ZIP-239: implement mempool transaction v5 data structures and network messages

[jvff]

Motivation

When the mempool is implemented, Zebra must conform to ZIP-239 in order to properly relay transactions to the network.

This ticket focuses on parsing the data structures from ZIP-239, and sending the corresponding network messages.

Specifications

ZIP-239 describes the consensus rules for a new MSG_WTX inventory type, that MUST be used when relaying V5 transactions.

A new inv type MSG_WTX (0x00000005) is added, for use in both inv messages and getdata requests, indicating that the hash being referenced is the wtxid (i.e. the 64-byte value txid || auth_digest).

NOTE: #2446 added a Message::Wtx variant, but the txid and auth_digest were not specifically defined.

This inv type MUST be used when announcing v5 transactions. The txid and auth_digest are as defined in 4.

An inv or getdata message MUST NOT use the MSG_WTX inv type for v4 or earlier transactions

Designs

Zebra currently parses the wide transaction ID Inv type in zebra_network::protocol::external.

But we also need to:

• split WtxId into id and auth_data fields
  • PR Implement a WtxId struct, and use it in Zebra's external network protocol #2618
• create UnminedTxId and UnminedTx enums, so we can abstract over v4 transactions with TxIds, and v5 transactions with WtxIds
  • PR Create types for unmined transactions and their IDs #2634
• calculate wide/narrow transaction IDs and store them in UnminedTx, because we're going to need them to store the transaction
  • PR Create types for unmined transactions and their IDs #2634
• change zebra-network's Request and Response to use UnminedTxId and UnminedTx for mempool/transaction messages
  • also rename the requests and responses, because we're not just using transaction hashes any more
  • PR Support witnessed transaction IDs in zebra-network requests and responses #2638

Related Work

#2233 and #2446 added an initial Message::Wtx variant for ZIP-239, and implemented serialization and deserialization of it.

The transaction ID for V5 transactions (with the auth_digest) is defined in ZIP-244, and implemented in #2129.