syscall: Parse and encode SCM_RIGHTS and SCM_CREDENTIALS.

R=rsc, agl, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/4667066

src/pkg/syscall/Makefile

@@ -36,6 +36,7 @@ GOFILES_linux=\
 	exec_unix.go\
 	lsf_linux.go\
 	netlink_linux.go\
+	sockcmsg_linux.go\
 	sockcmsg_unix.go\
 	syscall_unix.go\
 

src/pkg/syscall/sockcmsg_linux.go

+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Socket control messages
+
+package syscall
+
+import (
+	"unsafe"
+)
+
+// UnixCredentials encodes credentials into a socket control message
+// for sending to another process. This can be used for
+// authentication.
+func UnixCredentials(ucred *Ucred) []byte {
+	buf := make([]byte, CmsgSpace(SizeofUcred))
+	cmsg := (*Cmsghdr)(unsafe.Pointer(&buf[0]))
+	cmsg.Level = SOL_SOCKET
+	cmsg.Type = SCM_CREDENTIALS
+	cmsg.SetLen(CmsgLen(SizeofUcred))
+	*((*Ucred)(cmsgData(cmsg))) = *ucred
+	return buf
+}
+
+// ParseUnixCredentials decodes a socket control message that contains
+// credentials in a Ucred structure. To receive such a message, the
+// SO_PASSCRED option must be enabled on the socket.
+func ParseUnixCredentials(msg *SocketControlMessage) (*Ucred, int) {
+	if msg.Header.Level != SOL_SOCKET {
+		return nil, EINVAL
+	}
+	if msg.Header.Type != SCM_CREDENTIALS {
+		return nil, EINVAL
+	}
+	ucred := *(*Ucred)(unsafe.Pointer(&msg.Data[0]))
+	return &ucred, 0
+}

src/pkg/syscall/sockcmsg_unix.go

@@ -24,10 +24,22 @@ func cmsgAlignOf(salen int) int {
 	return (salen + salign - 1) & ^(salign - 1)
 }
 
-func cmsgLen(datalen int) int {
+// CmsgLen returns the value to store in the Len field of the Cmsghdr
+// structure, taking into account any necessary alignment.
+func CmsgLen(datalen int) int {
 	return cmsgAlignOf(SizeofCmsghdr) + datalen
 }
 
+// CmsgSpace returns the number of bytes an ancillary element with
+// payload of the passed data length occupies.
+func CmsgSpace(datalen int) int {
+	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
+}
+
+func cmsgData(cmsg *Cmsghdr) unsafe.Pointer {
+	return unsafe.Pointer(uintptr(unsafe.Pointer(cmsg)) + SizeofCmsghdr)
+}
+
 type SocketControlMessage struct {
 	Header Cmsghdr
 	Data   []byte
@@ -41,7 +53,7 @@ func ParseSocketControlMessage(buf []byte) ([]SocketControlMessage, int) {
 		cmsgs []SocketControlMessage
 	)
 
-	for len(buf) >= cmsgLen(0) {
+	for len(buf) >= CmsgLen(0) {
 		h, dbuf, e = socketControlMessageHeaderAndData(buf)
 		if e != 0 {
 			break
@@ -63,3 +75,39 @@ func socketControlMessageHeaderAndData(buf []byte) (*Cmsghdr, []byte, int) {
 	}
 	return h, buf[cmsgAlignOf(SizeofCmsghdr):], 0
 }
+
+// UnixRights encodes a set of open file descriptors into a socket
+// control message for sending to another process.
+func UnixRights(fds ...int) []byte {
+	datalen := len(fds) * 4
+	buf := make([]byte, CmsgSpace(datalen))
+	cmsg := (*Cmsghdr)(unsafe.Pointer(&buf[0]))
+	cmsg.Level = SOL_SOCKET
+	cmsg.Type = SCM_RIGHTS
+	cmsg.SetLen(CmsgLen(datalen))
+
+	data := uintptr(cmsgData(cmsg))
+	for _, fd := range fds {
+		*(*int32)(unsafe.Pointer(data)) = int32(fd)
+		data += 4
+	}
+
+	return buf
+}
+
+// ParseUnixRights decodes a socket control message that contains an
+// integer array of open file descriptors from another process.
+func ParseUnixRights(msg *SocketControlMessage) ([]int, int) {
+	if msg.Header.Level != SOL_SOCKET {
+		return nil, EINVAL
+	}
+	if msg.Header.Type != SCM_RIGHTS {
+		return nil, EINVAL
+	}
+	fds := make([]int, len(msg.Data)>>2)
+	for i, j := 0, 0; i < len(msg.Data); i += 4 {
+		fds[j] = int(*(*int32)(unsafe.Pointer(&msg.Data[i])))
+		j++
+	}
+	return fds, 0
+}