ipn/localapi,client/tailscale,cmd/derper: add WhoIs lookup by nodekey, use in derper

Fixes #12465

Change-Id: I9b7c87315a3d2b2ecae2b8db9e94b4f5a1eef74a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

client/tailscale/localclient.go

@@ -253,11 +253,16 @@ func (lc *LocalClient) sendWithHeaders(
 	}
 	if res.StatusCode != wantStatus {
 		err = fmt.Errorf("%v: %s", res.Status, bytes.TrimSpace(slurp))
-		return nil, nil, bestError(err, slurp)
+		return nil, nil, httpStatusError{bestError(err, slurp), res.StatusCode}
 	}
 	return slurp, res.Header, nil
 }
 
+type httpStatusError struct {
+	error
+	HTTPStatus int
+}
+
 func (lc *LocalClient) get200(ctx context.Context, path string) ([]byte, error) {
 	return lc.send(ctx, "GET", path, 200, nil)
 }
@@ -278,9 +283,31 @@ func decodeJSON[T any](b []byte) (ret T, err error) {
 }
 
 // WhoIs returns the owner of the remoteAddr, which must be an IP or IP:port.
+//
+// If not found, the error is ErrPeerNotFound.
 func (lc *LocalClient) WhoIs(ctx context.Context, remoteAddr string) (*apitype.WhoIsResponse, error) {
 	body, err := lc.get200(ctx, "/localapi/v0/whois?addr="+url.QueryEscape(remoteAddr))
 	if err != nil {
+		if hs, ok := err.(httpStatusError); ok && hs.HTTPStatus == http.StatusNotFound {
+			return nil, ErrPeerNotFound
+		}
+		return nil, err
+	}
+	return decodeJSON[*apitype.WhoIsResponse](body)
+}
+
+// ErrPeerNotFound is returned by WhoIs and WhoIsNodeKey when a peer is not found.
+var ErrPeerNotFound = errors.New("peer not found")
+
+// WhoIsNodeKey returns the owner of the given wireguard public key.
+//
+// If not found, the error is ErrPeerNotFound.
+func (lc *LocalClient) WhoIsNodeKey(ctx context.Context, key key.NodePublic) (*apitype.WhoIsResponse, error) {
+	body, err := lc.get200(ctx, "/localapi/v0/whois?addr="+url.QueryEscape(key.String()))
+	if err != nil {
+		if hs, ok := err.(httpStatusError); ok && hs.HTTPStatus == http.StatusNotFound {
+			return nil, ErrPeerNotFound
+		}
 		return nil, err
 	}
 	return decodeJSON[*apitype.WhoIsResponse](body)

client/tailscale/localclient_test.go

@@ -6,9 +6,14 @@
 package tailscale
 
 import (
+	"context"
+	"net"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"tailscale.com/tstest/deptest"
+	"tailscale.com/types/key"
 )
 
 func TestGetServeConfigFromJSON(t *testing.T) {
@@ -30,6 +35,32 @@ func TestGetServeConfigFromJSON(t *testing.T) {
 	}
 }
 
+func TestWhoIsPeerNotFound(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(404)
+	}))
+	defer ts.Close()
+
+	lc := &LocalClient{
+		Dial: func(ctx context.Context, network, addr string) (net.Conn, error) {
+			var std net.Dialer
+			return std.DialContext(ctx, network, ts.Listener.Addr().(*net.TCPAddr).String())
+		},
+	}
+	var k key.NodePublic
+	if err := k.UnmarshalText([]byte("nodekey:5c8f86d5fc70d924e55f02446165a5dae8f822994ad26bcf4b08fd841f9bf261")); err != nil {
+		t.Fatal(err)
+	}
+	res, err := lc.WhoIsNodeKey(context.Background(), k)
+	if err != ErrPeerNotFound {
+		t.Errorf("got (%v, %v), want ErrPeerNotFound", res, err)
+	}
+	res, err = lc.WhoIs(context.Background(), "1.2.3.4:5678")
+	if err != ErrPeerNotFound {
+		t.Errorf("got (%v, %v), want ErrPeerNotFound", res, err)
+	}
+}
+
 func TestDeps(t *testing.T) {
 	deptest.DepChecker{
 		BadDeps: map[string]string{