Change nghttp2_session_get_stream_remote_window_size behavior

Now it returns only stream's available remote window size, without
considering connection level window size.  For connection-level window
size, nghttp2_session_get_remote_window_size() is added by this
commit.  To get old behavior of
nghttp2_session_get_stream_remote_window_size() is use
min(nghttp2_session_get_stream_remote_window_size(),
nghttp2_session_get_remote_window_size()).  The reason of this change
is that it is desirable to know just stream level window size without
taking into connection level window size.  This is useful for
debugging purpose.

lib/includes/nghttp2/nghttp2.h

@@ -2152,14 +2152,28 @@ int32_t nghttp2_session_get_effective_local_window_size
  * @function
  *
  * Returns the remote window size for a given stream |stream_id|.
+ *
  * This is the amount of flow-controlled payload (e.g., DATA) that the
- * local endpoint can send without WINDOW_UPDATE.
+ * local endpoint can send without stream level WINDOW_UPDATE.  There
+ * is also connection level flow control, so the effective size of
+ * payload that the local endpoint can actually send is
+ * min(`nghttp2_session_get_stream_remote_window_size()`,
+ * `nghttp2_session_get_remote_window_size()`).
  *
  * This function returns -1 if it fails.
  */
 int32_t nghttp2_session_get_stream_remote_window_size(nghttp2_session* session,
                                                       int32_t stream_id);
 
+/**
+ * @function
+ *
+ * Returns the remote window size for a connection.
+ *
+ * This function always succeeds.
+ */
+int32_t nghttp2_session_get_remote_window_size(nghttp2_session* session);
+
 /**
  * @function
  *

lib/nghttp2_session.c

@@ -5812,8 +5812,8 @@ int32_t nghttp2_session_get_effective_local_window_size
   return session->local_window_size;
 }
 
-int32_t nghttp2_session_get_stream_remote_window_size(nghttp2_session* session,
-                                                      int32_t stream_id)
+int32_t nghttp2_session_get_stream_remote_window_size
+(nghttp2_session *session, int32_t stream_id)
 {
   nghttp2_stream *stream;
 
@@ -5822,7 +5822,14 @@ int32_t nghttp2_session_get_stream_remote_window_size(nghttp2_session* session,
     return -1;
   }
 
-  return (int32_t)nghttp2_session_next_data_read(session, stream);
+  /* stream->remote_window_size can be negative when
+     SETTINGS_INITIAL_WINDOW_SIZE is changed. */
+  return nghttp2_max(0, stream->remote_window_size);
+}
+
+int32_t nghttp2_session_get_remote_window_size(nghttp2_session *session)
+{
+  return session->remote_window_size;
 }
 
 uint32_t nghttp2_session_get_remote_settings(nghttp2_session *session,

src/HttpServer.cc

@@ -1359,8 +1359,9 @@ int hd_on_frame_send_callback
 
     if(frame->hd.flags & NGHTTP2_FLAG_END_STREAM) {
       remove_stream_write_timeout(stream);
-    } else if(nghttp2_session_get_stream_remote_window_size
-              (session, frame->hd.stream_id) == 0) {
+    } else if(std::min(nghttp2_session_get_stream_remote_window_size
+                       (session, frame->hd.stream_id),
+                       nghttp2_session_get_remote_window_size(session)) <= 0) {
       // If stream is blocked by flow control, enable write timeout.
       add_stream_read_timeout_if_pending(stream);
       add_stream_write_timeout(stream);

tests/nghttp2_session_test.c

@@ -2201,6 +2201,13 @@ void test_nghttp2_session_on_settings_received(void)
   CU_ASSERT(16*1024 == stream1->remote_window_size);
   CU_ASSERT(-48*1024 == stream2->remote_window_size);
 
+  CU_ASSERT(16*1024 ==
+            nghttp2_session_get_stream_remote_window_size(session,
+                                                          stream1->stream_id));
+  CU_ASSERT(0 ==
+            nghttp2_session_get_stream_remote_window_size(session,
+                                                          stream2->stream_id));
+
   nghttp2_frame_settings_free(&frame.settings);
 
   nghttp2_session_del(session);