Data frame size sent by server

[Valentin V. Bartenev]

On Sunday 18 October 2015 16:02:04 Muhui Jiang wrote:
> Hi
> 
> I made a request to nginx 1.9.5 for a large file. Here is a part of debug
> file:
> 
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 9
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 9
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 8174
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL to write: 16384
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL_write: 16384
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 18
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 9
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 9
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 8156
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL to write: 16384
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL_write: 16384
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 36
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 9
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL buf copy: 8182
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL to write: 8227
> 2015/10/18 15:55:34 [debug] 10707#0: *116 SSL_write: 8227
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2:1 DATA frame
> 00007F942205F7A0 was sent
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205F7A0 sid:1 bl:0 len:8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2:1 DATA frame
> 00007F942205F8A8 was sent
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205F8A8 sid:1 bl:0 len:8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2:1 DATA frame
> 00007F942205F9B0 was sent
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205F9B0 sid:1 bl:0 len:8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2:1 DATA frame
> 00007F942205FAB8 was sent
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205FAB8 sid:1 bl:0 len:8192
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2:1 DATA frame
> 00007F942205FBC0 was sent
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205FBC0 sid:1 bl:0 len:8182
> 
> It seems that the default max frame size is 8192. But I don't under stand
> the buffer mechanism. I marked them in red color. why there is a very small
> buffer 9, and why some value is 8174, 8156.

You shouldn't care about these numbers as long as they are related to nginx
internal buffers.

9 is a buffer used for HTTP/2 header of the DATA frame (the header is always
9 bytes long).

8174 is the rest in the SSL buffer (see the ssl_buffer_size directive) after
coping two DATA headers and 8k of one DATA frame.

So the rest 18 bytes of DATA frame will be sent in the next TLS record.


> 
> BTW: what is the 116 means in the beginning of every row as below:
> 2015/10/18 15:55:34 [debug] 10707#0: *116 http2 frame sent:
> 00007F942205FBC0 sid:1 bl:0 len:8182

It is a connection identificator for the worker process.

  wbr, Valentin V. Bartenev