daemon: use per-store state directory for socket path

Author: amaanq

src/libstore/globals.cc

@@ -48,13 +48,6 @@
 
 namespace nix {
 
-/* The default location of the daemon socket, relative to nixStateDir.
-   The socket is in a directory to allow you to control access to the
-   Nix daemon by setting the mode/ownership of the directory
-   appropriately.  (This wouldn't work on the socket itself since it
-   must be deleted and recreated on startup.) */
-#define DEFAULT_SOCKET_PATH "daemon-socket" / "socket"
-
 LogFileSettings::LogFileSettings()
     : nixLogDir(getEnvOsNonEmpty(OS_STR("NIX_LOG_DIR"))
                     .transform([](auto && s) { return std::filesystem::path(s); })
@@ -92,12 +85,6 @@ Settings::Settings()
                       })
                       .transform([](auto && s) { return canonPath(s); })
                       .value())
-    , nixDaemonSocketFile(
-          getEnvOsNonEmpty(OS_STR("NIX_DAEMON_SOCKET_PATH"))
-              .transform([](auto && s) { return std::filesystem::path(s); })
-              .or_else([this]() -> std::optional<std::filesystem::path> { return nixStateDir / DEFAULT_SOCKET_PATH; })
-              .transform([](auto && s) { return canonPath(s); })
-              .value())
 {
 #ifndef _WIN32
     buildUsersGroup = isRootUser() ? "nixbld" : "";

src/libstore/include/nix/store/globals.hh

@@ -174,11 +174,6 @@ public:
      */
     std::filesystem::path nixStateDir;
 
-    /**
-     * File name of the socket the daemon listens to.
-     */
-    std::filesystem::path nixDaemonSocketFile;
-
     Setting<StoreReference> storeUri{
         this,
         StoreReference::parse(getEnv("NIX_REMOTE").value_or("auto")),

src/libstore/include/nix/store/local-fs-store.hh

@@ -71,6 +71,14 @@ public:
         "real",
         "Physical path of the Nix store.",
     };
+
+    /**
+     * The default daemon socket path for this store.
+     *
+     * Returns `NIX_DAEMON_SOCKET_PATH` if set, otherwise
+     * `stateDir / "daemon-socket" / "socket"`.
+     */
+    std::filesystem::path getDefaultDaemonSocketPath() const;
 };
 
 struct alignas(8) /* Work around ASAN failures on i686-linux. */

src/libstore/include/nix/store/uds-remote-store.hh

@@ -28,8 +28,8 @@ struct UDSRemoteStoreConfig : std::enable_shared_from_this<UDSRemoteStoreConfig>
     /**
      * The path to the unix domain socket.
      *
-     * The default is `settings.nixDaemonSocketFile`, but we don't write
-     * that below, instead putting in the constructor.
+     * The default is `stateDir / "daemon-socket/socket"`, overridden by
+     * `NIX_DAEMON_SOCKET_PATH` if set.
      */
     std::filesystem::path path;
 

src/libstore/local-fs-store.cc

@@ -1,4 +1,5 @@
 #include "nix/util/archive.hh"
+#include "nix/util/environment-variables.hh"
 #include "nix/util/posix-source-accessor.hh"
 #include "nix/store/store-api.hh"
 #include "nix/store/local-fs-store.hh"
@@ -18,6 +19,12 @@ std::filesystem::path LocalFSStoreConfig::getDefaultLogDir()
     return settings.getLogFileSettings().nixLogDir;
 }
 
