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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
// Package memnet implements an in-memory network implementation.
// It is useful for dialing and listening on in-memory addresses
// in tests and other situations where you don't want to use the
// network.
package memnet
import (
"context"
"fmt"
"net"
"net/netip"
"tailscale.com/net/netx"
"tailscale.com/syncs"
)
var _ netx.Network = (*Network)(nil)
// Network implements [Network] using an in-memory network, usually
// used for testing.
//
// As of 2025-04-08, it only supports TCP.
//
// Its zero value is a valid [netx.Network] implementation.
type Network struct {
mu syncs.Mutex
lns map[string]*Listener // address -> listener
}
func (m *Network) Listen(network, address string) (net.Listener, error) {
if network != "tcp" && network != "tcp4" && network != "tcp6" {
return nil, fmt.Errorf("memNetwork: Listen called with unsupported network %q", network)
}
ap, err := netip.ParseAddrPort(address)
if err != nil {
return nil, fmt.Errorf("memNetwork: Listen called with invalid address %q: %w", address, err)
}
m.mu.Lock()
defer m.mu.Unlock()
if m.lns == nil {
m.lns = make(map[string]*Listener)
}
port := ap.Port()
for {
if port == 0 {
port = 33000
}
key := net.JoinHostPort(ap.Addr().String(), fmt.Sprint(port))
_, ok := m.lns[key]
if ok {
if ap.Port() != 0 {
return nil, fmt.Errorf("memNetwork: Listen called with duplicate address %q", address)
}
port++
continue
}
ln := Listen(key)
m.lns[key] = ln
ln.onClose = func() {
m.mu.Lock()
delete(m.lns, key)
m.mu.Unlock()
}
return ln, nil
}
}
func (m *Network) NewLocalTCPListener() net.Listener {
ln, err := m.Listen("tcp", "127.0.0.1:0")
if err != nil {
panic(fmt.Sprintf("memNetwork: failed to create local TCP listener: %v", err))
}
return ln
}
func (m *Network) Dial(ctx context.Context, network, address string) (net.Conn, error) {
if network != "tcp" && network != "tcp4" && network != "tcp6" {
return nil, fmt.Errorf("memNetwork: Dial called with unsupported network %q", network)
}
m.mu.Lock()
ln, ok := m.lns[address]
m.mu.Unlock()
if !ok {
return nil, fmt.Errorf("memNetwork: Dial called on unknown address %q", address)
}
return ln.Dial(ctx, network, address)
}
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