CTV Hash Generator in Javascript

ctv_hash_generator_in_javascript.js

//dependencies:
//https://unpkg.com/@cmdcode/[email protected]
var sha256 = s => {
    if ( typeof s == "string" ) s = new TextEncoder().encode( s );
    return crypto.subtle.digest( 'SHA-256', s ).then( hashBuffer => {
        var hashArray = Array.from( new Uint8Array( hashBuffer ) );
        var hashHex = hashArray
            .map( bytes => bytes.toString( 16 ).padStart( 2, '0' ) )
            .join( '' );
        return hashHex;
    });
}
var hexToBytes = hex => Uint8Array.from( hex.match( /.{1,2}/g ).map( byte => parseInt( byte, 16 ) ) );
var reverseHexString = s => s.match(/[a-fA-F0-9]{2}/g).reverse().join('');
var getStandardTemplateHash = async ( rawtx, inputnum ) => {
    var tx = tapscript.Tx.decode( rawtx );
    var ctv_hash_preimage = "";
    //add the tx version number to the ctv preimage
    var version = tx.version.toString( 16 );
    version = version.padStart( 8, "0" );
    version = reverseHexString( version );
    ctv_hash_preimage = ctv_hash_preimage + version;
    //add the tx locktime to the ctv preimage
    var locktime = tx.locktime.toString( 16 );
    locktime = locktime.padStart( 8, "0" );
    var locktime = reverseHexString( locktime );
    ctv_hash_preimage = ctv_hash_preimage + locktime;
    //go through each input and concatenate the scriptSigs, if any; then hash them and add the hash to the ctv preimage
    var vin = tx.vin || [];
    var scriptsigs = [];
    if ( vin.length ) {
        vin.forEach( ( input, index ) => {
            var length = ( input.scriptSig.length / 2 ).toString( 16 );
            if ( length.length % 2 ) length = "0" + length;
            length = reverseHexString( length );
            //I'm not sure why I have to prefix fd to a 2-byte scriptsig length, but that made it match the test cases I was testing against,
            //which are available here: https://github.com/jamesob/simple-ctv-vault/blob/master/ctvhash-test-vectors.json
            if ( length.length === 4 ) length = "fd" + length;
            //I'm also not sure why ff turns into fdff00, but that's what it does in the test vectors
            if ( length === "ff" ) length = "fdff00";
            scriptsigs.push( length + input.scriptSig );
        });
    }
    var scriptsigs_has_nonempty_elements = false;
    scriptsigs.every( scriptsig => {
        if ( scriptsig !== "00" ) {
            scriptsigs_has_nonempty_elements = true;
            return;
        }
        return true;
    });
    if ( !scriptsigs_has_nonempty_elements ) scriptsigs = [];
    var scriptsigs_bytes = [];
    scriptsigs.forEach( scriptsig => scriptsigs_bytes.push( hexToBytes( scriptsig ) ) );
    var all_scriptsigs_together = [];
    scriptsigs_bytes.forEach( scriptsig => all_scriptsigs_together = [ ...all_scriptsigs_together, ...scriptsig ] );
    scriptsigs = Uint8Array.from( all_scriptsigs_together );
    if ( scriptsigs.length ) var hash = await sha256( scriptsigs );
    else var hash = "";
    ctv_hash_preimage = ctv_hash_preimage + hash;
    //add the number of inputs to the ctv preimage
    var num_of_inputs = reverseHexString( tx.vin.length.toString( 16 ).padStart( 8, "0" ) );
    ctv_hash_preimage = ctv_hash_preimage + num_of_inputs;
    //concatenate the sequence numbers of every input, hash them, and add the hash to the ctv preimage
    var sequences = "";
    tx.vin.forEach( input => sequences = sequences + reverseHexString( input.sequence ) );
    sequences_hash = await sha256( hexToBytes( sequences ) );
    ctv_hash_preimage = ctv_hash_preimage + sequences_hash;
    //add the number of outputs to the ctv preimage
    var num_of_outputs = reverseHexString( tx.vout.length.toString( 16 ).padStart( 8, "0" ) );
    ctv_hash_preimage = ctv_hash_preimage + num_of_outputs;
    //concatenate the outputs, hash them, and add the hash to the ctv preimage
    var outputs_preimage = "";
    tx.vout.forEach( output => {
        var value = output.value.toString( 16 );
        value = value.padStart( 16, "0" );
        value = reverseHexString( value );
        outputs_preimage = outputs_preimage + value;
        var length = ( output.scriptPubKey.length / 2 ).toString( 16 );
        if ( length % 2 ) length = "0" + length;
        outputs_preimage = outputs_preimage + length;
        outputs_preimage = outputs_preimage + output.scriptPubKey;
    });
    var outputs_hash = await sha256( hexToBytes( outputs_preimage ) );
    ctv_hash_preimage = ctv_hash_preimage + outputs_hash;
    //add the index number of the input being spent to the ctv preimage
    var inputnum = reverseHexString( inputnum.toString( 16 ).padStart( 8, "0" ) );
    ctv_hash_preimage = ctv_hash_preimage + inputnum;
    //hash the ctv preimage
    var ctv_hash = await sha256( hexToBytes( ctv_hash_preimage ) );
    //return the ctv hash
    return ctv_hash;
}

🙌🏻 good work

Javascript Maxi🙌🙌🙌