Modernize AutoCloseFD

11 files changed, 137 insertions, 151 deletions

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 0b6311516..515d80091 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -325,7 +325,7 @@ RunPager::RunPager()
     toPager.create();
 
     pid = startProcess([&]() {
-        if (dup2(toPager.readSide, STDIN_FILENO) == -1)
+        if (dup2(toPager.readSide.get(), STDIN_FILENO) == -1)
             throw SysError("dupping stdin");
         if (!getenv("LESS"))
             setenv("LESS", "FRSXMK", 1);
@@ -337,7 +337,7 @@ RunPager::RunPager()
         throw SysError(format("executing ‘%1%’") % pager);
     });
 
-    if (dup2(toPager.writeSide, STDOUT_FILENO) == -1)
+    if (dup2(toPager.writeSide.get(), STDOUT_FILENO) == -1)
         throw SysError("dupping stdout");
 }
 
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 36fcdb845..0a4df8ca7 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -403,7 +403,7 @@ static void commonChildInit(Pipe & logPipe)
         throw SysError(format("creating a new session"));
 
     /* Dup the write side of the logger pipe into stderr. */
-    if (dup2(logPipe.writeSide, STDERR_FILENO) == -1)
+    if (dup2(logPipe.writeSide.get(), STDERR_FILENO) == -1)
         throw SysError("cannot pipe standard error into log file");
 
     /* Dup stderr to stdout. */
@@ -510,11 +510,11 @@ void UserLock::acquire()
             continue;
 
         AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
-        if (fd == -1)
+        if (!fd)
             throw SysError(format("opening user lock ‘%1%’") % fnUserLock);
 
-        if (lockFile(fd, ltWrite, false)) {
-            fdUserLock = fd.borrow();
+        if (lockFile(fd.get(), ltWrite, false)) {
+            fdUserLock = std::move(fd);
             lockedPaths.insert(fnUserLock);
             user = i;
             uid = pw->pw_uid;
@@ -550,7 +550,7 @@ void UserLock::acquire()
 void UserLock::release()
 {
     if (uid == 0) return;
-    fdUserLock.close(); /* releases lock */
+    fdUserLock = -1; /* releases lock */
     assert(lockedPaths.find(fnUserLock) != lockedPaths.end());
     lockedPaths.erase(fnUserLock);
     fnUserLock = "";
@@ -613,11 +613,11 @@ HookInstance::HookInstance()
         if (chdir("/") == -1) throw SysError("changing into /");
 
         /* Dup the communication pipes. */
-        if (dup2(toHook.readSide, STDIN_FILENO) == -1)
+        if (dup2(toHook.readSide.get(), STDIN_FILENO) == -1)
             throw SysError("dupping to-hook read side");
 
         /* Use fd 4 for the builder's stdout/stderr. */
-        if (dup2(builderOut.writeSide, 4) == -1)
+        if (dup2(builderOut.writeSide.get(), 4) == -1)
             throw SysError("dupping builder's stdout/stderr");
 
         Strings args = {
@@ -633,15 +633,15 @@ HookInstance::HookInstance()
     });
 
     pid.setSeparatePG(true);
-    fromHook.writeSide.close();
-    toHook.readSide.close();
+    fromHook.writeSide = -1;
+    toHook.readSide = -1;
 }
 
 
 HookInstance::~HookInstance()
 {
     try {
-        toHook.writeSide.close();
+        toHook.writeSide = -1;
         pid.kill(true);
     } catch (...) {
         ignoreException();
@@ -1414,10 +1414,10 @@ void DerivationGoal::buildDone()
 
     /* Close the read side of the logger pipe. */
     if (hook) {
-        hook->builderOut.readSide.close();
-        hook->fromHook.readSide.close();
+        hook->builderOut.readSide = -1;
+        hook->fromHook.readSide = -1;
     }
-    else builderOut.readSide.close();
+    else builderOut.readSide = -1;
 
     /* Close the log file. */
     closeLogFile();
@@ -1557,7 +1557,7 @@ HookReply DerivationGoal::tryBuildHook()
     for (auto & i : features) checkStoreName(i); /* !!! abuse */
 
     /* Send the request to the hook. */
-    writeLine(worker.hook->toHook.writeSide, (format("%1% %2% %3% %4%")
+    writeLine(worker.hook->toHook.writeSide.get(), (format("%1% %2% %3% %4%")
         % (worker.getNrLocalBuilds() < settings.maxBuildJobs ? "1" : "0")
         % drv->platform % drvPath % concatStringsSep(",", features)).str());
 
