vendor/golang.org/x/net/ipv4/payload_cmsg.go

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// Copyright 2012 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 aix darwin dragonfly freebsd linux netbsd openbsd solaris

package ipv4

import (
	"net"

	"golang.org/x/net/internal/socket"
)

// ReadFrom reads a payload of the received IPv4 datagram, from the
// endpoint c, copying the payload into b. It returns the number of
// bytes copied into b, the control message cm and the source address
// src of the received datagram.
func (c *payloadHandler) ReadFrom(b []byte) (n int, cm *ControlMessage, src net.Addr, err error) {
	if !c.ok() {
		return 0, nil, nil, errInvalidConn
	}
	c.rawOpt.RLock()
	m := socket.Message{
		OOB: NewControlMessage(c.rawOpt.cflags),
	}
	c.rawOpt.RUnlock()
	switch c.PacketConn.(type) {
	case *net.UDPConn:
		m.Buffers = [][]byte{b}
		if err := c.RecvMsg(&m, 0); err != nil {
			return 0, nil, nil, &net.OpError{Op: "read", Net: c.PacketConn.LocalAddr().Network(), Source: c.PacketConn.LocalAddr(), Err: err}
		}
	case *net.IPConn:
		h := make([]byte, HeaderLen)
		m.Buffers = [][]byte{h, b}
		if err := c.RecvMsg(&m, 0); err != nil {
			return 0, nil, nil, &net.OpError{Op: "read", Net: c.PacketConn.LocalAddr().Network(), Source: c.PacketConn.LocalAddr(), Err: err}
		}
		hdrlen := int(h[0]&0x0f) << 2
		if hdrlen > len(h) {
			d := hdrlen - len(h)
			copy(b, b[d:])
			m.N -= d
		} else {
			m.N -= hdrlen
		}
	default:
		return 0, nil, nil, &net.OpError{Op: "read", Net: c.PacketConn.LocalAddr().Network(), Source: c.PacketConn.LocalAddr(), Err: errInvalidConnType}
	}
	if m.NN > 0 {
		if compatFreeBSD32 {
			adjustFreeBSD32(&m)
		}
		cm = new(ControlMessage)
		if err := cm.Parse(m.OOB[:m.NN]); err != nil {
			return 0, nil, nil, &net.OpError{Op: "read", Net: c.PacketConn.LocalAddr().Network(), Source: c.PacketConn.LocalAddr(), Err: err}
		}
		cm.Src = netAddrToIP4(m.Addr)
	}