[nginx] gRPC: special handling of "trailer only" responses.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/c2a0a838c40f
branches:  
changeset: 7235:c2a0a838c40f
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Sat Mar 17 23:04:26 2018 +0300
description:
gRPC: special handling of "trailer only" responses.

The gRPC protocol makes a distinction between HEADERS frame with
the END_STREAM flag set, and a HEADERS frame followed by an empty
DATA frame with the END_STREAM flag.  The latter is not permitted,
and results in errors not being propagated through nginx.  Instead,
gRPC clients complain that "server closed the stream without sending
trailers" (seen in grpc-go) or "13: Received RST_STREAM with error
code 2" (seen in grpc-c).

To fix this, nginx now returns HEADERS with the END_STREAM flag if
the response length is known to be 0, and we are not expecting
any trailer headers to be added.  And the response length is
explicitly set to 0 in the gRPC proxy if we see initial HEADERS frame
with the END_STREAM flag set.

diffstat:

 src/http/modules/ngx_http_grpc_module.c |  17 ++++++++++-------
 src/http/v2/ngx_http_v2_filter_module.c |   9 ++++++---
 2 files changed, 16 insertions(+), 10 deletions(-)

diffs (60 lines):

diff --git a/src/http/modules/ngx_http_grpc_module.c b/src/http/modules/ngx_http_grpc_module.c
--- a/src/http/modules/ngx_http_grpc_module.c
+++ b/src/http/modules/ngx_http_grpc_module.c
@@ -1743,13 +1743,16 @@ ngx_http_grpc_process_header(ngx_http_re
                 ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                                "grpc header done");
 
-                if (ctx->end_stream
-                    && ctx->in == NULL
-                    && ctx->out == NULL
-                    && ctx->output_closed
-                    && b->last == b->pos)
-                {
-                    u->keepalive = 1;
+                if (ctx->end_stream) {
+                    u->headers_in.content_length_n = 0;
+
+                    if (ctx->in == NULL
+                        && ctx->out == NULL
+                        && ctx->output_closed
+                        && b->last == b->pos)
+                    {
+                        u->keepalive = 1;
+                    }
                 }
 
                 return NGX_OK;
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
@@ -136,7 +136,7 @@ ngx_http_v2_header_filter(ngx_http_reque
     u_char                     status, *pos, *start, *p, *tmp;
     size_t                     len, tmp_len;
     ngx_str_t                  host, location;
-    ngx_uint_t                 i, port;
+    ngx_uint_t                 i, port, fin;
     ngx_list_part_t           *part;
     ngx_table_elt_t           *header;
     ngx_connection_t          *fc;
@@ -643,7 +643,10 @@ ngx_http_v2_header_filter(ngx_http_reque
                                       header[i].value.len, tmp);
     }
 
-    frame = ngx_http_v2_create_headers_frame(r, start, pos, r->header_only);
+    fin = r->header_only
+          || (r->headers_out.content_length_n == 0 && !r->expect_trailers);
+
+    frame = ngx_http_v2_create_headers_frame(r, start, pos, fin);
     if (frame == NULL) {
         return NGX_ERROR;
     }
@@ -1437,7 +1440,7 @@ ngx_http_v2_send_chain(ngx_connection_t 
         in = in->next;
     }
 
-    if (in == NULL) {
+    if (in == NULL || stream->out_closed) {
 
         if (stream->queued) {
             fc->write->active = 1;