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Extension Blocks (peer services)

Layer: Peer Services
Title: Extension Blocks (peer services)
Author: Christopher Jeffrey <chjj@purse.io>
Status: Draft
Created: 2017-03-17
License: Public Domain

Abstract

This specification defines peer services for extension blocks.

Specification

Peer Services

Extension blocks defines a new service bit (service bit 5) to signal whether extension blocks is supported by the remote node.

Block and transaction relay

This specification defines new INV types for GETDATA requests. Similar to the INV types defined in BIP144, an extended bit is to be set on both tx and block inv types. The extended bit exists as the 30th bit, e.g. 1 would become 536870913 ((1 << 29) | 1).

Newly defined inv types are as follows:

  • EXT_TX: 536870913 ((1 << 29) | 1)
  • EXT_BLOCK: 536870914 ((1 << 29) | 2)

Backward Compatability

To avoid an enormous amount of orphan transactions on non-upgraded nodes, upgraded nodes shall respond with a NOTFOUND message in response to any regular GETDATA TX request which maps to an extension chain transaction. Invs containing extension transactions shall not be broadcast to non-upgraded peers.

Responses GETDATA EXT_TX shall include both extension and non-extension transactions.

EXT_BLOCK message serialization

block messages requested with the EXT_BLOCK inv type are to use the canonical serialization with an extra varint count appended. Following the varint count shall be a transaction vector using BIP141 serialization. Clients MUST disregard blocks which use BIP141 serialization in the canonical transaction vector.

Extensions to Compact Block Relay (BIP152)

Compact block relay shall be initiated using the previously specified (BIP152) sendcmpct message, with a version of 3. Serialization for cmpctblock, blocktxnrequest, and blocktxn are modified to include two transaction vectors. The first being canonical, and the second being extended.

Reference Implementation

https://github.com/bcoin-org/bcoin-extension-blocks

Copyright

This document is hereby placed in the public domain.