From cbc43442977a6fbbd046a98fcb09362a60323b5d Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Wed, 12 Aug 2020 03:47:36 +0000
Subject: Trustless remote building

Co-authored-by: Matthew Bauer <mjbauer95@gmail.com>
---
 src/build-remote/build-remote.cc              | 22 ++++++++----
 src/libstore/daemon.cc                        |  2 ++
 src/libstore/store-api.cc                     | 18 +++++++++-
 src/libstore/store-api.hh                     |  4 ++-
 src/nix-daemon/nix-daemon.cc                  | 19 ++++++++--
 tests/build-hook-ca.nix                       | 52 +++++++++++++++++++++++++++
 tests/build-remote-trustless-should-fail-0.sh | 11 ++++++
 tests/build-remote-trustless-should-pass-0.sh |  9 +++++
 tests/build-remote-trustless-should-pass-1.sh |  9 +++++
 tests/build-remote-trustless-should-pass-2.sh |  9 +++++
 tests/build-remote-trustless-should-pass-3.sh | 10 ++++++
 tests/build-remote-trustless.sh               | 18 ++++++++++
 tests/init.sh                                 |  2 +-
 tests/local.mk                                |  5 +++
 tests/nix-daemon-untrusting.sh                |  3 ++
 15 files changed, 181 insertions(+), 12 deletions(-)
 create mode 100644 tests/build-hook-ca.nix
 create mode 100644 tests/build-remote-trustless-should-fail-0.sh
 create mode 100644 tests/build-remote-trustless-should-pass-0.sh
 create mode 100644 tests/build-remote-trustless-should-pass-1.sh
 create mode 100644 tests/build-remote-trustless-should-pass-2.sh
 create mode 100644 tests/build-remote-trustless-should-pass-3.sh
 create mode 100644 tests/build-remote-trustless.sh
 create mode 100755 tests/nix-daemon-untrusting.sh

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index ce5127113..8ae1cabfe 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -247,6 +247,9 @@ static int _main(int argc, char * * argv)
 connected:
         close(5);
 
+        assert(sshStore);
+        auto sshStore2 = ref<Store>(sshStore);
+
         std::cerr << "# accept\n" << storeUri << "\n";
 
         auto inputs = readStrings<PathSet>(source);
@@ -269,18 +272,23 @@ connected:
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(store, ref<Store>(sshStore), store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
+            copyPaths(store, sshStore2, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
         }
 
         uploadLock = -1;
 
-        auto drv = store->readDerivation(*drvPath);
-        drv.inputSrcs = store->parseStorePathSet(inputs);
+        BasicDerivation drv = store->readDerivation(*drvPath);
 
-        auto result = sshStore->buildDerivation(*drvPath, drv);
+        if (sshStore2->isTrusting || derivationIsCA(drv.type())) {
+            drv.inputSrcs = store->parseStorePathSet(inputs);
+            auto result = sshStore2->buildDerivation(*drvPath, drv);
+            if (!result.success())
+                throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
+        } else {
+            copyPaths(store, sshStore2, {*drvPath}, NoRepair, NoCheckSigs, substitute);
+            sshStore2->buildPaths({{*drvPath}});
+        }
 
-        if (!result.success())
-            throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
 
         StorePathSet missing;
         for (auto & path : outputs)
@@ -290,7 +298,7 @@ connected:
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri));
             for (auto & i : missing)
                 store->locksHeld.insert(store->printStorePath(i)); /* FIXME: ugly */
-            copyPaths(ref<Store>(sshStore), store, missing, NoRepair, NoCheckSigs, NoSubstitute);
+            copyPaths(sshStore2, store, missing, NoRepair, NoCheckSigs, NoSubstitute);
         }
 
         return 0;
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 45e81c8da..ffa7e0dcd 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -914,6 +914,8 @@ void processConnection(
 
             opCount++;
 
+            debug("performing daemon worker op: %d", op);
+
             try {
                 performOp(tunnelLogger, store, trusted, recursive, clientVersion, from, to, op);
             } catch (Error & e) {
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 3d07e2d38..360820b1b 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -834,7 +834,23 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                 MaintainCount<decltype(nrRunning)> mc(nrRunning);
                 showProgress();
                 try {
-                    copyStorePath(srcStore, dstStore, storePath, repair, checkSigs);
+                    if (dstStore->isTrusting || info->ca) {
+                        copyStorePath(srcStore, dstStore, storePath, repair, checkSigs);
+                    } else if (info->deriver && dstStore->storeDir == srcStore->storeDir) {
+                        auto drvPath = *info->deriver;
+                        auto outputMap = srcStore->queryDerivationOutputMap(drvPath);
+                        auto p = std::find_if(outputMap.begin(), outputMap.end(), [&](auto & i) {
+                            return i.second == storePath;
+                        });
+                        // drv file is always CA
+                        copyStorePath(srcStore, dstStore, drvPath, repair, checkSigs);
+                        dstStore->buildPaths({{
+                            drvPath,
+                            p != outputMap.end() ? StringSet { p->first } : StringSet {},
+                        }});
+                    } else {
+                        dstStore->ensurePath(storePath);
+                    }
                 } catch (Error &e) {
                     nrFailed++;
                     if (!settings.keepGoing)
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 1e940e6a8..4ba51a9e5 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -158,7 +158,9 @@ public:
 
     const Setting<int> pathInfoCacheSize{this, 65536, "path-info-cache-size", "size of the in-memory store path information cache"};
 
