Add lightning-block-sync package and library

Defines an interface and related types for fetching block headers and
data from a block source (e.g., Bitcoin Core). Used to keep lightning in
sync with chain activity.

Author: jkczyz

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
                      1.30.0,
                      # 1.34.2 is Debian stable
                      1.34.2,
-                     # 1.39.0 is MSRV for lightning-net-tokio and generates coverage
+                     # 1.39.0 is MSRV for lightning-net-tokio and lightning-block-sync and generates coverage
                      1.39.0]
         include:
           - toolchain: stable
@@ -48,6 +48,15 @@ jobs:
       - name: Build on Rust ${{ matrix.toolchain }}
         if: "! matrix.build-net-tokio"
         run: cargo build --verbose  --color always -p lightning
+      - name: Build Block Sync Clients on Rust ${{ matrix.toolchain }} with features
+        if: matrix.build-net-tokio
+        run: |
+          cd lightning-block-sync
+          RUSTFLAGS="-C link-dead-code" cargo build --verbose --color always --features rest-client
+          RUSTFLAGS="-C link-dead-code" cargo build --verbose --color always --features rpc-client
+          RUSTFLAGS="-C link-dead-code" cargo build --verbose --color always --features rpc-client,rest-client
+          RUSTFLAGS="-C link-dead-code" cargo build --verbose --color always --features rpc-client,rest-client,tokio
+          cd ..
       - name: Test on Rust ${{ matrix.toolchain }} with net-tokio
         if: "matrix.build-net-tokio && !matrix.coverage"
         run: cargo test --verbose --color always

Cargo.toml

@@ -2,6 +2,7 @@
 
 members = [
     "lightning",
+    "lightning-block-sync",
     "lightning-net-tokio",
     "lightning-persister",
 ]

lightning-block-sync/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "lightning-block-sync"
+version = "0.0.1"
+authors = ["Jeffrey Czyz", "Matt Corallo"]
+license = "Apache-2.0"
+edition = "2018"
+description = """
+Utilities to fetch the chain data from a block source and feed them into Rust Lightning.
+"""
+
+[dependencies]
+bitcoin = "0.24"
+lightning = { version = "0.0.12", path = "../lightning" }

lightning-block-sync/src/lib.rs

@@ -0,0 +1,70 @@
+//! A lightweight client for keeping in sync with chain activity.
+//!
+//! Defines a [`BlockSource`] trait, which is an asynchronous interface for retrieving block headers
+//! and data.
+//!
+//! [`BlockSource`]: trait.BlockSource.html
+
+use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::hash_types::BlockHash;
+use bitcoin::util::uint::Uint256;
+
+use std::future::Future;
+use std::pin::Pin;
+
+/// Abstract type for retrieving block headers and data.
+pub trait BlockSource : Sync + Send {
+	/// Returns the header for a given hash. A height hint may be provided in case a source cannot
+	/// easily find headers based on a hash. This is merely a hint and thus the returned header must
+	/// have the same hash as was requested. Otherwise, an error must be returned.
+	///
+	/// Implementations that cannot find headers based on the hash should return a `Transient` error
+	/// when `height_hint` is `None`. In such a case, `get_best_block` should never return `None`
+	/// for the height. Otherwise, the source could not be used independently for an initial sync.
+	fn get_header<'a>(&'a mut self, header_hash: &'a BlockHash, height_hint: Option<u32>) -> AsyncBlockSourceResult<'a, BlockHeaderData>;
+
+	/// Returns the block for a given hash. A headers-only block source should return a `Transient`
+	/// error.
+	fn get_block<'a>(&'a mut self, header_hash: &'a BlockHash) -> AsyncBlockSourceResult<'a, Block>;
+
+	/// Returns the hash of the best block and, optionally, its height. The height is passed to
+	/// `get_header` to allow a more efficient lookup on some block sources.
+	fn get_best_block<'a>(&'a mut self) -> AsyncBlockSourceResult<(BlockHash, Option<u32>)>;
+}
+
+/// Result type for `BlockSource` requests.
+type BlockSourceResult<T> = Result<T, BlockSourceError>;
+
+/// Result type for asynchronous `BlockSource` requests.
+///
+/// TODO: Replace with BlockSourceResult once `async` trait functions are supported. For details,
+/// see: https://areweasyncyet.rs.
+type AsyncBlockSourceResult<'a, T> = Pin<Box<dyn Future<Output = BlockSourceResult<T>> + 'a + Send>>;
+
+/// Error type for `BlockSource` requests.
+///
+/// Transient errors may be resolved when re-polling, but no attempt will be made to re-poll on
+/// persistent errors.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum BlockSourceError {
+	/// Indicates an error that won't resolve when retrying a request (e.g., invalid data).
+	Persistent,
+
+	/// Indicates an error that may resolve when retrying a request (e.g., unresponsive).
+	Transient,
+}
+
+/// A block header and some associated data. This information should be available from most block
+/// sources (and, notably, is available in Bitcoin Core's RPC and REST interfaces).
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct BlockHeaderData {
+	/// The block header itself.
+	pub header: BlockHeader,
+
+	/// The block height where the genesis block has height 0.
+	pub height: u32,
+
+	/// The total chain work in expected number of double-SHA256 hashes required to build a chain
+	/// of equivalent weight.
+	pub chainwork: Uint256,
+}