added Content-Length header population to Common downloader middleware

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40754

scrapy/trunk/docs/ref/downloader-middleware.rst

@@ -34,6 +34,9 @@ thus it's recommended to leave it always enabled. Those tasks are:
     * If the request method is ``POST`` and the ``Content-Type`` header is not
       set, then set it to ``'application/x-www-form-urlencoded'``, the `default
       Form content type`_.
+
+    * If the request contains a body and the ``Content-Length`` headers it not
+      set, then set it to the ``len(body)``.
     
 .. _default Form content type: http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.1
 

scrapy/trunk/scrapy/contrib/downloadermiddleware/common.py

@@ -17,4 +17,6 @@ class CommonMiddleware(object):
         request.headers.setdefault('Accept-Language', self.header_accept_language)
         if request.method == 'POST':
             request.headers.setdefault('Content-Type', 'application/x-www-form-urlencoded')
+            if request.body:
+                request.headers.setdefault('Content-Length', '%d' % len(request.body))