-    const Setting<bool> isTrusted{this, false, "trusted", "whether paths from this store can be used as substitutes even when they lack trusted signatures"};
+    const Setting<bool> isTrusted{this, false, "trusted", "whether paths from this store can be used as substitutes even when they lack trusted signatures. Compare \"trusting\""};
+
+    Setting<bool> isTrusting{this, true, "trusting", "whether (we think) paths can be added to this store even when they lack trusted signatures. Compare \"trusted\""};
 
     Setting<int> priority{this, 0, "priority", "priority of this substituter (lower value means higher priority)"};
 
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index cfa634a44..ce963acdc 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -268,6 +268,7 @@ static int _main(int argc, char * * argv)
 {
     {
         auto stdio = false;
+        std::optional<TrustedFlag> isTrustedOpt;
 
         parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--daemon")
@@ -278,14 +279,26 @@ static int _main(int argc, char * * argv)
                 printVersion("nix-daemon");
             else if (*arg == "--stdio")
                 stdio = true;
-            else return false;
+            else if (*arg == "--trust") {
+                settings.requireExperimentalFeature("nix-testing");
+                isTrustedOpt = Trusted;
+            } else if (*arg == "--no-trust") {
+                settings.requireExperimentalFeature("nix-testing");
+                isTrustedOpt = NotTrusted;
+            } else return false;
             return true;
         });
 
         initPlugins();
 
+        auto ensureNoTrustedFlag = [&]() {
+            if (isTrustedOpt)
+                throw Error("--trust and --no-trust flags are only for use with --stdio when this nix-daemon process is not proxying another");
+        };
+
         if (stdio) {
             if (getStoreType() == tDaemon) {
+                ensureNoTrustedFlag();
                 //  Forward on this connection to the real daemon
                 auto socketPath = settings.nixDaemonSocketFile;
                 auto s = socket(PF_UNIX, SOCK_STREAM, 0);
@@ -335,9 +348,11 @@ static int _main(int argc, char * * argv)
                 /* Auth hook is empty because in this mode we blindly trust the
                    standard streams. Limitting access to thoses is explicitly
                    not `nix-daemon`'s responsibility. */
-                processConnection(openUncachedStore(), from, to, Trusted, NotRecursive, [&](Store & _){});
+                auto isTrusted = isTrustedOpt.value_or(Trusted);
+                processConnection(openUncachedStore(), from, to, isTrusted, NotRecursive, [&](Store & _){});
             }
         } else {
+            ensureNoTrustedFlag();
             daemonLoop(argv);
         }
 
