Question

I simply want to upload an image to a server with POST. As simple as this task sounds, there seems to be no simple solution in Ruby.

In my application I am using WWW::Mechanize for most things so I wanted to use it for this too, and had a source like this:

f = File.new(filename, File::RDWR)
reply = agent.post(
    'http://rest-test.heroku.com',
    {
         :pict       =>  f,
         :function   =>  'picture2',
         :username   =>  @username,
         :password   =>  @password,
         :pict_to    =>  0,
         :pict_type  =>  0
    }
)
f.close

This results in a totally garbage-ready file on the server that looks scrambled all over:

alt text http://imagehub.org/f/1tk8/garbage.png

My next step was to downgrade WWW::Mechanize to version 0.8.5. This worked until I tried to run it, which failed with an error like “Module not found in hpricot_scan.so”. Using the Dependency Walker tool I could find out that hpricot_scan.so needed msvcrt-ruby18.dll. Yet after I put that .dll into my Ruby/bin-folder it gave me an empty error box from where on I couldn’t debug very much further. So the problem here is that Mechanize 0.8.5 has a dependency on Hpricot instead of Nokogiri (which works flawlessly).

---

The next idea was to use a different gem, so I tried using Net::HTTP. After short research I could find out that there is no native support for multipart forms in Net::HTTP and instead you have to build a class that encodes etc. for you. The most helpful I could find was the Multipart-class by Stanislav Vitvitskiy. This class looked good so far, but it does not do what I need, because I don’t want to post only files, I also want to post normal data, and that is not possible with his class.

---

My last attempt was to use RestClient. This looked promising, as there have been examples on how to upload files. Yet I can’t get it to post the form as multipart.

f = File.new(filename, File::RDWR)
reply = RestClient.post(
    'http://rest-test.heroku.com',
    :pict       =>  f,
    :function   =>  'picture2',
    :username   =>  @username,
    :password   =>  @password,
    :pict_to    =>  0,
    :pict_type  =>  0
)
f.close

I am using http://rest-test.heroku.com which sends back the request to debug if it is sent correctly, and I always get this back:

POST http://rest-test.heroku.com/ with a 101 byte payload,
content type application/x-www-form-urlencoded
{
    "pict" => "#<File:0x30d30c4>",
    "username" => "s1kx",
    "pict_to" => "0",
    "function" => "picture2",
    "pict_type" => "0",
    "password" => "password"
}

This clearly shows that it does not use multipart/form-data as content-type but the standard application/x-www-form-urlencoded, although it definitely sees that pict is a file.

---

How can I upload a file in Ruby to a multipart form without implementing the whole encoding and data aligning myself?

Answer 1

Long problem, short answer: I was missing the binary mode for reading the image under Windows.

f = File.new(filename, File::RDWR)

had to be

f = File.new(filename, "rb")