+std::filesystem::path LocalFSStoreConfig::getDefaultDaemonSocketPath() const
+{
+    auto env = getEnvOsNonEmpty(OS_STR("NIX_DAEMON_SOCKET_PATH"));
+    return env ? std::filesystem::path{*env} : std::filesystem::path{stateDir.get()} / "daemon-socket" / "socket";
+}
+
 LocalFSStoreConfig::LocalFSStoreConfig(const std::filesystem::path & rootDir, const Params & params)
     : StoreConfig(params)
     /* Default `?root` from `rootDir` if non set

src/libstore/store-registration.cc

@@ -3,6 +3,9 @@
 #include "nix/store/local-store.hh"
 #include "nix/store/uds-remote-store.hh"
 #include "nix/store/globals.hh"
+#include "nix/util/environment-variables.hh"
+
+#include <filesystem>
 
 namespace nix {
 
@@ -33,7 +36,9 @@ ref<StoreConfig> resolveStoreConfig(StoreReference && storeURI)
                 auto stateDir = getOr(params, "state", settings.nixStateDir.string());
                 if (access(stateDir.c_str(), R_OK | W_OK) == 0)
                     return make_ref<LocalStore::Config>(params);
-                else if (pathExists(settings.nixDaemonSocketFile))
+                else if (pathExists(
+                             getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH")
+                                 .value_or((std::filesystem::path{stateDir} / "daemon-socket" / "socket").string())))
                     return make_ref<UDSRemoteStore::Config>(params);
 #ifdef __linux__
                 else if (

src/libstore/uds-remote-store.cc

@@ -23,7 +23,9 @@ UDSRemoteStoreConfig::UDSRemoteStoreConfig(const std::filesystem::path & path, c
     : Store::Config{params}
     , LocalFSStore::Config{params}
     , RemoteStore::Config{params}
-    , path{path.empty() ? settings.nixDaemonSocketFile : path}
+    , path{
+          path.empty() ? getDefaultDaemonSocketPath() : path,
+      }
 {
 }
 
@@ -34,10 +36,8 @@ std::string UDSRemoteStoreConfig::doc()
         ;
 }
 
-// A bit gross that we now pass empty string but this is knowing that
-// empty string will later default to the same nixDaemonSocketFile. Why
-// don't we just wire it all through? I believe there are cases where it
-// will live reload so we want to continue to account for that.
+// Empty authority will default to the per-store socket path based on
+// stateDir.
 UDSRemoteStoreConfig::UDSRemoteStoreConfig(const Params & params)
     : UDSRemoteStoreConfig("", params)
 {
@@ -56,7 +56,7 @@ StoreReference UDSRemoteStoreConfig::getReference() const
     /* We specifically return "daemon" here instead of "unix://" or "unix://${path}"
      * to be more compatible with older versions of nix. Some tooling out there
      * tries hard to parse store references and it might not be able to handle "unix://". */
-    if (path == settings.nixDaemonSocketFile)
+    if (path == getEnvOsNonEmpty(OS_STR("NIX_DAEMON_SOCKET_PATH")).value_or(getDefaultDaemonSocketPath().string()))
         return {
             .variant = StoreReference::Daemon{},
             .params = getQueryParams(),

src/nix/unix/daemon.cc

@@ -4,6 +4,7 @@
 #include "nix/util/unix-domain-socket.hh"
 #include "nix/cmd/command.hh"
 #include "nix/main/shared.hh"
+#include "nix/store/local-fs-store.hh"
 #include "nix/store/local-store.hh"
 #include "nix/store/remote-store.hh"
 #include "nix/store/remote-store-connection.hh"
@@ -280,10 +281,16 @@ static void daemonLoop(ref<const StoreConfig> storeConfig, std::optional<Trusted
     }
 #endif
 
+    auto socketPath = [&]() -> std::filesystem::path {
+        if (auto * localFSConfig = dynamic_cast<const LocalFSStoreConfig *>(&*storeConfig))
+            return localFSConfig->getDefaultDaemonSocketPath();
+        throw Error("cannot run daemon for non-local-filesystem store");
+    }();
+
     try {
         unix::serveUnixSocket(
             {
-                .socketPath = settings.nixDaemonSocketFile,
+                .socketPath = socketPath,
                 .socketMode = 0666,
                 .auxiliaryFd = sigChldPipe.readSide.get(),
                 .onAuxiliaryFdPollin =