sockcmsg_unix.go

Documentation: syscall

		 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  //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
		 6  // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
		 7  
		 8  // Socket control messages
		 9  
		10  package syscall
		11  
		12  import (
		13  	"unsafe"
		14  )
		15  
		16  // CmsgLen returns the value to store in the Len field of the Cmsghdr
		17  // structure, taking into account any necessary alignment.
		18  func CmsgLen(datalen int) int {
		19  	return cmsgAlignOf(SizeofCmsghdr) + datalen
		20  }
		21  
		22  // CmsgSpace returns the number of bytes an ancillary element with
		23  // payload of the passed data length occupies.
		24  func CmsgSpace(datalen int) int {
		25  	return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
		26  }
		27  
		28  func (h *Cmsghdr) data(offset uintptr) unsafe.Pointer {
		29  	return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)) + offset)
		30  }
		31  
		32  // SocketControlMessage represents a socket control message.
		33  type SocketControlMessage struct {
		34  	Header Cmsghdr
		35  	Data	 []byte
		36  }
		37  
		38  // ParseSocketControlMessage parses b as an array of socket control
		39  // messages.
		40  func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
		41  	var msgs []SocketControlMessage
		42  	i := 0
		43  	for i+CmsgLen(0) <= len(b) {
		44  		h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
		45  		if err != nil {
		46  			return nil, err
		47  		}
		48  		m := SocketControlMessage{Header: *h, Data: dbuf}
		49  		msgs = append(msgs, m)
		50  		i += cmsgAlignOf(int(h.Len))
		51  	}
		52  	return msgs, nil
		53  }
		54  
		55  func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
		56  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
		57  	if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
		58  		return nil, nil, EINVAL
		59  	}
		60  	return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
		61  }
		62  
		63  // UnixRights encodes a set of open file descriptors into a socket
		64  // control message for sending to another process.
		65  func UnixRights(fds ...int) []byte {
		66  	datalen := len(fds) * 4
		67  	b := make([]byte, CmsgSpace(datalen))
		68  	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
		69  	h.Level = SOL_SOCKET
		70  	h.Type = SCM_RIGHTS
		71  	h.SetLen(CmsgLen(datalen))
		72  	for i, fd := range fds {
		73  		*(*int32)(h.data(4 * uintptr(i))) = int32(fd)
		74  	}
		75  	return b
		76  }
		77  
		78  // ParseUnixRights decodes a socket control message that contains an
		79  // integer array of open file descriptors from another process.
		80  func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
		81  	if m.Header.Level != SOL_SOCKET {
		82  		return nil, EINVAL
		83  	}
		84  	if m.Header.Type != SCM_RIGHTS {
		85  		return nil, EINVAL
		86  	}
		87  	fds := make([]int, len(m.Data)>>2)
		88  	for i, j := 0, 0; i < len(m.Data); i += 4 {
		89  		fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
		90  		j++
		91  	}
		92  	return fds, nil
		93  }
		94
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