feat/webserver: support serving over Unix sockets

cmd/zoekt-webserver/main.go

@@ -131,6 +131,7 @@ func main() {
 	logRefresh := flag.Duration("log_refresh", 24*time.Hour, "if using --log_dir, start writing a new file this often.")
 
 	listen := flag.String("listen", ":6070", "listen on this address.")
+	listenUnix := flag.String("listen_unix", "", "listen on this Unix socket path instead of TCP")
 	indexDir := flag.String("index", index.DefaultDir, "set index directory to use")
 	html := flag.Bool("html", true, "enable HTML interface")
 	enableRPC := flag.Bool("rpc", false, "enable go/net RPC")
@@ -182,6 +183,9 @@ func main() {
 		// caller to divert stderr output if necessary.
 		go divertLogs(*logDir, *logRefresh)
 	}
+	if *listenUnix != "" && (*sslCert != "" || *sslKey != "") {
+		log.Fatal("-listen_unix cannot be combined with -ssl_cert or -ssl_key")
+	}
 
 	// Tune GOMAXPROCS to match Linux container CPU quota.
 	_, _ = maxprocs.Set()
@@ -278,10 +282,15 @@ func main() {
 	if *sslCert != "" || *sslKey != "" {
 		watchdogAddr = "https://" + *listen
 	}
+	watchdogUnixSocket := ""
+	if *listenUnix != "" {
+		watchdogUnixSocket = *listenUnix
+		watchdogAddr = "http://unix"
+	}
 	watchdogAddr += "/healthz"
 
 	if watchdogErrCount > 0 && watchdogTick > 0 {
-		go watchdog(watchdogTick, watchdogErrCount, watchdogAddr)
+		go watchdog(watchdogTick, watchdogErrCount, watchdogAddr, watchdogUnixSocket)
 	} else {
 		log.Println("watchdog disabled")
 	}
@@ -299,19 +308,15 @@ func main() {
 		Handler: handler,
 	}
 
+	serveErrCh := make(chan error, 1)
 	go func() {
-		sglog.Scoped("server").Info("starting server", sglog.Stringp("address", listen))
-		var err error
-		if *sslCert != "" || *sslKey != "" {
-			err = srv.ListenAndServeTLS(*sslCert, *sslKey)
-		} else {
-			err = srv.ListenAndServe()
-		}
+		err := serveHTTP(srv, *listenUnix, *sslCert, *sslKey)
 
 		if err != http.ErrServerClosed {
 			// Fatal otherwise shutdownOnSignal will block
 			log.Fatalf("ListenAndServe: %v", err)
 		}
+		serveErrCh <- err
 	}()
 
 	if s.RPC {
@@ -326,6 +331,47 @@ func main() {
 			log.Fatalf("http.Server.Shutdown: %v", err)
 		}
 	}
+	<-serveErrCh
+}
+
+func serveHTTP(srv *http.Server, unixSocket, sslCert, sslKey string) error {
+	logger := sglog.Scoped("server")
+	if unixSocket != "" {
+		l, err := listenUnixSocket(unixSocket)
+		if err != nil {
+			return err
+		}
+		logger.Info("starting server", sglog.String("unixSocket", unixSocket))
+		return srv.Serve(l)
+	}
+
+	logger.Info("starting server", sglog.String("address", srv.Addr))
+	if sslCert != "" || sslKey != "" {
+		return srv.ListenAndServeTLS(sslCert, sslKey)
+	}
+	return srv.ListenAndServe()
+}
+
+func listenUnixSocket(socket string) (net.Listener, error) {
+	// We cannot bind a socket to an existing pathname.
+	if err := os.Remove(socket); err != nil && !os.IsNotExist(err) {
+		return nil, fmt.Errorf("error removing socket file: %s", socket)
+	}
+
+	l, err := net.Listen("unix", socket)
+	if err != nil {
+		return nil, fmt.Errorf("failed to listen on socket %s: %w", socket, err)
+	}
+
+	// nginx and zoekt-webserver often run as different users. Make the socket
+	// broadly connectable like the indexserver socket used by this binary's
+	// reverse proxy support.
+	if err := os.Chmod(socket, 0o777); err != nil {
+		_ = l.Close()
+		return nil, fmt.Errorf("failed to change permission of socket %s: %w", socket, err)
+	}
+
+	return l, nil
 }
 
 // addProxyHandler adds a handler to "mux" that proxies all requests with base
@@ -424,10 +470,16 @@ func watchdogOnce(ctx context.Context, client *http.Client, addr string) error {
 	return nil
 }
 
-func watchdog(dt time.Duration, maxErrCount int, addr string) {
+func watchdog(dt time.Duration, maxErrCount int, addr, unixSocket string) {
 	tr := &http.Transport{
 		TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
 	}
+	if unixSocket != "" {
+		tr.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
+			var d net.Dialer
+			return d.DialContext(ctx, "unix", unixSocket)
+		}
+	}
 	client := &http.Client{
 		Transport: tr,
 	}

cmd/zoekt-webserver/main_test.go

@@ -0,0 +1,96 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net"
+	"net/http"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestServeHTTPUnixSocket(t *testing.T) {
+	socket := filepath.Join(t.TempDir(), "zoekt.sock")
+	if err := os.WriteFile(socket, []byte("stale"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	srv := &http.Server{
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.URL.Path != "/healthz" {
+				http.NotFound(w, r)
+				return
+			}
+			_, _ = io.WriteString(w, "ok")
+		}),
+	}
+
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- serveHTTP(srv, socket, "", "")
+	}()
+
+	client := &http.Client{
+		Timeout: time.Second,
+		Transport: &http.Transport{
+			DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+				var d net.Dialer
+				return d.DialContext(ctx, "unix", socket)
+			},
+		},
+	}
+
+	var resp *http.Response
+	var err error
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		resp, err = client.Get("http://unix/healthz")
+		if err == nil {
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	if err != nil {
+		t.Fatalf("GET over unix socket failed: %v", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("got status %d, want %d", resp.StatusCode, http.StatusOK)
+	}
+	body, err := io.ReadAll(resp.Body)
+	_ = resp.Body.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(body) != "ok" {
+		t.Fatalf("got body %q, want %q", string(body), "ok")
+	}
+	if mode := socketMode(t, socket); mode != 0o777 {
+		t.Fatalf("got socket mode %o, want 777", mode)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	if err := srv.Shutdown(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := <-errCh; !errors.Is(err, http.ErrServerClosed) {
+		t.Fatalf("serveHTTP returned %v, want %v", err, http.ErrServerClosed)
+	}
+	if _, err := os.Stat(socket); !os.IsNotExist(err) {
+		t.Fatalf("socket was not removed after shutdown: %v", err)
+	}
+}
+
+func socketMode(t *testing.T, socket string) os.FileMode {
+	t.Helper()
+	fi, err := os.Stat(socket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return fi.Mode().Perm()
+}