98 lines
2.7 KiB
Go
98 lines
2.7 KiB
Go
// Copyright 2012 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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package ipv4
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import (
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"net"
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"syscall"
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)
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// A packetHandler represents the IPv4 datagram handler.
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type packetHandler struct {
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c *net.IPConn
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rawOpt
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}
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func (c *packetHandler) ok() bool { return c != nil && c.c != nil }
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// ReadFrom reads an IPv4 datagram from the endpoint c, copying the
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// datagram into b. It returns the received datagram as the IPv4
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// header h, the payload p and the control message cm.
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func (c *packetHandler) ReadFrom(b []byte) (h *Header, p []byte, cm *ControlMessage, err error) {
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if !c.ok() {
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return nil, nil, nil, syscall.EINVAL
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}
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oob := newControlMessage(&c.rawOpt)
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n, oobn, _, src, err := c.c.ReadMsgIP(b, oob)
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if err != nil {
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return nil, nil, nil, err
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}
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var hs []byte
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if hs, p, err = slicePacket(b[:n]); err != nil {
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return nil, nil, nil, err
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}
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if h, err = ParseHeader(hs); err != nil {
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return nil, nil, nil, err
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}
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if cm, err = parseControlMessage(oob[:oobn]); err != nil {
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return nil, nil, nil, err
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}
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if src != nil && cm != nil {
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cm.Src = src.IP
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}
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return
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}
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func slicePacket(b []byte) (h, p []byte, err error) {
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if len(b) < HeaderLen {
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return nil, nil, errHeaderTooShort
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}
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hdrlen := int(b[0]&0x0f) << 2
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return b[:hdrlen], b[hdrlen:], nil
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}
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// WriteTo writes an IPv4 datagram through the endpoint c, copying the
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// datagram from the IPv4 header h and the payload p. The control
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// message cm allows the datagram path and the outgoing interface to be
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// specified. Currently only Darwin and Linux support this. The cm
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// may be nil if control of the outgoing datagram is not required.
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//
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// The IPv4 header h must contain appropriate fields that include:
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//
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// Version = ipv4.Version
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// Len = <must be specified>
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// TOS = <must be specified>
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// TotalLen = <must be specified>
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// ID = platform sets an appropriate value if ID is zero
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// FragOff = <must be specified>
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// TTL = <must be specified>
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// Protocol = <must be specified>
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// Checksum = platform sets an appropriate value if Checksum is zero
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// Src = platform sets an appropriate value if Src is nil
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// Dst = <must be specified>
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// Options = optional
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func (c *packetHandler) WriteTo(h *Header, p []byte, cm *ControlMessage) error {
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if !c.ok() {
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return syscall.EINVAL
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}
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oob := marshalControlMessage(cm)
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wh, err := h.Marshal()
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if err != nil {
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return err
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}
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dst := &net.IPAddr{}
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if cm != nil {
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if ip := cm.Dst.To4(); ip != nil {
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dst.IP = ip
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}
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}
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if dst.IP == nil {
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dst.IP = h.Dst
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}
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wh = append(wh, p...)
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_, _, err = c.c.WriteMsgIP(wh, oob, dst)
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return err
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}
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