Merge pull request #10073 from ctiller/be_permissive

Verbosely log flow control failures due to buggy implementations

src/core/ext/transport/chttp2/transport/parsing.c

@@ -381,16 +381,38 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
         s->incoming_window_delta +
             t->settings[GRPC_ACKED_SETTINGS]
                        [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]) {
-      char *msg;
-      gpr_asprintf(&msg,
-                   "frame of size %d overflows incoming window of %" PRId64,
-                   t->incoming_frame_size,
-                   s->incoming_window_delta +
-                       t->settings[GRPC_ACKED_SETTINGS]
-                                  [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
-      grpc_error *err = GRPC_ERROR_CREATE(msg);
-      gpr_free(msg);
-      return err;
+      if (incoming_frame_size <=
+          s->incoming_window_delta +
+              t->settings[GRPC_SENT_SETTINGS]
+                         [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]) {
+        gpr_log(
+            GPR_ERROR,
+            "Incoming frame of size %d exceeds incoming window size of %" PRId64
+            ".\n"
+            "The (un-acked, future) window size would be %" PRId64
+            " which is not exceeded.\n"
+            "This would usually cause a disconnection, but allowing it due to "
+            "broken HTTP2 implementations in the wild.\n"
+            "See (for example) https://github.com/netty/netty/issues/6520.",
+            t->incoming_frame_size,
+            s->incoming_window_delta +
+                t->settings[GRPC_ACKED_SETTINGS]
+                           [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
+            s->incoming_window_delta +
+                t->settings[GRPC_SENT_SETTINGS]
+                           [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
+      } else {
+        char *msg;
+        gpr_asprintf(&msg,
+                     "frame of size %d overflows incoming window of %" PRId64,
+                     t->incoming_frame_size,
+                     s->incoming_window_delta +
+                         t->settings[GRPC_ACKED_SETTINGS]
+                                    [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]);
+        grpc_error *err = GRPC_ERROR_CREATE(msg);
+        gpr_free(msg);
+        return err;
+      }
     }
 
     GRPC_CHTTP2_FLOW_DEBIT_STREAM_INCOMING_WINDOW_DELTA("parse", t, s,