io: expose underlying codec (#686)

tokio-io/src/_tokio_codec/framed.rs

@@ -97,6 +97,24 @@ impl<T, U> Framed<T, U> {
         &mut self.inner.get_mut().get_mut().0
     }
 
+    /// Returns a reference to the underlying codec wrapped by
+    /// `Frame`.
+    ///
+    /// Note that care should be taken to not tamper with the underlying codec
+    /// as it may corrupt the stream of frames otherwise being worked with.
+    pub fn codec(&self) -> &U {
+        &self.inner.get_ref().get_ref().1
+    }
+
+    /// Returns a mutable reference to the underlying codec wrapped by
+    /// `Frame`.
+    ///
+    /// Note that care should be taken to not tamper with the underlying codec
+    /// as it may corrupt the stream of frames otherwise being worked with.
+    pub fn codec_mut(&mut self) -> &mut U {
+        &mut self.inner.get_mut().get_mut().1
+    }
+
     /// Consumes the `Frame`, returning its underlying I/O stream.
     ///
     /// Note that care should be taken to not tamper with the underlying stream