3) src.js

Now we will add logic for parsing our Json file we grabbed from our Bitcoin full node. This will parse the hexadecimal witness data and output a text file with hexadecimal chunks sorted accordingly.

1. Locate tx.json file we grabbed from our Bitcoin full node. Place this in our project directory MyDigitalArtifact.

2. Create a new file in the MyDigitalArtifact directory titled src.js

3. Insert the following code.

const fs = require('fs');
const bitcoinjs = require('bitcoinjs-lib');

const inputFile = 'tx.json';
const outputPath = 'DigitalArtifactParsed.txt';

function getOpName(op) {
    for (let key in bitcoinjs.script.OPS) {
        if (bitcoinjs.script.OPS[key] === op) {
            return key;
        }
    }
    return null;
}

function parseTx() {
    const jsonContent = JSON.parse(fs.readFileSync(inputFile));
    const witness = Buffer.from(jsonContent['vin'][0]['txinwitness'][1], 'hex');

    let position = 0;
    let opChunks = [];

    while (position < witness.length) {
        // Determine the next opcode's size
        const opcode = witness[position];
        position++;

        if (opcode <= bitcoinjs.script.OPS.OP_PUSHDATA4) {
            let size;
            if (opcode < bitcoinjs.script.OPS.OP_PUSHDATA1) {
                size = opcode;
            } else if (opcode === bitcoinjs.script.OPS.OP_PUSHDATA1) {
                size = witness.readUInt8(position);
                position++;
            } else if (opcode === bitcoinjs.script.OPS.OP_PUSHDATA2) {
                size = witness.readUInt16LE(position);
                position += 2;
            } else {
                size = witness.readUInt32LE(position);
                position += 4;
            }
            opChunks.push(`OP_PUSHBYTES_${size} ${witness.slice(position, position + size).toString('hex')}`);
            position += size;
        } else {
            // Map the opcode to its corresponding string representation
            const opName = Object.keys(bitcoinjs.script.OPS).find(key => bitcoinjs.script.OPS[key] === opcode);
            opChunks.push(opName);
        }
    }

    // Write the results to a file
    fs.writeFileSync(outputPath, opChunks.join('\\n'));
}

parseTx();

1. In your terminal window inside the directory run node src.js