It took me some time to get this right as I couldn't find an easy-to-follow example on the web. Since this is a common use case, this post may hopefully help someone.
This example has a single template for the main webpage that has the file upload form. The backend handler serves this template on a GET request and handles the upload on a POST request. If you're not familiar with Go's html templates, I would recommend reading this well written document first.
The uploadHandler method is where the action happens. This handler responds to a GET request by displaying the upload form. This form POSTs to the same URL - the handler responds by parsing the posted form, saving the uploaded files and displaying a success message.
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| package main | |
| import ( | |
| "html/template" | |
| "io" | |
| "net/http" | |
| "os" | |
| ) | |
| //Compile templates on start | |
| var templates = template.Must(template.ParseFiles("tmpl/upload.html")) | |
| //Display the named template | |
| func display(w http.ResponseWriter, tmpl string, data interface{}) { | |
| templates.ExecuteTemplate(w, tmpl+".html", data) | |
| } | |
| //This is where the action happens. | |
| func uploadHandler(w http.ResponseWriter, r *http.Request) { | |
| switch r.Method { | |
| //GET displays the upload form. | |
| case "GET": | |
| display(w, "upload", nil) | |
| //POST takes the uploaded file(s) and saves it to disk. | |
| case "POST": | |
| //parse the multipart form in the request | |
| err := r.ParseMultipartForm(100000) | |
| if err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| //get a ref to the parsed multipart form | |
| m := r.MultipartForm | |
| //get the *fileheaders | |
| files := m.File["myfiles"] | |
| for i, _ := range files { | |
| //for each fileheader, get a handle to the actual file | |
| file, err := files[i].Open() | |
| defer file.Close() | |
| if err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| //create destination file making sure the path is writeable. | |
| dst, err := os.Create("/home/sanat/" + files[i].Filename) | |
| defer dst.Close() | |
| if err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| //copy the uploaded file to the destination file | |
| if _, err := io.Copy(dst, file); err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| } | |
| //display success message. | |
| display(w, "upload", "Upload successful.") | |
| default: | |
| w.WriteHeader(http.StatusMethodNotAllowed) | |
| } | |
| } | |
| func main() { | |
| http.HandleFunc("/upload", uploadHandler) | |
| //static file handler. | |
| http.Handle("/assets/", http.StripPrefix("/assets/", http.FileServer(http.Dir("assets")))) | |
| //Listen on port 8080 | |
| http.ListenAndServe(":8080", nil) | |
| } |
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| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <title>File Upload Demo</title> | |
| <link type="text/css" rel="stylesheet" href="/assets/css/style.css" /> | |
| </head> | |
| <body> | |
| <div class="container"> | |
| <h1>File Upload Demo</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="Submit"> | |
| </fieldset> | |
| </form> | |
| </div> | |
| </body> | |
| </html> |
You can find the complete project at - https://github.com/sanatgersappa/Go-MultipleFileUpload
Update: As pointed out by Luit in the comments, an alternate way of doing this is to use a mime/multipart.Reader exposed by r.MultipartReader() instead of r.MultiparseForm(). This approach has the advantage that it doesn't write to a temporary location on the disk, but processes bytes as they come in.
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| package main | |
| import ( | |
| "html/template" | |
| "io" | |
| "net/http" | |
| "os" | |
| ) | |
| //Compile templates on start | |
| var templates = template.Must(template.ParseFiles("tmpl/upload.html")) | |
| //Display the named template | |
| func display(w http.ResponseWriter, tmpl string, data interface{}) { | |
| templates.ExecuteTemplate(w, tmpl+".html", data) | |
| } | |
| //This is where the action happens. | |
| func uploadHandler(w http.ResponseWriter, r *http.Request) { | |
| switch r.Method { | |
| //GET displays the upload form. | |
| case "GET": | |
| display(w, "upload", nil) | |
| //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 destination. | |
| for { | |
| part, err := reader.NextPart() | |
| if err == io.EOF { | |
| break | |
| } | |
| //if part.FileName() is empty, skip this iteration. | |
| if part.FileName() == "" { | |
| continue | |
| } | |
| dst, err := os.Create("/home/sanat/" + part.FileName()) | |
| defer dst.Close() | |
| if err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| if _, err := io.Copy(dst, part); err != nil { | |
| http.Error(w, err.Error(), http.StatusInternalServerError) | |
| return | |
| } | |
| } | |
| //display success message. | |
| display(w, "upload", "Upload successful.") | |
| default: | |
| w.WriteHeader(http.StatusMethodNotAllowed) | |
| } | |
| } | |
| func main() { | |
| http.HandleFunc("/upload", uploadHandler) | |
| //static file handler. | |
| http.Handle("/assets/", http.StripPrefix("/assets/", http.FileServer(http.Dir("assets")))) | |
| //Listen on port 8080 | |
| http.ListenAndServe(":8080", nil) | |
| } |
