Holger Hildebrandt | fa07499 | 2020-03-27 15:42:06 +0000 | [diff] [blame] | 1 | // Copyright 2012 Google, Inc. All rights reserved. |
| 2 | // |
| 3 | // Use of this source code is governed by a BSD-style license |
| 4 | // that can be found in the LICENSE file in the root of the source |
| 5 | // tree. |
| 6 | |
| 7 | package gopacket |
| 8 | |
| 9 | import ( |
| 10 | "fmt" |
| 11 | "strconv" |
| 12 | ) |
| 13 | |
| 14 | // LayerType is a unique identifier for each type of layer. This enumeration |
| 15 | // does not match with any externally available numbering scheme... it's solely |
| 16 | // usable/useful within this library as a means for requesting layer types |
| 17 | // (see Packet.Layer) and determining which types of layers have been decoded. |
| 18 | // |
| 19 | // New LayerTypes may be created by calling gopacket.RegisterLayerType. |
| 20 | type LayerType int64 |
| 21 | |
| 22 | // LayerTypeMetadata contains metadata associated with each LayerType. |
| 23 | type LayerTypeMetadata struct { |
| 24 | // Name is the string returned by each layer type's String method. |
| 25 | Name string |
| 26 | // Decoder is the decoder to use when the layer type is passed in as a |
| 27 | // Decoder. |
| 28 | Decoder Decoder |
| 29 | } |
| 30 | |
| 31 | type layerTypeMetadata struct { |
| 32 | inUse bool |
| 33 | LayerTypeMetadata |
| 34 | } |
| 35 | |
| 36 | // DecodersByLayerName maps layer names to decoders for those layers. |
| 37 | // This allows users to specify decoders by name to a program and have that |
| 38 | // program pick the correct decoder accordingly. |
| 39 | var DecodersByLayerName = map[string]Decoder{} |
| 40 | |
| 41 | const maxLayerType = 2000 |
| 42 | |
| 43 | var ltMeta [maxLayerType]layerTypeMetadata |
| 44 | var ltMetaMap = map[LayerType]layerTypeMetadata{} |
| 45 | |
| 46 | // RegisterLayerType creates a new layer type and registers it globally. |
| 47 | // The number passed in must be unique, or a runtime panic will occur. Numbers |
| 48 | // 0-999 are reserved for the gopacket library. Numbers 1000-1999 should be |
| 49 | // used for common application-specific types, and are very fast. Any other |
| 50 | // number (negative or >= 2000) may be used for uncommon application-specific |
| 51 | // types, and are somewhat slower (they require a map lookup over an array |
| 52 | // index). |
| 53 | func RegisterLayerType(num int, meta LayerTypeMetadata) LayerType { |
| 54 | if 0 <= num && num < maxLayerType { |
| 55 | if ltMeta[num].inUse { |
| 56 | panic("Layer type already exists") |
| 57 | } |
| 58 | } else { |
| 59 | if ltMetaMap[LayerType(num)].inUse { |
| 60 | panic("Layer type already exists") |
| 61 | } |
| 62 | } |
| 63 | return OverrideLayerType(num, meta) |
| 64 | } |
| 65 | |
| 66 | // OverrideLayerType acts like RegisterLayerType, except that if the layer type |
| 67 | // has already been registered, it overrides the metadata with the passed-in |
| 68 | // metadata intead of panicing. |
| 69 | func OverrideLayerType(num int, meta LayerTypeMetadata) LayerType { |
| 70 | if 0 <= num && num < maxLayerType { |
| 71 | ltMeta[num] = layerTypeMetadata{ |
| 72 | inUse: true, |
| 73 | LayerTypeMetadata: meta, |
| 74 | } |
| 75 | } else { |
| 76 | ltMetaMap[LayerType(num)] = layerTypeMetadata{ |
| 77 | inUse: true, |
| 78 | LayerTypeMetadata: meta, |
| 79 | } |
| 80 | } |
| 81 | DecodersByLayerName[meta.Name] = meta.Decoder |
| 82 | return LayerType(num) |
| 83 | } |
| 84 | |
| 85 | // Decode decodes the given data using the decoder registered with the layer |
| 86 | // type. |
| 87 | func (t LayerType) Decode(data []byte, c PacketBuilder) error { |
| 88 | var d Decoder |
| 89 | if 0 <= int(t) && int(t) < maxLayerType { |
| 90 | d = ltMeta[int(t)].Decoder |
| 91 | } else { |
| 92 | d = ltMetaMap[t].Decoder |
| 93 | } |
| 94 | if d != nil { |
| 95 | return d.Decode(data, c) |
| 96 | } |
| 97 | return fmt.Errorf("Layer type %v has no associated decoder", t) |
| 98 | } |
| 99 | |
| 100 | // String returns the string associated with this layer type. |
| 101 | func (t LayerType) String() (s string) { |
| 102 | if 0 <= int(t) && int(t) < maxLayerType { |
| 103 | s = ltMeta[int(t)].Name |
| 104 | } else { |
| 105 | s = ltMetaMap[t].Name |
| 106 | } |
| 107 | if s == "" { |
| 108 | s = strconv.Itoa(int(t)) |
| 109 | } |
| 110 | return |
| 111 | } |