TUN-6666: Define packet package

This package defines IP and ICMP packet, decoders, encoder and flow

vendor/github.com/google/gopacket/layers/doc.go

@@ -0,0 +1,61 @@
+// Copyright 2012 Google, Inc. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree.
+
+/*
+Package layers provides decoding layers for many common protocols.
+
+The layers package contains decode implementations for a number of different
+types of packet layers.  Users of gopacket will almost always want to also use
+layers to actually decode packet data into useful pieces. To see the set of
+protocols that gopacket/layers is currently able to decode,
+look at the set of LayerTypes defined in the Variables sections. The
+layers package also defines endpoints for many of the common packet layers
+that have source/destination addresses associated with them, for example IPv4/6
+(IPs) and TCP/UDP (ports).
+Finally, layers contains a number of useful enumerations (IPProtocol,
+EthernetType, LinkType, PPPType, etc...).  Many of these implement the
+gopacket.Decoder interface, so they can be passed into gopacket as decoders.
+
+Most common protocol layers are named using acronyms or other industry-common
+names (IPv4, TCP, PPP).  Some of the less common ones have their names expanded
+(CiscoDiscoveryProtocol).
+For certain protocols, sub-parts of the protocol are split out into their own
+layers (SCTP, for example).  This is done mostly in cases where portions of the
+protocol may fulfill the capabilities of interesting layers (SCTPData implements
+ApplicationLayer, while base SCTP implements TransportLayer), or possibly
+because splitting a protocol into a few layers makes decoding easier.
+
+This package is meant to be used with its parent,
+http://github.com/google/gopacket.
+
+Port Types
+
+Instead of using raw uint16 or uint8 values for ports, we use a different port
+type for every protocol, for example TCPPort and UDPPort.  This allows us to
+override string behavior for each port, which we do by setting up port name
+maps (TCPPortNames, UDPPortNames, etc...).  Well-known ports are annotated with
+their protocol names, and their String function displays these names:
+
+  p := TCPPort(80)
+  fmt.Printf("Number: %d  String: %v", p, p)
+  // Prints: "Number: 80  String: 80(http)"
+
+Modifying Decode Behavior
+
+layers links together decoding through its enumerations.  For example, after
+decoding layer type Ethernet, it uses Ethernet.EthernetType as its next decoder.
+All enumerations that act as decoders, like EthernetType, can be modified by
+users depending on their preferences.  For example, if you have a spiffy new
+IPv4 decoder that works way better than the one built into layers, you can do
+this:
+
+ var mySpiffyIPv4Decoder gopacket.Decoder = ...
+ layers.EthernetTypeMetadata[EthernetTypeIPv4].DecodeWith = mySpiffyIPv4Decoder
+
+This will make all future ethernet packets use your new decoder to decode IPv4
+packets, instead of the built-in decoder used by gopacket.
+*/
+package layers