How to create and use HTML forms with file uploads in Go?

To create and use HTML forms with file uploads in Go, follow these steps:

Import the necessary packages:

import (
	"fmt"
	"html/template"
	"io"
	"log"
	"net/http"
	"os"
)

Implement a handler function to handle the form submission:

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method == "POST" {
		// Parse the form data
		r.ParseMultipartForm(10 << 20) // 10MB

		// Access the uploaded file
		file, handler, err := r.FormFile("file")
		if err != nil {
			fmt.Println(err)
			return
		}
		defer file.Close()

		// Create a new file on the server
		f, err := os.OpenFile(handler.Filename, os.O_WRONLY|os.O_CREATE, 0666)
		if err != nil {
			fmt.Println(err)
			return
		}
		defer f.Close()

		// Copy the uploaded file data to the new file
		io.Copy(f, file)

		fmt.Fprintf(w, "File uploaded successfully!")
	} else {
		// Display the upload form
		tmpl, _ := template.ParseFiles("upload.html")
		tmpl.Execute(w, nil)
	}
}

Implement the main function to set up the server and route the requests:

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

Create an HTML form (upload.html) that includes a file input field:

<form action="/upload" method="post" enctype="multipart/form-data">
  <input type="file" name="file" />
  <input type="submit" value="Upload" />
</form>

Run the Go program and access http://localhost:8080/upload in your browser. You should see the upload form. Select a file to upload, and click the "Upload" button.

This implementation sets up a simple HTTP server in Go that can handle file uploads. When a file is uploaded, it is saved to the server with the same filename as the uploaded file.

Note: Ensure that you have appropriate error handling and security measures in place when implementing file uploads in a production environment.