fix: perform read only if ibuff is empty

If ibuff is not empty we should read messages from the buffer.
Reading messages when the buffer is not empty may lead to deadlock,
for instance, if the frontend send a series of queries and waits backend
response to send other messages, while backend tries to read new
messages.

pgproto/src/stream.rs

@@ -69,12 +69,14 @@ impl<S: io::Read> PgStream<S> {
     /// Receive a new message from client.
     pub fn read_message(&mut self) -> PgWireResult<FeMessage> {
         loop {
-            let cnt = read_into_buf(&mut self.raw, &mut self.ibuf)?;
-            log::debug!("received {cnt} bytes from client");
-            assert!(
-                cnt > 0,
-                "TODO: check if coio wrapper returns 0 or EOF error"
-            );
+            if self.ibuf.is_empty() {
+                let cnt = read_into_buf(&mut self.raw, &mut self.ibuf)?;
+                log::debug!("received {cnt} bytes from client");
+                assert!(
+                    cnt > 0,
+                    "TODO: check if coio wrapper returns 0 or EOF error"
+                );
+            }
 
             if let Some(message) = self.try_decode_message()? {
                 return Ok(message);