104 lines
2.9 KiB
Go
104 lines
2.9 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build darwin dragonfly freebsd linux netbsd openbsd solaris
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// Socket control messages
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package unix
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import "unsafe"
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// Round the length of a raw sockaddr up to align it properly.
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func cmsgAlignOf(salen int) int {
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salign := sizeofPtr
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// NOTE: It seems like 64-bit Darwin and DragonFly BSD kernels
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// still require 32-bit aligned access to network subsystem.
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if darwin64Bit || dragonfly64Bit {
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salign = 4
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}
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return (salen + salign - 1) & ^(salign - 1)
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}
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// CmsgLen returns the value to store in the Len field of the Cmsghdr
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// structure, taking into account any necessary alignment.
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func CmsgLen(datalen int) int {
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return cmsgAlignOf(SizeofCmsghdr) + datalen
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}
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// CmsgSpace returns the number of bytes an ancillary element with
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// payload of the passed data length occupies.
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func CmsgSpace(datalen int) int {
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return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
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}
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func cmsgData(h *Cmsghdr) unsafe.Pointer {
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return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
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}
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// SocketControlMessage represents a socket control message.
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type SocketControlMessage struct {
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Header Cmsghdr
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Data []byte
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}
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// ParseSocketControlMessage parses b as an array of socket control
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// messages.
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func ParseSocketControlMessage(b []byte) ([]SocketControlMessage, error) {
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var msgs []SocketControlMessage
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i := 0
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for i+CmsgLen(0) <= len(b) {
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h, dbuf, err := socketControlMessageHeaderAndData(b[i:])
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if err != nil {
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return nil, err
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}
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m := SocketControlMessage{Header: *h, Data: dbuf}
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msgs = append(msgs, m)
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i += cmsgAlignOf(int(h.Len))
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}
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return msgs, nil
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}
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func socketControlMessageHeaderAndData(b []byte) (*Cmsghdr, []byte, error) {
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h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
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if h.Len < SizeofCmsghdr || uint64(h.Len) > uint64(len(b)) {
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return nil, nil, EINVAL
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}
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return h, b[cmsgAlignOf(SizeofCmsghdr):h.Len], nil
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}
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// UnixRights encodes a set of open file descriptors into a socket
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// control message for sending to another process.
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func UnixRights(fds ...int) []byte {
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datalen := len(fds) * 4
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b := make([]byte, CmsgSpace(datalen))
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h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
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h.Level = SOL_SOCKET
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h.Type = SCM_RIGHTS
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h.SetLen(CmsgLen(datalen))
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data := cmsgData(h)
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for _, fd := range fds {
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*(*int32)(data) = int32(fd)
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data = unsafe.Pointer(uintptr(data) + 4)
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}
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return b
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}
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// ParseUnixRights decodes a socket control message that contains an
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// integer array of open file descriptors from another process.
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func ParseUnixRights(m *SocketControlMessage) ([]int, error) {
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if m.Header.Level != SOL_SOCKET {
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return nil, EINVAL
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}
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if m.Header.Type != SCM_RIGHTS {
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return nil, EINVAL
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}
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fds := make([]int, len(m.Data)>>2)
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for i, j := 0, 0; i < len(m.Data); i += 4 {
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fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
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j++
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}
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return fds, nil
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}
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