Add setting 'client-only-settings' to prevent forwarding to the daemon

src/libstore/daemon.cc

@@ -238,9 +238,13 @@ struct ClientSettings
                 return true;
             };
 
+            auto clientOnlySettings = settings.clientOnlySettings.get();
+
             try {
                 if (name == "ssh-auth-sock") // obsolete
                     ;
+                else if (clientOnlySettings.contains(name))
+                    ;
                 else if (name == experimentalFeatureSettings.experimentalFeatures.name) {
                     // We don’t want to forward the experimental features to
                     // the daemon, as that could cause some pretty weird stuff

src/libstore/globals.hh

@@ -94,6 +94,12 @@ public:
      */
     Path nixDaemonSocketFile;
 
+    Setting<StringSet> clientOnlySettings{this, {}, "client-only-settings",
+        R"(
+          The names of settings that will not be forwarded from the
+          Nix client to the Nix daemon.
+        )"};
+
     Setting<std::string> storeUri{this, getEnv("NIX_REMOTE").value_or("auto"), "store",
         R"(
           The [URL of the Nix store](@docroot@/store/types/index.md#store-url-format)

src/libstore/remote-store.cc

@@ -135,6 +135,9 @@ void RemoteStore::setOptions(Connection & conn)
         overrides.erase(loggerSettings.showTrace.name);
         overrides.erase(experimentalFeatureSettings.experimentalFeatures.name);
         overrides.erase("plugin-files");
+        overrides.erase(settings.clientOnlySettings.name);
+        for (auto & i : settings.clientOnlySettings.get())
+            overrides.erase(i);
         conn.to << overrides.size();
         for (auto & i : overrides)
             conn.to << i.first << i.second.value;

tests/functional/common/functions.sh

@@ -62,6 +62,8 @@ clearCacheCache() {
     rm -f "$TEST_HOME/.cache/nix/binary-cache"*
 }
 
+extraDaemonFlags=()
+
 startDaemon() {
     if isTestOnNixOS; then
       die "startDaemon: not supported when testing on NixOS. Is it really needed? If so add conditionals; e.g. if ! isTestOnNixOS; then ..."
@@ -73,7 +75,7 @@ startDaemon() {
     fi
     # Start the daemon, wait for the socket to appear.
     rm -f "$NIX_DAEMON_SOCKET_PATH"
-    PATH=$DAEMON_PATH nix --extra-experimental-features 'nix-command' daemon &
+    PATH=$DAEMON_PATH nix --extra-experimental-features 'nix-command' daemon "${extraDaemonFlags[@]}" &
     _NIX_TEST_DAEMON_PID=$!
     export _NIX_TEST_DAEMON_PID
     for ((i = 0; i < 300; i++)); do

tests/functional/remote-store.sh

@@ -36,3 +36,20 @@ NIX_REMOTE= nix-store --dump-db > $TEST_ROOT/d2
 cmp $TEST_ROOT/d1 $TEST_ROOT/d2
 
 killDaemon
+
+# Test 'client-only-settings' on the client.
+extraDaemonFlags=("--trusted-users" "")
+startDaemon
+nix store info --netrc-file /foo 2>&1 | grepQuiet "ignoring the client-specified setting 'netrc-file'"
+if nix store info --netrc-file /foo --client-only-settings netrc-file 2>&1 | grep "ignoring the client-specified setting 'netrc-file'"; then
+    exit 1
+fi
+killDaemon
+
+# Test 'client-only-settings' on the daemon.
+extraDaemonFlags=("--trusted-users" "" "--option" "client-only-settings" "netrc-file")
+startDaemon
+if nix store info --netrc-file /foo 2>&1 | grep "ignoring the client-specified setting 'netrc-file'"; then
+    exit 1
+fi
+killDaemon