diff --git a/tests/build-hook-ca.nix b/tests/build-hook-ca.nix
new file mode 100644
index 000000000..c0bc6d211
--- /dev/null
+++ b/tests/build-hook-ca.nix
@@ -0,0 +1,52 @@
+{ busybox }:
+
+with import ./config.nix;
+
+let
+
+  mkDerivation = args:
+    derivation ({
+      inherit system;
+      builder = busybox;
+      args = ["sh" "-e" args.builder or (builtins.toFile "builder-${args.name}.sh" "if [ -e .attrs.sh ]; then source .attrs.sh; fi; eval \"$buildCommand\"")];
+      outputHashMode = "recursive";
+      outputHashAlgo = "sha256";
+    } // removeAttrs args ["builder" "meta"])
+    // { meta = args.meta or {}; };
+
+  input1 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-1";
+    buildCommand = "echo FOO > $out";
+    outputHash = "sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc=";
+  };
+
+  input2 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-2";
+    buildCommand = "echo BAR > $out";
+    outputHash = "sha256-XArauVH91AVwP9hBBQNlkX9ccuPpSYx9o0zeIHb6e+Q=";
+  };
+
+  input3 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-3";
+    buildCommand = ''
+      read x < ${input2}
+      echo $x BAZ > $out
+    '';
+    outputHash = "sha256-daKAcPp/+BYMQsVi/YYMlCKoNAxCNDsaivwSHgQqD2s=";
+  };
+
+in
+
+  mkDerivation {
+    shell = busybox;
+    name = "build-remote";
+    buildCommand = ''
+      read x < ${input1}
+      read y < ${input3}
+      echo "$x $y" > $out
+    '';
+    outputHash = "sha256-5SxbkUw6xe2l9TE1uwCvTtTDysD1vhRor38OtDF0LqQ=";
+  }
diff --git a/tests/build-remote-trustless-should-fail-0.sh b/tests/build-remote-trustless-should-fail-0.sh
new file mode 100644
index 000000000..b72c134e7
--- /dev/null
+++ b/tests/build-remote-trustless-should-fail-0.sh
@@ -0,0 +1,11 @@
+source common.sh
+
+# We act as if remote trusts us, but it doesn't. This fails since we are
+# building input-addressed derivations with `buildDerivation`, which
+# depends on trust.
+file=build-hook.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+trusting=true
+
+! source build-remote-trustless.sh
diff --git a/tests/build-remote-trustless-should-pass-0.sh b/tests/build-remote-trustless-should-pass-0.sh
new file mode 100644
index 000000000..82c3f4520
--- /dev/null
+++ b/tests/build-remote-trustless-should-pass-0.sh
@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us but we pretend it doesn't.
+file=build-hook.nix
+prog=nix-store
+proto=ssh
+trusting=false
+
+source build-remote-trustless.sh
diff --git a/tests/build-remote-trustless-should-pass-1.sh b/tests/build-remote-trustless-should-pass-1.sh
new file mode 100644
index 000000000..22c304bc2
--- /dev/null
+++ b/tests/build-remote-trustless-should-pass-1.sh
@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us but we pretend it doesn't.
+file=build-hook.nix
+prog=nix-daemon
+proto=ssh-ng
+trusting=false
+
+source build-remote-trustless.sh
diff --git a/tests/build-remote-trustless-should-pass-2.sh b/tests/build-remote-trustless-should-pass-2.sh
new file mode 100644
index 000000000..941ddca05
--- /dev/null
+++ b/tests/build-remote-trustless-should-pass-2.sh
@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote doesn't trust us nor do we think it does
+file=build-hook.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+trusting=false
+
+source build-remote-trustless.sh
diff --git a/tests/build-remote-trustless-should-pass-3.sh b/tests/build-remote-trustless-should-pass-3.sh
new file mode 100644
index 000000000..d4f7e863a
--- /dev/null
+++ b/tests/build-remote-trustless-should-pass-3.sh
@@ -0,0 +1,10 @@
+source common.sh
+
+# We act as if remote trusts us, but it doesn't. This is fine because we
+# are only building (fixed) CA derivations.
+file=build-hook-ca.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+trusting=true
+
+source build-remote-trustless.sh
diff --git a/tests/build-remote-trustless.sh b/tests/build-remote-trustless.sh
new file mode 100644
index 000000000..2689e5727
--- /dev/null
+++ b/tests/build-remote-trustless.sh
@@ -0,0 +1,18 @@
+if ! canUseSandbox; then exit; fi
+if ! [[ $busybox =~ busybox ]]; then exit; fi
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+# Note: ssh://localhost bypasses ssh, directly invoking nix-store as a
+# child process. This allows us to test LegacySSHStore::buildDerivation().
+# ssh-ng://... likewise allows us to test RemoteStore::buildDerivation().
+
+nix build -L -v -f $file -o $TEST_ROOT/result --max-jobs 0 \
+  --arg busybox $busybox \
+  --store $TEST_ROOT/local \
+  --builders "$proto://localhost?remote-program=$prog&trusting=$trusting&remote-store=$TEST_ROOT/remote%3Fsystem-features=foo%20bar%20baz - - 1 1 foo,bar,baz"
+
+outPath=$(readlink -f $TEST_ROOT/result)
+
+grep 'FOO BAR BAZ' $TEST_ROOT/${subDir}/local${outPath}
diff --git a/tests/init.sh b/tests/init.sh
index f9ced6b0d..7adababf9 100644
--- a/tests/init.sh
+++ b/tests/init.sh
@@ -17,7 +17,7 @@ cat > "$NIX_CONF_DIR"/nix.conf <<EOF
 build-users-group =
 keep-derivations = false
 sandbox = false
-experimental-features = nix-command flakes
+experimental-features = nix-command flakes nix-testing
 gc-reserved-space = 0
 flake-registry = $TEST_ROOT/registry.json
 include nix.conf.extra
diff --git a/tests/local.mk b/tests/local.mk
index 5c77b9bb7..b17d7f900 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -15,6 +15,10 @@ nix_tests = \
   linux-sandbox.sh \
   build-dry.sh \
   build-remote.sh \
+  build-remote-trustless-should-pass-1.sh \
+  build-remote-trustless-should-pass-2.sh \
+  build-remote-trustless-should-pass-3.sh \
+  build-remote-trustless-should-fail-0.sh \
   nar-access.sh \
   structured-attrs.sh \
   fetchGit.sh \
@@ -34,6 +38,7 @@ nix_tests = \
   recursive.sh \
   flakes.sh
   # parallel.sh
+  # build-remote-trustless-should-pass-0.sh # problem with legacy ssh-store only
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))
 
diff --git a/tests/nix-daemon-untrusting.sh b/tests/nix-daemon-untrusting.sh
new file mode 100755
index 000000000..a3a420147
--- /dev/null
+++ b/tests/nix-daemon-untrusting.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec nix-daemon --no-trust "$@"
-- 
cgit v1.2.3


From 1bf31bad5fa65f61afa1ddd96a3d8e16ffc5525e Mon Sep 17 00:00:00 2001
From: Carlo Nucera <carlo.nucera@protonmail.com>
Date: Mon, 17 Aug 2020 13:15:08 -0400
Subject: Disable failing tests

---
 tests/local.mk | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/local.mk b/tests/local.mk
index 75fdd8332..efe193356 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -15,10 +15,8 @@ nix_tests = \
   linux-sandbox.sh \
   build-dry.sh \
   build-remote-input-addressed.sh \
-  build-remote-content-addressed-fixed.sh \
   build-remote-trustless-should-pass-1.sh \
   build-remote-trustless-should-pass-2.sh \
-  build-remote-trustless-should-pass-3.sh \
   build-remote-trustless-should-fail-0.sh \
   nar-access.sh \
   structured-attrs.sh \
@@ -30,7 +28,6 @@ nix_tests = \
   shell.sh \
   brotli.sh \
   pure-eval.sh \
-  check.sh \
   plugins.sh \
   search.sh \
   nix-copy-ssh.sh \
@@ -39,7 +36,10 @@ nix_tests = \
   recursive.sh \
   flakes.sh
   # parallel.sh
+  # build-remote-content-addressed-fixed.sh \
+  # build-remote-trustless-should-pass-3.sh \
   # build-remote-trustless-should-pass-0.sh # problem with legacy ssh-store only
+  # check.sh \
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))
 
-- 
cgit v1.2.3


From 36758a1a09d75ad18d04ce2f5650eec455198ee4 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 17 Aug 2020 18:01:38 +0000
Subject: But back check.sh

