink(Source & source) : source(source) { }
+    TeeParseSink(Source & source) : source(source, saved) { }
 };
 
 void parseDump(ParseSink & sink, Source & source);
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index a4ee7afc2..fd6f69b7f 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -355,26 +355,21 @@ std::ostream& showErrorInfo(std::ostream &out, const ErrorInfo &einfo, bool show
 
         for (auto iter = einfo.traces.rbegin(); iter != einfo.traces.rend(); ++iter)
         {
-            try {
+            out << std::endl << prefix;
+            out << ANSI_BLUE << "trace: " << ANSI_NORMAL << iter->hint.str();
+
+            if (iter->pos.has_value() && (*iter->pos)) {
+                auto pos = iter->pos.value();
                 out << std::endl << prefix;
-                out << ANSI_BLUE << "trace: " << ANSI_NORMAL << iter->hint.str();
+                printAtPos(prefix, pos, out);
 
-                nl = true;
-                if (*iter->pos) {
-                    auto pos = iter->pos.value();
+                auto loc = getCodeLines(pos);
+                if (loc.has_value())
+                {
+                    out << std::endl << prefix;
+                    printCodeLines(out, prefix, pos, *loc);
                     out << std::endl << prefix;
-
-                    printAtPos(prefix, pos, out);
-                    auto loc = getCodeLines(pos);
-                    if (loc.has_value())
-                    {
-                        out << std::endl << prefix;
-                        printCodeLines(out, prefix, pos, *loc);
-                        out << std::endl << prefix;
-                    }
                 }
-            } catch(const std::bad_optional_access& e) {
-                out << iter->hint.str() << std::endl;
             }
         }
     }
diff --git a/src/libutil/error.hh b/src/libutil/error.hh
index 1b0fb43b8..f4b3f11bb 100644
--- a/src/libutil/error.hh
+++ b/src/libutil/error.hh
@@ -1,8 +1,8 @@
 #pragma once
 
-
 #include "ref.hh"
 #include "types.hh"
+#include "fmt.hh"
 
 #include <cstring>
 #include <list>
@@ -10,7 +10,9 @@
 #include <map>
 #include <optional>
 
-#include "fmt.hh"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 
 /* Before 4.7, gcc's std::exception uses empty throw() specifiers for
  * its (virtual) destructor and what() in c++11 mode, in violation of spec
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 1a3e7c5d8..f0d7754d1 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -8,7 +8,6 @@
 #include "hash.hh"
 #include "archive.hh"
 #include "util.hh"
-#include "istringstream_nocopy.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
diff --git a/src/libutil/istringstream_nocopy.hh b/src/libutil/istringstream_nocopy.hh
deleted file mode 100644
index f7beac578..000000000
--- a/src/libutil/istringstream_nocopy.hh
+++ /dev/null
@@ -1,92 +0,0 @@
-/* This file provides a variant of std::istringstream that doesn't
-   copy its string argument. This is useful for large strings. The
-   caller must ensure that the string object is not destroyed while
-   it's referenced by this object. */
-
-#pragma once
-
-#include <string>
-#include <iostream>
-
-template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
-class basic_istringbuf_nocopy : public std::basic_streambuf<CharT, Traits>
-{
-public:
-    typedef std::basic_string<CharT, Traits, Allocator> string_type;
-
-    typedef typename std::basic_streambuf<CharT, Traits>::off_type off_type;
-
-    typedef typename std::basic_streambuf<CharT, Traits>::pos_type pos_type;
-
-    typedef typename std::basic_streambuf<CharT, Traits>::int_type int_type;
-
-    typedef typename std::basic_streambuf<CharT, Traits>::traits_type traits_type;
-
-private:
-    const string_type & s;
-
-    off_type off;
-
-public:
-    basic_istringbuf_nocopy(const string_type & s) : s{s}, off{0}
-    {
-    }
-
-private:
-    pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode which)
-    {
-        if (which & std::ios_base::in) {
-            this->off = dir == std::ios_base::beg
-                ? off
-                : (dir == std::ios_base::end
-                    ? s.size() + off
-                    : this->off + off);
-        }
-        return pos_type(this->off);
-    }
-
-    pos_type seekpos(pos_type pos, std::ios_base::openmode which)
-    {
-        return seekoff(pos, std::ios_base::beg, which);
-    }
-
-    std::streamsize showmanyc()
-    {
-        return s.size() - off;
-    }
-
-    int_type underflow()
-    {
-        if (typename string_type::size_type(off) == s.size())
-            return traits_type::eof();
-        return traits_type::to_int_type(s[off]);
-    }
-
-    int_type uflow()
-    {
-        if (typename string_type::size_type(off) == s.size())
-            return traits_type::eof();
-        return traits_type::to_int_type(s[off++]);
-    }
-
-    int_type pbackfail(int_type ch)
-    {
-        if (off == 0 || (ch != traits_type::eof() && ch != s[off - 1]))
-            return traits_type::eof();
-
-        return traits_type::to_int_type(s[--off]);
-    }
-
-};
-
-template <class CharT, class Traits = std::char_traits<CharT>, class Allocator = std::allocator<CharT>>
-class basic_istringstream_nocopy : public std::basic_iostream<CharT, Traits>
-{
-    typedef basic_istringbuf_nocopy<CharT, Traits, Allocator> buf_type;
-    buf_type buf;
-public:
-    basic_istringstream_nocopy(const typename buf_type::string_type & s) :
-        std::basic_iostream<CharT, Traits>(&buf), buf(s) {};
-};
-
-typedef basic_istringstream_nocopy<char> istringstream_nocopy;
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 90c6afe81..832aee783 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -81,7 +81,6 @@ public:
 
