Fix validation, stream window update edge triggering

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

@@ -385,14 +385,12 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
     grpc_chttp2_initiate_write(exec_ctx, t, false, "flow_control");
   }
 
-  if (s != NULL) {
   if (incoming_frame_size >
       s->incoming_window_delta +
           t->settings[GRPC_ACKED_SETTINGS]
                      [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE]) {
     char *msg;
-      gpr_asprintf(&msg,
+    gpr_asprintf(&msg, "frame of size %d overflows incoming window of %" PRId64,
-                   "frame of size %d overflows incoming window of %" PRId64,
                  t->incoming_frame_size,
                  s->incoming_window_delta +
                      t->settings[GRPC_ACKED_SETTINGS]
@@ -402,8 +400,13 @@ static grpc_error *update_incoming_window(grpc_exec_ctx *exec_ctx,
     return err;
   }
 
+  if (s != NULL) {
     GRPC_CHTTP2_FLOW_DEBIT_STREAM("parse", t, s, incoming_window_delta,
                                   incoming_frame_size);
+    if (s->incoming_window_delta < -target_incoming_window / 2) {
+      grpc_chttp2_become_writable(exec_ctx, t, s, false,
+                                  "window-update-required");
+    }
     s->received_bytes += incoming_frame_size;
   }