libutil: make AutoCloseFD a better resource

add a reset() method to close the wrapped fd instead of assigning magic
constants. also make the from-fd constructor explicit so you can't
accidentally assign the *wrong* magic constant, or even an unrelated
integer that also just happens to be an fd by pure chance.

Change-Id: I51311b0f6e040240886b5103d39d1794a6acc325

2 files changed, 5 insertions, 5 deletions

diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
index 4f9907ad7..9d4afb6d9 100644
--- a/src/nix/daemon.cc
+++ b/src/nix/daemon.cc
@@ -294,7 +294,7 @@ static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
     if (listenFds) {
         if (getEnv("LISTEN_PID") != std::to_string(getpid()) || listenFds != "1")
             throw Error("unexpected systemd environment variables");
-        fdSocket = SD_LISTEN_FDS_START;
+        fdSocket = AutoCloseFD{SD_LISTEN_FDS_START};
         closeOnExec(fdSocket.get());
     }
 
@@ -315,8 +315,8 @@ static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
             struct sockaddr_un remoteAddr;
             socklen_t remoteAddrLen = sizeof(remoteAddr);
 
-            AutoCloseFD remote = accept(fdSocket.get(),
-                (struct sockaddr *) &remoteAddr, &remoteAddrLen);
+            AutoCloseFD remote{accept(fdSocket.get(),
+                    (struct sockaddr *) &remoteAddr, &remoteAddrLen)};
             checkInterrupt();
             if (!remote) {
                 if (errno == EINTR) continue;
@@ -348,7 +348,7 @@ static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
             options.dieWithParent = false;
             options.runExitHandlers = true;
             startProcess([&]() {
-                fdSocket = -1;
+                fdSocket.reset();
 
                 //  Background the daemon.
                 if (setsid() == -1)
diff --git a/src/nix/prefetch.cc b/src/nix/prefetch.cc
index 0104635fb..8f74984e0 100644
--- a/src/nix/prefetch.cc
+++ b/src/nix/prefetch.cc
@@ -92,7 +92,7 @@ std::tuple<StorePath, Hash> prefetchFile(
             if (executable)
                 mode = 0700;
 
-            AutoCloseFD fd = open(tmpFile.c_str(), O_WRONLY | O_CREAT | O_EXCL, mode);
+            AutoCloseFD fd{open(tmpFile.c_str(), O_WRONLY | O_CREAT | O_EXCL, mode)};
             if (!fd) throw SysError("creating temporary file '%s'", tmpFile);
 
             FdSink sink(fd.get());