Introduce helper for the capacity of the entire transmit

Author: flub

quinn-proto/src/connection/mod.rs

@@ -576,9 +576,10 @@ impl Connection {
                 // for starting another datagram. If there is any anti-amplification
                 // budget left, we always allow a full MTU to be sent
                 // (see https://github.com/quinn-rs/quinn/issues/1082)
-                if self.path.anti_amplification_blocked(
-                    (transmit.segment_size() * transmit.num_datagrams()) as u64 + 1,
-                ) {
+                if self
+                    .path
+                    .anti_amplification_blocked(transmit.capacity() as u64 + 1)
+                {
                     trace!("blocked by anti-amplification");
                     break;
                 }

quinn-proto/src/connection/transmit_builder.rs

@@ -165,6 +165,17 @@ impl<'a> TransmitBuilder<'a> {
         self.num_datagrams >= self.max_datagrams
     }
 
+    /// The sum of the capacity of all started datagrams in the transmit
+    ///
+    /// This might be more than [`len`] when the current datagram is not yet fully
+    /// written. In other words: this is the length of the transmit when the current
+    /// datagram would fill the entire segment size.
+    ///
+    /// [`len`]: TransmitBuf::len
+    pub(super) fn capacity(&self) -> usize {
+        self.segment_size * self.num_datagrams
+    }
+
     /// Returns the GSO segment size
     ///
     /// This is also the maximum size datagrams are allowed to be. The first and last