         log(ei.level, oss.str());
     }
-    
 
     void startActivity(ActivityId act, Verbosity lvl, ActivityType type,
         const std::string & s, const Fields & fields, ActivityId parent)
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index a04118512..8386a4991 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -166,17 +166,30 @@ struct StringSource : Source
 };
 
 
-/* Adapter class of a Source that saves all data read to `s'. */
+/* A sink that writes all incoming data to two other sinks. */
+struct TeeSink : Sink
+{
+    Sink & sink1, & sink2;
+    TeeSink(Sink & sink1, Sink & sink2) : sink1(sink1), sink2(sink2) { }
+    virtual void operator () (const unsigned char * data, size_t len)
+    {
+        sink1(data, len);
+        sink2(data, len);
+    }
+};
+
+
+/* Adapter class of a Source that saves all data read to a sink. */
 struct TeeSource : Source
 {
     Source & orig;
-    ref<std::string> data;
-    TeeSource(Source & orig)
-        : orig(orig), data(make_ref<std::string>()) { }
+    Sink & sink;
+    TeeSource(Source & orig, Sink & sink)
+        : orig(orig), sink(sink) { }
     size_t read(unsigned char * data, size_t len)
     {
         size_t n = orig.read(data, len);
-        this->data->append((const char *) data, n);
+        sink(data, len);
         return n;
     }
 };
@@ -336,4 +349,27 @@ Source & operator >> (Source & in, bool & b)
 }
 
 
+/* An adapter that converts a std::basic_istream into a source. */
+struct StreamToSourceAdapter : Source
+{
+    std::shared_ptr<std::basic_istream<char>> istream;
+
+    StreamToSourceAdapter(std::shared_ptr<std::basic_istream<char>> istream)
+        : istream(istream)
+    { }
+
+    size_t read(unsigned char * data, size_t len) override
+    {
+        if (!istream->read((char *) data, len)) {
+            if (istream->eof()) {
+                if (istream->gcount() == 0)
+                    throw EndOfFile("end of file");
+            } else
+                throw Error("I/O error in StreamToSourceAdapter");
+        }
+        return istream->gcount();
+    }
+};
+
+
 }
diff --git a/src/libutil/tests/logging.cc b/src/libutil/tests/logging.cc
index ef22e9966..ad588055f 100644
--- a/src/libutil/tests/logging.cc
+++ b/src/libutil/tests/logging.cc
@@ -251,18 +251,19 @@ namespace nix {
     TEST(addTrace, showTracesWithShowTrace) {
         SymbolTable testTable;
         auto problem_file = testTable.create(test_file);
-
         auto oneliner_file = testTable.create(one_liner);
+        auto invalidfilename = testTable.create("invalid filename");
 
