# Block Source

Implementing the BlockSource interface requires defining methods for fetching headers, blocks, and the best block hash.

  • Rust
impl BlockSource for Blockchain {
	fn get_header<'a>(&'a mut self, header_hash: &'a BlockHash, _height: Option<u32>) -> AsyncBlockSourceResult<'a, BlockHeaderData> {
		// <insert code for fetching block headers>

	fn get_block<'a>(&'a mut self, header_hash: &'a BlockHash) -> AsyncBlockSourceResult<'a, Block> {
		// <insert code for fetching block>

	fn get_best_block<'a>(&'a mut self) -> AsyncBlockSourceResult<'a, (BlockHash, Option<u32>)> {
		// <insert code for fetching the best block hash>

For instance, you may implement this interface by querying Bitcoin Core's JSON RPC interface, which happens to be a sample implementation provided by lightning-block-sync.

Let's walk through the use case where LDK receives full blocks.