Count ansi colors with node.js

numberOfSupportedAnsiColors.js

var fs = require('fs');

function awaitEcho() {
    var buf = new Buffer(100);

    var numRead;
    var offset = 0;
    var startTime = Date.now();
    do {
        if (offset >= buf.length) {
            var reallocBuffer = new Buffer(2 * buf.length);
            buf.copy(reallocBuffer);
            buf = reallocBuffer;
        }
        try {
            numRead = fs.readSync(0, buf, offset, 1);
            offset += numRead;
        } catch (e) {
            if (e.code !== 'EAGAIN') {
                throw e;
            }
        }
    } while (buf.lastIndexOf(0x07, offset) === -1 && Date.now() - 100 <= startTime);
    return buf.slice(0, offset);
}

var preamble = new Buffer([0x1b, 0x5d, 0x34, 0x3b]);
var postamble = new Buffer([0x3b, 0x3f, 0x07]);
function supportsColorNumber(tty, num) {
    var e = Buffer.concat([preamble, new Buffer(String(num)), postamble]);
    tty.write(e, 0, e.length);

    var reply = awaitEcho();

    return reply.length <= 1;
}

if (process.stdin.isTTY) {
    process.stdout.setNoDelay(true);
    process.stdin.setNoDelay(true);
    var stdinWasRaw = process.stdin.isRaw;
    process.stdin.setRawMode(true);

    var rawStdout = new fs.SyncWriteStream(1, { autoClose: false });

    // Binary search
    var min = 0;
    var max = 256;
    var i;
    while (min + 1 < max) {
        i = Math.round((min + max) / 2);
        if (supportsColorNumber(rawStdout, i)) {
            max = i;
        } else {
            min = i;
        }
    }
    console.log('Number of colors supported', max);

    if (!stdinWasRaw) {
        process.stdin.setRawMode(false);
    }
    process.stdin.setNoDelay(false);
}