Fix severe performance issue by POSTing data as application/octet-stream

This depends on wendelin!28.

/reviewed-on !1

lib/fluent/plugin/wendelin_client.rb

@@ -41,11 +41,11 @@ class WendelinClient
         req.basic_auth @credentials['user'], @credentials['password']
       end
 
-      # TODO ensure content-type is 'raw', e.g. this way
-      # (but then querystring ?reference=... is lost)
-      # req.body = data_chunk
-      # req.content_type = 'application/octet-stream'
-      req.set_form_data('data_chunk' => data_chunk)
+      # When using 'application/x-www-form-urlencoded', Ruby encodes with regex
+      # and it is far too slow. Such POST is legit:
+      # https://stackoverflow.com/a/14710450
+      req.body = data_chunk
+      req.content_type = 'application/octet-stream'
 
       @log.on_trace do
           @log.trace '>>> REQUEST'