TUN-10563: introduce QUICConnection interface

The bump of the QUIC library introduces a cyclic dependency between the connection and quic modules hence it is necessary to break this coupling.

Right now, the connection module depends on the quic module for the datagram v2/v3 and to which a QUIC connection (currently an interface) is passed.

As it is there is no issue however, under the hood, interface is a wrapper around an UDP connection and a QUIC connection meaning this type must be exposed to the quic module since the QUIC Connection will no longer be a interface but a struct.

Given the above, these changes introduce an interface, QUICConnection, with the surface used today in cloudflared and a struct, ConnWithCloser, that implements said interface within the quic module.

Closes TUN-10563

quic/quic_connection_test.go

@@ -0,0 +1,108 @@
+package quic
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/quic-go/quic-go"
+	"github.com/stretchr/testify/require"
+)
+
+// mockCloser is an [io.Closer] that returns a configurable error.
+type mockCloser struct {
+	closeErr error
+}
+
+func (m *mockCloser) Close() error {
+	return m.closeErr
+}
+
+// mockQuicConnection is a minimal test double for [quic.Connection].
+type mockQuicConnection struct {
+	quic.Connection
+	closeWithErrorErr error
+}
+
+func (m *mockQuicConnection) CloseWithError(_ quic.ApplicationErrorCode, _ string) error {
+	return m.closeWithErrorErr
+}
+
+func TestNewConnWithCloser_NilConn(t *testing.T) {
+	t.Parallel()
+	conn, err := NewQUICConnection(nil, &mockCloser{})
+	require.ErrorIs(t, err, ErrNilQuicConnection)
+	require.Nil(t, conn)
+}
+
+func TestNewConnWithCloser_NilCloser(t *testing.T) {
+	t.Parallel()
+	conn, err := NewQUICConnection(&mockQuicConnection{}, nil)
+	require.ErrorIs(t, err, ErrNilCloser)
+	require.Nil(t, conn)
+}
+
+func TestNewConnWithCloser_Success(t *testing.T) {
+	t.Parallel()
+	qc := &mockQuicConnection{}
+	cl := &mockCloser{}
+	conn, err := NewQUICConnection(qc, cl)
+	require.NoError(t, err)
+	require.NotNil(t, conn)
+}
+
+func TestConnWithCloser_CloseWithError_BothSucceed(t *testing.T) {
+	t.Parallel()
+	qc := &mockQuicConnection{}
+	cl := &mockCloser{}
+	conn, err := NewQUICConnection(qc, cl)
+	require.NoError(t, err)
+
+	err = conn.CloseWithError(0, "test")
+	require.NoError(t, err)
+}
+
+func TestConnWithCloser_CloseWithError_QuicFails(t *testing.T) {
+	t.Parallel()
+	quicErr := errors.New("quic close failed")
+	qc := &mockQuicConnection{closeWithErrorErr: quicErr}
+	cl := &mockCloser{}
+	conn, err := NewQUICConnection(qc, cl)
+	require.NoError(t, err)
+
+	err = conn.CloseWithError(0, "test")
+	require.ErrorIs(t, err, quicErr)
+}
+
+func TestConnWithCloser_CloseWithError_CloserFails(t *testing.T) {
+	t.Parallel()
+	closerErr := errors.New("closer failed")
+	qc := &mockQuicConnection{}
+	cl := &mockCloser{closeErr: closerErr}
+	conn, err := NewQUICConnection(qc, cl)
+	require.NoError(t, err)
+
+	err = conn.CloseWithError(0, "test")
+	require.ErrorIs(t, err, closerErr)
+}
+
+func TestConnWithCloser_CloseWithError_BothFail(t *testing.T) {
+	t.Parallel()
+	quicErr := errors.New("quic close failed")
+	closerErr := errors.New("closer failed")
+	qc := &mockQuicConnection{closeWithErrorErr: quicErr}
+	cl := &mockCloser{closeErr: closerErr}
+	conn, err := NewQUICConnection(qc, cl)
+	require.NoError(t, err)
+
+	err = conn.CloseWithError(0, "test")
+	require.ErrorIs(t, err, quicErr)
+	require.ErrorIs(t, err, closerErr)
+}
+
+// TestConnWithCloser_ImplementsInterface is a runtime assertion that
+// *ConnWithCloser satisfies QUICConnection. The compile-time assertion is in
+// quic_connection.go.
+func TestConnWithCloser_ImplementsInterface(t *testing.T) {
+	t.Parallel()
+	var _ QUICConnection = (*ConnWithCloser)(nil)
+}