How to Track Upload Progress for POST Requests in Go?

Achieving Upload Progress Tracking for POST Requests in Go

In the quest to create a ShareX clone for Linux that seamlessly uploads files via HTTP POST requests, a critical question arises: how to effectively track upload progress, especially for larger files that may take minutes to transfer?

While manually establishing a TCP connection and sending HTTP requests in chunks is a viable solution, it carries limitations when dealing with HTTPS sites and may not be the most efficient approach. Fortunately, Go offers an alternative that effortlessly integrates progress tracking into your request process.

Customizing io.Reader for Progress Monitoring

The key insight lies in creating a custom io.Reader that wraps the actual reader. By overriding the Read() method, you can capture the progress at each Read invocation.

Consider the following code snippet:

type ProgressReader struct {
    io.Reader
    Reporter func(r int64)
}

func (pr *ProgressReader) Read(p []byte) (n int, err error) {
    n, err = pr.Reader.Read(p)
    pr.Reporter(int64(n))
    return
}

In this structure, Reporter is a callback function that receives the number of bytes read as an argument. The ProgressReader then intercepts the Read operation and reports the progress to the callback.

Implementation in Practice

To put this concept into practice, you can employ the following steps:

1. Create an instance of ProgressReader, wrapping your file reader:

   file, _ := os.Open("/tmp/blah.go")
   pr := &ProgressReader{file, func(r int64) { ... }}

2. Define the Reporter function to handle progress updates:

   pr.Reporter = func(r int64) {
       total += r
       if r > 0 {
           fmt.Println("progress", r)
       } else {
           fmt.Println("done", r)
       }
   }

3. Perform the file copy using your custom reader:

   io.Copy(ioutil.Discard, pr)

By utilizing this approach, you can effortlessly monitor upload progress for POST requests in Go, providing users with real-time insights into the file transfer process.

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