nodejs synchronization read large file line by line?

Question

I have a large file (utf8). I know fs.createReadStream can create stream to read a large file, but not synchronized. So i try to use fs.readSync, b

Answer 1

I built a simpler version JB Kohn's answer that uses split() on the buffer. It works on the larger files I tried.

/*
 * Synchronously call fn(text, lineNum) on each line read from file descriptor fd.
 */
function forEachLine (fd, fn) {
    var bufSize = 64 * 1024;
    var buf = new Buffer(bufSize);
    var leftOver = '';
    var lineNum = 0;
    var lines, n;

    while ((n = fs.readSync(fd, buf, 0, bufSize, null)) !== 0) {
        lines = buf.toString('utf8', 0 , n).split('\n');
        lines[0] = leftOver+lines[0];       // add leftover string from previous read
        while (lines.length > 1) {          // process all but the last line
            fn(lines.shift(), lineNum);
            lineNum++;
        }
        leftOver = lines.shift();           // save last line fragment (may be '')
    }
    if (leftOver) {                         // process any remaining line
        fn(leftOver, lineNum);
    }
}