Encapsulate access to TransmitBuf::max_datagrams

Also to avoid mutation outside of the transmit_buf module.

Author: flub

quinn-proto/src/connection/mod.rs

@@ -562,7 +562,7 @@ impl Connection {
                 // We need to send 1 more datagram and extend the buffer for that.
 
                 // Is 1 more datagram allowed?
-                if buf.datagram_max_offset() >= buf.segment_size() * buf.max_datagrams {
+                if !buf.has_datagram_capacity() {
                     // No more datagrams allowed
                     break;
                 }

quinn-proto/src/connection/transmit_buf.rs

@@ -37,7 +37,7 @@ pub(super) struct TransmitBuf<'a> {
     /// size.  All datagrams in between need to be exactly this size.
     buf_capacity: usize,
     /// The maximum number of datagrams allowed to write into [`TransmitBuf::buf`]
-    pub(super) max_datagrams: usize,
+    max_datagrams: usize,
     /// The number of datagrams already (partially) written into the buffer
     ///
     /// Incremented by a call to [`TransmitBuf::start_new_datagram`].
@@ -106,6 +106,12 @@ impl<'a> TransmitBuf<'a> {
         self.buf_capacity
     }
 
+    /// Whether the buffer has capacity for another datagram after the current one
+    pub(super) fn has_datagram_capacity(&self) -> bool {
+        let max_buffer_size = self.segment_size * self.max_datagrams;
+        self.buf_capacity < max_buffer_size
+    }
+
     /// Clips the datagram size to the current size
     ///
     /// Only valid for the first datagram, when the datagram might be smaller than the