@@ -1565,7 +1565,7 @@ HookReply DerivationGoal::tryBuildHook()
        whether the hook wishes to perform the build. */
     string reply;
     while (true) {
-        string s = readLine(worker.hook->fromHook.readSide);
+        string s = readLine(worker.hook->fromHook.readSide.get());
         if (string(s, 0, 2) == "# ") {
             reply = string(s, 2);
             break;
@@ -1597,22 +1597,22 @@ HookReply DerivationGoal::tryBuildHook()
 
     string s;
     for (auto & i : allInputs) { s += i; s += ' '; }
-    writeLine(hook->toHook.writeSide, s);
+    writeLine(hook->toHook.writeSide.get(), s);
 
     /* Tell the hooks the missing outputs that have to be copied back
        from the remote system. */
     s = "";
     for (auto & i : missingPaths) { s += i; s += ' '; }
-    writeLine(hook->toHook.writeSide, s);
+    writeLine(hook->toHook.writeSide.get(), s);
 
-    hook->toHook.writeSide.close();
+    hook->toHook.writeSide = -1;
 
     /* Create the log file and pipe. */
     Path logFile = openLogFile();
 
     set<int> fds;
-    fds.insert(hook->fromHook.readSide);
-    fds.insert(hook->builderOut.readSide);
+    fds.insert(hook->fromHook.readSide.get());
+    fds.insert(hook->builderOut.readSide.get());
     worker.childStarted(shared_from_this(), fds, false, false);
 
     return rpAccept;
@@ -2142,17 +2142,17 @@ void DerivationGoal::startBuilder()
                 child = clone(childEntry, stack + stackSize, flags & ~CLONE_NEWPID, this);
             if (child == -1) throw SysError("cloning builder process");
 
-            writeFull(builderOut.writeSide, std::to_string(child) + "\n");
+            writeFull(builderOut.writeSide.get(), std::to_string(child) + "\n");
             _exit(0);
         }, options);
 
         if (helper.wait(true) != 0)
             throw Error("unable to start build process");
 
-        userNamespaceSync.readSide.close();
+        userNamespaceSync.readSide = -1;
 
         pid_t tmp;
-        if (!string2Int<pid_t>(readLine(builderOut.readSide), tmp)) abort();
+        if (!string2Int<pid_t>(readLine(builderOut.readSide.get()), tmp)) abort();
         pid = tmp;
 
         /* Set the UID/GID mapping of the builder's user
@@ -2171,8 +2171,8 @@ void DerivationGoal::startBuilder()
 
         /* Signal the builder that we've updated its user
            namespace. */
-        writeFull(userNamespaceSync.writeSide, "1");
-        userNamespaceSync.writeSide.close();
+        writeFull(userNamespaceSync.writeSide.get(), "1");
+        userNamespaceSync.writeSide = -1;
 
     } else
 #endif
@@ -2186,12 +2186,12 @@ void DerivationGoal::startBuilder()
 
     /* parent */
     pid.setSeparatePG(true);
-    builderOut.writeSide.close();
-    worker.childStarted(shared_from_this(), {builderOut.readSide}, true, true);
+    builderOut.writeSide = -1;
+    worker.childStarted(shared_from_this(), {builderOut.readSide.get()}, true, true);
 
     /* Check if setting up the build environment failed. */
     while (true) {
-        string msg = readLine(builderOut.readSide);
+        string msg = readLine(builderOut.readSide.get());
         if (string(msg, 0, 1) == "\1") {
             if (msg.size() == 1) break;
             throw Error(string(msg, 1));
@@ -2215,26 +2215,24 @@ void DerivationGoal::runChild()
 #if __linux__
         if (useChroot) {
 
-            userNamespaceSync.writeSide.close();
+            userNamespaceSync.writeSide = -1;
 
-            if (drainFD(userNamespaceSync.readSide) != "1")
+            if (drainFD(userNamespaceSync.readSide.get()) != "1")
                 throw Error("user namespace initialisation failed");
 
