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canonical-transaction-index-network.md

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Execution Canonical Transaction Index Network

This document is the specification for the sub-protocol that supports on-demand availability of the index necessary for clients to lookup transactions by their hash.

Overview

The canonical transaction index network is a Kademlia DHT that uses the Portal Wire Protocol to establish an overlay network on top of the Discovery v5 protocol.

The canonical transaction index consists of a mapping from transaction hash to the canonical block hash within which the transaction was included and the index of the transaction within the set of transactions executed within that block.

Data

Types

  • Transaction Index Entry

Retrieval

  • Transaction index entries can be retrieved by transaction hash.

Specification

Distance Function

The canonical transaction index network uses the stock XOR distance metric defined in the portal wire protocol specification.

Content ID Derivation Function

The canonical transaction index network uses the SHA256 Content ID derivation function from the portal wire protocol specification.

Wire Protocol

The Portal wire protocol is used as wire protocol for the canonical transaction index network.

Protocol Identifier

As specified in the Protocol identifiers section of the Portal wire protocol, the protocol field in the TALKREQ message MUST contain the value of 0x500D.

Supported Message Types

The canonical transaction index network supports the following protocol messages:

  • Ping - Pong
  • Find Nodes - Nodes
  • Find Content - Found Content
  • Offer - Accept

Ping.custom_data & Pong.custom_data

In the canonical transaction index network the custom_payload field of the Ping and Pong messages. The first packet between another client MUST be Type 0: Client Info, Radius, and Capabilities Payload. Then upgraded to the latest payload supported by both of the clients.

List of currently supported payloads, by latest to oldest.

Routing Table

The canonical transaction index network uses the standard routing table structure from the Portal Wire Protocol.

Node State

Data Radius

The canonical transaction index network includes one additional piece of node state that should be tracked. Nodes must track the data_radius from the Ping and Pong messages for other nodes in the network. This value is a 256 bit integer and represents the data that a node is "interested" in. We define the following function to determine whether node in the network should be interested in a piece of content.

interested(node, content) = distance(node.id, content.id) <= node.radius

A node is expected to maintain radius information for each node in its local node table. A node's radius value may fluctuate as the contents of its local key-value store change.

A node should track their own radius value and provide this value in all Ping or Pong messages it sends to other nodes.

Data Types

Transaction Hash Mapping

transaction_index_key  := Container(transaction-hash: Bytes32)
selector               := 0x00

content_key            := selector + SSZ.encode(transaction_index_key)
content                := TODO: block hash & merkle proof against header.transactions_trie