Add --listen-unsafe=ADDR to allow remote process execution (#3498)

CHANGELOG.md

@@ -16,6 +16,10 @@ CHANGELOG
   # FZF_API_KEY is required for a non-localhost listen address
   export FZF_API_KEY="$(head -c 32 /dev/urandom | base64)"
   fzf --listen 0.0.0.0:6266
+
+  # To allow remote process execution, use `--listen-unsafe` instead
+  # (execute, reload, become, preview, change-preview, tranform-*, etc.)
+  fzf --listen-unsafe 0.0.0.0:6266
   ```
 - Bug fixes
 

man/man1/fzf.1

@@ -793,14 +793,19 @@ ncurses finder only after the input stream is complete.
 e.g. \fBfzf --multi | fzf --sync\fR
 .RE
 .TP
-.B "--listen[=[ADDR:]PORT]"
+.B "--listen[=[ADDR:]PORT]" "--listen-unsafe[=[ADDR:]PORT]"
 Start HTTP server and listen on the given address. It allows external processes
-to send actions to perform via POST method. If the port number is omitted or
-given as 0, fzf will automatically choose a port and export it as
-\fBFZF_PORT\fR environment variable to the child processes. If
-\fBFZF_API_KEY\fR environment variable is set, the server would require sending
-an API key with the same value in the \fBx-api-key\fR HTTP header.
-\fBFZF_API_KEY\fR is required for a non-localhost listen address.
+to send actions to perform via POST method.
+
+- If the port number is omitted or given as 0, fzf will automatically choose
+a port and export it as \fBFZF_PORT\fR environment variable to the child processes
+
+- If \fBFZF_API_KEY\fR environment variable is set, the server would require
+sending an API key with the same value in the \fBx-api-key\fR HTTP header
+
+- \fBFZF_API_KEY\fR is required for a non-localhost listen address
+
+- To allow remote process execution, use \fB--listen-unsafe\fR
 
 e.g.
      \fB# Start HTTP server on port 6266

src/options.go

@@ -119,6 +119,7 @@ const usage = `usage: fzf [options]
     --print0               Print output delimited by ASCII NUL characters
     --sync                 Synchronous search for multi-staged filtering
     --listen[=[ADDR:]PORT] Start HTTP server to receive actions (POST /)
+                           (To allow remote process execution, use --listen-unsafe)
     --version              Display version information and exit
 
   Environment variables
@@ -334,7 +335,8 @@ type Options struct {
 	PreviewLabel labelOpts
 	Unicode      bool
 	Tabstop      int
-	ListenAddr   *string
+	ListenAddr   *listenAddress
+	Unsafe       bool
 	ClearOnExit  bool
 	Version      bool
 }
@@ -404,6 +406,7 @@ func defaultOptions() *Options {
 		Tabstop:      8,
 		BorderLabel:  labelOpts{},
 		PreviewLabel: labelOpts{},
+		Unsafe:       false,
 		ClearOnExit:  true,
 		Version:      false}
 }
@@ -1832,14 +1835,21 @@ func parseOptions(opts *Options, allArgs []string) {
 				nextString(allArgs, &i, "padding required (TRBL / TB,RL / T,RL,B / T,R,B,L)"))
 		case "--tabstop":
 			opts.Tabstop = nextInt(allArgs, &i, "tab stop required")
-		case "--listen":
-			given, addr := optionalNextString(allArgs, &i)
-			if !given {
-				addr = defaultListenAddr
+		case "--listen", "--listen-unsafe":
+			given, str := optionalNextString(allArgs, &i)
+			addr := defaultListenAddr
+			if given {
+				var err error
+				err, addr = parseListenAddress(str)
+				if err != nil {
+					errorExit(err.Error())
+				}
 			}
 			opts.ListenAddr = &addr
-		case "--no-listen":
+			opts.Unsafe = arg == "--listen-unsafe"
+		case "--no-listen", "--no-listen-unsafe":
 			opts.ListenAddr = nil
+			opts.Unsafe = false
 		case "--clear":
 			opts.ClearOnExit = true
 		case "--no-clear":
@@ -1930,7 +1940,19 @@ func parseOptions(opts *Options, allArgs []string) {
 			} else if match, value := optString(arg, "--tabstop="); match {
