wgengine/packet: refactor and expose UDP header marshaling (#408)
Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>main
Dmytro Shynkevych
6 years ago
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GitHub
parent
5e0ff494a5
commit
059b1d10bb
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// Copyright (c) 2020 Tailscale Inc & 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 packet |
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import ( |
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"errors" |
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"math" |
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) |
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const tcpHeaderLength = 20 |
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// maxPacketLength is the largest length that all headers support.
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// IPv4 headers using uint16 for this forces an upper bound of 64KB.
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const maxPacketLength = math.MaxUint16 |
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var ( |
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errSmallBuffer = errors.New("buffer too small") |
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errLargePacket = errors.New("packet too large") |
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) |
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// Header is a packet header capable of marshaling itself into a byte buffer.
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type Header interface { |
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// Len returns the length of the header after marshaling.
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Len() int |
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// Marshal serializes the header into buf in wire format.
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// It clobbers the header region, which is the first h.Length() bytes of buf.
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// It explicitly initializes every byte of the header region,
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// so pre-zeroing it on reuse is not required. It does not allocate memory.
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// It fails if and only if len(buf) < Length().
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Marshal(buf []byte) error |
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// ToResponse transforms the header into one for a response packet.
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// For instance, this swaps the source and destination IPs.
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ToResponse() |
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} |
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// Generate generates a new packet with the given header and payload.
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// Unlike Header.Marshal, this does allocate memory.
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func Generate(h Header, payload []byte) []byte { |
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hlen := h.Len() |
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buf := make([]byte, hlen+len(payload)) |
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copy(buf[hlen:], payload) |
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h.Marshal(buf) |
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return buf |
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} |
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// Copyright (c) 2020 Tailscale Inc & 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 packet |
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type ICMPType uint8 |
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const ( |
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ICMPEchoReply ICMPType = 0x00 |
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ICMPEchoRequest ICMPType = 0x08 |
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ICMPUnreachable ICMPType = 0x03 |
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ICMPTimeExceeded ICMPType = 0x0b |
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) |
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func (t ICMPType) String() string { |
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switch t { |
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case ICMPEchoReply: |
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return "EchoReply" |
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case ICMPEchoRequest: |
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return "EchoRequest" |
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case ICMPUnreachable: |
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return "Unreachable" |
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case ICMPTimeExceeded: |
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return "TimeExceeded" |
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default: |
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return "Unknown" |
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} |
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} |
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type ICMPCode uint8 |
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const ( |
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ICMPNoCode ICMPCode = 0 |
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) |
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// ICMPHeader represents an ICMP packet header.
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type ICMPHeader struct { |
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IPHeader |
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Type ICMPType |
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Code ICMPCode |
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} |
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const ( |
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icmpHeaderLength = 4 |
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// icmpTotalHeaderLength is the length of all headers in a ICMP packet.
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icmpAllHeadersLength = ipHeaderLength + icmpHeaderLength |
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) |
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func (ICMPHeader) Len() int { |
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return icmpAllHeadersLength |
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} |
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func (h ICMPHeader) Marshal(buf []byte) error { |
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if len(buf) < icmpAllHeadersLength { |
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return errSmallBuffer |
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} |
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if len(buf) > maxPacketLength { |
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return errLargePacket |
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} |
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// The caller does not need to set this.
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h.IPProto = ICMP |
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buf[20] = uint8(h.Type) |
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buf[21] = uint8(h.Code) |
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h.IPHeader.Marshal(buf) |
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put16(buf[22:24], ipChecksum(buf)) |
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return nil |
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} |
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func (h *ICMPHeader) ToResponse() { |
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h.Type = ICMPEchoReply |
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h.Code = ICMPNoCode |
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h.IPHeader.ToResponse() |
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} |
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@ -0,0 +1,127 @@ |
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// Copyright (c) 2020 Tailscale Inc & 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 packet |
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import ( |
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"fmt" |
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"net" |
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) |
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// IP is an IPv4 address.
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type IP uint32 |
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// NewIP converts a standard library IP address into an IP.
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// It panics if b is not an IPv4 address.
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func NewIP(b net.IP) IP { |
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b4 := b.To4() |
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if b4 == nil { |
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panic(fmt.Sprintf("To4(%v) failed", b)) |
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} |
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return IP(get32(b4)) |
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} |
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func (ip IP) String() string { |
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return fmt.Sprintf("%d.%d.%d.%d", byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip)) |
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} |
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// IPProto is either a real IP protocol (ITCP, UDP, ...) or an special value like Unknown.
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// If it is a real IP protocol, its value corresponds to its IP protocol number.
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type IPProto uint8 |
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const ( |
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// Unknown represents an unknown or unsupported protocol; it's deliberately the zero value.