Whether it fails or not, it is no a new test so we have to leave it.
---
 tests/local.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/local.mk b/tests/local.mk
index efe193356..ff3063d58 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -28,6 +28,7 @@ nix_tests = \
   shell.sh \
   brotli.sh \
   pure-eval.sh \
+  check.sh \
   plugins.sh \
   search.sh \
   nix-copy-ssh.sh \
@@ -39,7 +40,6 @@ nix_tests = \
   # build-remote-content-addressed-fixed.sh \
   # build-remote-trustless-should-pass-3.sh \
   # build-remote-trustless-should-pass-0.sh # problem with legacy ssh-store only
-  # check.sh \
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))
 
-- 
cgit v1.2.3


From 6c7b81047f8ead0bb2f8dd588dfcb5f50d1554a9 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Wed, 9 Sep 2020 17:35:54 +0000
Subject: Make sure srcStore has path before coppying

---
 src/libstore/store-api.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index aed43543f..8075b3ff9 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -847,6 +847,7 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                             return i.second == storePath;
                         });
                         // drv file is always CA
+                        srcStore->ensurePath(drvPath);
                         copyStorePath(srcStore, dstStore, drvPath, repair, checkSigs);
                         dstStore->buildPaths({{
                             drvPath,
-- 
cgit v1.2.3


From 141cb9a706f73725fd4f8d62569f45bbbf9b6c3b Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 22 Jan 2021 17:56:28 +0000
Subject: Make regular `copyPaths` only copy again

The is new function parameter so just the build hook can opt into the
remote-side building.
---
 src/build-remote/build-remote.cc |  7 ++++--
 src/libstore/store-api.cc        | 53 ++++++++++++++++++++++++++--------------
 src/libstore/store-api.hh        | 20 +++++++++++++--
 3 files changed, 57 insertions(+), 23 deletions(-)

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 402754c3c..ef943ee11 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -270,9 +270,11 @@ connected:
 
         auto substitute = settings.buildersUseSubstitutes ? Substitute : NoSubstitute;
 
+        auto copyStorePathImpl = sshStore2->isTrusting ? copyStorePathAdapter : copyOrBuildStorePath;
+
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(store, sshStore2, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
+            copyPaths(store, sshStore2, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute, copyStorePathImpl);
         }
 
         uploadLock = -1;
@@ -285,7 +287,7 @@ connected:
             if (!result.success())
                 throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
         } else {
-            copyPaths(store, sshStore2, {*drvPath}, NoRepair, NoCheckSigs, substitute);
+            copyPaths(store, sshStore2, {*drvPath}, NoRepair, NoCheckSigs, substitute, copyStorePathImpl);
             sshStore2->buildPaths({{*drvPath}});
         }
 
@@ -298,6 +300,7 @@ connected:
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri));
             for (auto & i : missing)
                 store->locksHeld.insert(store->printStorePath(i)); /* FIXME: ugly */
+            /* No `copyStorePathImpl` because we always trust ourselves. */
             copyPaths(sshStore2, store, missing, NoRepair, NoCheckSigs, NoSubstitute);
         }
 
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index cce95e4cf..ad773bb0f 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -819,8 +819,40 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
 }
 
 
+void copyStorePathAdapter(ref<Store> srcStore, ref<Store> dstStore,
+    const ValidPathInfo & info, RepairFlag repair, CheckSigsFlag checkSigs)
+{
+    copyStorePath(srcStore, dstStore, info.path, repair, checkSigs);
+}
+
+void copyOrBuildStorePath(ref<Store> srcStore, ref<Store> dstStore,
+    const ValidPathInfo & info, RepairFlag repair, CheckSigsFlag checkSigs)
+{
+    auto storePath = info.path;
+    if (dstStore->isTrusting || info.ca) {
+        copyStorePath(srcStore, dstStore, storePath, repair, checkSigs);
+    } else if (info.deriver && dstStore->storeDir == srcStore->storeDir) {
+        auto drvPath = *info.deriver;
+        auto outputMap = srcStore->queryDerivationOutputMap(drvPath);
+        auto p = std::find_if(outputMap.begin(), outputMap.end(), [&](auto & i) {
+            return i.second == storePath;
+        });
+        // drv file is always CA
+        srcStore->ensurePath(drvPath);
+        copyStorePath(srcStore, dstStore, drvPath, repair, checkSigs);
+        dstStore->buildPaths({{
+            drvPath,
+            p != outputMap.end() ? StringSet { p->first } : StringSet {},
+        }});
+    } else {
+        dstStore->ensurePath(storePath);
+    }
+}
+
+
 std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore, const StorePathSet & storePaths,
-    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute)
+    RepairFlag repair, CheckSigsFlag checkSigs, SubstituteFlag substitute,
+    std::function<void(ref<Store>, ref<Store>, const ValidPathInfo &, RepairFlag, CheckSigsFlag)> copyStorePathImpl)
 {
     auto valid = dstStore->queryValidPaths(storePaths, substitute);
 
@@ -893,24 +925,7 @@ std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStor
                 MaintainCount<decltype(nrRunning)> mc(nrRunning);
                 showProgress();
                 try {
-                    if (dstStore->isTrusting || info->ca) {
-                        copyStorePath(srcStore, dstStore, storePath, repair, checkSigs);
-                    } else if (info->deriver && dstStore->storeDir == srcStore->storeDir) {
-                        auto drvPath = *info->deriver;
-                        auto outputMap = srcStore->queryDerivationOutputMap(drvPath);
-                        auto p = std::find_if(outputMap.begin(), outputMap.end(), [&](auto & i) {
-                            return i.second == storePath;
-                        });
-                        // drv file is always CA
-                        srcStore->ensurePath(drvPath);
-                        copyStorePath(srcStore, dstStore, drvPath, repair, checkSigs);
-                        dstStore->buildPaths({{
-                            drvPath,
-                            p != outputMap.end() ? StringSet { p->first } : StringSet {},
-                        }});
-                    } else {
-                        dstStore->ensurePath(storePath);
-                    }
+                    copyStorePathImpl(srcStore, dstStore, *info, repair, checkSigs);
                 } catch (Error &e) {
                     nrFailed++;
                     if (!settings.keepGoing)
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 696a2d3fd..5597ebb22 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -738,17 +738,33 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     const StorePath & storePath, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
 
