Add NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS option

And utilize it in nghttp to limit initial max concurrent streams.

lib/includes/nghttp2/nghttp2.h

@@ -1202,7 +1202,21 @@ typedef enum {
    * is responsible for sending WINDOW_UPDATE with stream ID 0 using
    * `nghttp2_submit_window_update`.
    */
-  NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE = 2
+  NGHTTP2_OPT_NO_AUTO_CONNECTION_WINDOW_UPDATE = 2,
+  /**
+   * This option sets the SETTINGS_MAX_CONCURRENT_STREAMS value of
+   * remote endpoint as if it is received in SETTINGS frame. Without
+   * specifying this option, before the local endpoint receives
+   * SETTINGS_MAX_CONCURRENT_STREAMS in SETTINGS frame from remote
+   * endpoint, SETTINGS_MAX_CONCURRENT_STREAMS is unlimited. This may
+   * cause problem if local endpoint submits lots of requests
+   * initially and sending them at once to the remote peer may lead to
+   * the rejection of some requests. Specifying this option to the
+   * sensible value, say 100, may avoid this kind of issue. This value
+   * will be overwritten if the local endpoint receives
+   * SETTINGS_MAX_CONCURRENT_STREAMS from the remote endpoint.
+   */
+  NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS = 3
 } nghttp2_opt;
 
 /**
@@ -1230,6 +1244,10 @@ typedef enum {
  *     sending WINDOW_UPDATE using
  *     `nghttp2_submit_window_update`. This option defaults to 0.
  *
+ * :enum:`NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS`
+ *     The |optval| must be a pointer to ``ssize_t``. It is an error
+ *     if |*optval| is 0 or negative.
+ *
  * This function returns 0 if it succeeds, or one of the following
  * negative error codes:
  *

lib/nghttp2_session.c

@@ -3264,6 +3264,19 @@ int nghttp2_session_set_option(nghttp2_session *session,
     }
     break;
   }
+  case NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS: {
+    ssize_t sszval;
+    if(optlen != sizeof(ssize_t)) {
+      return NGHTTP2_ERR_INVALID_ARGUMENT;
+    }
+    sszval = *(ssize_t*)optval;
+    if(sszval <= 0) {
+      return NGHTTP2_ERR_INVALID_ARGUMENT;
+    }
+    session->remote_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS] =
+      sszval;
+    break;
+  }
   default:
     return NGHTTP2_ERR_INVALID_ARGUMENT;
   }

src/nghttp.cc

@@ -91,6 +91,7 @@ struct Config {
   std::map<std::string, std::string> headers;
   std::string datafile;
   size_t output_upper_thres;
+  ssize_t peer_max_concurrent_streams;
   Config()
     : null_out(false),
       remote_name(false),
@@ -103,7 +104,8 @@ struct Config {
       multiply(1),
       timeout(-1),
       window_bits(-1),
-      output_upper_thres(1024*1024)
+      output_upper_thres(1024*1024),
+      peer_max_concurrent_streams(NGHTTP2_INITIAL_MAX_CONCURRENT_STREAMS)
   {}
 };
 
@@ -623,6 +625,13 @@ struct HttpClient {
     if(rv != 0) {
       return -1;
     }
+    rv = nghttp2_session_set_option(session,
+                                    NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS,
+                                    &config.peer_max_concurrent_streams,
+                                    sizeof(config.peer_max_concurrent_streams));
+    if(rv != 0) {
+      return -1;
+    }
     if(need_upgrade()) {
       // Adjust stream user-data depending on the existence of upload
       // data
@@ -1471,6 +1480,11 @@ void print_help(std::ostream& out)
       << "    -p, --pri=<PRIORITY>\n"
       << "                       Sets stream priority. Default: "
       << NGHTTP2_PRI_DEFAULT << "\n"
+      << "    --peer-max-concurrent-streams=<N>\n"
+      << "                       Use <N> as SETTINGS_MAX_CONCURRENT_STREAMS\n"
+      << "                       value of remote endpoint as if it is\n"
+      << "                       received in SETTINGS frame. The default\n"
+      << "                       is large enough as it is seen as unlimited.\n"
       << std::endl;
 }
 
@@ -1495,6 +1509,7 @@ int main(int argc, char **argv)
       {"no-flow-control", no_argument, nullptr, 'f'},
       {"upgrade", no_argument, nullptr, 'u'},
       {"pri", required_argument, nullptr, 'p'},
+      {"peer-max-concurrent-streams", required_argument, &flag, 3},
       {nullptr, 0, nullptr, 0 }
     };
     int option_index = 0;
@@ -1602,6 +1617,10 @@ int main(int argc, char **argv)
         // key option
         config.keyfile = optarg;
         break;
+      case 3:
+        // peer-max-concurrent-streams option
+        config.peer_max_concurrent_streams = strtoul(optarg, nullptr, 10);
+        break;
       }
       break;
     default:

tests/nghttp2_session_test.c

@@ -3248,6 +3248,7 @@ void test_nghttp2_session_set_option(void)
   nghttp2_session_callbacks callbacks;
   int intval;
   char charval;
+  ssize_t sszval;
   memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
   nghttp2_session_client_new(&session, &callbacks, NULL);
 
@@ -3288,6 +3289,29 @@ void test_nghttp2_session_set_option(void)
   CU_ASSERT(session->opt_flags &
             NGHTTP2_OPTMASK_NO_AUTO_CONNECTION_WINDOW_UPDATE);
 
+  sszval = 100;
+  CU_ASSERT(0 ==
+            nghttp2_session_set_option
+            (session,
+             NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS,
+             &sszval, sizeof(sszval)));
+  CU_ASSERT(sszval ==
+            session->remote_settings[NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS]);
+
+  sszval = 0;
+  CU_ASSERT(NGHTTP2_ERR_INVALID_ARGUMENT ==
+            nghttp2_session_set_option
+            (session,
+             NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS,
+             &sszval, sizeof(sszval)));
+
+  intval = 100;
+  CU_ASSERT(NGHTTP2_ERR_INVALID_ARGUMENT ==
+            nghttp2_session_set_option
+            (session,
+             NGHTTP2_OPT_PEER_MAX_CONCURRENT_STREAMS,
+             &intval, sizeof(intval)));
+
   nghttp2_session_del(session);
 }