Noob try first cut

go.mod

@@ -36,6 +36,7 @@ require (
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
+	github.com/huin/goupnp v1.3.0 // indirect
 	github.com/jinzhu/inflection v1.0.0 // indirect
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/klauspost/compress v1.18.0 // indirect
@@ -70,6 +71,7 @@ require (
 	go.uber.org/atomic v1.9.0 // indirect
 	go.uber.org/multierr v1.9.0 // indirect
 	go4.org v0.0.0-20230225012048-214862532bf5 // indirect
+	golang.org/x/sync v0.17.0 // indirect
 	golang.org/x/sys v0.34.0 // indirect
 	golang.org/x/text v0.29.0 // indirect
 	golang.org/x/time v0.12.0 // indirect

go.sum

@@ -115,6 +115,8 @@ github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
 github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
+github.com/huin/goupnp v1.3.0 h1:UvLUlWDNpoUdYzb2TCn+MuTWtcjXKSza2n6CBdQ0xXc=
+github.com/huin/goupnp v1.3.0/go.mod h1:gnGPsThkYa7bFi/KWmEysQRf48l2dvR5bxr2OFckNX8=
 github.com/ianlancetaylor/demangle v0.0.0-20181102032728-5e5cf60278f6/go.mod h1:aSSvb/t6k1mPoxDqO4vJh6VOCGPwU4O0C2/Eqndh1Sc=
 github.com/jinzhu/inflection v1.0.0 h1:K317FqzuhWc8YvSVlFMCCUb36O/S9MCKRDI7QkRKD/E=
 github.com/jinzhu/inflection v1.0.0/go.mod h1:h+uFLlag+Qp1Va5pdKtLDYj+kHp5pxUVkryuEj+Srlc=
@@ -303,6 +305,7 @@ golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.17.0 h1:l60nONMj9l5drqw6jlhIELNv9I0A4OFgRsG9k2oT9Ug=
 golang.org/x/sync v0.17.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=

internal/proxy/mapper.go

@@ -0,0 +1,139 @@
+package proxy
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+
+	"github.com/huin/goupnp/dcps/internetgateway2"
+	"golang.org/x/sync/errgroup"
+)
+
+// Shamelessly stolen from the guide on the github.
+type routerClient interface {
+	AddPortMapping(
+		NewRemoteHost string,
+		NewExternalPort uint16,
+		NewProtocol string,
+		NewInternalPort uint16,
+		NewInternalClient string,
+		NewEnabled bool,
+		NewPortMappingDescription string,
+		NewLeaseDuration uint32,
+	) (err error)
+
+	GetExternalIPAddress() (
+		NewExternalIPAddress string,
+		err error,
+	)
+}
+
+type PortMapper struct {
+	conn routerClient
+}
+
+func TryMapper(ctx context.Context) (*PortMapper, error) {
+	tasks, _ := errgroup.WithContext(ctx)
+	// Request each type of client in parallel, and return what is found.
+	var ip1Clients []*internetgateway2.WANIPConnection1
+	tasks.Go(func() error {
+		var err error
+		ip1Clients, _, err = internetgateway2.NewWANIPConnection1ClientsCtx(ctx)
+		return err
+	})
+	var ip2Clients []*internetgateway2.WANIPConnection2
+	tasks.Go(func() error {
+		var err error
+		ip2Clients, _, err = internetgateway2.NewWANIPConnection2ClientsCtx(ctx)
+		return err
+	})
+	var ppp1Clients []*internetgateway2.WANPPPConnection1
+	tasks.Go(func() error {
+		var err error
+		ppp1Clients, _, err = internetgateway2.NewWANPPPConnection1ClientsCtx(ctx)
+		return err
+	})
+
+	if err := tasks.Wait(); err != nil {
+		return nil, err
+	}
+
+	var client routerClient
+	// There are some pretty nasty assumptions here that are most likely correct but not always:
+	// 1. There is only a single client: this won't be true for some complicated setups
+	// 2. The server only has a single network interface that has UPnP available.
+	// The second one becomes an issue during TryMap
+	switch {
+	case len(ip2Clients) == 1:
+		client = ip2Clients[0]
+	case len(ip1Clients) == 1:
+		client = ip1Clients[0]
+	case len(ppp1Clients) == 1:
+		client = ppp1Clients[0]
+	default:
+		return nil, errors.New("multiple or no services found")
+	}
+
+	return &PortMapper{
+		conn: client,
+	}, nil
+}
+
+// Get the address of the first interface that reports one
+// hacky assuming there is only one
+func yoinkFirstIntfAddr() (string, error) {
+	intfs, err := net.Interfaces()
+	if err != nil {
+		return "", err
+	}
+	for _, intf := range intfs {
+		addrs, err := intf.Addrs()
+		if err != nil {
+			return "", err
+		}
+		for _, addr := range addrs {
+			return addr.String(), nil
+		}
+	}
+
+	return "", fmt.Errorf("Couldn't enumerate IP from interfaces")
+}
+
+func (pm *PortMapper) TryMap(addr net.Addr) error {
+	host, port, err := net.SplitHostPort(addr.String())
+	if err != nil {
+		return err
+	}
+
+	ip := net.ParseIP(host)
+	if ip == nil {
+		return fmt.Errorf("Host IP invalid: %s", host)
+	}
+
+	// Check if they bound all interfaces
+	if ip.IsUnspecified() {
+		// Assume: only a single network interface
+		host, err = yoinkFirstIntfAddr()
+		if err != nil {
+			return err
+		}
+	}
+
+	pval, err := strconv.ParseUint(port, 10, 16)
+	if err != nil {
+		return fmt.Errorf("Port number parse failed? %v", err)
+	}
+
+	return pm.conn.AddPortMapping(
+		"",
+		uint16(pval),
+		"TCP",
+		uint16(pval),
+		host,
+		true,
+		"DiscoPanel",
+		3600,
+	)
+}

internal/proxy/proxy.go

@@ -21,6 +21,7 @@ type Proxy struct {
 	listenAddr   string
 	running      bool
 	runningMutex sync.RWMutex
+	portMapper   *PortMapper
 	ctx          context.Context
 	cancel       context.CancelFunc
 }
@@ -123,7 +124,15 @@ func (p *Proxy) Start() error {
 
 	p.listener = listener
 	p.running = true
-
+	portMapper, err := TryMapper(p.ctx)
+	if err != nil {
+		return fmt.Errorf("Failed mapper creation: %w", err)
+	}
+	p.portMapper = portMapper
+	err = p.portMapper.TryMap(p.listener.Addr())
+	if err != nil {
+		return fmt.Errorf("Failed try map: %w", err)
+	}
 	go p.acceptLoop()
 
 	p.logger.Info("Proxy started on %s", p.listenAddr)