gateway: determine default local IP (#3936)

Determine default local IP for SIG as documented in config sample,
analogous to old SIG implementation.
Instead of copying the findDefaultLocalIP logic again, move to
addrutil.DefaultLocalIP library function.

go/lib/snet/addrutil/BUILD.bazel

@@ -8,6 +8,7 @@ go_library(
     deps = [
         "//go/lib/addr:go_default_library",
         "//go/lib/ctrl/seg:go_default_library",
+        "//go/lib/sciond:go_default_library",
         "//go/lib/serrors:go_default_library",
         "//go/lib/slayers:go_default_library",
         "//go/lib/slayers/path:go_default_library",

go/lib/snet/addrutil/addrutil.go

@@ -15,11 +15,13 @@
 package addrutil
 
 import (
+	"context"
 	"encoding/binary"
 	"net"
 
 	"github.com/scionproto/scion/go/lib/addr"
 	"github.com/scionproto/scion/go/lib/ctrl/seg"
+	"github.com/scionproto/scion/go/lib/sciond"
 	"github.com/scionproto/scion/go/lib/serrors"
 	"github.com/scionproto/scion/go/lib/slayers"
 	"github.com/scionproto/scion/go/lib/slayers/path"
@@ -94,6 +96,25 @@ func (p Pather) GetPath(svc addr.HostSVC, ps *seg.PathSegment) (*snet.SVCAddr, e
 
 }
 
+// DefaultLocalIP returns _an_ IP of this host in the local AS.
+//
+// This returns a sensible but arbitrary local IP. In the general case the
+// local IP would depend on the next hop of selected path. This approach will
+// not work in more complicated setups where e.g. different network interfaces
+// are used to talk to different AS interfaces.
+//
+// This is a simple workaround for not being able to use wildcard addresses
+// with snet. Once available, a wildcard address should be used instead and
+// this should be removed.
+func DefaultLocalIP(ctx context.Context, sdConn sciond.Connector) (net.IP, error) {
+	// Choose CS as default routing "target". Using any of the interfaces would also make sense.
+	csAddr, err := sciond.TopoQuerier{Connector: sdConn}.UnderlayAnycast(ctx, addr.SvcCS)
+	if err != nil {
+		return nil, err
+	}
+	return ResolveLocal(csAddr.IP)
+}
+
 // ResolveLocal returns the local IP address used for traffic destined to dst.
 func ResolveLocal(dst net.IP) (net.IP, error) {
 	udpAddr := net.UDPAddr{IP: dst, Port: 1}

go/pkg/showpaths/showpaths.go

@@ -159,7 +159,7 @@ func Run(ctx context.Context, dst addr.IA, cfg Config) (*Result, error) {
 	if !cfg.NoProbe {
 		// Resolve local IP in case it is not configured.
 		if localIP = cfg.Local; localIP == nil {
-			localIP, err = findDefaultLocalIP(ctx, sdConn)
+			localIP, err = addrutil.DefaultLocalIP(ctx, sdConn)
 			if err != nil {
 				return nil, serrors.WrapStr("failed to determine local IP", err)
 			}
@@ -206,30 +206,3 @@ func Run(ctx context.Context, dst addr.IA, cfg Config) (*Result, error) {
 	}
 	return res, nil
 }
-
-// TODO(matzf): this is a simple, hopefully temporary, workaround to not having
-// wildcard addresses in snet.
-// Here we just use a seemingly sensible default IP, but in the general case
-// the local IP would depend on the next hop of selected path. This approach
-// will not work in more complicated setups where e.g. different network
-// interface are used to talk to different AS interfaces.
-// Once a available, a wildcard address should be used and this should simply
-// be removed.
-//
-// findDefaultLocalIP returns _a_ IP of this host in the local AS.
-func findDefaultLocalIP(ctx context.Context, sciondConn sciond.Connector) (net.IP, error) {
-	hostInLocalAS, err := findAnyHostInLocalAS(ctx, sciondConn)
-	if err != nil {
-		return nil, err
-	}
-	return addrutil.ResolveLocal(hostInLocalAS)
-}
-
-// findAnyHostInLocalAS returns the IP address of some (infrastructure) host in the local AS.
-func findAnyHostInLocalAS(ctx context.Context, sciondConn sciond.Connector) (net.IP, error) {
-	addr, err := sciond.TopoQuerier{Connector: sciondConn}.UnderlayAnycast(ctx, addr.SvcCS)
-	if err != nil {
-		return nil, err
-	}
-	return addr.IP, nil
-}

go/posix-gateway/BUILD.bazel

@@ -14,6 +14,7 @@ go_library(
         "//go/lib/prom:go_default_library",
         "//go/lib/sciond:go_default_library",
         "//go/lib/serrors:go_default_library",
+        "//go/lib/snet/addrutil:go_default_library",
         "//go/lib/sock/reliable:go_default_library",
         "//go/pkg/command:go_default_library",
         "//go/pkg/gateway:go_default_library",

go/posix-gateway/main.go

@@ -35,6 +35,7 @@ import (
 	"github.com/scionproto/scion/go/lib/prom"
 	"github.com/scionproto/scion/go/lib/sciond"
 	"github.com/scionproto/scion/go/lib/serrors"
+	"github.com/scionproto/scion/go/lib/snet/addrutil"
 	"github.com/scionproto/scion/go/lib/sock/reliable"
 	"github.com/scionproto/scion/go/pkg/command"
 	"github.com/scionproto/scion/go/pkg/gateway"
@@ -115,6 +116,12 @@ func run(file string) error {
 	if err != nil {
 		return serrors.WrapStr("parsing control address", err)
 	}
+	if len(controlAddress.IP) == 0 {
+		controlAddress.IP, err = addrutil.DefaultLocalIP(context.Background(), daemon)
+		if err != nil {
+			return serrors.WrapStr("determine default local IP", err)
+		}
+	}
 	dataAddress, err := net.ResolveUDPAddr("udp", cfg.Gateway.DataAddr)
 	if err != nil {
 		return serrors.WrapStr("parsing data address", err)

go/scion-pki/certs/renew.go

@@ -507,11 +507,7 @@ func findLocalAddr(ctx context.Context, sds sciond.Service) (*snet.UDPAddr, erro
 	if err != nil {
 		return nil, err
 	}
-	csAddr, err := sciond.TopoQuerier{Connector: sdConn}.UnderlayAnycast(ctx, addr.SvcCS)
-	if err != nil {
-		return nil, err
-	}
-	localIP, err := addrutil.ResolveLocal(csAddr.IP)
+	localIP, err := addrutil.DefaultLocalIP(ctx, sdConn)
 	if err != nil {
 		return nil, err
 	}