wip

Signed-off-by: Maisem Ali <maisem@tailscale.com>

cmd/tailproxy/proxy.go

@@ -0,0 +1,107 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"slices"
+	"strings"
+	"sync"
+
+	"github.com/inetaf/tcpproxy"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/net/netutil"
+	"tailscale.com/tailcfg"
+	"tailscale.com/tsnet"
+	"tailscale.com/types/logger"
+	"tailscale.com/util/dnsname"
+	"tailscale.com/util/must"
+)
+
+type proxyGrantRule struct {
+	AllowedHosts []dnsname.FQDN
+}
+
+func handleConn(ctx context.Context, c net.Conn, lc *tailscale.LocalClient, dialCtx func(context.Context, string, string) (net.Conn, error)) {
+	addrPortStr := c.LocalAddr().String()
+	_, port, err := net.SplitHostPort(addrPortStr)
+	if err != nil {
+		log.Printf("tcpSNIHandler.Handle: bogus addrPort %q", addrPortStr)
+		c.Close()
+		return
+	}
+	who, err := lc.WhoIs(ctx, c.RemoteAddr().String())
+	if err != nil {
+		c.Close()
+		log.Printf("tcpSNIHandler.Handle: WhoIs: %v", err)
+		return
+	}
+	rules, err := tailcfg.UnmarshalCapJSON[proxyGrantRule](who.CapMap, "maisem.com/tailproxy")
+	if err != nil {
+		c.Close()
+		log.Printf("tcpSNIHandler.Handle: UnmarshalCapJSON: %v", err)
+		return
+	}
+
+	var p tcpproxy.Proxy
+	p.ListenFunc = func(net, laddr string) (net.Listener, error) {
+		return netutil.NewOneConnListener(c, nil), nil
+	}
+	p.AddSNIRouteFunc(addrPortStr, func(ctx context.Context, sniName string) (t tcpproxy.Target, ok bool) {
+		sniFQDN, err := dnsname.ToFQDN(sniName)
+		if err != nil {
+			log.Printf("tcpSNIHandler.Handle: ToFQDN: %v", err)
+			return nil, false
+		}
+		for _, rule := range rules {
+			if slices.ContainsFunc(rule.AllowedHosts, func(fqdn dnsname.FQDN) bool {
+				return fqdn == "*" || fqdn.Contains(sniFQDN)
+			}) {
+				log.Printf("tcpSNIHandler.Handle: %s is allowed", sniName)
+				return &tcpproxy.DialProxy{
+					Addr:        net.JoinHostPort(sniName, port),
+					DialContext: dialCtx,
+				}, true
+			}
+		}
+		log.Printf("tcpSNIHandler.Handle: %s is not allowed", sniName)
+		return nil, false
+	})
+	p.Start()
+}
+
+func main() {
+	var (
+		ports    = flag.String("ports", "443", "comma-separated list of ports to proxy")
+		hostname = flag.String("hostname", "", "Hostname to register the service under")
+	)
+	flag.Parse()
+
+	ctx := context.Background()
+	s := &tsnet.Server{
+		Hostname: *hostname,
+		Logf:     logger.Discard,
+	}
+	must.Get(s.Up(ctx))
+	var wg sync.WaitGroup
+	log.Printf("Listening on ports: %s", *ports)
+	for _, port := range strings.Split(*ports, ",") {
+		wg.Add(1)
+		ln := must.Get(s.Listen("tcp", ":"+port))
+		lc := must.Get(s.LocalClient())
+		go func() {
+			defer wg.Done()
+			for {
+				c, err := ln.Accept()
+				if err != nil {
+					continue
+				}
+				fmt.Println("Accepted connection")
+				go handleConn(ctx, c, lc, s.Dial)
+			}
+		}()
+	}
+	wg.Wait()
+}