fix(handshake): budget CRYPTO fragmentation off peer max_udp_payload_size, not local 1200 floor (#5)

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.2] - 2026-06-08
+
+### Fixed
+
+- Budget CRYPTO handshake fragmentation off the peer's advertised `max_udp_payload_size` rather than the local 1200-byte floor, so the handshake flight fits the peer's datagram limit (#5)
+
 ## [1.0.1] - 2026-06-03
 
 ### Fixed

README.md

@@ -8,7 +8,7 @@ Pure Erlang QUIC transport for Erlang/OTP 27+.
 ## Getting started
 
 ```erlang
-{deps, [{nquic, "1.0.1"}]}.
+{deps, [{nquic, "1.0.2"}]}.
 ```
 
 ### Client

src/nquic.app.src

@@ -1,6 +1,6 @@
 {application, nquic, [
     {description, "QUIC transport protocol (RFC 9000/9001/9002) for Erlang/OTP 27+"},
-    {vsn, "1.0.1"},
+    {vsn, "1.0.2"},
     {registered, []},
     {applications, [
         kernel,

src/nquic_protocol_send.erl

@@ -274,16 +274,15 @@ batch_frames([F | Rest], Budget, Used, Cur, Batches) ->
 
 -spec handshake_payload_budget(nquic_protocol:state()) -> pos_integer().
 handshake_payload_budget(#conn_state{
-    dcid = DCID, scid = SCID, max_payload_size = MaxPayload, remote_params = RP
+    dcid = DCID, scid = SCID, remote_params = RP
 }) ->
     PeerMax =
         case RP of
             #transport_params{max_udp_payload_size = M} when is_integer(M), M >= 1200 -> M;
             _ -> 1200
         end,
-    Limit = min(MaxPayload, PeerMax),
     Overhead = 1 + 4 + 1 + byte_size(DCID) + 1 + byte_size(SCID) + 2 + 4 + ?AEAD_TAG_SIZE,
-    max(1, Limit - Overhead).
+    PeerMax - Overhead.
 
 -spec presplit_crypto_frames([nquic_frame:t()], pos_integer()) -> [nquic_frame:t()].
 presplit_crypto_frames(Frames, Budget) ->

test/nquic_protocol_tests.erl

@@ -1675,14 +1675,24 @@ build_handshake_packets_small_flight_single_packet_test() ->
     ?assertEqual(1, length(Packets)).
 
 build_handshake_packets_splits_large_flight_test() ->
-    State = queue_handshake_flight(make_handshake_send_state(1472), crypto:strong_rand_bytes(4000)),
+    PeerMax = 1472,
+    State = queue_handshake_flight(
+        make_handshake_send_state(PeerMax), crypto:strong_rand_bytes(4000)
+    ),
     {Packets, _State1} = nquic_protocol_send_queues:flush_handshake(State),
-    ?assert(length(Packets) >= 4),
+    ?assert(length(Packets) >= 2),
     lists:foreach(
-        fun(P) -> ?assert(byte_size(iolist_to_binary(P)) =< 1200) end,
+        fun(P) -> ?assert(byte_size(iolist_to_binary(P)) =< PeerMax) end,
         Packets
     ).
 
+build_handshake_packets_large_peer_keeps_flight_single_test() ->
+    State = queue_handshake_flight(
+        make_handshake_send_state(65527), crypto:strong_rand_bytes(1500)
+    ),
+    {Packets, _State1} = nquic_protocol_send_queues:flush_handshake(State),
+    ?assertEqual(1, length(Packets)).
+
 build_handshake_packets_respects_peer_max_udp_payload_test() ->
     PeerMax = 1300,
     State0 = (make_handshake_send_state(PeerMax))#conn_state{max_payload_size = 9000},