Flight3: respect curves configuration

Reuse logic from Flight1 to ensure correct behaviour.

Signed-off-by: Vladislav Yarmak <vladislav-ex-src@vm-0.com>

Author: Snawoot

flight3handler.go

@@ -249,10 +249,11 @@ func flight3Generate(_ flightConn, state *State, _ *handshakeCache, cfg *handsha
 			RenegotiatedConnection: 0,
 		},
 	}
+
 	if state.namedCurve != 0 {
 		extensions = append(extensions, []extension.Extension{
 			&extension.SupportedEllipticCurves{
-				EllipticCurves: []elliptic.Curve{elliptic.X25519, elliptic.P256, elliptic.P384},
+				EllipticCurves: cfg.ellipticCurves,
 			},
 			&extension.SupportedPointFormats{
 				PointFormats: []elliptic.CurvePointFormat{elliptic.CurvePointFormatUncompressed},

flight3handler_test.go

@@ -0,0 +1,109 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package dtls
+
+import (
+	"context"
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/pion/dtls/v2/pkg/crypto/elliptic"
+	dtlsnet "github.com/pion/dtls/v2/pkg/net"
+	"github.com/pion/dtls/v2/pkg/protocol/extension"
+	"github.com/pion/dtls/v2/pkg/protocol/handshake"
+	"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
+	"github.com/pion/transport/v3/dpipe"
+	"github.com/pion/transport/v3/test"
+)
+
+// Assert that SupportedEllipticCurves is only sent when a ECC CipherSuite is available
+func TestSupportedEllipticCurves(t *testing.T) {
+	// Limit runtime in case of deadlocks
+	lim := test.TimeOut(time.Second * 20)
+	defer lim.Stop()
+
+	// Check for leaking routines
+	report := test.CheckRoutines(t)
+	defer report()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	expectedCurves := defaultCurves
+	var actualCurves []elliptic.Curve
+
+	rand.Shuffle(len(expectedCurves), func(i, j int) {
+		expectedCurves[i], expectedCurves[j] = expectedCurves[j], expectedCurves[i]
+	})
+
+	clientErr := make(chan error, 1)
+	ca, cb := dpipe.Pipe()
+	caAnalyzer := &connWithCallback{Conn: ca}
+	caAnalyzer.onWrite = func(in []byte) {
+		messages, err := recordlayer.UnpackDatagram(in)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		for i := range messages {
+			h := &handshake.Handshake{}
+			_ = h.Unmarshal(messages[i][recordlayer.FixedHeaderSize:])
+
+			if h.Header.Type == handshake.TypeClientHello {
+				clientHello := &handshake.MessageClientHello{}
+				msg, err := h.Message.Marshal()
+
+				if err != nil {
+					t.Fatal(err)
+				} else if err = clientHello.Unmarshal(msg); err != nil {
+					t.Fatal(err)
+				}
+
+				for _, e := range clientHello.Extensions {
+					if e.TypeValue() == extension.SupportedEllipticCurvesTypeValue {
+						if c, ok := e.(*extension.SupportedEllipticCurves); ok {
+							actualCurves = c.EllipticCurves
+						}
+					}
+				}
+			}
+		}
+	}
+
+	go func() {
+		conf := &Config{
+			CipherSuites:   []CipherSuiteID{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256},
+			EllipticCurves: expectedCurves,
+		}
+
+		if client, err := testClient(ctx, dtlsnet.PacketConnFromConn(caAnalyzer), caAnalyzer.RemoteAddr(), conf, false); err != nil {
+			clientErr <- err
+		} else {
+			clientErr <- client.Close() //nolint
+		}
+	}()
+
+	config := &Config{
+		CipherSuites: []CipherSuiteID{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256},
+	}
+
+	if server, err := testServer(ctx, dtlsnet.PacketConnFromConn(cb), cb.RemoteAddr(), config, true); err != nil {
+		t.Fatalf("Server error %v", err)
+	} else {
+		if err = server.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	if err := <-clientErr; err != nil {
+		t.Fatalf("Client error %v", err)
+	}
+
+	for i := range expectedCurves {
+		if expectedCurves[i] != actualCurves[i] {
+			t.Fatal("List of curves in SupportedEllipticCurves does not match config")
+		}
+	}
+}