POST data using the Content-Type multipart/form-data

Question

I'm trying to upload images from my computer to a website using go. Usually, I use a bash script that sends a file and a key to the server:

curl -F "image"=@"IMAGEFILE" -F "key"="KEY" URL 

it works fine, but I'm trying to convert this request into my golang program.

http://matt.aimonetti.net/posts/2013/07/01/golang-multipart-file-upload-example/

I tried this link and many others, but, for each code that I try, the response from the server is "no image sent", and I've no idea why. If someone knows what's happening with the example above.

Answer 1

Here's some sample code.

In short, you'll need to use the mime/multipart package to build the form.

package main  import (     "bytes"     "fmt"     "io"     "mime/multipart"     "net/http"     "net/http/httptest"     "net/http/httputil"     "os"     "strings" )  func main() {      var client *http.Client     var remoteURL string     {         //setup a mocked http client.         ts := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {             b, err := httputil.DumpRequest(r, true)             if err != nil {                 panic(err)             }             fmt.Printf("%s", b)         }))         defer ts.Close()         client = ts.Client()         remoteURL = ts.URL     }      //prepare the reader instances to encode     values := map[string]io.Reader{         "file":  mustOpen("main.go"), // lets assume its this file         "other": strings.NewReader("hello world!"),     }     err := Upload(client, remoteURL, values)     if err != nil {         panic(err)     } }  func Upload(client *http.Client, url string, values map[string]io.Reader) (err error) {     // Prepare a form that you will submit to that URL.     var b bytes.Buffer     w := multipart.NewWriter(&b)     for key, r := range values {         var fw io.Writer         if x, ok := r.(io.Closer); ok {             defer x.Close()         }         // Add an image file         if x, ok := r.(*os.File); ok {             if fw, err = w.CreateFormFile(key, x.Name()); err != nil {                 return             }         } else {             // Add other fields             if fw, err = w.CreateFormField(key); err != nil {                 return             }         }         if _, err = io.Copy(fw, r); err != nil {             return err         }      }     // Don't forget to close the multipart writer.     // If you don't close it, your request will be missing the terminating boundary.     w.Close()      // Now that you have a form, you can submit it to your handler.     req, err := http.NewRequest("POST", url, &b)     if err != nil {         return     }     // Don't forget to set the content type, this will contain the boundary.     req.Header.Set("Content-Type", w.FormDataContentType())      // Submit the request     res, err := client.Do(req)     if err != nil {         return     }      // Check the response     if res.StatusCode != http.StatusOK {         err = fmt.Errorf("bad status: %s", res.Status)     }     return }  func mustOpen(f string) *os.File {     r, err := os.Open(f)     if err != nil {         panic(err)     }     return r }