         auto e = AssertionError(ErrorInfo {
                 .name = "wat",
-                .description = "a well-known problem occurred",
+                .description = "show-traces",
                 .hint = hintfmt("it has been %1% days since our last error", "zero"),
                 .errPos = Pos(foString, problem_file, 2, 13),
             });
 
         e.addTrace(Pos(foStdin, oneliner_file, 1, 19), "while trying to compute %1%", 42);
         e.addTrace(std::nullopt, "while doing something without a %1%", "pos");
+        e.addTrace(Pos(foFile, invalidfilename, 100, 1), "missing %s", "nix file");
 
         testing::internal::CaptureStderr();
 
@@ -271,24 +272,25 @@ namespace nix {
         logError(e.info());
 
         auto str = testing::internal::GetCapturedStderr();
-        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- AssertionError --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from string\x1B[0m\n\na well-known problem occurred\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nit has been \x1B[33;1mzero\x1B[0m days since our last error\n\x1B[34;1m---- show-trace ----\x1B[0m\n\x1B[34;1mtrace: \x1B[0mwhile trying to compute \x1B[33;1m42\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(1:19)\x1B[34;1m from stdin\x1B[0m\n\n     1| this is the other problem line of code\n      |                   \x1B[31;1m^\x1B[0m\n\n\x1B[34;1mtrace: \x1B[0mwhile doing something without a \x1B[33;1mpos\x1B[0m\n");
+        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- SysError --- error-unit-test\x1B[0m\nopening file '\x1B[33;1minvalid filename\x1B[0m': \x1B[33;1mNo such file or directory\x1B[0m\n\x1B[31;1merror:\x1B[0m\x1B[34;1m --- AssertionError --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from string\x1B[0m\n\nshow-traces\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nit has been \x1B[33;1mzero\x1B[0m days since our last error\n\x1B[34;1m---- show-trace ----\x1B[0m\n\x1B[34;1mtrace: \x1B[0mwhile trying to compute \x1B[33;1m42\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(1:19)\x1B[34;1m from stdin\x1B[0m\n\n     1| this is the other problem line of code\n      |                   \x1B[31;1m^\x1B[0m\n\n\x1B[34;1mtrace: \x1B[0mwhile doing something without a \x1B[33;1mpos\x1B[0m\n\x1B[34;1mtrace: \x1B[0mmissing \x1B[33;1mnix file\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(100:1)\x1B[34;1m in file: \x1B[0minvalid filename\n");
     }
 
     TEST(addTrace, hideTracesWithoutShowTrace) {
         SymbolTable testTable;
         auto problem_file = testTable.create(test_file);
-
         auto oneliner_file = testTable.create(one_liner);
+        auto invalidfilename = testTable.create("invalid filename");
 
         auto e = AssertionError(ErrorInfo {
                 .name = "wat",
-                .description = "a well-known problem occurred",
+                .description = "hide traces",
                 .hint = hintfmt("it has been %1% days since our last error", "zero"),
                 .errPos = Pos(foString, problem_file, 2, 13),
             });
 
         e.addTrace(Pos(foStdin, oneliner_file, 1, 19), "while trying to compute %1%", 42);
         e.addTrace(std::nullopt, "while doing something without a %1%", "pos");
+        e.addTrace(Pos(foFile, invalidfilename, 100, 1), "missing %s", "nix file");
 
         testing::internal::CaptureStderr();
 
