Add comment on cancellation

src/message.rs

@@ -499,6 +499,11 @@ impl RespEnc {
 		let msg_len = reader.read_u32().await?;
 		let msg = reader.read_exact(msg_len as usize).await?;
 
+		// Check whether the response stream still has data or not.
+		// If no more data is coming, this will defuse the request canceller.
+		// If we didn't do this, and the client doesn't try to read from the stream,
+		// the request canceller doesn't know that we read everything and
+		// sends a cancellation message to the server (which they don't care about).
 		reader.fill_buffer().await;
 
 		Ok(Self {