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// 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.
// +build darwin freebsd linux netbsd openbsd
// Socket control messages
package syscall
import (
"unsafe"
)
// Round the length of a raw sockaddr up to align it propery.
func cmsgAlignOf(salen int) int {
salign := int(sizeofPtr)
// NOTE: It seems like 64-bit Darwin kernel still requires 32-bit
// aligned access to BSD subsystem.
if darwinAMD64 {
salign = 4
}
if salen == 0 {
return salign
}
return (salen + salign - 1) & ^(salign - 1)
}
// 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)) + uintptr(SizeofCmsghdr))
}
type SocketControlMessage struct {
Header Cmsghdr
Data []byte
}
func ParseSocketControlMessage(buf []byte) ([]SocketControlMessage, error) {
var (
h *Cmsghdr
dbuf []byte
e error
cmsgs []SocketControlMessage
)
for len(buf) >= CmsgLen(0) {
h, dbuf, e = socketControlMessageHeaderAndData(buf)
if e != nil {
break
}
m := SocketControlMessage{}
m.Header = *h
m.Data = dbuf[:int(h.Len)-cmsgAlignOf(SizeofCmsghdr)]
cmsgs = append(cmsgs, m)
buf = buf[cmsgAlignOf(int(h.Len)):]
}
return cmsgs, e
}
func socketControlMessageHeaderAndData(buf []byte) (*Cmsghdr, []byte, error) {
h := (*Cmsghdr)(unsafe.Pointer(&buf[0]))
if int(h.Len) < SizeofCmsghdr || int(h.Len) > len(buf) {
return nil, nil, EINVAL
}
return h, buf[cmsgAlignOf(SizeofCmsghdr):], nil
}
// 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, error) {
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, nil
}
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