@@ -297,9 +299,10 @@ namespace nix {
         logError(e.info());
 
         auto str = testing::internal::GetCapturedStderr();
-        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- AssertionError --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from string\x1B[0m\n\na well-known problem occurred\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nit has been \x1B[33;1mzero\x1B[0m days since our last error\n");
+        ASSERT_STREQ(str.c_str(), "\x1B[31;1merror:\x1B[0m\x1B[34;1m --- AssertionError --- error-unit-test\x1B[0m\n\x1B[34;1mat: \x1B[33;1m(2:13)\x1B[34;1m from string\x1B[0m\n\nhide traces\n\n     1| previous line of code\n     2| this is the problem line of code\n      |             \x1B[31;1m^\x1B[0m\n     3| next line of code\n\nit has been \x1B[33;1mzero\x1B[0m days since our last error\n");
     }
 
+
     /* ----------------------------------------------------------------------------
      * hintfmt
      * --------------------------------------------------------------------------*/
diff --git a/src/nix-prefetch-url/nix-prefetch-url.cc b/src/nix-prefetch-url/nix-prefetch-url.cc
index 40b05a2f3..961e7fb6d 100644
--- a/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -153,14 +153,15 @@ static int _main(int argc, char * * argv)
 
         /* If an expected hash is given, the file may already exist in
            the store. */
-        Hash hash, expectedHash(ht);
+        std::optional<Hash> expectedHash;
+        Hash hash;
         std::optional<StorePath> storePath;
         if (args.size() == 2) {
             expectedHash = Hash(args[1], ht);
             const auto recursive = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
-            storePath = store->makeFixedOutputPath(recursive, expectedHash, name);
+            storePath = store->makeFixedOutputPath(recursive, *expectedHash, name);
             if (store->isValidPath(*storePath))
-                hash = expectedHash;
+                hash = *expectedHash;
             else
                 storePath.reset();
         }
@@ -200,22 +201,12 @@ static int _main(int argc, char * * argv)
                     tmpFile = unpacked;
             }
 
-            /* FIXME: inefficient; addToStore() will also hash
-               this. */
-            hash = unpack ? hashPath(ht, tmpFile).first : hashFile(ht, tmpFile);
+            const auto method = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
 
-            if (expectedHash != Hash(ht) && expectedHash != hash)
-                throw Error("hash mismatch for '%1%'", uri);
-
-            const auto recursive = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
-
-            /* Copy the file to the Nix store. FIXME: if RemoteStore
-               implemented addToStoreFromDump() and downloadFile()
-               supported a sink, we could stream the download directly
-               into the Nix store. */
-            storePath = store->addToStore(name, tmpFile, recursive, ht);
-
-            assert(*storePath == store->makeFixedOutputPath(recursive, hash, name));
+            auto info = store->addToStoreSlow(name, tmpFile, method, ht, expectedHash);
+            storePath = info.path;
+            assert(info.ca);
+            hash = getContentAddressHash(*info.ca);
         }
 
         stopProgressBar();
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 7d81bf54f..23bb48d88 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -174,10 +174,10 @@ static void opAdd(Strings opFlags, Strings opArgs)
    store. */
 static void opAddFixed(Strings opFlags, Strings opArgs)
 {
-    auto recursive = FileIngestionMethod::Flat;
+    auto method = FileIngestionMethod::Flat;
 
     for (auto & i : opFlags)
-        if (i == "--recursive") recursive = FileIngestionMethod::Recursive;
+        if (i == "--recursive") method = FileIngestionMethod::Recursive;
         else throw UsageError("unknown flag '%1%'", i);
 
     if (opArgs.empty())
@@ -187,7 +187,7 @@ static void opAddFixed(Strings opFlags, Strings opArgs)
     opArgs.pop_front();
 
     for (auto & i : opArgs)
-        cout << fmt("%s\n", store->printStorePath(store->addToStore(std::string(baseNameOf(i)), i, recursive, hashAlgo)));
+        std::cout << fmt("%s\n", store->printStorePath(store->addToStoreSlow(baseNameOf(i), i, method, hashAlgo).path));
 }
 
