How would I limit upload and download speed from the server in golang?

Question

How would I limit upload and download speed from the server in golang?

I'm writing a golang server to allow users to upload and download files. And file is big, about 1GB bytes. I want to limit the upload and download speed to (for instance) 1MB/s (configurable of course).

below is my upload code:

func uploadFile(w http.ResponseWriter, r *http.Request) {
    file, _, err := r.FormFile("file")

    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }

    defer file.Close()

    os.MkdirAll(`e:\test`, os.ModePerm)
    out, err := os.Create(`e:\test\test.mpg`)
    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }

    defer out.Close()

    _, err = io.Copy(out, file)
    if err != nil {
        http.Error(w, err.Error(), 500)
    }
}

Answer 1

There's a token bucket algorithm that can be helpful to implement such the rate limit. I found an example implementation, which you can use: https://github.com/juju/ratelimit

package main

import (
    "bytes"
    "fmt"
    "io"
    "time"

    "github.com/juju/ratelimit"
)

func main() {
    // Source holding 1MB
    src := bytes.NewReader(make([]byte, 1024*1024))
    // Destination
    dst := &bytes.Buffer{}

    // Bucket adding 100KB every second, holding max 100KB
    bucket := ratelimit.NewBucketWithRate(100*1024, 100*1024)

    start := time.Now()

    // Copy source to destination, but wrap our reader with rate limited one
    io.Copy(dst, ratelimit.Reader(src, bucket))

    fmt.Printf("Copied %d bytes in %s\n", dst.Len(), time.Since(start))
}

After running it, the output is:

Copied 1048576 bytes in 9.239607694s

You can use different bucket implementations to provide desired behaviour. In your code, after setting up right token bucket, you would call:

_, err = io.Copy(out, ratelimit.Reader(file, bucket))