[nginx] HTTP/2: signal 0-byte HPACK's dynamic table size.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/12cadc4669a7
branches:  
changeset: 7100:12cadc4669a7
user:      Piotr Sikora <piotrsikora at google.com>
date:      Wed Aug 30 14:52:11 2017 -0700
description:
HTTP/2: signal 0-byte HPACK's dynamic table size.

This change lets NGINX talk to clients with SETTINGS_HEADER_TABLE_SIZE
smaller than the default 4KB. Previously, NGINX would ACK the SETTINGS
frame with a small dynamic table size, but it would never send dynamic
table size update, leading to a connection-level COMPRESSION_ERROR.

Also, it allows clients to release 4KB of memory per connection, since
NGINX doesn't use HPACK's dynamic table when encoding headers, however
clients had to maintain it, since NGINX never signaled that it doesn't
use it.

Signed-off-by: Piotr Sikora <piotrsikora at google.com>

diffstat:

 src/http/v2/ngx_http_v2.c               |   2 ++
 src/http/v2/ngx_http_v2.h               |   1 +
 src/http/v2/ngx_http_v2_filter_module.c |  14 +++++++++++++-
 3 files changed, 16 insertions(+), 1 deletions(-)

diffs (61 lines):

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -245,6 +245,8 @@ ngx_http_v2_init(ngx_event_t *rev)
 
     h2c->frame_size = NGX_HTTP_V2_DEFAULT_FRAME_SIZE;
 
+    h2c->table_update = 1;
+
     h2scf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_v2_module);
 
     h2c->pool = ngx_create_pool(h2scf->pool_size, h2c->connection->log);
diff --git a/src/http/v2/ngx_http_v2.h b/src/http/v2/ngx_http_v2.h
--- a/src/http/v2/ngx_http_v2.h
+++ b/src/http/v2/ngx_http_v2.h
@@ -144,6 +144,7 @@ struct ngx_http_v2_connection_s {
 
     unsigned                         closed_nodes:8;
     unsigned                         settings_ack:1;
+    unsigned                         table_update:1;
     unsigned                         blocked:1;
     unsigned                         goaway:1;
 };
diff --git a/src/http/v2/ngx_http_v2_filter_module.c b/src/http/v2/ngx_http_v2_filter_module.c
--- a/src/http/v2/ngx_http_v2_filter_module.c
+++ b/src/http/v2/ngx_http_v2_filter_module.c
@@ -139,6 +139,7 @@ ngx_http_v2_header_filter(ngx_http_reque
     ngx_connection_t          *fc;
     ngx_http_cleanup_t        *cln;
     ngx_http_v2_out_frame_t   *frame;
+    ngx_http_v2_connection_t  *h2c;
     ngx_http_core_loc_conf_t  *clcf;
     ngx_http_core_srv_conf_t  *cscf;
     u_char                     addr[NGX_SOCKADDR_STRLEN];
@@ -235,7 +236,11 @@ ngx_http_v2_header_filter(ngx_http_reque
         }
     }
 
-    len = status ? 1 : 1 + ngx_http_v2_literal_size("418");
+    h2c = r->stream->connection;
+
+    len = h2c->table_update ? 1 : 0;
+
+    len += status ? 1 : 1 + ngx_http_v2_literal_size("418");
 
     clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
 
@@ -423,6 +428,13 @@ ngx_http_v2_header_filter(ngx_http_reque
 
     start = pos;
 
+    if (h2c->table_update) {
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, fc->log, 0,
+                       "http2 table size update: 0");
+        *pos++ = (1 << 5) | 0;
+        h2c->table_update = 0;
+    }
+
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, fc->log, 0,
                    "http2 output header: \":status: %03ui\"",
                    r->headers_out.status);