[GitHub] [trafficserver] masaori335 commented on issue #6899: request buffer doesn't work with the new HTTP2 WINDOW_UPDATE sending logic

[GitBox <gi...@apache.org>]

masaori335 commented on issue #6899:
URL: https://github.com/apache/trafficserver/issues/6899#issuecomment-644550392


   ## Summary
   
   After `50441b39e6631389ef95c4133f06bbf94544879c` (#6643) change, if the request buffer feature[*1] is enabled, POST requests (over 65535) on HTTP/2 connection are stalled.
   
   *1 : [proxy.config.http.request_buffer_enabled](https://docs.trafficserver.apache.org/en/latest/admin-guide/files/records.config.en.html#proxy-config-http-request-buffer-enabled)
   
   ## Root cause
   
   ATS sends WINDOW_UPDATE frames only if the buffer is consumed & buffering data is small enough. However, when the request buffer feature is enabled, the buffer is not consumed intentionally.
   
   https://github.com/apache/trafficserver/blob/50441b39e6631389ef95c4133f06bbf94544879c/proxy/http2/Http2ConnectionState.cc#L1303-L1307
   
   ## Workaround Fix
   
   A workaround fix is adjust `proxy.config.http2.initial_window_size_in` to the same value to the `proxy.config.http.post_copy_size`. For example in above, it will be below
   
   ```
   CONFIG proxy.config.http.request_buffer_enabled INT 1
   CONFIG proxy.config.http.post_copy_size INT 1073741824
   CONFIG proxy.config.http2.initial_window_size_in INT 1073741824
   ```
   
   We can use this workaround fix up to buffering 2^31 - 1 (2,147,483,647) bytes, which is the maximum value of HTTP/2 flow-control window size. ( [rfc7540#section-6.5.2](https://tools.ietf.org/html/rfc7540#section-6.5.2) )
   However, we can't apply this on a specific remap, because `proxy.config.http2.initial_window_size_in` is a global config.
   
   ## TODOs
   
   - [ ] Check the feature is enabled on the logic that stops updating window
   - [ ] Add test cases to cover this (#6901)


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