How to Track POST Request Progress for Large Files in Go?

Tracking POST Request Progress in Go

Problem:

Developers aiming to build file-sharing applications in Go using POST requests face challenges in monitoring upload progress for large files that require extended upload times.

Solution:

Wrapped io.Reader with Progress Tracking:

Instead of leveraging an intermediary TCP connection, an alternative approach is to create a custom io.Reader wrapper around the actual file reader. This allows for progress tracking each time the Read function is invoked.

Code Implementation:

Here's an example implementation:

<code class="go">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
}</code>

To utilize this wrapper, wrap the actual file reader within the ProgressReader:

<code class="go">file, _ := os.Open("/tmp/blah.go")
total := int64(0)
pr := &ProgressReader{file, func(r int64) {
    total += r
    if r > 0 {
        fmt.Println("progress", r)
    } else {
        fmt.Println("done", r)
    }
}}</code>

Subsequently, the progress can be tracked by copying the content to a discarding location:

<code class="go">io.Copy(ioutil.Discard, pr)</code>

This method enables seamless monitoring of upload progress for large files using POST requests.

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