How to encode a file from the file system as multipart/form-data?

Question

I want to let users upload photos to Facebook in my image viewer app. As seen in this post, Facebook Graph API - upload photo using JavaScript, I have to encode my photos as multipart/form-data to be able to upload them. How to archive this encoding on Windows.Storage.StorageFile items?

Answer 1

You need to open that photo (of type Windows.Storage.StorageFile) for reading, convert it's stream to blob, append it to FormData object and upload using whatever Ajax library you want (WinJS.xhr, jQuery.ajax etc).

Following code illustrates it better than words:

file.openReadAsync().done(function(fileStream) {                
   var fileData = MSApp.createBlobFromRandomAccessStream(file.contentType, fileStream);
   var formData = new FormData();
   formData.append('upload', fileData, file.name);

   ... // send formData as xhr request body
});