Golang golang-httpupload (snippet)

Go programming example 'golang-httpupload'
golang-httpupload

Golang beginners example: golang-httpupload
package main

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

var templates *template.Template
var uploadDir string

func display(w http.ResponseWriter, tmpl string, data interface{}) {
    templates.Execute(w, data)
}

func uploadHandler(w http.ResponseWriter, r *http.Request) {
    switch r.Method {
    //GET requests will be redirected
    case "GET":
        // redirect to . (http://localhost:8080/)
        http.Redirect(w, r, ".", 301)

    //POST takes the uploaded file(s) and saves it to disk
    case "POST":
        //get the multipart reader for the request
        reader, err := r.MultipartReader()

        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }

        //copy each part to dir
        for {
            part, err := reader.NextPart()
            if err == io.EOF {
                break
            }

            //if FileName() is empty, skip this part
            if part.FileName() == "" {
                continue
            }
            dst, err := os.Create(uploadDir + part.FileName())
            if err == nil {
                defer dst.Close()
                log.Println("file upload started:", part.FileName())
            } else {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
            }

            if _, err := io.Copy(dst, part); err != nil {
                http.Error(w, err.Error(), http.StatusInternalServerError)
                return
            } else {
                log.Println("file uploaded:", part.FileName())
            }
        }
        //display success message via html template
        display(w, "upload", "Upload successful.")
    default:
        //only allow GET- and POST-Requests, otherwise respond with HTTP-Code 405
        w.WriteHeader(http.StatusMethodNotAllowed)
    }
}

func formHandler(w http.ResponseWriter, r *http.Request) {
    if r.URL.RawQuery == "" && r.Method == "GET" {
        display(w, "upload", nil)
    }
}

func main() {
    uploadDir = "./"
    templates, _ = template.New("tmpl").Parse(templateString)

    http.HandleFunc("/upload", uploadHandler)
    http.HandleFunc("/", formHandler)

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

//this is the HTML template - usually this would be stored in a separate file
var templateString = `
<!DOCTYPE html>
<html lang="en">
    <head>
        <title>File Upload Example</title>
        <style>
            body {
                    font-family: Sans-serif;
                    padding-bottom: 20px;
                    background-color: #ffffff;
            }
            h1 a {
                color: black;
                text-decoration: none;
            }
            h1 {text-align: left; margin-bottom: 20px;}
            .message {font-weight:bold}
            fieldset {width:400px}
        </style>
    </head>
    <body>
        <div class="container">
            <h1><a href="./">File Upload Example</a></h1>
            <div class="message">{{.}}</div>
            <form class="form-signin" method="post" action="/upload" enctype="multipart/form-data">
                    <fieldset>
                        <input type="file" name="myfiles" id="myfiles" multiple="multiple">
                        <input type="submit" name="submit" value="Upload">
                </fieldset>
            </form>
        </div>
    </body>
</html>`
Useful links

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