-            userNamespaceSync.readSide.close();
+            userNamespaceSync.readSide = -1;
 
             if (privateNetwork) {
 
                 /* Initialise the loopback interface. */
                 AutoCloseFD fd(socket(PF_INET, SOCK_DGRAM, IPPROTO_IP));
-                if (fd == -1) throw SysError("cannot open IP socket");
+                if (!fd) throw SysError("cannot open IP socket");
 
                 struct ifreq ifr;
                 strcpy(ifr.ifr_name, "lo");
                 ifr.ifr_flags = IFF_UP | IFF_LOOPBACK | IFF_RUNNING;
-                if (ioctl(fd, SIOCSIFFLAGS, &ifr) == -1)
+                if (ioctl(fd.get(), SIOCSIFFLAGS, &ifr) == -1)
                     throw SysError("cannot set loopback interface flags");
-
-                fd.close();
             }
 
             /* Set the hostname etc. to fixed values. */
@@ -2919,9 +2917,9 @@ Path DerivationGoal::openLogFile()
         % (settings.compressLog ? ".bz2" : "")).str();
 
     fdLogFile = open(logFileName.c_str(), O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, 0666);
-    if (fdLogFile == -1) throw SysError(format("creating log file ‘%1%’") % logFileName);
+    if (!fdLogFile) throw SysError(format("creating log file ‘%1%’") % logFileName);
 
-    logFileSink = std::make_shared<FdSink>(fdLogFile);
+    logFileSink = std::make_shared<FdSink>(fdLogFile.get());
 
     if (settings.compressLog)
         logSink = std::shared_ptr<CompressionSink>(makeCompressionSink("bzip2", *logFileSink));
@@ -2938,7 +2936,7 @@ void DerivationGoal::closeLogFile()
     if (logSink2) logSink2->finish();
     if (logFileSink) logFileSink->flush();
     logSink = logFileSink = 0;
-    fdLogFile.close();
+    fdLogFile = -1;
 }
 
 
@@ -2960,8 +2958,8 @@ void DerivationGoal::deleteTmpDir(bool force)
 
 void DerivationGoal::handleChildOutput(int fd, const string & data)
 {
-    if ((hook && fd == hook->builderOut.readSide) ||
-        (!hook && fd == builderOut.readSide))
+    if ((hook && fd == hook->builderOut.readSide.get()) ||
+        (!hook && fd == builderOut.readSide.get()))
     {
         logSize += data.size();
         if (settings.maxLogSize && logSize > settings.maxLogSize) {
@@ -2987,7 +2985,7 @@ void DerivationGoal::handleChildOutput(int fd, const string & data)
         if (logSink) (*logSink)(data);
     }
 
-    if (hook && fd == hook->fromHook.readSide)
+    if (hook && fd == hook->fromHook.readSide.get())
         printMsg(lvlError, data); // FIXME?
 }
 
@@ -3274,7 +3272,7 @@ void SubstitutionGoal::tryToRun()
     thr = std::thread([this]() {
         try {
             /* Wake up the worker loop when we're done. */
-            Finally updateStats([this]() { outPipe.writeSide.close(); });
+            Finally updateStats([this]() { outPipe.writeSide = -1; });
 
             copyStorePath(ref<Store>(sub), ref<Store>(worker.store.shared_from_this()),
                 storePath, repair);
@@ -3285,7 +3283,7 @@ void SubstitutionGoal::tryToRun()
         }
     });
 
-    worker.childStarted(shared_from_this(), {outPipe.readSide}, true, false);
+    worker.childStarted(shared_from_this(), {outPipe.readSide.get()}, true, false);
 
     state = &SubstitutionGoal::finished;
 }
@@ -3325,7 +3323,7 @@ void SubstitutionGoal::handleChildOutput(int fd, const string & data)
 
 void SubstitutionGoal::handleEOF(int fd)
 {
-    if (fd == outPipe.readSide) worker.wakeUp(shared_from_this());
+    if (fd == outPipe.readSide.get()) worker.wakeUp(shared_from_this());
 }
 
 
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 986608d6b..9324508cc 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -34,19 +34,19 @@ int LocalStore::openGCLock(LockType lockType)
     debug(format("acquiring global GC lock ‘%1%’") % fnGCLock);
 
     AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
-    if (fdGCLock == -1)
+    if (!fdGCLock)
         throw SysError(format("opening global GC lock ‘%1%’") % fnGCLock);
 
-    if (!lockFile(fdGCLock, lockType, false)) {
+    if (!lockFile(fdGCLock.get(), lockType, false)) {
         printMsg(lvlError, format("waiting for the big garbage collector lock..."));
-        lockFile(fdGCLock, lockType, true);
+        lockFile(fdGCLock.get(), lockType, true);
     }
 
