// 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. package ipv4 import ( "net" "syscall" ) // A packetHandler represents the IPv4 datagram handler. type packetHandler struct { c *net.IPConn rawOpt } func (c *packetHandler) ok() bool { return c != nil && c.c != nil } // ReadFrom reads an IPv4 datagram from the endpoint c, copying the // datagram into b. It returns the received datagram as the IPv4 // header h, the payload p and the control message cm. func (c *packetHandler) ReadFrom(b []byte) (h *Header, p []byte, cm *ControlMessage, err error) { if !c.ok() { return nil, nil, nil, syscall.EINVAL } oob := newControlMessage(&c.rawOpt) n, oobn, _, src, err := c.c.ReadMsgIP(b, oob) if err != nil { return nil, nil, nil, err } var hs []byte if hs, p, err = slicePacket(b[:n]); err != nil { return nil, nil, nil, err } if h, err = ParseHeader(hs); err != nil { return nil, nil, nil, err } if cm, err = parseControlMessage(oob[:oobn]); err != nil { return nil, nil, nil, err } if src != nil && cm != nil { cm.Src = src.IP } return } func slicePacket(b []byte) (h, p []byte, err error) { if len(b) < HeaderLen { return nil, nil, errHeaderTooShort } hdrlen := int(b[0]&0x0f) << 2 return b[:hdrlen], b[hdrlen:], nil } // WriteTo writes an IPv4 datagram through the endpoint c, copying the // datagram from the IPv4 header h and the payload p. The control // message cm allows the datagram path and the outgoing interface to be // specified. Currently only Darwin and Linux support this. The cm // may be nil if control of the outgoing datagram is not required. // // The IPv4 header h must contain appropriate fields that include: // // Version = ipv4.Version // Len = <must be specified> // TOS = <must be specified> // TotalLen = <must be specified> // ID = platform sets an appropriate value if ID is zero // FragOff = <must be specified> // TTL = <must be specified> // Protocol = <must be specified> // Checksum = platform sets an appropriate value if Checksum is zero // Src = platform sets an appropriate value if Src is nil // Dst = <must be specified> // Options = optional func (c *packetHandler) WriteTo(h *Header, p []byte, cm *ControlMessage) error { if !c.ok() { return syscall.EINVAL } oob := marshalControlMessage(cm) wh, err := h.Marshal() if err != nil { return err } dst := &net.IPAddr{} if cm != nil { if ip := cm.Dst.To4(); ip != nil { dst.IP = ip } } if dst.IP == nil { dst.IP = h.Dst } wh = append(wh, p...) _, _, err = c.c.WriteMsgIP(wh, oob, dst) return err }