Predicate

This package contains the predicate data structure and its encoding and helper functions to unpack/pack the data structure.

Encoding

A byte slice of size N is encoded as:

Slice of N bytes
Delimiter byte 0xff
Appended 0s to the nearest multiple of 32 bytes

Results

This defines how to encode PredicateResults within the block header's Extra data field.

For more information on the motivation for encoding the results of predicate verification within a block, see here.

Serialization

Results have a maximum size of 1MB enforced by the codec. The actual size depends on how much data the Precompile predicates may put into the results, the gas cost they charge, and the block gas limit. PredicateResults are encoded using the AvalancheGo codec, which serializes a map by serializing the length of the map as a uint32 and then serializes each key-value pair sequentially.

PredicateResults:

Field	Type	Size
codecID	uint16	2 bytes
results	map[[32]byte]TxPredicateResults	4 + size(results) bytes
Total		6 + size(results)

codecID is the codec version used to serialize the payload and is hardcoded to 0x0000
results is a map of transaction hashes to the corresponding TxPredicateResults

TxPredicateResults

Field	Type	Size
txPredicateResults	map[[20]byte][]byte	4 + size(txPredicateResults) bytes

txPredicateResults is a map of precompile addresses to the corresponding byte array returned by the predicate

Examples

Empty Predicate Results Map

// codecID
0x00, 0x00,
// results length
0x00, 0x00, 0x00, 0x00

Predicate Map with a Single Transaction Result

// codecID
0x00, 0x00,
// Results length
0x00, 0x00, 0x00, 0x01,
// txHash (key in results map)
0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
// TxPredicateResults (value in results map)
// TxPredicateResults length
0x00, 0x00, 0x00, 0x01,
// precompile address (key in TxPredicateResults map)
0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00,
// Byte array results (value in TxPredicateResults map)
// Length of bytes result
0x00, 0x00, 0x00, 0x03,
// bytes
0x01, 0x02, 0x03

Predicate Map with Two Transaction Results

// codecID
0x00, 0x00,
// Results length
0x00, 0x00, 0x00, 0x02,
// txHash (key in results map)
0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
// TxPredicateResults (value in results map)
// TxPredicateResults length
0x00, 0x00, 0x00, 0x01,
// precompile address (key in TxPredicateResults map)
0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00,
// Byte array results (value in TxPredicateResults map)
// Length of bytes result
0x00, 0x00, 0x00, 0x03,
// bytes
0x01, 0x02, 0x03
// txHash2 (key in results map)
0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
// TxPredicateResults (value in results map)
// TxPredicateResults length
0x00, 0x00, 0x00, 0x01,
// precompile address (key in TxPredicateResults map)
0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00,
// Byte array results (value in TxPredicateResults map)
// Length of bytes result
0x00, 0x00, 0x00, 0x03,
// bytes
0x01, 0x02, 0x03

# README