How to Build a File Upload Service in Go

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2026-04-17T12:05:42+00:00
Build a Go file upload service using net/http to handle POST requests and os.Create to save files.

Use the net/http standard library to handle POST requests and os.Create to save the file to disk.

package main

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

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
		return
	}
	file, _, err := r.FormFile("file")
	if err != nil {
		http.Error(w, "Error retrieving file", http.StatusBadRequest)
		return
	}
	defer file.Close()
	out, err := os.Create("uploaded.txt")
	if err != nil {
		http.Error(w, "Error creating file", http.StatusInternalServerError)
		return
	}
	defer out.Close()
	_, err = io.Copy(out, file)
	if err != nil {
		http.Error(w, "Error saving file", http.StatusInternalServerError)
		return
	}
	w.WriteHeader(http.StatusOK)
}

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