renaming helper and add some descriptions

Author: TingDaoK

source/s3_meta_request.c

@@ -1985,14 +1985,17 @@ static struct aws_s3_request_metrics *s_s3_request_finish_up_and_release_metrics
     return NULL;
 }
 
-static bool s_apply_backpressure(struct aws_s3_request *request) {
+static bool s_should_apply_backpressure(struct aws_s3_request *request) {
     struct aws_s3_meta_request *meta_request = request->meta_request;
-    if (!meta_request->body_callback) {
+    if (!meta_request->client->enable_read_backpressure) {
+        /* Backpressure is disabled. */
         return false;
     }
-    if (!meta_request->client->enable_read_backpressure) {
+    if (!meta_request->body_callback) {
+        /* No callback to deliver the body, don't apply backpressure */
         return false;
     }
+    /* Apply backpressure only for GetObject request */
     if (meta_request->type == AWS_S3_META_REQUEST_TYPE_GET_OBJECT) {
         return true;
     }
@@ -2076,7 +2079,7 @@ static void s_s3_meta_request_event_delivery_task(struct aws_task *task, void *a
                     break;
                 }
 
-                if (s_apply_backpressure(request)) {
+                if (s_should_apply_backpressure(request)) {
                     /* Apply backpressure for the request, only deliver the bytes that allowed to deliver. */
                     aws_byte_cursor_advance(&response_body, bytes_delivered_for_request);
                     if (response_body.len > (size_t)bytes_allowed_to_deliver) {