main-1.go

total := head.ContentLength
// Say I want to make 50 connections.
// bpc is bytes per connection
bpc := total / 50

// Get the filename....
outfile := path.Base(url)

// Create a directory for our temp sections.
err = os.Mkdir(filepath.Join("/tmp/", outfile), 0755)

// `check err` means the usual check err block,
// you know with `if err != nil {...}`
check err

// This is for storing "from which byte index should be asked for from the server" for
// a new connection.
from := int64(0)

// loop variable tracking the no. of connections. (loop???... wait for it)
count := 0

// We are going to run the 50 connections concurrently.
// So we have to wait for the connections to end. Else corrupted downloads.
// When we make a new connection, we'll add 1 Job to c.(c.Add(1))
// When the connection is done, c.Done() will be called.
c := &sync.WaitGroup{}

// This is a optional variable to get how much has been written
// every go routine will be sending the amount they write at any write cycle
// through this channel... I made a progress bar.
written := make(chan int64)
// To store all the tmp filenames in an array.
files := make([]string, 0)