Tutorial on uploading multiple files with Go

Uploading multiple files to Go server can be done easily as well. All you need to do is to parse the multiform data and loop through the files in the array. In this tutorial, we will use Go and HTML to achieve the following :

A simple HTML file upload form to upload multiple files to a server
Go program on server side to receive and process the uploaded files
Verify the uploaded file location and content on server.

1) HTML file upload form to upload file to server - goupload_multiple.html

 <html>
 <title>Go upload</title>
 <body>

 <form action="http://localhost.com:8080/receive_multiple" method="post" enctype="multipart/form-data">
 <label for="file">Filenames:</label>
 <input type="file" name="multiplefiles" id="multiplefiles" multiple>
 <input type="submit" name="submit" value="Submit">
 </form>

 </body>
 </html>

NOTE: The input id multiplefiles will be handled by the MultipartForm function in the code below.

2) Go program on server side to receive the uploaded file - receive_multiple.go

 package main

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

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

  err := r.ParseMultipartForm(200000) // grab the multipart form
  if err != nil {
 fmt.Fprintln(w, err)
 return
  }

  formdata := r.MultipartForm // ok, no problem so far, read the Form data

  //get the *fileheaders
  files := formdata.File["multiplefiles"] // grab the filenames

  for i, _ := range files { // loop through the files one by one
 file, err := files[i].Open()
 defer file.Close()
 if err != nil {
 fmt.Fprintln(w, err)
 return
 }

 out, err := os.Create("/tmp/" + files[i].Filename)

 defer out.Close()
 if err != nil {
 fmt.Fprintf(w, "Unable to create the file for writing. Check your write access privilege")
 return
 }

 _, err = io.Copy(out, file) // file not files[i] !

 if err != nil {
 fmt.Fprintln(w, err)
 return
 }

 fmt.Fprintf(w, "Files uploaded successfully : ")
 fmt.Fprintf(w, files[i].Filename+"\n")

  }
 }

 func main() {
  http.HandleFunc("/", uploadHandler)
  http.ListenAndServe(":8080", nil)
 }

the code above uses the ParseMultipartForm method to parse the submitted form data and MultipartForm method to process the POST multiple files the input data.

run receive_multiple.go at the server

> go run receive_multiple.go

point your browser to goupload_multiple.html and upload couple of files of your choice. The uploaded files will be copied to the /tmp directory

3) Verify the uploaded file location and content on server.

See if the file is uploaded to the /tmp with ls command and cat to see the content

References:

accessing uploaded files

Upload multiple files with Go

See also : Golang : Upload file from web browser to server

By Adam Ng

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