DirectStreamWriter's performance with chunked encoding

I’m using SS 4.5.8, self-hosted with AppSelfHostBase.

It looks like ServiceStack.Text’s DirectStreamWriter has a detrimental effect on both performance and response size. This is because frequent flushing of the stream causes many more chunks to be written to the HTTP response using Transfer-Encoding: chunked. Previously, responses were written in chunks of 1024 bytes, the default buffer size for StreamWriter. HTTP responses now look like this:


One of my heavier responses went from 181,715 bytes in 0.248 seconds to 522,338 bytes in 1.433 seconds.

This can be mitigated by using [CompressResponse] (which is awesome, thank you!!!) on all services. CompressResponseAttribute serializes the response DTO to a string before compressing it, so chunked encoding isn’t used since a Content-Length is known. One downside to [CompressResponse] in 4.5.8 is that all exceptions are returned as HTTP 200s instead of 4xx/5xx after being compressed. In the source in master it looks like they will be excluded from compression which means that a large serialized exception would still suffer from this problem. Also, some people may upgrade and not enable response compression.

I’m not sure what the best solution is here:

  • keep JsonSerializer.SerializeToStream using DirectStreamWriter, but add an overload that accepts a buffer size and uses StreamWriter, then reference that method from ContentTypes.GetStreamSerializer?
  • have ContentTypes.GetStreamSerializer wrap the stream parameter ‘s’ in a BufferStream before passing to JsonSerializer.SerializeToStream?
  • something else?

Can you show an example, when you get different size of response messages? DirectStreamWriter should not increase the final size of the message, it was created to serialize only small messages faster without allocating 1024 bytes buffer by default as StreamWriter uses for every serialization and it should not affect on large responses.

Thanks for the quick response! Here is a very simple solution that reproduces what I’m seeing between 4.5.6 and 4.5.8:

HttpWebRequest will automatically decode chunked responses, but the command line apps should at least demonstrate the difference in response times. If you launch Fiddler you should be able to see the difference in response body sizes (I’m seeing 6k vs 26k).

Please let me know if there’s anything else you need to see.

Yes, I see this behavior in your sample.