gRPC: improved keepalive handling.

The code is now able to parse additional control frames after
the response is received, and can send control frames as well.
This fixes keepalive problems as observed with grpc-c, which can
send window update and ping frames after the response, see
http://mailman.nginx.org/pipermail/nginx/2018-August/056620.html.

src/http/modules/ngx_http_grpc_module.c

@@ -111,6 +111,7 @@ typedef struct {
     unsigned                   output_closed:1;
     unsigned                   parsing_headers:1;
     unsigned                   end_stream:1;
+    unsigned                   done:1;
     unsigned                   status:1;
 
     ngx_http_request_t        *request;
@@ -1074,6 +1075,7 @@ ngx_http_grpc_reinit_request(ngx_http_request_t *r)
     ctx->output_closed = 0;
     ctx->parsing_headers = 0;
     ctx->end_stream = 0;
+    ctx->done = 0;
     ctx->status = 0;
     ctx->connection = NULL;
 
@@ -1093,6 +1095,7 @@ ngx_http_grpc_body_output_filter(void *data, ngx_chain_t *in)
     ngx_int_t               rc;
     ngx_uint_t              next, last;
     ngx_chain_t            *cl, *out, **ll;
+    ngx_http_upstream_t    *u;
     ngx_http_grpc_ctx_t    *ctx;
     ngx_http_grpc_frame_t  *f;
 
@@ -1407,6 +1410,28 @@ ngx_http_grpc_body_output_filter(void *data, ngx_chain_t *in)
         rc = NGX_AGAIN;
     }
 
+    if (ctx->done) {
+
+        /*
+         * We have already got the response and were sending some additional
+         * control frames.  Even if there is still something unsent, stop
+         * here anyway.
+         */
+
+        u = r->upstream;
+        u->length = 0;
+
+        if (ctx->in == NULL
+            && ctx->out == NULL
+            && ctx->output_closed
+            && ctx->state == ngx_http_grpc_st_start)
+        {
+            u->keepalive = 1;
+        }
+
+        ngx_post_event(u->peer.connection->read, &ngx_posted_events);
+    }
+
     return rc;
 }
 
@@ -1832,6 +1857,33 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
             rc = ngx_http_grpc_parse_frame(r, ctx, b);
 
             if (rc == NGX_AGAIN) {
+
+                if (ctx->done) {
+
+                    /*
+                     * We have finished parsing the response and the
+                     * remaining control frames.  If there are unsent
+                     * control frames, post a write event to send them.
+                     */
+
+                    if (ctx->out) {
+                        ngx_post_event(u->peer.connection->write,
+                                       &ngx_posted_events);
+                        return NGX_AGAIN;
+                    }
+
+                    u->length = 0;
+
+                    if (ctx->in == NULL
+                        && ctx->output_closed
+                        && ctx->state == ngx_http_grpc_st_start)
+                    {
+                        u->keepalive = 1;
+                    }
+
+                    break;
+                }
+
                 return NGX_AGAIN;
             }
 
@@ -1898,6 +1950,13 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
                 return NGX_ERROR;
             }
 
+            if (ctx->stream_id && ctx->done) {
+                ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                              "upstream sent frame for closed stream %ui",
+                              ctx->stream_id);
+                return NGX_ERROR;
+            }
+
             ctx->padding = 0;
         }
 
@@ -1914,17 +1973,7 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
             ctx->state = ngx_http_grpc_st_start;
 
             if (ctx->flags & NGX_HTTP_V2_END_STREAM_FLAG) {
-                u->length = 0;
+                ctx->done = 1;
-
-                if (ctx->in == NULL
-                    && ctx->out == NULL
-                    && ctx->output_closed
-                    && b->last == b->pos)
-                {
-                    u->keepalive = 1;
-                }
-
-                break;
             }
 
             continue;
@@ -2094,17 +2143,8 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
                                    "grpc trailer done");
 
                     if (ctx->end_stream) {
-                        u->length = 0;
+                        ctx->done = 1;
-
+                        break;
-                        if (ctx->in == NULL
-                            && ctx->out == NULL
-                            && ctx->output_closed
-                            && b->last == b->pos)
-                        {
-                            u->keepalive = 1;
-                        }
-
-                        return NGX_OK;
                     }
 
                     ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
@@ -2121,6 +2161,10 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
                 return NGX_ERROR;
             }
 
+            if (rc == NGX_HTTP_PARSE_HEADER_DONE) {
+                continue;
+            }
+
             /* rc == NGX_AGAIN */
 
             if (ctx->rest == 0) {
@@ -2237,17 +2281,7 @@ ngx_http_grpc_filter(void *data, ssize_t bytes)
         ctx->state = ngx_http_grpc_st_start;
 
         if (ctx->flags & NGX_HTTP_V2_END_STREAM_FLAG) {
-            u->length = 0;
+            ctx->done = 1;
-
-            if (ctx->in == NULL
-                && ctx->out == NULL
-                && ctx->output_closed
-                && b->last == b->pos)
-            {
-                u->keepalive = 1;
-            }
-
-            break;
         }
     }