Module compact_blocks 

Compact Block Relay (BIP152)

Implements the compact block protocol that allows peers to relay blocks using short transaction IDs rather than full transactions. Since most transactions in a new block are already in the receiver’s mempool, only a compact summary needs to be sent.

Protocol Flow

1. Sender constructs a CompactBlock from a full block:

   • Header + nonce
   • Short transaction IDs (first 6 bytes of SipHash)
   • A few “prefilled” transactions (always the coinbase, plus any the sender guesses the receiver doesn’t have)

2. Receiver matches short IDs against its mempool:

   • If all transactions are found → reconstruct the full block
   • If some are missing → send GetBlockTxn to request them
   • Sender replies with BlockTxn containing the missing transactions

References

• BIP152: https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki

Structs

BlockTransactions

Response with the missing transactions.

CompactBlock

A compact block (BIP152 cmpctblock).

GetBlockTransactions

A request for missing transactions from a compact block.

PrefilledTransaction

A prefilled transaction: index in the block + the full transaction.

Enums

ReconstructResult

Result of attempting to reconstruct a block from a compact block.

Functions

compute_short_txid

Compute a 6-byte short transaction ID for a given txid.

Type Aliases

ShortTxId

A 6-byte short transaction ID used in compact blocks.