how to save a image from js client to blobstore?

Question

I want to save a image from my browser into google blobstore. What I already tried: Transform my img into a base64 string:

reader = new FileReader();
reader.readAsBinaryString(file);

call my Endpoint Function to send it to google app engine.

var request = gapi.client.helloworldendpoints.uploadImage({'imageData': __upload.imageData, 'fileName': __upload.fileName, 'mimeType': __upload.mimeType, 'size': __upload.size});
    request.execute(
            function (result) {
                console.log("Callback:");
                console.log(result);
            }
    );

My EndPoint in Java looks like this:

 @ApiMethod(name = "uploadImage", path = "/uploadImage", httpMethod = "POST")
public ImageUploadRequest uploadImage(@Named("imageData") byte[] imageData, @Named("fileName") String fileName, @Named("mimeType") String mimeType, @Named("size") float size) { 

return new ImageUploadRequest(imageData, fileName, mimeType, size);
}

The problem is, that my endpoint seems to be unable to handle the transfer of my base64. i always get 503 backend error

What would be the best way to send the data from my js client via app engine to blobstore?

Answer 1

UPDATE The main Problem is solved. I managed to upload the blob.

Javascript

var request = gapi.client.helloworldendpoints.uploadImage({
    'imageData': __upload.imageData, 
    'fileName': __upload.fileName, 
    'mimeType': __upload.mimeType, 
    'size': __upload.size
});

Java Endpoint

public ImageUploadRequest uploadImage(
    Request imageData, 
    @Named("fileName") String fileName, 
    @Named("mimeType") String mimeType, 
    @Named("size") float size
) { ... }

Request is just this

public class Request {
      public Blob image;
}

My next Problem is the following How can i send a MultipartRequest from my Java Endpoint at GAE to my UploadServlet to create a blobkey and save the data into blobstorage, since Blobstorage only accepts data send to servlet?