1 // Copyright (c) 2013-2016 The btcsuite developers
2 // Use of this source code is governed by an ISC
3 // license that can be found in the LICENSE file.
6 Package wire implements the bitcoin wire protocol.
8 For the complete details of the bitcoin protocol, see the official wiki entry
9 at https://en.bitcoin.it/wiki/Protocol_specification. The following only serves
10 as a quick overview to provide information on how to use the package.
12 At a high level, this package provides support for marshalling and unmarshalling
13 supported bitcoin messages to and from the wire. This package does not deal
14 with the specifics of message handling such as what to do when a message is
15 received. This provides the caller with a high level of flexibility.
17 Bitcoin Message Overview
19 The bitcoin protocol consists of exchanging messages between peers. Each
20 message is preceded by a header which identifies information about it such as
21 which bitcoin network it is a part of, its type, how big it is, and a checksum
22 to verify validity. All encoding and decoding of message headers is handled by
25 To accomplish this, there is a generic interface for bitcoin messages named
26 Message which allows messages of any type to be read, written, or passed around
27 through channels, functions, etc. In addition, concrete implementations of most
28 of the currently supported bitcoin messages are provided. For these supported
29 messages, all of the details of marshalling and unmarshalling to and from the
30 wire using bitcoin encoding are handled so the caller doesn't have to concern
31 themselves with the specifics.
35 The following provides a quick summary of how the bitcoin messages are intended
36 to interact with one another. As stated above, these interactions are not
37 directly handled by this package. For more in-depth details about the
38 appropriate interactions, see the official bitcoin protocol wiki entry at
39 https://en.bitcoin.it/wiki/Protocol_specification.
41 The initial handshake consists of two peers sending each other a version message
42 (MsgVersion) followed by responding with a verack message (MsgVerAck). Both
43 peers use the information in the version message (MsgVersion) to negotiate
44 things such as protocol version and supported services with each other. Once
45 the initial handshake is complete, the following chart indicates message
46 interactions in no particular order.
48 Peer A Sends Peer B Responds
49 ----------------------------------------------------------------------------
50 getaddr message (MsgGetAddr) addr message (MsgAddr)
51 getblocks message (MsgGetBlocks) inv message (MsgInv)
52 inv message (MsgInv) getdata message (MsgGetData)
53 getdata message (MsgGetData) block message (MsgBlock) -or-
54 tx message (MsgTx) -or-
55 notfound message (MsgNotFound)
56 getheaders message (MsgGetHeaders) headers message (MsgHeaders)
57 ping message (MsgPing) pong message (MsgHeaders)* -or-
58 (none -- Ability to send message is enough)
61 * The pong message was not added until later protocol versions as defined
62 in BIP0031. The BIP0031Version constant can be used to detect a recent
63 enough protocol version for this purpose (version > BIP0031Version).
67 There are several common parameters that arise when using this package to read
68 and write bitcoin messages. The following sections provide a quick overview of
69 these parameters so the next sections can build on them.
73 The protocol version should be negotiated with the remote peer at a higher
74 level than this package via the version (MsgVersion) message exchange, however,
75 this package provides the wire.ProtocolVersion constant which indicates the
76 latest protocol version this package supports and is typically the value to use
77 for all outbound connections before a potentially lower protocol version is
82 The bitcoin network is a magic number which is used to identify the start of a
83 message and which bitcoin network the message applies to. This package provides
84 the following constants:
87 wire.TestNet (Regression test network)
88 wire.TestNet3 (Test network version 3)
89 wire.SimNet (Simulation test network)
91 Determining Message Type
93 As discussed in the bitcoin message overview section, this package reads
94 and writes bitcoin messages using a generic interface named Message. In
95 order to determine the actual concrete type of the message, use a type
96 switch or type assertion. An example of a type switch follows:
98 // Assumes msg is already a valid concrete message such as one created
99 // via NewMsgVersion or read via ReadMessage.
100 switch msg := msg.(type) {
101 case *wire.MsgVersion:
102 // The message is a pointer to a MsgVersion struct.
103 fmt.Printf("Protocol version: %v", msg.ProtocolVersion)
105 // The message is a pointer to a MsgBlock struct.
106 fmt.Printf("Number of tx in block: %v", msg.Header.TxnCount)
111 In order to unmarshall bitcoin messages from the wire, use the ReadMessage
112 function. It accepts any io.Reader, but typically this will be a net.Conn to
113 a remote node running a bitcoin peer. Example syntax is:
115 // Reads and validates the next bitcoin message from conn using the
116 // protocol version pver and the bitcoin network btcnet. The returns
117 // are a wire.Message, a []byte which contains the unmarshalled
118 // raw payload, and a possible error.
119 msg, rawPayload, err := wire.ReadMessage(conn, pver, btcnet)
121 // Log and handle the error
126 In order to marshall bitcoin messages to the wire, use the WriteMessage
127 function. It accepts any io.Writer, but typically this will be a net.Conn to
128 a remote node running a bitcoin peer. Example syntax to request addresses
129 from a remote peer is:
131 // Create a new getaddr bitcoin message.
132 msg := wire.NewMsgGetAddr()
134 // Writes a bitcoin message msg to conn using the protocol version
135 // pver, and the bitcoin network btcnet. The return is a possible
137 err := wire.WriteMessage(conn, msg, pver, btcnet)
139 // Log and handle the error
144 Errors returned by this package are either the raw errors provided by underlying
145 calls to read/write from streams such as io.EOF, io.ErrUnexpectedEOF, and
146 io.ErrShortWrite, or of type wire.MessageError. This allows the caller to
147 differentiate between general IO errors and malformed messages through type
150 Bitcoin Improvement Proposals
152 This package includes spec changes outlined by the following BIPs:
154 BIP0014 (https://github.com/bitcoin/bips/blob/master/bip-0014.mediawiki)
155 BIP0031 (https://github.com/bitcoin/bips/blob/master/bip-0031.mediawiki)
156 BIP0035 (https://github.com/bitcoin/bips/blob/master/bip-0035.mediawiki)
157 BIP0037 (https://github.com/bitcoin/bips/blob/master/bip-0037.mediawiki)
158 BIP0111 (https://github.com/bitcoin/bips/blob/master/bip-0111.mediawiki)
159 BIP0130 (https://github.com/bitcoin/bips/blob/master/bip-0130.mediawiki)
160 BIP0133 (https://github.com/bitcoin/bips/blob/master/bip-0133.mediawiki)