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// Copyright 2013-2015 Docker, Inc.
// Copyright 2014 CoreOS, Inc.
// Copyright 2015-2017 Luke Shumaker
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sd_daemon
import (
"bytes"
"net"
"os"
"golang.org/x/sys/unix"
)
// Notification is a message to be sent to the service manager about
// state changes.
type Notification struct {
// PID specifies which process to send a notification about.
// 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.
PID int
// State should countain a newline-separated list of variable
// assignments. See the documentation for sd_notify(3) for
// well-known variable assignments.
//
// https://www.freedesktop.org/software/systemd/man/sd_notify.html
State string
// Files is a list of file descriptors to send to the service
// manager with the message. This is useful for keeping files
// open across restarts, as it enables the service manager to
// 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 (again,
// see sd_notify(3) for well-known variable assignments).
Files []*os.File
}
// Send sends the Notification to the service manager.
//
// 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 notify operations to fail.
//
// If the service manager is not listening for notifications from this
// process tree (or a Notification has has already been send 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, then 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 (msg Notification) Send(unsetEnv bool) error {
if unsetEnv {
defer func() { _ = os.Unsetenv("NOTIFY_SOCKET") }()
}
socketAddr := &net.UnixAddr{
Name: os.Getenv("NOTIFY_SOCKET"),
Net: "unixgram",
}
if socketAddr.Name == "" {
return ErrDisabled
}
conn, err := socketUnixgram(socketAddr.Name)
if err != nil {
return err
}
defer func() { _ = conn.Close() }()
var cmsgs [][]byte
if len(msg.Files) > 0 {
fds := make([]int, len(msg.Files))
for i := range msg.Files {
fds[i] = int(msg.Files[i].Fd())
}
cmsg := unix.UnixRights(fds...)
cmsgs = append(cmsgs, cmsg)
}
havePid := msg.PID > 0 && msg.PID != os.Getpid()
if havePid {
cmsg := unix.UnixCredentials(&unix.Ucred{
Pid: int32(msg.PID),
Uid: uint32(os.Getuid()),
Gid: uint32(os.Getgid()),
})
cmsgs = append(cmsgs, cmsg)
}
// If the 2nd argument is empty, this is equivalent to
//
// conn, _ := net.DialUnix(socketAddr.Net, nil, socketAddr)
// conn.Write([]byte(msg.State))
_, _, err = conn.WriteMsgUnix([]byte(msg.State), bytes.Join(cmsgs, nil), socketAddr)
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 we do this silently without
// notifying the caller, but that's what
// sd_pid_notify_with_fds does.
cmsgs = cmsgs[:len(cmsgs)-1]
_, _, err = conn.WriteMsgUnix([]byte(msg.State), bytes.Join(cmsgs, nil), socketAddr)
}
return err
}
// socketUnixgram wraps socket(2), but doesn't bind(2) or connect(2)
// the socket to anything. This is an ugly hack because none of the
// functions in "net" actually allow you to get a AF_UNIX socket not
// bound/connected to anything.
//
// At some point you begin to question if it is worth it to keep up
// the high-level interface of "net", and messing around with FileConn
// and UnixConn. Maybe we just drop to using unix.Socket and
// unix.SendmsgN directly.
func socketUnixgram(name string) (*net.UnixConn, error) {
fd, err := unix.Socket(unix.AF_UNIX, unix.SOCK_DGRAM|unix.SOCK_CLOEXEC, 0)
if err != nil {
return nil, err
}
conn, err := net.FileConn(os.NewFile(uintptr(fd), name))
if err != nil {
return nil, err
}
unixConn := conn.(*net.UnixConn)
return unixConn, nil
}
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