Extracts JPEG from transaction 033d185d1a04c4bd6de9bb23985f8c15aa46234206ad29101c31f4b33f1a0e49

augustana-college.js

#! /usr/bin/env node

const { Transaction } = require("bitcoinjs-lib");
const fs = require("fs");

const inputFile = "txhex";
const outputFile = "output.bin";

let hex = fs.readFileSync(inputFile, "utf8");
let tx = Transaction.fromHex(Buffer.from(hex, "hex"));
let data = Buffer.alloc(0);

for (let input of tx.ins) {
    let script = input.script;

    let cursor = 0;
    while (cursor < script.length) {
        let opcode = script[cursor];
        cursor++;

        if (opcode === 0x4c) {
            let size = script.readUIntLE(cursor, 1);
            cursor += 1;

            let chunk = script.subarray(cursor, cursor + size);
            data = Buffer.concat([data, chunk]);
            cursor += size;
        } else if (opcode === 0x4d) {
            let size = script.readUIntLE(cursor, 2);
            cursor += 2;

            let chunk = script.subarray(cursor, cursor + size);
            data = Buffer.concat([data, chunk]);
            cursor += size;
        } else if (opcode >= 0x01 && opcode <= 0x4b) {
            break; // redeem script
        } else {
            console.error(`unexpected opcode: ${opcode.toString(16)}`);
            process.exit(1);
        }
    }
}

fs.writeFileSync(outputFile, data);
console.log(`wrote: ${data.length} bytes to ${outputFile}`);