     /* !!! Restrict read permission on the GC root.  Otherwise any
        process that can open the file for reading can DoS the
        collector. */
 
-    return fdGCLock.borrow();
+    return fdGCLock.release();
 }
 
 
@@ -149,7 +149,7 @@ void LocalStore::addTempRoot(const Path & path)
     auto state(_state.lock());
 
     /* Create the temporary roots file for this process. */
-    if (state->fdTempRoots == -1) {
+    if (!state->fdTempRoots) {
 
         while (1) {
             Path dir = (format("%1%/%2%") % stateDir % tempRootsDir).str();
@@ -166,15 +166,15 @@ void LocalStore::addTempRoot(const Path & path)
 
             state->fdTempRoots = openLockFile(state->fnTempRoots, true);
 
-            fdGCLock.close();
+            fdGCLock = -1;
 
             debug(format("acquiring read lock on ‘%1%’") % state->fnTempRoots);
-            lockFile(state->fdTempRoots, ltRead, true);
+            lockFile(state->fdTempRoots.get(), ltRead, true);
 
             /* Check whether the garbage collector didn't get in our
                way. */
             struct stat st;
-            if (fstat(state->fdTempRoots, &st) == -1)
+            if (fstat(state->fdTempRoots.get(), &st) == -1)
                 throw SysError(format("statting ‘%1%’") % state->fnTempRoots);
             if (st.st_size == 0) break;
 
@@ -188,14 +188,14 @@ void LocalStore::addTempRoot(const Path & path)
     /* Upgrade the lock to a write lock.  This will cause us to block
        if the garbage collector is holding our lock. */
     debug(format("acquiring write lock on ‘%1%’") % state->fnTempRoots);
-    lockFile(state->fdTempRoots, ltWrite, true);
+    lockFile(state->fdTempRoots.get(), ltWrite, true);
 
     string s = path + '\0';
-    writeFull(state->fdTempRoots, s);
+    writeFull(state->fdTempRoots.get(), s);
 
     /* Downgrade to a read lock. */
     debug(format("downgrading to read lock on ‘%1%’") % state->fnTempRoots);
-    lockFile(state->fdTempRoots, ltRead, true);
+    lockFile(state->fdTempRoots.get(), ltRead, true);
 }
 
 
@@ -211,7 +211,7 @@ void LocalStore::readTempRoots(PathSet & tempRoots, FDs & fds)
 
         debug(format("reading temporary root file ‘%1%’") % path);
         FDPtr fd(new AutoCloseFD(open(path.c_str(), O_CLOEXEC | O_RDWR, 0666)));
-        if (*fd == -1) {
+        if (!*fd) {
             /* It's okay if the file has disappeared. */
             if (errno == ENOENT) continue;
             throw SysError(format("opening temporary roots file ‘%1%’") % path);
@@ -224,10 +224,10 @@ void LocalStore::readTempRoots(PathSet & tempRoots, FDs & fds)
         /* Try to acquire a write lock without blocking.  This can
            only succeed if the owning process has died.  In that case
            we don't care about its temporary roots. */
-        if (lockFile(*fd, ltWrite, false)) {
+        if (lockFile(fd->get(), ltWrite, false)) {
             printMsg(lvlError, format("removing stale temporary roots file ‘%1%’") % path);
             unlink(path.c_str());
-            writeFull(*fd, "d");
+            writeFull(fd->get(), "d");
             continue;
         }
 
@@ -235,10 +235,10 @@ void LocalStore::readTempRoots(PathSet & tempRoots, FDs & fds)
            from upgrading to a write lock, therefore it will block in
            addTempRoot(). */
         debug(format("waiting for read lock on ‘%1%’") % path);
-        lockFile(*fd, ltRead, true);
+        lockFile(fd->get(), ltRead, true);
 
         /* Read the entire file. */
-        string contents = readFile(*fd);
+        string contents = readFile(fd->get());
 
         /* Extract the roots. */
         string::size_type pos = 0, end;
@@ -721,7 +721,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     }
 
     /* Allow other processes to add to the store from here on. */
-    fdGCLock.close();
+    fdGCLock = -1;
     fds.clear();
 
