Michael Stapelberg
49 lines
1.3 KiB
Go
49 lines
1.3 KiB
Go
// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package dhcp4
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import (
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"net"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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)
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const (
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minIPHdrLen = 20
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maxIPHdrLen = 60
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udpHdrLen = 8
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ip4Ver = 0x40
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ttl = 16
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srcPort = 68
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dstPort = 67
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maxDHCPLen = 576
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)
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// Read decodes an IPv4 packet from pc, returning its DHCPv4 layer or nil.
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func Read(pc net.PacketConn) (*layers.DHCPv4, error) {
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buf := make([]byte, maxIPHdrLen+udpHdrLen+maxDHCPLen)
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n, _, err := pc.ReadFrom(buf)
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if err != nil {
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return nil, err
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}
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pkt := gopacket.NewPacket(buf[:n], layers.LayerTypeIPv4, gopacket.DecodeOptions{})
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dhcp := pkt.Layer(layers.LayerTypeDHCPv4)
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if dhcp == nil {
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return nil, nil
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}
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return dhcp.(*layers.DHCPv4), nil
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}
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