File upload failing in golang

In my use case I am trying to upload a file to server in golang. I have the following html code,

<div class="form-input upload-file" enctype="multipart/form-data" >
	<input type="file"name="file" id="file" />
    <input type="hidden"name="token" value="{{.}}" />
   	<a href="/uploadfile/" data-toggle="tooltip" title="upload">
    	<input type="button upload-video" class="btn btn-primary btn-filled btn-xs" value="upload" />
    </a>
</div>

And the server side,

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	// the FormFile function takes in the POST input id file
	file, header, err := r.FormFile("file")
	if err != nil {
		fmt.Fprintln(w, err)
		return
	}
	defer file.Close()

	out, err := os.Create("/tmp/uploadedfile")
	if err != nil {
		fmt.Fprintf(w, "Unable to create the file for writing. Check your write access privilege")
		return
	}
	defer out.Close()

	// write the content from POST to the file
	_, err = io.Copy(out, file)
	if err != nil {
		fmt.Fprintln(w, err)
	}

	fmt.Fprintf(w, "File uploaded successfully : ")
	fmt.Fprintf(w, header.Filename)
}

When I try to upload the file, I am getting request Content-Type isn't multipart/form-data error in server side.

Could anyone help me on this?

To be honest I have no idea how do you even get error as your HTML is not form. But I think you getting error because by default form is send as GET request while multipart/form-data should be send via POST. Here is example of minimal form which should work.

<form action="/uploadfile/" enctype="multipart/form-data" method="post">
    <input type="file" name="file" id="file" />
    <input type="hidden"name="token" value="{{.}}" />
    <input type="submit" value="upload" />
</form>

The issue is that you must include the header that contains the content type.

req.Header.Add("Content-Type", writer.FormDataContentType())

This is included in the mime/multipart package.

For a working example please check this blog post.