The Content-Length header should be the size in bytes

From http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.

lib/savon/soap/request.rb

@@ -40,7 +40,7 @@ def configure(http)
         http.url = soap.endpoint
         http.body = soap.to_xml
         http.headers["Content-Type"] = ContentType[soap.version]
-        http.headers["Content-Length"] = soap.to_xml.length.to_s
+        http.headers["Content-Length"] = soap.to_xml.bytesize.to_s
         http
       end