Composable helpers for decoding blockchain transactions
WARNING: This package is deprecated. Use tx-builder which includes both transaction builder and decoder.
This package contains composable helpers for decoding a blockchain transaction and implements an example of bitcoin transaction decoder.
It can be useful for blockchain projects forked from BitcoinCore that want to add custom data to a transaction.
Every composable helper expects a buffer and returns a pair (array of two elements) of a result and a buffer left.
Compared to bitcoinjs-lib which implements decoding in an imperative style where every helper uses buffer
of the outer scope and mutates outer offset. Thus its helpers cannot be reused for a different transaction structure.
Here is how bitcoin transaction decoder is implemented (the main export of the package):
const Buffer = require("safe-buffer").Buffer
const { readInt32, readUInt32 } = require("tx-decoder/src/buffer-utils")
const { compose, addProp } = require("tx-decoder/src/compose")
const { readInputs, readInput, readOutput } = require("tx-decoder/src/tx-decoder")
// Create a buffer from a transaction hex:
const txHex = "0100000001545f6161d2be3bdfe71..." // see `test/fixture.js` for a full tx example
const buffer = Buffer.from(txHex, 'hex')
// decodeTx :: Buffer -> [Object<version,vin,vout,locktime>, BufferLeft]
const decodeTx = buffer =>
(
compose([
addProp('version', readInt32), // 4 bytes
addProp('vin', readInputs(readInput)), // 1-9 bytes (VarInt), Input counter; Variable, Inputs
addProp('vout', readInputs(readOutput)), // 1-9 bytes (VarInt), Output counter; Variable, Outputs
addProp('locktime', readUInt32) // 4 bytes
])({}, buffer)
)
console.log( decodeTx( buffer ) )
// > [{version: 1, vin: [...], vout: [...]}, <Buffer >]Here is how readInput is defined in the same composable manner:
const { readSlice, readVarSlice, readUInt32 } = require("tx-decoder/src/buffer-utils")
const { compose, addProp } = require("tx-decoder/src/compose")
// readInput :: Buffer -> [Res, Buffer]
const readInput = buffer =>
(
compose([
addProp('hash', readSlice(32)), // 32 bytes, Transaction Hash
addProp('index', readUInt32), // 4 bytes, Output Index
addProp('script', readVarSlice), // 1-9 bytes (VarInt), Unlocking-Script Size; Variable, Unlocking-Script
addProp('sequence', readUInt32) // 4 bytes, Sequence Number
])({}, buffer)
)Checkout tests/manual-decode.js if you are not familiar with how to decode a transaction. It has a step-by-step imperative-style example.
Checkout tests for exact examples of how to use the package helpers.
- decode script
- create a transaction builder (see tx-builder package)
- 0.2.0 Added readHash helper
- Reverse the hash (tx id) after its read from hex.
- 0.1.2 Initial version
- buffer utils, compose helpers, bitcoin tx decode example.