feat: create opts package

x/sockopt/sockopt.go

@@ -0,0 +1,91 @@
+// Copyright 2024 The Outline Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package sockopt provides cross-platform ways to interact with socket options.
+package sockopt
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
+
+// HasHopLimit enables manipulation of the hop limit option.
+type HasHopLimit interface {
+	// HopLimit returns the hop limit field value for outgoing packets.
+	HopLimit() (int, error)
+	// SetHopLimit sets the hop limit field value for future outgoing packets.
+	SetHopLimit(hoplim int) error
+}
+
+// hopLimitOption implements HasHopLimit.
+type hopLimitOption struct {
+	hopLimit    func() (int, error)
+	setHopLimit func(hoplim int) error
+}
+
+func (o *hopLimitOption) HopLimit() (int, error) {
+	return o.hopLimit()
+}
+
+func (o *hopLimitOption) SetHopLimit(hoplim int) error {
+	return o.setHopLimit(hoplim)
+}
+
+var _ HasHopLimit = (*hopLimitOption)(nil)
+
+// TCPOptions represents options for TCP connections.
+type TCPOptions interface {
+	HasHopLimit
+}
+
+type tcpOptions struct {
+	hopLimitOption
+}
+
+var _ TCPOptions = (*tcpOptions)(nil)
+
+// newHopLimit creates a hopLimitOption from a [net.Conn]. Works for both TCP or UDP.
+func newHopLimit(conn net.Conn) (*hopLimitOption, error) {
+	addr, err := netip.ParseAddrPort(conn.LocalAddr().String())
+	if err != nil {
+		return nil, err
+	}
+	opt := &hopLimitOption{}
+	switch {
+	case addr.Addr().Is4():
+		conn := ipv4.NewConn(conn)
+		opt.hopLimit = conn.TTL
+		opt.setHopLimit = conn.SetTTL
+	case addr.Addr().Is6():
+		conn := ipv6.NewConn(conn)
+		opt.hopLimit = conn.HopLimit
+		opt.setHopLimit = conn.SetHopLimit
+	default:
+		return nil, fmt.Errorf("address is not IPv4 or IPv6 (%v)", addr.Addr().String())
+	}
+	return opt, nil
+}
+
+// NewTCPOptions creates a [TCPOptions] for the given [net.TCPConn].
+func NewTCPOptions(conn *net.TCPConn) (TCPOptions, error) {
+	hopLimit, err := newHopLimit(conn)
+	if err != nil {
+		return nil, err
+	}
+	return &tcpOptions{hopLimitOption: *hopLimit}, nil
+}

x/sockopt/sockopt_test.go

@@ -0,0 +1,54 @@
+// Copyright 2024 The Outline Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sockopt
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestTCPOptions(t *testing.T) {
+	type Params struct {
+		Net  string
+		Addr string
+	}
+	for _, params := range []Params{{Net: "tcp4", Addr: "127.0.0.1:0"}, {Net: "tcp6", Addr: "[::1]:0"}} {
+		l, err := net.Listen(params.Net, params.Addr)
+		require.NoError(t, err)
+		defer l.Close()
+
+		conn, err := net.Dial("tcp", l.Addr().String())
+		require.NoError(t, err)
+		tcpConn, ok := conn.(*net.TCPConn)
+		require.True(t, ok)
+
+		opts, err := NewTCPOptions(tcpConn)
+		require.NoError(t, err)
+
+		require.NoError(t, opts.SetHopLimit(1))
+
+		hoplim, err := opts.HopLimit()
+		require.NoError(t, err)
+		require.Equal(t, 1, hoplim)
+
+		require.NoError(t, opts.SetHopLimit(20))
+
+		hoplim, err = opts.HopLimit()
+		require.NoError(t, err)
+		require.Equal(t, 20, hoplim)
+	}
+}