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How to do it…

In this recipe, we are going to create an HTML form with a field of type file, which lets the user pick one or more files to upload to a server via a form submission. Perform the following steps:

Create upload-file.html inside the templates directory, as follows:

$ mkdir templates && cd templates && touch upload-file.html

Copy the following content to upload-file.html:

<html>
  <head>
    <meta charset="utf-8">
    <title>File Upload</title>
  </head>
  <body>
    <form action="/upload" method="post" enctype="multipart/
    form-data">
      <label for="file">File:</label>
      <input type="file" name="file" id="file">
      <input type="submit" name="submit" value="Submit">
    </form>
  </body>
</html>

In the preceding template, we defined a field of type file along with a Submit button.

On clicking the Submit button, the client encodes the data that forms the body of the request and makes a POST call to the form action, which is /upload in our case.

Create upload-file.go, where we will define handlers to render the file upload template, get the file from the request, process it, and write the response to an HTTP response stream, as follows:

package main
import 
(
  "fmt"
  "html/template"
  "io"
  "log"
  "net/http"
  "os"
)
const 
(
  CONN_HOST = "localhost"
  CONN_PORT = "8080"
)
func fileHandler(w http.ResponseWriter, r *http.Request) 
{
  file, header, err := r.FormFile("file")
  if err != nil 
  {
    log.Printf("error getting a file for the provided form key : ",
    err)
    return
  }
  defer file.Close()
  out, pathError := os.Create("/tmp/uploadedFile")
  if pathError != nil 
  {
    log.Printf("error creating a file for writing : ", pathError)
    return
  }
  defer out.Close()
  _, copyFileError := io.Copy(out, file)
  if copyFileError != nil 
  {
    log.Printf("error occurred while file copy : ", copyFileError)
  }
  fmt.Fprintf(w, "File uploaded successfully : "+header.Filename)
}
func index(w http.ResponseWriter, r *http.Request) 
{
  parsedTemplate, _ := template.ParseFiles("templates/
  upload-file.html")
  parsedTemplate.Execute(w, nil)
}
func main() 
{
  http.HandleFunc("/", index)
  http.HandleFunc("/upload", fileHandler)
  err := http.ListenAndServe(CONN_HOST+":"+CONN_PORT, nil)
  if err != nil 
  {
    log.Fatal("error starting http server : ", err)
    return
  }
}

With everything in place, the directory structure should look like the following:

Run the program with the following command:

$ go run upload-file.go