1 files changed, 69 insertions, 15 deletions

diff --git a/sd_daemon/notify.go b/sd_daemon/notify.go
index b159a22..ad63659 100644
--- a/sd_daemon/notify.go
+++ b/sd_daemon/notify.go
@@ -1,6 +1,6 @@
 // Copyright 2013-2015 Docker, Inc.
 // Copyright 2014 CoreOS, Inc.
-// Copyright 2015 Luke Shumaker
+// Copyright 2015-2016 Luke Shumaker
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -14,31 +14,47 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package sd
+package sd_daemon
 
 import (
-	"errors"
 	"net"
 	"os"
+	"syscall"
+	"bytes"
 )
 
-// errNotifyNoSocket is an error returned if no socket was specified.
-var errNotifyNoSocket = errors.New("No socket")
-
-// Notify sends a message to the service manager aobout state
-// changes.  It is common to ignore the error.
+// Notify sends a message from process pid to the service manager
+// about state changes. If pid <= 0, or if the current process does
+// not have priveleges to send messages on behalf of other processes,
+// then the message is simply sent from the current process.
 //
-// If unsetEnv is true, then (regarless of whether the function call
+// If unsetEnv is true, then (regardless of whether the function call
 // itself succeeds or not) it will unset the environmental variable
 // NOTIFY_SOCKET, which will cause further calls to this function to
 // fail.
 //
 // The state parameter should countain a newline-separated list of
-// variable assignments.
+// variable assignments.  See the documentation for sd_notify(3) for
+// well-known variable assignments.
+// https://www.freedesktop.org/software/systemd/man/sd_notify.html
+//
+// It is possible to include a set of file descriptors with the
+// message.  This is useful for keeping files open across restarts, as
+// it enables the service manager will pass those files to the new
+// process when it is restarted (see ListenFds).  Note: The service
+// manager will only actually store the file descriptors if you
+// include "FDSTORE=1" in the state.
 //
-// See the documentation for sd_notify(3) for well-known variable
-// assignments.
-func Notify(unsetEnv bool, state string) error {
+// If the service manager is not listening for notifications from this
+// process (or this has already been called with unsetEnv=true), then
+// ErrDisabled is returned.  If the service manager appears to be
+// listening, but there is an error sending the message, then that
+// error is returned.  It is generally recommended that you ignore the
+// return value: if there is an error, this is function no-op; meaning
+// that by calling the function but ignoring the return value, you can
+// easily support both service managers that support these
+// notifications and those that do not.
+func Notify(pid int, unsetEnv bool, state string, files []*os.File) error {
 	if unsetEnv {
 		defer func() { _ = os.Unsetenv("NOTIFY_SOCKET") }()
 	}
@@ -49,7 +65,7 @@ func Notify(unsetEnv bool, state string) error {
 	}
 
 	if socketAddr.Name == "" {
-		return errNotifyNoSocket
+		return ErrDisabled
 	}
 
 	conn, err := net.DialUnix(socketAddr.Net, nil, socketAddr)
@@ -58,6 +74,44 @@ func Notify(unsetEnv bool, state string) error {
 	}
 	defer func() { _ = conn.Close() }()
 
-	_, err = conn.Write([]byte(state))
+	var cmsgs [][]byte
+
+	if len(files) > 0 {
+		fds := make([]int, len(files))
+		for i := range files {
+			fds[i] = int(files[i].Fd())
+		}
+		cmsg := syscall.UnixRights(fds...)
+		cmsgs = append(cmsgs, cmsg)
+	}
+
+	havePid := pid > 0 && pid != os.Getpid()
+	if havePid {
+		// The types of members of syscall.Ucred aren't
+		// guaranteed across processors.  However,
+		// fortunately, they are the same on all supported
+		// processors as of go 1.7.4.
+		cmsg := syscall.UnixCredentials(&syscall.Ucred{
+			Pid: int32(pid),
+			Uid: uint32(os.Getuid()),
+			Gid: uint32(os.Getgid()),
+		})
+		cmsgs = append(cmsgs, cmsg)
+	}
+
+	// If the 2nd argument is empty, this is equivalent to .Write([]byte(state))
+	_, _, err = conn.WriteMsgUnix([]byte(state), bytes.Join(cmsgs, nil), nil)
+
+	if err != nil && havePid {
+		// Maybe it failed because we don't have privileges to
+		// spoof our pid, retry without spoofing the pid.
+		//
+		// I'm not too happy that does this silently without
+		// notifying the user, but that's what
+		// sd_pid_notify_with_fds does.
+		cmsgs = cmsgs[:len(cmsgs)-1]
+		_, _, err = conn.WriteMsgUnix([]byte(state), bytes.Join(cmsgs, nil), nil)
+	}
+
 	return err
 }