main-Out.go

func Out(file *os.File, c *sync.WaitGroup, nth int, from, size int64, written chan int64) {
	// Parameters :
	//  + file *os.File : temp file where contents have to be written.
	//  + c *sync.WaitGroup : To inform the main function that this connection has ended....
	//  + nth int    : Nth connection. Not needed. but say ou want to print nth connection failed or 
	//                 something like that.
	//  + from int64 : from which byte 
	//  + size int64 : how much have to returned
	//  + written chan int64 : as said before used send how much have been written from various connections.

	// Make new request. I know it is a bad bad practice to access os.Args like this...
	// Come on this is just a prototype.
	r, err := http.NewRequest("GET", os.Args[1], nil)
	check err
	
	// Here is the MEATY part. Set the Range Header.....
	r.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", from, from+size))
	
	// Execute the request.
	resp, err := http.DefaultClient.Do(r)
	check err
	
	// Make a byte buffer. for reading in each cycle...
	// You should know this if you have done Go.
	// I'm not `io.Copy`ing because I want to know how much have been 
	// written to be sent through channel `written`.
	// But the following loop is stolen from io.Copy source code.. :P
	buf := make([]byte, 32*1024)
	for {
		nr, er := resp.Body.Read(buf) // read from response body.
		if nr > 0 {
			// if something read ? then write it to the temp file passed as parameter.
			nw, ew := file.Write(buf[0:nr])
			// Send how much have been written in the file..... through that channel.
			if nw > 0 {
				written <- int64(nw)
			}
			
			// Err??? check err.
			// Go people really don't like errors I guess.... ew :P
			// Well, who does??
			check ew
			
			// If read amount is not written, that an error...
			// check that too....
			if nr != nw {
				check errors.New("Error short write")
				// This is not a syntax like return.... I'm just lazy to write the whole thing...
			}
		}
		// if any error in readin from resp? no worries get out of the loop.
		if er != nil {
			break
		}
	}
	// Close remote connection
	resp.Body.Close()
	// Close the local temp file...
	file.Close()
	// Say the Job controller or the WaitGroup this Job is done....
	c.Done()
	// Thats it....
}