tstest/integration/vms: add in-process DERP server (#2108)

Previously this test would reach out to the public DERP servers in order
to help machines connect with eachother. This is not ideal given our
plans to run these tests completely disconnected from the internet. This
patch introduces an in-process DERP server running on its own randomly
assigned HTTP port.

Updates #1988

Signed-off-by: Christine Dodrill <xe@tailscale.com>

tstest/integration/integration.go

@@ -9,6 +9,11 @@
 package integration
 
 import (
+	"crypto/rand"
+	"crypto/tls"
+	"net"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"os/exec"
 	"path"
@@ -19,6 +24,13 @@ import (
 	"testing"
 	"time"
 
+	"tailscale.com/derp"
+	"tailscale.com/derp/derphttp"
+	"tailscale.com/net/stun/stuntest"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
+	"tailscale.com/types/nettype"
 	"tailscale.com/version"
 )
 
@@ -98,3 +110,53 @@ func exe() string {
 	}
 	return ""
 }
+
+// RunDERPAndSTUN runs a local DERP and STUN server for tests, returning the derpMap
+// that clients should use. This creates resources that must be cleaned up with the
+// returned cleanup function.
+func RunDERPAndSTUN(t testing.TB, logf logger.Logf, ipAddress string) (derpMap *tailcfg.DERPMap) {
+	t.Helper()
+
+	var serverPrivateKey key.Private
+	if _, err := rand.Read(serverPrivateKey[:]); err != nil {
+		t.Fatal(err)
+	}
+	d := derp.NewServer(serverPrivateKey, logf)
+
+	httpsrv := httptest.NewUnstartedServer(derphttp.Handler(d))
+	httpsrv.Config.ErrorLog = logger.StdLogger(logf)
+	httpsrv.Config.TLSNextProto = make(map[string]func(*http.Server, *tls.Conn, http.Handler))
+	httpsrv.StartTLS()
+
+	stunAddr, stunCleanup := stuntest.ServeWithPacketListener(t, nettype.Std{})
+
+	m := &tailcfg.DERPMap{
+		Regions: map[int]*tailcfg.DERPRegion{
+			1: {
+				RegionID:   1,
+				RegionCode: "test",
+				Nodes: []*tailcfg.DERPNode{
+					{
+						Name:         "t1",
+						RegionID:     1,
+						HostName:     ipAddress,
+						IPv4:         ipAddress,
+						IPv6:         "none",
+						STUNPort:     stunAddr.Port,
+						DERPTestPort: httpsrv.Listener.Addr().(*net.TCPAddr).Port,
+						STUNTestIP:   stunAddr.IP.String(),
+					},
+				},
+			},
+		},
+	}
+
+	t.Cleanup(func() {
+		httpsrv.CloseClientConnections()
+		httpsrv.Close()
+		d.Close()
+		stunCleanup()
+	})
+
+	return m
+}