     /* Delete the trash directory. */
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 409eb1a8a..822d5fce3 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -120,11 +120,11 @@ LocalStore::LocalStore(const Params & params)
             AutoCloseFD fd = open(reservedPath.c_str(), O_WRONLY | O_CREAT | O_CLOEXEC, 0600);
             int res = -1;
 #if HAVE_POSIX_FALLOCATE
-            res = posix_fallocate(fd, 0, settings.reservedSize);
+            res = posix_fallocate(fd.get(), 0, settings.reservedSize);
 #endif
             if (res == -1) {
-                writeFull(fd, string(settings.reservedSize, 'X'));
-                ftruncate(fd, settings.reservedSize);
+                writeFull(fd.get(), string(settings.reservedSize, 'X'));
+                ftruncate(fd.get(), settings.reservedSize);
             }
         }
     } catch (SysError & e) { /* don't care about errors */
@@ -135,9 +135,9 @@ LocalStore::LocalStore(const Params & params)
     Path globalLockPath = dbDir + "/big-lock";
     globalLock = openLockFile(globalLockPath.c_str(), true);
 
-    if (!lockFile(globalLock, ltRead, false)) {
+    if (!lockFile(globalLock.get(), ltRead, false)) {
         printMsg(lvlError, "waiting for the big Nix store lock...");
-        lockFile(globalLock, ltRead, true);
+        lockFile(globalLock.get(), ltRead, true);
     }
 
     /* Check the current database schema and if necessary do an
@@ -166,9 +166,9 @@ LocalStore::LocalStore(const Params & params)
                 "which is no longer supported. To convert to the new format,\n"
                 "please upgrade Nix to version 1.11 first.");
 
-        if (!lockFile(globalLock, ltWrite, false)) {
+        if (!lockFile(globalLock.get(), ltWrite, false)) {
             printMsg(lvlError, "waiting for exclusive access to the Nix store...");
-            lockFile(globalLock, ltWrite, true);
+            lockFile(globalLock.get(), ltWrite, true);
         }
 
         /* Get the schema version again, because another process may
@@ -197,7 +197,7 @@ LocalStore::LocalStore(const Params & params)
 
         writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
 
-        lockFile(globalLock, ltRead, true);
+        lockFile(globalLock.get(), ltRead, true);
     }
 
     else openDB(*state, false);
@@ -236,8 +236,8 @@ LocalStore::~LocalStore()
     auto state(_state.lock());
 
     try {
-        if (state->fdTempRoots != -1) {
-            state->fdTempRoots.close();
+        if (state->fdTempRoots) {
+            state->fdTempRoots = -1;
             unlink(state->fnTempRoots.c_str());
         }
     } catch (...) {
@@ -1115,7 +1115,7 @@ bool LocalStore::verifyStore(bool checkContents, bool repair)
 
     /* Release the GC lock so that checking content hashes (which can
        take ages) doesn't block the GC or builds. */
-    fdGCLock.close();
+    fdGCLock = -1;
 
     /* Optionally, check the content hashes (slow). */
     if (checkContents) {
diff --git a/src/libstore/pathlocks.cc b/src/libstore/pathlocks.cc
index d0a0f812e..b9e178d61 100644
--- a/src/libstore/pathlocks.cc
+++ b/src/libstore/pathlocks.cc
@@ -17,10 +17,10 @@ int openLockFile(const Path & path, bool create)
     AutoCloseFD fd;
 
     fd = open(path.c_str(), O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600);
-    if (fd == -1 && (create || errno != ENOENT))
+    if (!fd && (create || errno != ENOENT))
         throw SysError(format("opening lock file ‘%1%’") % path);
 
-    return fd.borrow();
+    return fd.release();
 }
 
 
@@ -119,10 +119,10 @@ bool PathLocks::lockPaths(const PathSet & _paths,
             fd = openLockFile(lockPath, true);
 
             /* Acquire an exclusive lock. */
-            if (!lockFile(fd, ltWrite, false)) {
+            if (!lockFile(fd.get(), ltWrite, false)) {
                 if (wait) {
                     if (waitMsg != "") printMsg(lvlError, waitMsg);
-                    lockFile(fd, ltWrite, true);
+                    lockFile(fd.get(), ltWrite, true);
                 } else {
                     /* Failed to lock this path; release all other
                        locks. */
@@ -136,7 +136,7 @@ bool PathLocks::lockPaths(const PathSet & _paths,
             /* Check that the lock file hasn't become stale (i.e.,
                hasn't been unlinked). */
             struct stat st;
-            if (fstat(fd, &st) == -1)
+            if (fstat(fd.get(), &st) == -1)
                 throw SysError(format("statting lock file ‘%1%’") % lockPath);
             if (st.st_size != 0)
                 /* This lock file has been unlinked, so we're holding
@@ -149,7 +149,7 @@ bool PathLocks::lockPaths(const PathSet & _paths,
         }
 
