https://github.com/hyperium/http-body/pull/90

src/lib.rs

@@ -58,6 +58,20 @@ pub trait Body {
         cx: &mut Context<'_>,
     ) -> Poll<Option<Result<Self::Data, Self::Error>>>;
 
+    /// Attempt to progress the body's state without pulling a new frame.
+    ///
+    /// `Body` consumers can use this method to allow the `Body` implementation to continue to
+    /// perform work even when the consumer is not yet ready to read the next frame.  For example,
+    /// a `Body` implementation could maintain a timer counting down between `poll_data` calls and
+    /// report an error from `poll_progress` when time expires.
+    ///
+    /// Consumers are *not* required to call this method. A `Body` implementation should not depend
+    /// on calls to `poll_progress` to occur.
+    fn poll_progress(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        let _ = cx;
+        Poll::Ready(Ok(()))
+    }
+
     /// Poll for an optional **single** `HeaderMap` of trailers.
     ///
     /// This function should only be called once `poll_data` returns `None`.