 
@@ -671,7 +671,7 @@ static void opImport(Strings opFlags, Strings opArgs)
     if (!opArgs.empty()) throw UsageError("no arguments expected");
 
     FdSource source(STDIN_FILENO);
-    auto paths = store->importPaths(source, nullptr, NoCheckSigs);
+    auto paths = store->importPaths(source, NoCheckSigs);
 
     for (auto & i : paths)
         cout << fmt("%s\n", store->printStorePath(i)) << std::flush;
@@ -878,7 +878,7 @@ static void opServe(Strings opFlags, Strings opArgs)
 
             case cmdImportPaths: {
                 if (!writeAllowed) throw Error("importing paths is not allowed");
-                store->importPaths(in, nullptr, NoCheckSigs); // FIXME: should we skip sig checking?
+                store->importPaths(in, NoCheckSigs); // FIXME: should we skip sig checking?
                 out << 1; // indicate success
                 break;
             }
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 708a0dc88..1b04b10d5 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -94,8 +94,8 @@ struct InstallableStorePath : Installable
     ref<Store> store;
     StorePath storePath;
 
-    InstallableStorePath(ref<Store> store, const Path & storePath)
-        : store(store), storePath(store->parseStorePath(storePath)) { }
+    InstallableStorePath(ref<Store> store, StorePath && storePath)
+        : store(store), storePath(std::move(storePath)) { }
 
     std::string what() override { return store->printStorePath(storePath); }
 
@@ -228,11 +228,11 @@ static std::vector<std::shared_ptr<Installable>> parseInstallables(
             result.push_back(std::make_shared<InstallableExpr>(cmd, s));
 
         else if (s.find("/") != std::string::npos) {
-
-            auto path = store->toStorePath(store->followLinksToStore(s));
-
-            if (store->isStorePath(path))
-                result.push_back(std::make_shared<InstallableStorePath>(store, path));
+            try {
+                result.push_back(std::make_shared<InstallableStorePath>(
+                        store,
+                        store->toStorePath(store->followLinksToStore(s)).first));
+            } catch (BadStorePath &) { }
         }
 
         else if (s == "" || std::regex_match(s, attrPathRegex))
diff --git a/src/nix/verify.cc b/src/nix/verify.cc
index bb5e4529b..ce90b0f6d 100644
--- a/src/nix/verify.cc
+++ b/src/nix/verify.cc
@@ -77,13 +77,16 @@ struct CmdVerify : StorePathsCommand
             try {
                 checkInterrupt();
 
-                Activity act2(*logger, lvlInfo, actUnknown, fmt("checking '%s'", storePath));
-
                 MaintainCount<std::atomic<size_t>> mcActive(active);
                 update();
 
                 auto info = store->queryPathInfo(store->parseStorePath(storePath));
 
+                // Note: info->path can be different from storePath
+                // for binary cache stores when using --all (since we
+                // can't enumerate names efficiently).
+                Activity act2(*logger, lvlInfo, actUnknown, fmt("checking '%s'", store->printStorePath(info->path)));
+
                 if (!noContents) {
 
                     std::unique_ptr<AbstractHashSink> hashSink;
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index 167c974ee..49da01c0a 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -106,7 +106,11 @@ struct CmdWhyDepends : SourceExprCommand
         std::map<StorePath, Node> graph;
 
         for (auto & path : closure)
-            graph.emplace(path, Node { .path = path, .refs = store->queryPathInfo(path)->references });
+            graph.emplace(path, Node {
+                .path = path,
+                .refs = store->queryPathInfo(path)->references,
+                .dist = path == dependencyPath ? 0 : inf
+            });
 
         // Transpose the graph.
         for (auto & node : graph)
@@ -115,8 +119,6 @@ struct CmdWhyDepends : SourceExprCommand
 
         /* Run Dijkstra's shortest path algorithm to get the distance
            of every path in the closure to 'dependency'. */
-        graph.emplace(dependencyPath, Node { .path = dependencyPath, .dist = 0 });
-
         std::priority_queue<Node *> queue;
 
         queue.push(&graph.at(dependencyPath));