downloadresume.js

// #!/usr/bin/env node

var spawn = require('child_process').spawn;
var path = require('path');
var url = require('url');

var dl_url = process.argv[2],
 
 fileName = decodeURIComponent(path.basename(url.parse(dl_url).pathname)),
 
 dest = process.argv[3] || process.cwd(),
 
 combinedFileName = path.join(dest,fileName),

 params = ['-o '+combinedFileName, '-L', '-C -', dl_url],
 
 speeds = [],

 alive = false;

 function speedCheck(speed) {
 	if (speeds.length < 3) {
 		speeds.push(speed);
 		return true;
 	}
 	else {
 		speeds.reverse().pop();
 		speeds.reverse();
 		speeds.push(speed);

 		//Check if last 3 speeds are zero

		if (speeds[0] != 0 && speeds[1] != 0 && speeds[2] != 0)
			alive = true;
 		return alive;
 	}
 }

//Spawning the process for the first time.
var child = spawn('curl',params);

console.log("Download started...........\n");

child.stdout.on('data', function(data) {

	console.log("Stdout received.............")

	//Break the output into an array of lines.
	var output_lines = data.split('\n');

	//Get the line which shows the speed. It will be 3rd line when starting download and 4th line while resuming.
	//I don't know what I'm doing here. Probably trying to get whichever is the last line of output
	var speed_line = output_lines[3] || output_lines[2] || output_lines[1] || output_lines[0];

	//Extract the speed part. It will be the last number in the line.
	var speed = Number(speed_line.trim().split(' ').reverse()[0]);

	//Some output for debugging
	console.log(data + "\n---------\nSPEED: " + speed);

	//If speedCheck() returns false, it implies the last 3 speeds were zero, hence the connection was dropped.
	//Restart the download by respawning the process.
	if (!speedCheck(speed)) {
		child.kill('SIGINT');
		console.log("\nResuming download........\n");
		child = spawn('curl',params);
	}
});

child.on('exit',function(code, signal){
	if (code == 0)
		console.log('\n\nDOWNLOAD COMPLETE.\n');
})