         /* Use borrow so that the descriptor isn't closed. */
-        fds.push_back(FDPair(fd.borrow(), lockPath));
+        fds.push_back(FDPair(fd.release(), lockPath));
         lockedPaths.insert(lockPath);
     }
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 50ad409a9..ab05c3844 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -66,9 +66,9 @@ ref<RemoteStore::Connection> RemoteStore::openConnection()
         | SOCK_CLOEXEC
         #endif
         , 0);
-    if (conn->fd == -1)
+    if (!conn->fd)
         throw SysError("cannot create Unix domain socket");
-    closeOnExec(conn->fd);
+    closeOnExec(conn->fd.get());
 
     string socketPath = settings.nixDaemonSocketFile;
 
@@ -78,11 +78,11 @@ ref<RemoteStore::Connection> RemoteStore::openConnection()
         throw Error(format("socket path ‘%1%’ is too long") % socketPath);
     strcpy(addr.sun_path, socketPath.c_str());
 
-    if (connect(conn->fd, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+    if (connect(conn->fd.get(), (struct sockaddr *) &addr, sizeof(addr)) == -1)
         throw SysError(format("cannot connect to daemon at ‘%1%’") % socketPath);
 
-    conn->from.fd = conn->fd;
-    conn->to.fd = conn->fd;
+    conn->from.fd = conn->fd.get();
+    conn->to.fd = conn->fd.get();
 
     /* Send the magic greeting, check for the reply. */
     try {
@@ -531,7 +531,7 @@ RemoteStore::Connection::~Connection()
 {
     try {
         to.flush();
-        fd.close();
+        fd = -1;
     } catch (...) {
         ignoreException();
     }
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index c3e4c87a5..edd4a881b 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -42,14 +42,14 @@ static void dumpContents(const Path & path, size_t size,
     sink << "contents" << size;
 
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
-    if (fd == -1) throw SysError(format("opening file ‘%1%’") % path);
+    if (!fd) throw SysError(format("opening file ‘%1%’") % path);
 
     unsigned char buf[65536];
     size_t left = size;
 
     while (left > 0) {
         size_t n = left > sizeof(buf) ? sizeof(buf) : left;
-        readFull(fd, buf, n);
+        readFull(fd.get(), buf, n);
         left -= n;
         sink(buf, n);
     }
@@ -303,17 +303,16 @@ struct RestoreSink : ParseSink
     void createRegularFile(const Path & path)
     {
         Path p = dstPath + path;
-        fd.close();
         fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
-        if (fd == -1) throw SysError(format("creating file ‘%1%’") % p);
+        if (!fd) throw SysError(format("creating file ‘%1%’") % p);
     }
 
     void isExecutable()
     {
         struct stat st;
-        if (fstat(fd, &st) == -1)
+        if (fstat(fd.get(), &st) == -1)
             throw SysError("fstat");
-        if (fchmod(fd, st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+        if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
             throw SysError("fchmod");
     }
 
@@ -321,7 +320,7 @@ struct RestoreSink : ParseSink
     {
 #if HAVE_POSIX_FALLOCATE
         if (len) {
-            errno = posix_fallocate(fd, 0, len);
+            errno = posix_fallocate(fd.get(), 0, len);
             /* Note that EINVAL may indicate that the underlying
                filesystem doesn't support preallocation (e.g. on
                OpenSolaris).  Since preallocation is just an
@@ -334,7 +333,7 @@ struct RestoreSink : ParseSink
 
     void receiveContents(unsigned char * data, unsigned int len)
     {
-        writeFull(fd, data, len);
+        writeFull(fd.get(), data, len);
     }
 
     void createSymlink(const Path & path, const string & target)
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 69ea95852..fa4258777 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -255,11 +255,11 @@ Hash hashFile(HashType ht, const Path & path)
     start(ht, ctx);
 
