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// 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 gopacket
import (
// DecodeFeedback is used by DecodingLayer layers to provide decoding metadata.
type DecodeFeedback interface {
// SetTruncated should be called if during decoding you notice that a packet
// is shorter than internal layer variables (HeaderLength, or the like) say it
// should be. It sets packet.Metadata().Truncated.
type nilDecodeFeedback struct{}
func (nilDecodeFeedback) SetTruncated() {}
// NilDecodeFeedback implements DecodeFeedback by doing nothing.
var NilDecodeFeedback DecodeFeedback = nilDecodeFeedback{}
// PacketBuilder is used by layer decoders to store the layers they've decoded,
// and to defer future decoding via NextDecoder.
// Typically, the pattern for use is:
// func (m *myDecoder) Decode(data []byte, p PacketBuilder) error {
// if myLayer, err := myDecodingLogic(data); err != nil {
// return err
// } else {
// p.AddLayer(myLayer)
// }
// // maybe do this, if myLayer is a LinkLayer
// p.SetLinkLayer(myLayer)
// return p.NextDecoder(nextDecoder)
// }
type PacketBuilder interface {
// AddLayer should be called by a decoder immediately upon successful
// decoding of a layer.
AddLayer(l Layer)
// The following functions set the various specific layers in the final
// packet. Note that if many layers call SetX, the first call is kept and all
// other calls are ignored.
// NextDecoder should be called by a decoder when they're done decoding a
// packet layer but not done with decoding the entire packet. The next
// decoder will be called to decode the last AddLayer's LayerPayload.
// Because of this, NextDecoder must only be called once all other
// PacketBuilder calls have been made. Set*Layer and AddLayer calls after
// NextDecoder calls will behave incorrectly.
NextDecoder(next Decoder) error
// DumpPacketData is used solely for decoding. If you come across an error
// you need to diagnose while processing a packet, call this and your packet's
// data will be dumped to stderr so you can create a test. This should never
// be called from a production decoder.
// DecodeOptions returns the decode options
DecodeOptions() *DecodeOptions
// Decoder is an interface for logic to decode a packet layer. Users may
// implement a Decoder to handle their own strange packet types, or may use one
// of the many decoders available in the 'layers' subpackage to decode things
// for them.
type Decoder interface {
// Decode decodes the bytes of a packet, sending decoded values and other
// information to PacketBuilder, and returning an error if unsuccessful. See
// the PacketBuilder documentation for more details.
Decode([]byte, PacketBuilder) error
// DecodeFunc wraps a function to make it a Decoder.
type DecodeFunc func([]byte, PacketBuilder) error
// Decode implements Decoder by calling itself.
func (d DecodeFunc) Decode(data []byte, p PacketBuilder) error {
// function, call thyself.
return d(data, p)
// DecodePayload is a Decoder that returns a Payload layer containing all
// remaining bytes.
var DecodePayload Decoder = DecodeFunc(decodePayload)
// DecodeUnknown is a Decoder that returns an Unknown layer containing all
// remaining bytes, useful if you run up against a layer that you're unable to
// decode yet. This layer is considered an ErrorLayer.
var DecodeUnknown Decoder = DecodeFunc(decodeUnknown)
// DecodeFragment is a Decoder that returns a Fragment layer containing all
// remaining bytes.
var DecodeFragment Decoder = DecodeFunc(decodeFragment)
// LayerTypeZero is an invalid layer type, but can be used to determine whether
// layer type has actually been set correctly.
var LayerTypeZero = RegisterLayerType(0, LayerTypeMetadata{Name: "Unknown", Decoder: DecodeUnknown})
// LayerTypeDecodeFailure is the layer type for the default error layer.
var LayerTypeDecodeFailure = RegisterLayerType(1, LayerTypeMetadata{Name: "DecodeFailure", Decoder: DecodeUnknown})
// LayerTypePayload is the layer type for a payload that we don't try to decode
// but treat as a success, IE: an application-level payload.
var LayerTypePayload = RegisterLayerType(2, LayerTypeMetadata{Name: "Payload", Decoder: DecodePayload})
// LayerTypeFragment is the layer type for a fragment of a layer transported
// by an underlying layer that supports fragmentation.
var LayerTypeFragment = RegisterLayerType(3, LayerTypeMetadata{Name: "Fragment", Decoder: DecodeFragment})
// DecodeFailure is a packet layer created if decoding of the packet data failed
// for some reason. It implements ErrorLayer. LayerContents will be the entire
// set of bytes that failed to parse, and Error will return the reason parsing
// failed.
type DecodeFailure struct {
data []byte
err error
stack []byte
// Error returns the error encountered during decoding.
func (d *DecodeFailure) Error() error { return d.err }
// LayerContents implements Layer.
func (d *DecodeFailure) LayerContents() []byte { return }
// LayerPayload implements Layer.
func (d *DecodeFailure) LayerPayload() []byte { return nil }
// String implements fmt.Stringer.
func (d *DecodeFailure) String() string {
return "Packet decoding error: " + d.Error().Error()
// Dump implements Dumper.
func (d *DecodeFailure) Dump() (s string) {
if d.stack != nil {
s = string(d.stack)
// LayerType returns LayerTypeDecodeFailure
func (d *DecodeFailure) LayerType() LayerType { return LayerTypeDecodeFailure }
// decodeUnknown "decodes" unsupported data types by returning an error.
// This decoder will thus always return a DecodeFailure layer.
func decodeUnknown(data []byte, p PacketBuilder) error {
return errors.New("Layer type not currently supported")
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