1// Copyright 2011 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris 6 7// Socket control messages 8 9package unix 10 11import ( 12 "runtime" 13 "unsafe" 14) 15 16// Round the length of a raw sockaddr up to align it properly. 17func cmsgAlignOf(salen int) int { 18 salign := SizeofPtr 19 20 switch runtime.GOOS { 21 case "darwin", "dragonfly", "solaris": 22 // NOTE: It seems like 64-bit Darwin, DragonFly BSD and 23 // Solaris kernels still require 32-bit aligned access to 24 // network subsystem. 25 if SizeofPtr == 8 { 26 salign = 4 27 } 28 case "openbsd": 29 // OpenBSD armv7 requires 64-bit alignment. 30 if runtime.GOARCH == "arm" { 31 salign = 8 32 } 33 } 34 35 return (salen + salign - 1) & ^(salign - 1) 36} 37 38// CmsgLen returns the value to store in the Len field of the Cmsghdr 39// structure, taking into account any necessary alignment. 40func CmsgLen(datalen int) int { 41 return cmsgAlignOf(SizeofCmsghdr) + datalen 42} 43 44// CmsgSpace returns the number of bytes an ancillary element with 45// payload of the passed data length occupies. 46func CmsgSpace(datalen int) int { 47 return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen) 48} 49 50func cmsgData(h *Cmsghdr) unsafe.Pointer { 51 return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr))) 52} 53 54// SocketControlMessage represents a socket control message. 55type SocketControlMessage struct { 56 Header Cmsghdr 57 Data []byte 58} 59 60// ParseSocketControlMessage parses b as an array of socket control 61// messages. 62func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) { 63 var msgs []SocketControlMessage 64 i := 0 65 for i+CmsgLen(0) <= len(b) { 66 h, dbuf, err := socketControlMessageHeaderAndData(b[i:]) 67 if err != nil { 68 return nil, err 69 } 70 m := SocketControlMessage{Header: *h, Data: dbuf} 71 msgs = append(msgs, m) 72 i += cmsgAlignOf(int(h.Len)) 73 } 74 return msgs, nil 75} 76 77func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) { 78 h := (*Cmsghdr)(unsafe.Pointer(&b[0])) 79 if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) { 80 return nil, nil, EINVAL 81 } 82 return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil 83} 84 85// UnixRights encodes a set of open file descriptors into a socket 86// control message for sending to another process. 87func UnixRights(fds ...int) []byte { 88 datalen := len(fds) * 4 89 b := make([]byte, CmsgSpace(datalen)) 90 h := (*Cmsghdr)(unsafe.Pointer(&b[0])) 91 h.Level = SOL_SOCKET 92 h.Type = SCM_RIGHTS 93 h.SetLen(CmsgLen(datalen)) 94 data := cmsgData(h) 95 for _, fd := range fds { 96 *(*int32)(data) = int32(fd) 97 data = unsafe.Pointer(uintptr(data) + 4) 98 } 99 return b 100} 101 102// ParseUnixRights decodes a socket control message that contains an 103// integer array of open file descriptors from another process. 104func ParseUnixRights(m *SocketControlMessage) ([]int, error) { 105 if m.Header.Level != SOL_SOCKET { 106 return nil, EINVAL 107 } 108 if m.Header.Type != SCM_RIGHTS { 109 return nil, EINVAL 110 } 111 fds := make([]int, len(m.Data)>>2) 112 for i, j := 0, 0; i < len(m.Data); i += 4 { 113 fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i]))) 114 j++ 115 } 116 return fds, nil 117} 118