Fix small padding invisible to the pacer (algesten#1020)

Padding smaller than the 800-byte average size divided to zero fake
packets, so queue_state_padding() returned None and the pacer never
scheduled it. Round up so any nonzero padding stays visible to the pacer.

Author: lherman-cs

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
 
+  * Fix small padding invisible to the pacer #1020
   * Fix H.264 negotiation: accept a negotiable (downgradable) level and recognize the Constrained High profile #1016
   * Expose the latest send queue information on `StreamTx` #1005
   * Fix VP9 non-flexible SS advertising a bogus R=0 GOF for single-layer streams #999

src/streams/send.rs

@@ -1134,7 +1134,7 @@ impl StreamTx {
         const AVERAGE_PADDING_PACKET_SIZE: usize = 800;
         const FAKE_PADDING_DURATION_MILLIS: usize = 5;
 
-        let fake_packets = self.padding / AVERAGE_PADDING_PACKET_SIZE;
+        let fake_packets = self.padding.div_ceil(AVERAGE_PADDING_PACKET_SIZE);
         let fake_millis = fake_packets * FAKE_PADDING_DURATION_MILLIS;
         let fake_duration = Duration::from_millis(fake_millis as u64);
 
@@ -1296,4 +1296,17 @@ mod test {
         stream.reset_buffers();
         assert!(stream.queue_info().is_none());
     }
+
+    #[test]
+    fn sub_average_padding_is_visible_to_the_pacer() {
+        let mut stream = StreamTx::new(42.into(), None, MidRid(Mid::from("0"), None), false, 1200);
+        stream.padding = 240;
+
+        let snapshot = stream
+            .queue_state_padding(Instant::now())
+            .expect("nonzero padding must produce a queue snapshot");
+
+        assert_eq!(snapshot.byte_size, 240);
+        assert_eq!(snapshot.packet_count, 1);
+    }
 }