 
+/* copyStorePath wrapped to be used with `copyPaths`. */
+void copyStorePathAdapter(ref<Store> srcStore, ref<Store> dstStore,
+    const ValidPathInfo & info, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
+
+/* The more liberal alternative to `copyStorePathAdapter`, useful for remote
+   stores that do not trust us. */
+void copyOrBuildStorePath(ref<Store> srcStore, ref<Store> dstStore,
+    const ValidPathInfo & info, RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs);
+
 /* Copy store paths from one store to another. The paths may be copied
    in parallel. They are copied in a topologically sorted order (i.e.
    if A is a reference of B, then A is copied before B), but the set
    of store paths is not automatically closed; use copyClosure() for
    that. Returns a map of what each path was copied to the dstStore
-   as. */
+   as.
+
+   The `copyStorePathImpl` parameter allows doing something other than just
+   copying. For example, this is used with the build hook to allow the other
+   side to build dependencies we don't have permission to copy. This behavior
+   isn't just the default that way `nix copy` etc. still can be relied upon to
+   not build anything. */
 std::map<StorePath, StorePath> copyPaths(ref<Store> srcStore, ref<Store> dstStore,
     const StorePathSet & storePaths,
     RepairFlag repair = NoRepair,
     CheckSigsFlag checkSigs = CheckSigs,
-    SubstituteFlag substitute = NoSubstitute);
+    SubstituteFlag substitute = NoSubstitute,
+    std::function<void(ref<Store>, ref<Store>, const ValidPathInfo &, RepairFlag, CheckSigsFlag)> copyStorePathImpl = copyStorePathAdapter);
 
 
 /* Copy the closure of the specified paths from one store to another. */
-- 
cgit v1.2.3


From 2dd11f07808c8b86513260b85f35a70cbe9b1249 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Sat, 27 Feb 2021 05:33:47 +0000
Subject: Reenable previously failing trustless remote builder tests

---
 tests/local.mk | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/local.mk b/tests/local.mk
index c8aed0390..2cb65867c 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -19,8 +19,10 @@ nix_tests = \
   build-remote-input-addressed.sh \
   build-remote-content-addressed-fixed.sh \
   build-remote-content-addressed-floating.sh \
+  build-remote-trustless-should-pass-0.sh \
   build-remote-trustless-should-pass-1.sh \
   build-remote-trustless-should-pass-2.sh \
+  build-remote-trustless-should-pass-3.sh \
   build-remote-trustless-should-fail-0.sh \
   ssh-relay.sh \
   nar-access.sh \
@@ -47,9 +49,6 @@ nix_tests = \
   build.sh \
   compute-levels.sh
   # parallel.sh
-  # build-remote-content-addressed-fixed.sh # problem with fixed output derivations
-  # build-remote-trustless-should-pass-0.sh # problem with legacy ssh-store only
-  # build-remote-trustless-should-pass-3.sh # problem with fixed output derivations
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))
 
-- 
cgit v1.2.3


From 6e1e15ffec69de8a3954100389f1d41494f8da8d Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 7 Apr 2023 11:13:23 -0400
Subject: Fix it!

---
 src/build-remote/build-remote.cc              | 19 ++++++++++++-------
 tests/build-remote-trustless-after.sh         |  2 ++
 tests/build-remote-trustless-should-fail-0.sh | 24 +++++++++++++++++++-----
 tests/build-remote-trustless-should-pass-0.sh |  4 ++--
 tests/build-remote-trustless-should-pass-1.sh |  4 ++--
 tests/build-remote-trustless-should-pass-2.sh |  4 ++--
 tests/build-remote-trustless-should-pass-3.sh |  6 +++---
 tests/build-remote-trustless.sh               | 14 ++++++--------
 8 files changed, 48 insertions(+), 29 deletions(-)
 create mode 100644 tests/build-remote-trustless-after.sh

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 649ad3e7c..3d4dbc3d6 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -290,14 +290,19 @@ connected:
         auto drv = store->readDerivation(*drvPath);
 
         std::optional<BuildResult> optResult;
-        if (sshStore->isTrustedClient() || drv.type().isCA()) {
-            // Hijack the inputs paths of the derivation to include all the paths
-            // that come from the `inputDrvs` set.
-            // We don’t do that for the derivations whose `inputDrvs` is empty
-            // because
+        // If we don't know whether we are trusted (e.g. `ssh://`
+        // stores), we assume we are. This is neccessary for backwards
+        // compat.
+        if (std::optional trust = sshStore->isTrustedClient(); (!trust || *trust) || drv.type().isCA()) {
+            // Hijack the inputs paths of the derivation to include all
+            // the paths that come from the `inputDrvs` set. We don’t do
+            // that for the derivations whose `inputDrvs` is empty
+            // because:
+            //
             // 1. It’s not needed
-            // 2. Changing the `inputSrcs` set changes the associated output ids,
-            //  which break CA derivations
+            //
+            // 2. Changing the `inputSrcs` set changes the associated
+            //    output ids, which break CA derivations
             if (!drv.inputDrvs.empty())
                 drv.inputSrcs = store->parseStorePathSet(inputs);
             optResult = sshStore->buildDerivation(*drvPath, (const BasicDerivation &) drv);
diff --git a/tests/build-remote-trustless-after.sh b/tests/build-remote-trustless-after.sh
new file mode 100644
index 000000000..19f59e6ae
--- /dev/null
+++ b/tests/build-remote-trustless-after.sh
@@ -0,0 +1,2 @@
+outPath=$(readlink -f $TEST_ROOT/result)
+grep 'FOO BAR BAZ' ${remoteDir}/${outPath}
diff --git a/tests/build-remote-trustless-should-fail-0.sh b/tests/build-remote-trustless-should-fail-0.sh
index b72c134e7..b5cedb544 100644
--- a/tests/build-remote-trustless-should-fail-0.sh
+++ b/tests/build-remote-trustless-should-fail-0.sh
@@ -1,11 +1,25 @@
 source common.sh
 
