Thursday, April 28, 2011

Reading AJAX XHR File Uploads in Sinatra

So in my last post I talked about Drag and Drop file uploading with qq.FileUploader (http://valums.com/ajax-upload/).

Anyways, I discovered that qq.FileUploader uses AJAX/XHR to post the file uploads. What I also discovered is that these file uploads need to be handled in a separate manner from a regular file upload form post.

A normal form post (when File upload XHR requests are not available on the client like in Internet Explorer) passes in the following parameters


params: {"qqfile"=>{:type=>"image/png", :head=>"Content-Disposition: form-data; name=\"qqfile\"; filename=\"bb2.png\"\r\nContent-Type: image/png\r\n", :tempfile=>#, :name=>"qqfile", :filename=>"bb2.png"}, "upload_type"=>"rec", "id"=>"24db8cab-285a-abcb-cb47-4daceee977ca"}

Sinatra then reads the :tempfile and :filename parameters to write the file to the server


name = params[:qqfile][:filename]

# create the file path
path = File.join(directory, name)
# write the file
File.open(path, "wb") { |f| f.write(params[:qqfile][:tempfile].read) }


However, if you use a browser that supports XHR uploads, the parameters look a little different


params: {"qqfile"=>"device1.jpg", "upload_type"=>"invoice", "id"=>"24db8cab-285a-abcb-cb47-4daceee977ca"}

So this had me stumped. There was an article I found on the internets (http://onehub.com/blog/posts/designing-an-html5-drag-drop-file-uploader-using-sinatra-and-jquery-part-1/) which talked extensively on how to do the JavaScript side but then at the bottom conveniently left out how to handle the server side (saying it was easy to work out). Well, it wasn't! So that's why I am writing this post

In any case, I won't keep you in suspense any longer...


name = env['HTTP_X_FILENAME']

string_io = request.body # will return a StringIO

data_bytes = string_io.read # read the stream as bytes

# create the file path
path = File.join(directory, name)

# Write it to disk...
File.open(path, 'w') {|f| f.write(data_bytes) }


The final part is that qq.FileUploader does not give you the option to specify which action to post to depending on the type of upload (XHR vs normal) so I had to put in a fork in the server code to figure out how to handle the request. I am basically checking to see if qqfile is of type String, in which case I handle it as an XHR upload, otherwise I handle it as a normal file upload.


# if qqfile is a string, we are using XHR upload, else use regular upload
if params[:qqfile].class == String
name = params[:qqfile]

string_io = request.body # will return a StringIO

data_bytes = string_io.read # read the stream as bytes

# create the file path
path = File.join(directory, name)

# Write it to disk...
File.open(path, 'w') {|f| f.write(data_bytes) }
else #regular file upload
name = params[:qqfile][:filename]

# create the file path
path = File.join(directory, name)
# write the file
File.open(path, "wb") { |f| f.write(params[:qqfile][:tempfile].read) }
end


I haven't tried it in Rails yet, but I am sure it will be similar. I hope this helps...

3 comments:

Ted said...

Hi, I'm new on Sinatra and Ruby and I don't understand how to use your tutorial. which method? post? put? Can you show your ".rb" complete file?

Ted said...

From my webkit console

"Request URL:http://MYURL/upload?qqfile=file.jpg
Request method:POST
Status:500 Internal Server Error
Intestazioni di richiesta
Content-Length:52446
Content-Type:application/octet-stream
Origin: http://MYURL
Referer:http://MYURL/upload
User-Agent:Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_6_7; it-it) AppleWebKit/533.21.1 (KHTML, like Gecko) Version/5.0.5 Safari/533.21.1
X-File-Name:file.jpg
X-Requested-With:XMLHttpRequest"

entropie said...

Thanks a lot, that request.body was what i missed. Works also for any rack apps like ramaze.