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
-    if (fd == -1) throw SysError(format("opening file ‘%1%’") % path);
+    if (!fd) throw SysError(format("opening file ‘%1%’") % path);
 
     unsigned char buf[8192];
     ssize_t n;
-    while ((n = read(fd, buf, sizeof(buf)))) {
+    while ((n = read(fd.get(), buf, sizeof(buf)))) {
         checkInterrupt();
         if (n == -1) throw SysError(format("reading file ‘%1%’") % path);
         update(ht, ctx, buf, n);
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 4cc4649c9..f1e714a66 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -274,18 +274,18 @@ string readFile(int fd)
 string readFile(const Path & path, bool drain)
 {
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
-    if (fd == -1)
+    if (!fd)
         throw SysError(format("opening file ‘%1%’") % path);
-    return drain ? drainFD(fd) : readFile(fd);
+    return drain ? drainFD(fd.get()) : readFile(fd.get());
 }
 
 
 void writeFile(const Path & path, const string & s)
 {
     AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC, 0666);
-    if (fd == -1)
+    if (!fd)
         throw SysError(format("opening file ‘%1%’") % path);
-    writeFull(fd, s);
+    writeFull(fd.get(), s);
 }
 
 
@@ -556,28 +556,24 @@ void AutoDelete::reset(const Path & p, bool recursive) {
 //////////////////////////////////////////////////////////////////////
 
 
-AutoCloseFD::AutoCloseFD()
-{
-    fd = -1;
-}
+AutoCloseFD::AutoCloseFD() : fd{-1} {}
+
+
+AutoCloseFD::AutoCloseFD(int fd) : fd{fd} {}
 
 
-AutoCloseFD::AutoCloseFD(int fd)
+AutoCloseFD::AutoCloseFD(AutoCloseFD&& that) : fd{that.fd}
 {
-    this->fd = fd;
+    that.fd = -1;
 }
 
 
-AutoCloseFD::AutoCloseFD(const AutoCloseFD & fd)
+AutoCloseFD& AutoCloseFD::operator =(AutoCloseFD&& that)
 {
-    /* Copying an AutoCloseFD isn't allowed (who should get to close
-       it?).  But as an edge case, allow copying of closed
-       AutoCloseFDs.  This is necessary due to tiresome reasons
-       involving copy constructor use on default object values in STL
-       containers (like when you do `map[value]' where value isn't in
-       the map yet). */
-    this->fd = fd.fd;
-    if (this->fd != -1) abort();
+    close();
+    fd = that.fd;
+    that.fd = -1;
+    return *this;
 }
 
 
@@ -591,14 +587,7 @@ AutoCloseFD::~AutoCloseFD()
 }
 
 
-void AutoCloseFD::operator =(int fd)
-{
-    if (this->fd != fd) close();
-    this->fd = fd;
-}
-
-
-AutoCloseFD::operator int() const
+int AutoCloseFD::get() const
 {
     return fd;
 }
@@ -610,19 +599,17 @@ void AutoCloseFD::close()
         if (::close(fd) == -1)
             /* This should never happen. */
             throw SysError(format("closing file descriptor %1%") % fd);
-        fd = -1;
     }
 }
 
 
-bool AutoCloseFD::isOpen()
+AutoCloseFD::operator bool() const
 {
     return fd != -1;
 }
 
 
-/* Pass responsibility for closing this fd to the caller. */
-int AutoCloseFD::borrow()
+int AutoCloseFD::release()
 {
     int oldFD = fd;
     fd = -1;
@@ -899,10 +886,10 @@ string runProgram(Path program, bool searchPath, const Strings & args,
 
     /* Fork. */
     Pid pid = startProcess([&]() {
-        if (dup2(out.writeSide, STDOUT_FILENO) == -1)
+        if (dup2(out.writeSide.get(), STDOUT_FILENO) == -1)
             throw SysError("dupping stdout");
         if (!input.empty()) {
-            if (dup2(in.readSide, STDIN_FILENO) == -1)
+            if (dup2(in.readSide.get(), STDIN_FILENO) == -1)
                 throw SysError("dupping stdin");
         }
 
@@ -917,16 +904,16 @@ string runProgram(Path program, bool searchPath, const Strings & args,
         throw SysError(format("executing ‘%1%’") % program);
     });
 
-    out.writeSide.close();
+    out.writeSide = -1;
 