-# We act as if remote trusts us, but it doesn't. This fails since we are
-# building input-addressed derivations with `buildDerivation`, which
-# depends on trust.
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+# We first build a dependency of the derivation we eventually want to
+# build.
+nix-build build-hook.nix -A passthru.input2 \
+  -o "$TEST_ROOT/input2" \
+  --arg busybox "$busybox" \
+  --store "$TEST_ROOT/local" \
+  --option system-features bar
+
+# Now when we go to build that downstream derivation, Nix will try to
+# copy our already-build `input2` to the remote store. That store object
+# is input-addressed, so this will fail.
+
 file=build-hook.nix
 prog=$(readlink -e ./nix-daemon-untrusting.sh)
 proto=ssh-ng
-trusting=true
 
-! source build-remote-trustless.sh
+expectStderr 1 source build-remote-trustless.sh \
+    | grepQuiet "cannot add path '[^ ]*' because it lacks a signature by a trusted key"
diff --git a/tests/build-remote-trustless-should-pass-0.sh b/tests/build-remote-trustless-should-pass-0.sh
index 82c3f4520..2a7ebd8c6 100644
--- a/tests/build-remote-trustless-should-pass-0.sh
+++ b/tests/build-remote-trustless-should-pass-0.sh
@@ -1,9 +1,9 @@
 source common.sh
 
-# Remote trusts us but we pretend it doesn't.
+# Remote trusts us
 file=build-hook.nix
 prog=nix-store
 proto=ssh
-trusting=false
 
 source build-remote-trustless.sh
+source build-remote-trustless-after.sh
diff --git a/tests/build-remote-trustless-should-pass-1.sh b/tests/build-remote-trustless-should-pass-1.sh
index 22c304bc2..516bdf092 100644
--- a/tests/build-remote-trustless-should-pass-1.sh
+++ b/tests/build-remote-trustless-should-pass-1.sh
@@ -1,9 +1,9 @@
 source common.sh
 
-# Remote trusts us but we pretend it doesn't.
+# Remote trusts us
 file=build-hook.nix
 prog=nix-daemon
 proto=ssh-ng
-trusting=false
 
 source build-remote-trustless.sh
+source build-remote-trustless-after.sh
diff --git a/tests/build-remote-trustless-should-pass-2.sh b/tests/build-remote-trustless-should-pass-2.sh
index 941ddca05..6383f5489 100644
--- a/tests/build-remote-trustless-should-pass-2.sh
+++ b/tests/build-remote-trustless-should-pass-2.sh
@@ -1,9 +1,9 @@
 source common.sh
 
-# Remote doesn't trust us nor do we think it does
+# Remote doesn't trust us
 file=build-hook.nix
 prog=$(readlink -e ./nix-daemon-untrusting.sh)
 proto=ssh-ng
-trusting=false
 
 source build-remote-trustless.sh
+source build-remote-trustless-after.sh
diff --git a/tests/build-remote-trustless-should-pass-3.sh b/tests/build-remote-trustless-should-pass-3.sh
index 0c4e191fc..c3ec359fb 100644
--- a/tests/build-remote-trustless-should-pass-3.sh
+++ b/tests/build-remote-trustless-should-pass-3.sh
@@ -1,10 +1,10 @@
 source common.sh
 
-# We act as if remote trusts us, but it doesn't. This is fine because we
-# are only building (fixed) CA derivations.
+# Remote doesn't trusts us, but this is fine because we are only
+# building (fixed) CA derivations.
 file=build-hook-ca-fixed.nix
 prog=$(readlink -e ./nix-daemon-untrusting.sh)
 proto=ssh-ng
-trusting=true
 
 source build-remote-trustless.sh
+source build-remote-trustless-after.sh
diff --git a/tests/build-remote-trustless.sh b/tests/build-remote-trustless.sh
index 8260c4dcd..9df44e0c5 100644
--- a/tests/build-remote-trustless.sh
+++ b/tests/build-remote-trustless.sh
@@ -1,16 +1,14 @@
-if ! canUseSandbox; then exit; fi
-if ! [[ $busybox =~ busybox ]]; then exit; fi
+requireSandboxSupport
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
 
 unset NIX_STORE_DIR
 unset NIX_STATE_DIR
 
+remoteDir=$TEST_ROOT/remote
+
 # Note: ssh{-ng}://localhost bypasses ssh. See tests/build-remote.sh for
 # more details.
-nix build -L -v -f $file -o $TEST_ROOT/result --max-jobs 0 \
+nix-build $file -o $TEST_ROOT/result --max-jobs 0 \
   --arg busybox $busybox \
   --store $TEST_ROOT/local \
-  --builders "$proto://localhost?remote-program=$prog&trusting=$trusting&remote-store=$TEST_ROOT/remote%3Fsystem-features=foo%20bar%20baz - - 1 1 foo,bar,baz"
-
-outPath=$(readlink -f $TEST_ROOT/result)
-
-grep 'FOO BAR BAZ' $TEST_ROOT/${subDir}/local${outPath}
+  --builders "$proto://localhost?remote-program=$prog&remote-store=${remoteDir}%3Fsystem-features=foo%20bar%20baz - - 1 1 foo,bar,baz"
-- 
cgit v1.2.3


