Microsoft Translator API answers 500 internal server error

I'm trying to use Microsoft's Translator API in my Rails app. Unfortunately and mostly unexpected, the server answers always with an internal server error. I also tried it manually with Poster[1] and I get the same results.

In more detail, what am I doing? I'm creating an XML string which goes into the body of the request. I used the C# Example of the API documentation. Well, and then I'm just invoking the RESTservice. My code looks like this:

xmlns1 = "http://schemas.datacontract.org/2004/07/Microsoft.MT.Web.Service.V2"
xmlns2 = "http://schemas.microsoft.com/2003/10/Serialization/Arrays"

xml_builder = Nokogiri::XML::Builder.new(:encoding => 'UTF-8') do |xml|
  xml.TranslateArrayRequest("xmlns:ms" => xmlns1, "xmlns:arr" => xmlns2) {
     xml.AppId token  #using temporary token instead of appId
     xml.From  source
     xml.To    target

     xml.Options {
       xml["ms"].ContentType {
         xml.text "text/html"
       }
     }

     xml.Texts {
       translate.each do |key,val|
          xml["arr"].string {
            xml.text CGI::unescape(val)
          }
       end
     }
   }
end

headers = {
   'Content-Type' => 'text/xml'
}

uri = URI.parse(@@msTranslatorBase + "/TranslateArray" + "?appId=" + token) 
req = Net::HTTP::Post.new(uri.path, headers)
req.body = xml_builder.to_xml

response = Net::HTTP.start(uri.host, uri.port) { |http| http.request(req) }
# [...]

The xml_builder produces something like the following XML. Differently to the example from the API page, I'm defining two namespaces instead of referencing them on the certain tags (mainly because I wanted to reduces the overhead) -- but this doesn't seem to be a problem, when I do it like the docu-example I also get an internal server error.

<?xml version="1.0" encoding="UTF-8"?>
<TranslateArrayRequest xmlns:ms="http://schemas.datacontract.org/2004/07/Microsoft.MT.Web.Service.V2" xmlns:arr="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
  <AppId>TX83NVx0MmIxxCzHjPwo2_HgYN7lmWIBqyjruYm7YzCpwnkZL5wtS5oucxqlEFKw9</AppId>
  <From>de</From>
  <To>en</To>
  <Options>
    <ms:ContentType>text/html</ms:ContentType>
  </Options>
  <Texts>
    <arr:string>Bitte übersetze diesen Text.</arr:string>
    <arr:string>Das hier muss auch noch übersetzt werden.</arr:string>
  </Texts>
</TranslateArrayRequest>

Every time I request the service it answers with

#<Net::HTTPInternalServerError 500 The server encountered an error processing the request. Please see the server logs for more details.>

... except I do some unspecified things, like using GET instead of POST, then it answers with something like "method not allowed".

I thought it might be something wrong with the XML stuff, because I can request an AppIdToken and invoke the 开发者_运维问答Translate method without problems. But to me, the XML looks just fine. The documentation states that there is a schema for the expected XML:

The request body is a xml string generated according to the schema specified at http:// api.microsofttranslator.com/v2/Http.svc/help

Unfortunately, I cannot find anything on that.

So now my question(s): Am I doing something wrong? Maybe someone experienced similar situations and can report on solutions or work-arounds?

[1] Poster FF plugin > addons.mozilla.org/en-US/firefox/addon/poster/

Well, after lot's of trial-and-error I think I made it. So in case someone has similar problems, here is how I fixed this:

Apparently, the API is kind of fussy with the incoming XML. But since there is no schema (or at least I couldn't find the one specified in the documentation) it's kind of hard to do it the right way: the ordering of the tags is crucial!

<TranslateArrayRequest>
  <AppId/>
  <From/>
  <Options />
  <Texts/>
  <To/>
</TranslateArrayRequest>

When the XML has this ordering it works. Otherwise you'll only see the useless internal server error response. Furthermore, I read a couple of times that the API also breaks if the XML contains improper UTF-8. One can force untrusted UTF-8 (e.g. coming from a user form) this way:

ic = Iconv.new('UTF-8//IGNORE', 'UTF-8')
valid_string = ic.iconv(untrusted_string + ' ')[0..-2]