     /* FIXME: This can deadlock if the input is too long. */
     if (!input.empty()) {
-        in.readSide.close();
-        writeFull(in.writeSide, input);
-        in.writeSide.close();
+        in.readSide = -1;
+        writeFull(in.writeSide.get(), input);
+        in.writeSide = -1;
     }
 
-    string result = drainFD(out.readSide);
+    string result = drainFD(out.readSide.get());
 
     /* Wait for the child to finish. */
     int status = pid.wait(true);
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index ab43637a5..819921dff 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -164,16 +164,18 @@ public:
 class AutoCloseFD
 {
     int fd;
+    void close();
 public:
     AutoCloseFD();
     AutoCloseFD(int fd);
-    AutoCloseFD(const AutoCloseFD & fd);
+    AutoCloseFD(const AutoCloseFD & fd) = delete;
+    AutoCloseFD(AutoCloseFD&& fd);
     ~AutoCloseFD();
-    void operator =(int fd);
-    operator int() const;
-    void close();
-    bool isOpen();
-    int borrow();
+    AutoCloseFD& operator =(const AutoCloseFD & fd) = delete;
+    AutoCloseFD& operator =(AutoCloseFD&& fd);
+    int get() const;
+    explicit operator bool() const;
+    int release();
 };
 
 
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
index 6a992b953..6e0d869f4 100644
--- a/src/nix-daemon/nix-daemon.cc
+++ b/src/nix-daemon/nix-daemon.cc
@@ -767,7 +767,7 @@ static void daemonLoop(char * * argv)
 
         /* Create and bind to a Unix domain socket. */
         fdSocket = socket(PF_UNIX, SOCK_STREAM, 0);
-        if (fdSocket == -1)
+        if (!fdSocket)
             throw SysError("cannot create Unix domain socket");
 
         string socketPath = settings.nixDaemonSocketFile;
@@ -793,7 +793,7 @@ static void daemonLoop(char * * argv)
            (everybody can connect --- provided they have access to the
            directory containing the socket). */
         mode_t oldMode = umask(0111);
-        int res = bind(fdSocket, (struct sockaddr *) &addr, sizeof(addr));
+        int res = bind(fdSocket.get(), (struct sockaddr *) &addr, sizeof(addr));
         umask(oldMode);
         if (res == -1)
             throw SysError(format("cannot bind to socket ‘%1%’") % socketPath);
@@ -801,11 +801,11 @@ static void daemonLoop(char * * argv)
         if (chdir("/") == -1) /* back to the root */
             throw SysError("cannot change current directory");
 
-        if (listen(fdSocket, 5) == -1)
+        if (listen(fdSocket.get(), 5) == -1)
             throw SysError(format("cannot listen on socket ‘%1%’") % socketPath);
     }
 
-    closeOnExec(fdSocket);
+    closeOnExec(fdSocket.get());
 
     /* Loop accepting connections. */
     while (1) {
@@ -815,18 +815,18 @@ static void daemonLoop(char * * argv)
             struct sockaddr_un remoteAddr;
             socklen_t remoteAddrLen = sizeof(remoteAddr);
 
-            AutoCloseFD remote = accept(fdSocket,
+            AutoCloseFD remote = accept(fdSocket.get(),
                 (struct sockaddr *) &remoteAddr, &remoteAddrLen);
             checkInterrupt();
-            if (remote == -1) {
+            if (!remote) {
                 if (errno == EINTR) continue;
                 throw SysError("accepting connection");
             }
 
-            closeOnExec(remote);
+            closeOnExec(remote.get());
 
             bool trusted = false;
-            PeerInfo peer = getPeerInfo(remote);
+            PeerInfo peer = getPeerInfo(remote.get());
 
             struct passwd * pw = peer.uidKnown ? getpwuid(peer.uid) : 0;
             string user = pw ? pw->pw_name : std::to_string(peer.uid);
@@ -854,7 +854,7 @@ static void daemonLoop(char * * argv)
             options.runExitHandlers = true;
             options.allowVfork = false;
             startProcess([&]() {
-                fdSocket.close();
+                fdSocket = -1;
 
                 /* Background the daemon. */
                 if (setsid() == -1)
@@ -870,8 +870,8 @@ static void daemonLoop(char * * argv)
                 }
 
                 /* Handle the connection. */
-                from.fd = remote;
-                to.fd = remote;
+                from.fd = remote.get();
+                to.fd = remote.get();
                 processConnection(trusted);
 
                 exit(0);