From e95db8f2b9aebbb4079805cb7ecfc751af41e0b4 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 17 Apr 2023 09:35:43 -0400
Subject: `nix-testing` -> `daemon-trust-override`

And only enable in the tests that need it. This makes it less of a
sledgehammer.
---
 src/libutil/experimental-features.cc          | 11 ++++++-----
 src/libutil/experimental-features.hh          |  2 +-
 src/nix/daemon.cc                             |  6 +++---
 tests/build-remote-trustless-should-fail-0.sh |  4 ++++
 tests/build-remote-trustless-should-pass-2.sh |  4 ++++
 tests/build-remote-trustless-should-pass-3.sh |  4 ++++
 tests/init.sh                                 |  2 +-
 7 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
index be5a2c088..bd1899662 100644
--- a/src/libutil/experimental-features.cc
+++ b/src/libutil/experimental-features.cc
@@ -190,12 +190,13 @@ constexpr std::array<ExperimentalFeatureDetails, 12> xpFeatureDetails = {{
         )",
     },
     {
-        .tag = Xp::NixTesting,
-        .name = "nix-testing",
+        .tag = Xp::DaemonTrustOverride,
+        .name = "daemon-trust-override",
         .description = R"(
-            A "permanent" experimental feature for extra features we just need
-            for testing. Not actually an "experiment" in the sense of being
-            prospective functionality for regular users.
+            Allow forcing trusting or not trusting clients with
+            `nix-daemon`. This is useful for testing, but possibly also
+            useful for various experiments with `nix-daemon --stdio`
+            networking.
         )",
     },
 }};
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
index c41f73fa0..3c00bc4e5 100644
--- a/src/libutil/experimental-features.hh
+++ b/src/libutil/experimental-features.hh
@@ -28,7 +28,7 @@ enum struct ExperimentalFeature
     AutoAllocateUids,
     Cgroups,
     DiscardReferences,
-    NixTesting,
+    DaemonTrustOverride,
 };
 
 /**
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 4be93bb1c..35e8a5f87 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -472,13 +472,13 @@ static int main_nix_daemon(int argc, char * * argv)
             else if (*arg == "--stdio")
                 stdio = true;
             else if (*arg == "--force-trusted") {
-                experimentalFeatureSettings.require(Xp::NixTesting);
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
                 isTrustedOpt = Trusted;
             } else if (*arg == "--force-untrusted") {
-                experimentalFeatureSettings.require(Xp::NixTesting);
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
                 isTrustedOpt = NotTrusted;
             } else if (*arg == "--default-trust") {
-                experimentalFeatureSettings.require(Xp::NixTesting);
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
                 isTrustedOpt = std::nullopt;
             } else return false;
             return true;
diff --git a/tests/build-remote-trustless-should-fail-0.sh b/tests/build-remote-trustless-should-fail-0.sh
index b5cedb544..fad1def59 100644
--- a/tests/build-remote-trustless-should-fail-0.sh
+++ b/tests/build-remote-trustless-should-fail-0.sh
@@ -1,5 +1,9 @@
 source common.sh
 
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
 [[ $busybox =~ busybox ]] || skipTest "no busybox"
 
 unset NIX_STORE_DIR
diff --git a/tests/build-remote-trustless-should-pass-2.sh b/tests/build-remote-trustless-should-pass-2.sh
index 6383f5489..b769a88f0 100644
--- a/tests/build-remote-trustless-should-pass-2.sh
+++ b/tests/build-remote-trustless-should-pass-2.sh
@@ -1,5 +1,9 @@
 source common.sh
 
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
 # Remote doesn't trust us
 file=build-hook.nix
 prog=$(readlink -e ./nix-daemon-untrusting.sh)
diff --git a/tests/build-remote-trustless-should-pass-3.sh b/tests/build-remote-trustless-should-pass-3.sh
index c3ec359fb..40f81da5a 100644
--- a/tests/build-remote-trustless-should-pass-3.sh
+++ b/tests/build-remote-trustless-should-pass-3.sh
@@ -1,5 +1,9 @@
 source common.sh
 
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
 # Remote doesn't trusts us, but this is fine because we are only
 # building (fixed) CA derivations.
 file=build-hook-ca-fixed.nix
diff --git a/tests/init.sh b/tests/init.sh
index 2c4f4a2f3..c420e8c9f 100755
--- a/tests/init.sh
+++ b/tests/init.sh
@@ -20,7 +20,7 @@ cat > "$NIX_CONF_DIR"/nix.conf <<EOF
 build-users-group =
 keep-derivations = false
 sandbox = false
-experimental-features = nix-command flakes nix-testing
+experimental-features = nix-command flakes
 gc-reserved-space = 0
 substituters =
 flake-registry = $TEST_ROOT/registry.json
-- 
cgit v1.2.3


From 79ba0ba37ab35ac5ea94fa1db1fc46a5b7588ece Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 17 Apr 2023 09:56:32 -0400
Subject: Improve the build remote comment.

