Using HttpWebRequest to POST data/upload image using multipart/form-data

Question

I am trying to use the ImageShack API to upload images. To use it, I am supposed to POST the image using multipart/form-data. I did it like ...

Answer 1

This is nothing like multipart/form-data

1. There's no boundaries between fields (needed even with one field).
2. Why are you base-64 encoding?
3. There's no indication of the content-type of the image.

Take a look at RFC 2388 for the actual format spec. It can also be useful to look at a Fiddler grab of a file upload from a web-page.

Answer 2

I believe that you are not building the request body correctly. First, you need to include part boundary (random text) in content type header. For example,

Content-Type: multipart/form-data; boundary=----WebKitFormBoundarySkAQdHysJKel8YBM

Now format of request body will be something like

------WebKitFormBoundarySkAQdHysJKel8YBM 
Content-Disposition: form-data;name="key"

KeyValueGoesHere
------WebKitFormBoundarySkAQdHysJKel8YBM 
Content-Disposition: form-data;name="param2"

ValueHere
------WebKitFormBoundarySkAQdHysJKel8YBM 
Content-Disposition: form-data;name="fileUpload"; filename="y1.jpg"
Content-Type: image/jpeg 

[image data goes here]

I will suggest you to use tool such as Fiddler to understand how these requests are built.

Answer 3

I finally got it with the following code ...

var boundary = "------------------------" + DateTime.Now.Ticks;
var newLine = Environment.NewLine;
var propFormat = "--" + boundary + newLine +
                    "Content-Disposition: form-data; name=\"{0}\"" + newLine + newLine + 
                    "{1}" + newLine;
var fileHeaderFormat = "--" + boundary + newLine +
                        "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" + newLine;

var req = (HttpWebRequest)HttpWebRequest.Create("http://jm/php/upload.php");
req.Method = WebRequestMethods.Http.Post;
req.ContentType = "multipart/form-data; boundary=" + boundary;

using (var reqStream = req.GetRequestStream()) {
    var reqWriter = new StreamWriter(reqStream);
    var tmp = string.Format(propFormat, "str1", "hello world");
    reqWriter.Write(tmp);
    tmp = string.Format(propFormat, "str2", "hello world 2");
    reqWriter.Write(tmp);
    reqWriter.Write("--" + boundary + "--");
    reqWriter.Flush();
}
var res = req.GetResponse();
using (var resStream = res.GetResponseStream()) {
    var reader = new StreamReader(resStream);
    txt1.Text = reader.ReadToEnd();
}

Notice boundaries have to begin with -- {boundary declared in ContentType} and ending boundary must begin & end with -- . in my case, I originally used

var propFormat = boundary + newLine +
                    "Content-Disposition: form-data; name=\"{0}\"" + newLine + newLine + 
                    "{1}" + newLine;

replace it with

var propFormat = "--" + boundary + newLine +
                    "Content-Disposition: form-data; name=\"{0}\"" + newLine + newLine + 
                    "{1}" + newLine;

and everything works