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Unknown IPProto = 0x00 |
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ICMP IPProto = 0x01 |
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TCP IPProto = 0x06 |
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UDP IPProto = 0x11 |
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// IPv6 and Fragment are special values. They're not really IPProto values
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// so we're using the unassigned 0xFE and 0xFF values for them.
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// TODO(dmytro): special values should be taken out of here.
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IPv6 IPProto = 0xFE |
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Fragment IPProto = 0xFF |
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) |
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func (p IPProto) String() string { |
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switch p { |
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case Fragment: |
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return "Frag" |
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case ICMP: |
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return "ICMP" |
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case UDP: |
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return "UDP" |
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case TCP: |
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return "TCP" |
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case IPv6: |
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return "IPv6" |
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default: |
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return "Unknown" |
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} |
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} |
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// IPHeader represents an IP packet header.
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type IPHeader struct { |
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IPProto IPProto |
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IPID uint16 |
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SrcIP IP |
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DstIP IP |
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} |
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const ipHeaderLength = 20 |
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func (IPHeader) Len() int { |
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return ipHeaderLength |
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} |
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func (h IPHeader) Marshal(buf []byte) error { |
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if len(buf) < ipHeaderLength { |
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return errSmallBuffer |
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} |
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if len(buf) > maxPacketLength { |
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return errLargePacket |
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} |
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buf[0] = 0x40 | (ipHeaderLength >> 2) // IPv4
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buf[1] = 0x00 // DHCP, ECN
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put16(buf[2:4], uint16(len(buf))) |
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put16(buf[4:6], h.IPID) |
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put16(buf[6:8], 0) // flags, offset
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buf[8] = 64 // TTL
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buf[9] = uint8(h.IPProto) |
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put16(buf[10:12], 0) // blank IP header checksum
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put32(buf[12:16], uint32(h.SrcIP)) |
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put32(buf[16:20], uint32(h.DstIP)) |
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put16(buf[10:12], ipChecksum(buf[0:20])) |
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return nil |
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} |
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// MarshalPseudo serializes the header into buf in pseudo format.
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// It clobbers the header region, which is the first h.Length() bytes of buf.
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// It explicitly initializes every byte of the header region,
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// so pre-zeroing it on reuse is not required. It does not allocate memory.
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func (h IPHeader) MarshalPseudo(buf []byte) error { |
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if len(buf) < ipHeaderLength { |
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return errSmallBuffer |
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} |
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if len(buf) > maxPacketLength { |
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return errLargePacket |
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} |
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length := len(buf) - ipHeaderLength |
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put32(buf[8:12], uint32(h.SrcIP)) |
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put32(buf[12:16], uint32(h.DstIP)) |
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buf[16] = 0x0 |
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buf[17] = uint8(h.IPProto) |
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put16(buf[18:20], uint16(length)) |
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return nil |
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} |
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func (h *IPHeader) ToResponse() { |
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h.SrcIP, h.DstIP = h.DstIP, h.SrcIP |
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// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
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h.IPID = ^h.IPID |
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} |
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@ -0,0 +1,53 @@ |
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// Copyright (c) 2020 Tailscale Inc & 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 packet |
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// UDPHeader represents an UDP packet header.
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type UDPHeader struct { |
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IPHeader |
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SrcPort uint16 |
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DstPort uint16 |
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} |
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const ( |
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udpHeaderLength = 8 |
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// udpTotalHeaderLength is the length of all headers in a UDP packet.
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udpTotalHeaderLength = ipHeaderLength + udpHeaderLength |
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) |
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func (UDPHeader) Len() int { |
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return udpTotalHeaderLength |
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} |
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func (h UDPHeader) Marshal(buf []byte) error { |
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if len(buf) < udpTotalHeaderLength { |
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return errSmallBuffer |
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} |
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if len(buf) > maxPacketLength { |
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return errLargePacket |
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} |
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// The caller does not need to set this.
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h.IPProto = UDP |
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length := len(buf) - h.IPHeader.Len() |
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put16(buf[20:22], h.SrcPort) |
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put16(buf[22:24], h.DstPort) |
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put16(buf[24:26], uint16(length)) |
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put16(buf[26:28], 0) // blank checksum
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h.IPHeader.MarshalPseudo(buf) |
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// UDP checksum with IP pseudo header.
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put16(buf[26:28], ipChecksum(buf[8:])) |
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h.IPHeader.Marshal(buf) |
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return nil |
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} |
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func (h *UDPHeader) ToResponse() { |
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h.SrcPort, h.DstPort = h.DstPort, h.SrcPort |
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h.IPHeader.ToResponse() |
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} |
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