---
 src/build-remote/build-remote.cc | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 3d4dbc3d6..b0bc8a9ff 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -290,9 +290,30 @@ connected:
         auto drv = store->readDerivation(*drvPath);
 
         std::optional<BuildResult> optResult;
+
+        // Let's break this down
+        //
+        // ### Trust part
+        //
+        // ```
+        // std::optional trust = sshStore->isTrustedClient(); (!trust || *trust)
+        // ```
+        //
         // If we don't know whether we are trusted (e.g. `ssh://`
-        // stores), we assume we are. This is neccessary for backwards
+        // stores), we assume we are. This is necessary for backwards
         // compat.
+        //
+        // ### Content-addressing part
+        //
+        // ```
+        // ...trustCond... || drv.type().isCA()
+        // ```
+        //
+        // See the very large comment in `case wopBuildDerivation:` in
+        // `src/libstore/daemon.cc` that explains the trust model here.
+        //
+        // This condition mirrors that: that code enforces the "rules";
+        // we do the best we can given those "rules".
         if (std::optional trust = sshStore->isTrustedClient(); (!trust || *trust) || drv.type().isCA()) {
             // Hijack the inputs paths of the derivation to include all
             // the paths that come from the `inputDrvs` set. We don’t do
-- 
cgit v1.2.3


From 23ee2d79a90ace2fe012f32c37121f50afc35223 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 17 Apr 2023 09:59:14 -0400
Subject: Use `buildPathsWithResults` in build-remote.cc trustless path

It handles failures more correctly; I am glad we have it now!
---
 src/build-remote/build-remote.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index b0bc8a9ff..403f0fb17 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -332,7 +332,10 @@ connected:
                 throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
         } else {
             copyPaths(*store, *sshStore, StorePathSet {*drvPath}, NoRepair, NoCheckSigs, substitute);
-            sshStore->buildPaths({ DerivedPath::Built { *drvPath, OutputsSpec::All {} } });
+            auto res = sshStore->buildPathsWithResults({ DerivedPath::Built { *drvPath, OutputsSpec::All {} } });
+            // One path to build should mean one result back
+            assert(res.size() == 1);
+            optResult = std::move(res[0]);
         }
 
 
-- 
cgit v1.2.3


From cd0d8e0bd50d7259057ac138a7227907f88b91d5 Mon Sep 17 00:00:00 2001
From: John Ericson <git@JohnEricson.me>
Date: Mon, 8 May 2023 09:57:05 -0400
Subject: Apply suggestions from code review

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
---
 src/build-remote/build-remote.cc | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 1467761c9..7366a7c27 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -312,9 +312,12 @@ connected:
         // See the very large comment in `case wopBuildDerivation:` in
         // `src/libstore/daemon.cc` that explains the trust model here.
         //
-        // This condition mirrors that: that code enforces the "rules";
+        // This condition mirrors that: that code enforces the "rules" outlined there;
         // we do the best we can given those "rules".
-        if (std::optional trust = sshStore->isTrustedClient(); (!trust || *trust) || drv.type().isCA()) {
+        std::optional trusted = sshStore->isTrustedClient();
+        // for backward compatibility (use existing comments here)
+        bool trustedOrLegacy = !trusted || *trusted;
+        if (trustedOrLegacy || drv.type().isCA())  {
             // Hijack the inputs paths of the derivation to include all
             // the paths that come from the `inputDrvs` set. We don’t do
             // that for the derivations whose `inputDrvs` is empty
@@ -331,9 +334,9 @@ connected:
             if (!result.success())
                 throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
         } else {
-            copyPaths(*store, *sshStore, StorePathSet {*drvPath}, NoRepair, NoCheckSigs, substitute);
+            copyClosure(*store, *sshStore, StorePathSet {*drvPath}, NoRepair, NoCheckSigs, substitute);
             auto res = sshStore->buildPathsWithResults({ DerivedPath::Built { *drvPath, OutputsSpec::All {} } });
-            // One path to build should mean one result back
+            // One path to build should produce exactly one build result
             assert(res.size() == 1);
             optResult = std::move(res[0]);
         }
-- 
cgit v1.2.3


From df53a7d26868d7ce432e34e5d0c397886f7772f8 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 8 May 2023 10:08:01 -0400
Subject: Split comment, match with each variable

---
 src/build-remote/build-remote.cc | 23 +++++------------------
 1 file changed, 5 insertions(+), 18 deletions(-)

diff --git a/src/build-remote/build-remote.cc b/src/build-remote/build-remote.cc
index 7366a7c27..323e04fdb 100644
--- a/src/build-remote/build-remote.cc
+++ b/src/build-remote/build-remote.cc
@@ -291,32 +291,19 @@ connected:
 
         std::optional<BuildResult> optResult;
 
-        // Let's break this down
-        //
-        // ### Trust part
-        //
-        // ```
-        // std::optional trust = sshStore->isTrustedClient(); (!trust || *trust)
-        // ```
-        //
         // If we don't know whether we are trusted (e.g. `ssh://`
         // stores), we assume we are. This is necessary for backwards
         // compat.
-        //
-        // ### Content-addressing part
-        //
-        // ```
-        // ...trustCond... || drv.type().isCA()
-        // ```
-        //
+        bool trustedOrLegacy = ({
+            std::optional trusted = sshStore->isTrustedClient();
+            !trusted || *trusted;
+        });
+
         // See the very large comment in `case wopBuildDerivation:` in
         // `src/libstore/daemon.cc` that explains the trust model here.
         //
         // This condition mirrors that: that code enforces the "rules" outlined there;
         // we do the best we can given those "rules".
-        std::optional trusted = sshStore->isTrustedClient();
-        // for backward compatibility (use existing comments here)
-        bool trustedOrLegacy = !trusted || *trusted;
         if (trustedOrLegacy || drv.type().isCA())  {
             // Hijack the inputs paths of the derivation to include all
             // the paths that come from the `inputDrvs` set. We don’t do
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