javascript can be as nice as Erlang for handling cascade callback

gistfile1.js

MultiPart.prototype.copy = function(writer, callback) {
	var mp = this;
	var parts = this.parts;
	if(this.part != '') { parts.push(this.part); }
	parts.push(CRLF + "--" + this.boundary + "--");
	parts.reverse();
	var BLOCKSIZE = 32*1024;
	var readFile = function(fd, total, writer) {
		var buffer = new Buffer(BLOCKSIZE);
		fs.read(fd, buffer, 0, BLOCKSIZE, null, function(err, bytesRead) {
			total -= BLOCKSIZE;
			util.log(total);
			writer.write(buffer.toString('binary', 0, bytesRead));
			if(total > 0) {
				readFile(fd, total, writer);
			} else {
				teardown();
			}
		});
		
	};
	var teardown = function() {
		if(parts.length == 0) {
			callback();
		} else {
			var part = parts.pop();
			if(part instanceof File) {
				var fd = fs.openSync(part.path, 'r');
				var total = fs.statSync(part.path).size;
				readFile(fd, total, writer);
			} else {
				writer.write(part, 'utf-8');
				teardown();
			}
		}
	};
	teardown();
};