Description

Package peer provides a common base for creating and managing Bitcoin network peers.

Overview

This package builds upon the wire package, which provides the fundamental primitives necessary to speak the bitcoin wire protocol, in order to simplify the process of creating fully functional peers. In essence, it provides a common base for creating concurrent safe fully validating nodes, Simplified Payment Verification (SPV) nodes, proxies, etc.

A quick overview of the major features peer provides are as follows:

- Provides a basic concurrent safe bitcoin peer for handling bitcoin
  communications via the peer-to-peer protocol
- Full duplex reading and writing of bitcoin protocol messages
- Automatic handling of the initial handshake process including protocol
  version negotiation
- Asynchronous message queuing of outbound messages with optional channel for
  notification when the message is actually sent
- Flexible peer configuration
  - Caller is responsible for creating outgoing connections and listening for
    incoming connections so they have flexibility to establish connections as
    they see fit (proxies, etc)
  - User agent name and version
  - Bitcoin network
  - Service support signalling (full nodes, bloom filters, etc)
  - Maximum supported protocol version
  - Ability to register callbacks for handling bitcoin protocol messages
- Inventory message batching and send trickling with known inventory detection
  and avoidance
- Automatic periodic keep-alive pinging and pong responses
- Random nonce generation and self connection detection
- Proper handling of bloom filter related commands when the caller does not
  specify the related flag to signal support
  - Disconnects the peer when the protocol version is high enough
  - Does not invoke the related callbacks for older protocol versions
- Snapshottable peer statistics such as the total number of bytes read and
  written, the remote address, user agent, and negotiated protocol version
- Helper functions pushing addresses, getblocks, getheaders, and reject
  messages
  - These could all be sent manually via the standard message output function,
    but the helpers provide additional nice functionality such as duplicate
    filtering and address randomization
- Ability to wait for shutdown/disconnect
- Comprehensive test coverage

Peer Configuration

All peer configuration is handled with the Config struct. This allows the caller to specify things such as the user agent name and version, the bitcoin network to use, which services it supports, and callbacks to invoke when bitcoin messages are received. See the documentation for each field of the Config struct for more details.

Inbound and Outbound Peers

A peer can either be inbound or outbound. The caller is responsible for establishing the connection to remote peers and listening for incoming peers. This provides high flexibility for things such as connecting via proxies, acting as a proxy, creating bridge peers, choosing whether to listen for inbound peers, etc.

NewOutboundPeer and NewInboundPeer functions must be followed by calling Connect with a net.Conn instance to the peer. This will start all async I/O goroutines and initiate the protocol negotiation process. Once finished with the peer call Disconnect to disconnect from the peer and clean up all resources. WaitForDisconnect can be used to block until peer disconnection and resource cleanup has completed.

Callbacks

In order to do anything useful with a peer, it is necessary to react to bitcoin messages. This is accomplished by creating an instance of the MessageListeners struct with the callbacks to be invoke specified and setting the Listeners field of the Config struct specified when creating a peer to it.

For convenience, a callback hook for all of the currently supported bitcoin messages is exposed which receives the peer instance and the concrete message type. In addition, a hook for OnRead is provided so even custom messages types for which this package does not directly provide a hook, as long as they implement the wire.Message interface, can be used. Finally, the OnWrite hook is provided, which in conjunction with OnRead, can be used to track server-wide byte counts.

It is often useful to use closures which encapsulate state when specifying the callback handlers. This provides a clean method for accessing that state when callbacks are invoked.

Queuing Messages and Inventory

The QueueMessage function provides the fundamental means to send messages to the remote peer. As the name implies, this employs a non-blocking queue. A done channel which will be notified when the message is actually sent can optionally be specified. There are certain message types which are better sent using other functions which provide additional functionality.

Of special interest are inventory messages. Rather than manually sending MsgInv messages via Queuemessage, the inventory vectors should be queued using the QueueInventory function. It employs batching and trickling along with intelligent known remote peer inventory detection and avoidance through the use of a most-recently used algorithm.

Message Sending Helper Functions

In addition to the bare QueueMessage function previously described, the PushAddrMsg, PushGetBlocksMsg, PushGetHeadersMsg, and PushRejectMsg functions are provided as a convenience. While it is of course possible to create and send these message manually via QueueMessage, these helper functions provided additional useful functionality that is typically desired.

For example, the PushAddrMsg function automatically limits the addresses to the maximum number allowed by the message and randomizes the chosen addresses when there are too many. This allows the caller to simply provide a slice of known addresses, such as that returned by the addrmgr package, without having to worry about the details.

Next, the PushGetBlocksMsg and PushGetHeadersMsg functions will construct proper messages using a block locator and ignore back to back duplicate requests.

Finally, the PushRejectMsg function can be used to easily create and send an appropriate reject message based on the provided parameters as well as optionally provides a flag to cause it to block until the message is actually sent.

Peer Statistics

A snapshot of the current peer statistics can be obtained with the StatsSnapshot function. This includes statistics such as the total number of bytes read and written, the remote address, user agent, and negotiated protocol version.

Logging

This package provides extensive logging capabilities through the UseLogger function which allows a btclog.Logger to be specified. For example, logging at the debug level provides summaries of every message sent and received, and logging at the trace level provides full dumps of parsed messages as well as the raw message bytes using a format similar to hexdump -C.

Bitcoin Improvement Proposals

This package supports all BIPS supported by the wire package. (https://godoc.org/github.com/btcsuite/btcd/wire#hdr-Bitcoin_Improvement_Proposals)

peer is referenced in 2 repositories

github.com/btcsuite/btcd

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