Unable to assemble multipart/form-data request

Question

Hi community!

I'm trying to implement file upload functionality in the iPhone app. Server code is tested and works when files are uploaded from the desktop browser, so I moved to implementing the Objective-C client code. I'm assembling HTTP requests body manually, and despite that it looks correct, it is rejected by the server (server handler unable to extract the parts from multipart content). In desperation I've simplified the form to having only one parameter, but it still does not work.

I've captured the network traffic and I could see that Wireshark could not parse my multipart content as well (have a look at screenshots: Firefox request, iPhone request). I'm pasting it below in hope that you could see the errors I can't see.

Thanks in advance.

Firefox:

POST /cubepaint/actions/gallery/post HTTP/1.1
Host: [...]
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-GB; rv:1.9.1.3) Gecko/20090824 Firefox/3.5.3
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Authorization: Basic [...]
Content-Type: multipart/form-data; boundary=---------------------------20072377098235644401115438165
Content-Length: 180

-----------------------------20072377098235644401115438165
Content-Disposition: form-data; name="deviceId"

12345
-----------------------------20072377098235644401115438165--
HTTP/1.1 200 OK
Date: Sat, 17 Oct 2009 22:09:21 GMT
Server: Apache/2.2.3 (Debian) DAV/2 SVN/1.4.2 mod_python/3.2.10 Python/2.4.4 mod_ssl/2.2.3 OpenSSL/0.9.8c
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8

iPhone:

POST /cubepaint/actions/gallery/post HTTP/1.1
Host: [...]
User-Agent: Copenhagen/1.0 CFNetwork/459 Darwin/9.8.0
Content-Type: multipart/form-data; boundary=----------0E7B16E6-CD3D-4213-9B42-07DA30822C74
Accept: */*
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Authorization: Basic [...]
Content-Length: 187
Connection: keep-alive

----------0E7B16E6-CD3D-4213-9B42-07DA30822C74
Content-Disposition: form-data; name="deviceId"

00000000-0000-1000-8000-0016CBCC0B61
----------0E7B16E6-CD3D-4213-9B42-07DA30822C74--
HTTP/1.1 200 OK
Date: Sat, 17 Oct 2009 22:04:07 GMT
Server: Apache/2.2.3 (Debian) DAV/2 SVN/1.4.2 mod_python/3.2.10 Python/2.4.4 mod_ssl/2.2.3 OpenSSL/0.9.8c
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8

Answer 1

Your iPhone version indicates keep-alive but doesn't specify a length. Not sure that's enough to cause trouble.

Also, is it possible your server is checking for user-agent strings it recognizes (say, for backward-compatibility mode)?

I'd also compare the two in a text editor that shows CR/LF characters to make sure you're getting proper line endings.

Another thing you could try is create a simple web-page that does a multipart POST and run it from the iPhone browser (instead of the Mac one) then check the headers that go across the wire. Or you could snag a toolkit like ASIHTTPRequest and see what kind of output it generates for multi-part posts (or just use the toolkit instead of trying to write your own).

Good luck

Answer 2

Solved by reading RFC 2046 (MIME specification): boundary between parts of multipart message should contain two leading '-'s, and last boundary should additionally contain two trailing '-'s. The boundary in the request header and request body in the Firefox request differ:

---------------------------20072377098235644401115438165

and

-----------------------------20072377098235644401115438165

The last boundary looks like this:

-----------------------------20072377098235644401115438165--

You really could not see this with the eye when there are so many leading '-'s in the original boundary.