test(proto): Never allow constructing empty packets

Author: matheus23

noq-proto/src/connection/mod.rs

@@ -7432,6 +7432,11 @@ impl SentFrames {
             && self.retransmits.is_empty(streams)
     }
 
+    /// Returns whether the packet contains any frames at all
+    fn is_empty(&self, streams: &StreamsState) -> bool {
+        !self.non_retransmits && self.stream_frames.is_empty() && self.retransmits.is_empty(streams)
+    }
+
     fn retransmits_mut(&mut self) -> &mut Retransmits {
         self.retransmits.get_or_create()
     }

noq-proto/src/connection/packet_builder.rs

@@ -327,6 +327,10 @@ impl<'a, 'b> PacketBuilder<'a, 'b> {
             self.buf.len() <= self.buf.datagram_max_offset() - self.tag_len,
             "packet exceeds maximum size"
         );
+        debug_assert!(
+            !self.sent_frames.is_empty(&conn.streams),
+            "constructed empty packet"
+        );
         let pad = self.buf.len() < self.min_size;
         if pad {
             let padding = self.min_size - self.buf.len();