bitcoin-s/node

Bitcoin-S SPV node

This module is a Bitcoin SPV (simplified payment verification) node that peers with a Bitcoin Core node over the P2P network. It syncs block headers and does as much verification as possible with the data it has available.

The node supports bloom filters, and provides optional callbacks that notify consumers on events such as new blocks, filtered merkle blocks and transactions.

Caveats:

1. This is a heavy work in progress, and should not be used for anything serious yet
2. The node can only peer with one node on the P2P network right now, and that node must be passed in on startup. Eventually we want to support peer discovery through DNS seeds, as well as supporting multiple peers at the same time.
3. The majority of the P2P code was written in late 2017, and as a consequence does not handle some of the newer P2P messages and functionality (including SegWit related messages).

Interesting files

Currently this project is a heavy WIP. The most important files are

• Client - this handles all of the networking code. Currently this uses Akka but the plan is to move away from Akka in the future and use a networking library with a smaller classpath footprint.
• PeerMessageReceiver - this handles messages we receive on the P2P network. All messages are algebraic data types, so we can easily pattern match on them and implement features in PeerMessageReceiver.handleControlPayload and PeerMessageReceiver.handleDataPayload
• PeerMessageReceiverState - the states that our peer message receiver can be in. It transitions through these states during the connect/disconnect process with our peer.
• PeerMessageSender - this handles sending messages to our peer on the P2P network. Since we are a light client, we probably won't be sending a lot of messages to peers so this isn't that interesting.
• PeerHandler - this combines a PeerMessageReceiver and a PeerMessageSender into a pair.
• Peer - The low level socket details need to connect to a peer

Interesting tests

There is still a lot of code commented out on the project, but the tests should pass for the ones that are not. Interesting tests are

• ClientTest - currently tests that we can connect with peers
• PeerMessageHandlerTest - tests that we can get our node into the PeerMessageReceiverState.Normal state. This means we can send/receive arbitrary messages from our peer.
• [SpvNodeTest] - tests that we can peer with a bitcoind and sync a block header

Main method

There's a main method available in SpvNodeMain.scala. Currently (June 17th, 2019) the node peers with a locally running bitcoind. It does not do much interesting beyond that, although you can make it more interesting if you modify the logging levels (look in common-logback.xml) and pass in some callbacks to the node on startup.