Golang : Upload/Receive file progress indicator

It is always nice to have a progress bar telling us how long to wait for the upload or download to complete. In this tutorial, we will learn how to display a text based progress indicator for receiving file.

Note : This is a server side program(console/terminal) and not for client side (web browser)

1) Run this code on your local machine.

 package main

 import (
 "fmt"
 "io"
 "net/http"
 "os"
 "time"
 )

 func uploadPage(w http.ResponseWriter, r *http.Request) {
 w.Write([]byte(fmt.Sprintf("<html><title>Go upload</title><body><form action='http://localhost:8080/receive' method='post' enctype='multipart/form-data'><label for='file'>Filename:</label><input type='file' name='file' id='file'><input type='submit' value='Upload' ></form></body></html>")))
 }

 func uploadProgress(w http.ResponseWriter, r *http.Request) {

 mr, err := r.MultipartReader()
 if err != nil {
 fmt.Fprintln(w, err)
 return
 }
 length := r.ContentLength

 //ticker := time.Tick(time.Millisecond) // <-- use this in production
 ticker := time.Tick(time.Second) // this is for demo purpose with longer delay

 for {

 var read int64
 var p float32
 part, err := mr.NextPart()

 if err == io.EOF {
 fmt.Printf("\nDone!")
 break
 }

 dst, err := os.OpenFile("upload.jpg", os.O_WRONLY|os.O_CREATE, 0666)

 if err != nil {
 return
 }

 for {

 buffer := make([]byte, 100000)
 cBytes, err := part.Read(buffer)
 if err == io.EOF {
 fmt.Printf("\nLast buffer read!")
 break
 }
 read = read + int64(cBytes)

 //fmt.Printf("\r read: %v  length : %v \n", read, length)

 if read > 0 {
 p = float32(read*100) / float32(length)
 //fmt.Printf("progress: %v \n", p)
 <-ticker
 fmt.Printf("\rUploading progress %v", p) // for console
 dst.Write(buffer[0:cBytes])
 } else {
 break
 }

 }
 }
 }

 func main() {
 mux := http.NewServeMux()
 mux.HandleFunc("/", uploadPage)
 mux.HandleFunc("/receive", uploadProgress)

 http.ListenAndServe(":8080", mux)
 }

2 ) open up your browser and point to http://localhost:8080

3) You will see a simple form for you to upload a file. Choose a file and press upload button.

4) At this point, you should be able to see something like this