Hi list:
This is v1 of the patchset the implementing the feature SSL Dynamic Record Sizing, inspiring by Google Front End (https://www.igvita.com/2013/10/24/optimizing-tls-record-size-and-buffering-latency/) .
There are 3 conditions, if true at the same time, may trigger SSL_write to send small record over the link, hard coded 1400 bytes at this time to keep it fit into MTU size. We just send out 3 of this small record at most to reduce framing overhead when serving large object, that is enough for browser to discovery other dependency of the page at top of html file. If the buffer chain is smaller than 4096 bytes, it will not justify the overhead of sending small record. After idle for 60s(hard coded at this moment), start all over again.


Any comments is welcome.


Regard
YM


hg export tip
# HG changeset patch
# User YM Chen <gzchenym@126.com>
# Date 1430828974 -28800
# Node ID 31bfe6403c340bdc4c04e8e87721736c07bceef8
# Parent 162b2d27d4e1ce45bb9217d6958348c64f726a28
[RFC] event/openssl: Add dynamic record size support for serving ssl trafic

SSL Dynamic Record Sizing is a long sought after feature for website that serving
huge amount of encrypted traffic. The rational behide this is that SSL record should
not overflow the congestion window at the beginning of slow-start period and by doing
so, we can let the browser decode the first ssl record within 1 rtt and establish other
connections to fetch other resources that are referenced at the top of the html file.

diff -r 162b2d27d4e1 -r 31bfe6403c34 src/event/ngx_event_openssl.c
--- a/src/event/ngx_event_openssl.c Wed Apr 29 14:59:02 2015 +0300
+++ b/src/event/ngx_event_openssl.c Tue May 05 20:29:34 2015 +0800
@@ -1508,6 +1508,11 @@
ngx_uint_t flush;
ssize_t send, size;
ngx_buf_t *buf;
+ ngx_msec_t last_sent_timer_diff;
+ ngx_uint_t loop_count;
+
+ last_sent_timer_diff = ngx_current_msec - c->ssl->last_write_msec;
+ loop_count = 0;

if (!c->ssl->buffer) {

@@ -1517,7 +1522,13 @@
continue;
}

- n = ngx_ssl_write(c, in->buf->pos, in->buf->last - in->buf->pos);
+ size = in->buf->last - in->buf->pos;
+
+ if(last_sent_timer_diff > 1000*60 && loop_count < 3 && size > 4096) {
+ size = 1400;
+ }
+
+ n = ngx_ssl_write(c, in->buf->pos, size);

if (n == NGX_ERROR) {
return NGX_CHAIN_ERROR;
@@ -1532,8 +1543,11 @@
if (in->buf->pos == in->buf->last) {
in = in->next;
}
+
+ loop_count ++;
}

+ c->ssl->last_write_msec = ngx_current_msec;
return in;
}

@@ -1614,9 +1628,14 @@
if (size == 0) {
buf->flush = 0;
c->buffered &= ~NGX_SSL_BUFFERED;
+ c->ssl->last_write_msec = ngx_current_msec;
return in;
}

+ if(last_sent_timer_diff > 1000*60 && loop_count < 3 && size > 4096) {
+ size = 1400;
+ }
+
n = ngx_ssl_write(c, buf->pos, size);

if (n == NGX_ERROR) {
@@ -1633,14 +1652,18 @@
break;
}

- flush = 0;
-
- buf->pos = buf->start;
- buf->last = buf->start;
+ if(buf->last == buf->pos) {
+ flush = 0;
+
+ buf->pos = buf->start;
+ buf->last = buf->start;
+ }

if (in == NULL || send == limit) {
break;
}
+
+ loop_count++;
}

buf->flush = flush;
@@ -1652,6 +1675,7 @@
c->buffered &= ~NGX_SSL_BUFFERED;
}

+ c->ssl->last_write_msec = ngx_current_msec;
return in;
}

diff -r 162b2d27d4e1 -r 31bfe6403c34 src/event/ngx_event_openssl.h
--- a/src/event/ngx_event_openssl.h Wed Apr 29 14:59:02 2015 +0300
+++ b/src/event/ngx_event_openssl.h Tue May 05 20:29:34 2015 +0800
@@ -51,6 +51,8 @@
ngx_buf_t *buf;
size_t buffer_size;

+ ngx_msec_t last_write_msec;
+
ngx_connection_handler_pt handler;

ngx_event_handler_pt saved_read_handler;



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