 				opts.Tabstop = atoi(value)
 			} else if match, value := optString(arg, "--listen="); match {
-				opts.ListenAddr = &value
+				err, addr := parseListenAddress(value)
+				if err != nil {
+					errorExit(err.Error())
+				}
+				opts.ListenAddr = &addr
+				opts.Unsafe = false
+			} else if match, value := optString(arg, "--listen-unsafe="); match {
+				err, addr := parseListenAddress(value)
+				if err != nil {
+					errorExit(err.Error())
+				}
+				opts.ListenAddr = &addr
+				opts.Unsafe = true
 			} else if match, value := optString(arg, "--hscroll-off="); match {
 				opts.HscrollOff = atoi(value)
 			} else if match, value := optString(arg, "--scroll-off="); match {

src/server.go

@@ -32,7 +32,6 @@ const (
 	httpUnauthorized = "HTTP/1.1 401 Unauthorized" + crlf
 	httpReadTimeout  = 10 * time.Second
 	maxContentLength = 1024 * 1024
-	defaultListenAddr = "localhost:0"
 )
 
 type httpServer struct {
@@ -41,38 +40,47 @@ type httpServer struct {
 	responseChannel chan string
 }
 
-func parseListenAddress(address string) (error, string, int) {
+type listenAddress struct {
+	host string
+	port int
+}
+
+func (addr listenAddress) IsLocal() bool {
+	return addr.host == "localhost" || addr.host == "127.0.0.1"
+}
+
+var defaultListenAddr = listenAddress{"localhost", 0}
+
+func parseListenAddress(address string) (error, listenAddress) {
 	parts := strings.SplitN(address, ":", 3)
 	if len(parts) == 1 {
 		parts = []string{"localhost", parts[0]}
 	}
 	if len(parts) != 2 {
-		return fmt.Errorf("invalid listen address: %s", address), "", 0
+		return fmt.Errorf("invalid listen address: %s", address), defaultListenAddr
 	}
 	portStr := parts[len(parts)-1]
 	port, err := strconv.Atoi(portStr)
 	if err != nil || port < 0 || port > 65535 {
-		return fmt.Errorf("invalid listen port: %s", portStr), "", 0
+		return fmt.Errorf("invalid listen port: %s", portStr), defaultListenAddr
 	}
 	if len(parts[0]) == 0 {
 		parts[0] = "localhost"
 	}
-	return nil, parts[0], port
+	return nil, listenAddress{parts[0], port}
 }
 
-func startHttpServer(address string, actionChannel chan []*action, responseChannel chan string) (error, int) {
-	err, host, port := parseListenAddress(address)
-	if err != nil {
-		return err, port
-	}
-
+func startHttpServer(address listenAddress, actionChannel chan []*action, responseChannel chan string) (error, int) {
+	host := address.host
+	port := address.port
 	apiKey := os.Getenv("FZF_API_KEY")
-	if host != "localhost" && host != "127.0.0.1" && len(apiKey) == 0 {
-		return fmt.Errorf("FZF_API_KEY is required for remote access"), port
+	if !address.IsLocal() && len(apiKey) == 0 {
+		return fmt.Errorf("FZF_API_KEY is required to allow remote access"), port
 	}
-	listener, err := net.Listen("tcp", fmt.Sprintf("%s:%d", host, port))
+	addrStr := fmt.Sprintf("%s:%d", host, port)
+	listener, err := net.Listen("tcp", addrStr)
 	if err != nil {
-		return fmt.Errorf("failed to listen on %s", address), port
+		return fmt.Errorf("failed to listen on %s", addrStr), port
 	}
 	if port == 0 {
 		addr := listener.Addr().String()

src/terminal.go

@@ -235,8 +235,9 @@ type Terminal struct {
 	margin             [4]sizeSpec
 	padding            [4]sizeSpec
 	unicode            bool
-	listenAddr         *string
+	listenAddr         *listenAddress
 	listenPort         *int
+	listenUnsafe       bool
 	borderShape        tui.BorderShape
 	cleanExit          bool
 	paused             bool
@@ -436,6 +437,26 @@ const (
 	actResponse
 )
 
+func processExecution(action actionType) bool {
+	switch action {
+	case actTransformBorderLabel,
+		actTransformHeader,
+		actTransformPreviewLabel,
+		actTransformPrompt,
+		actTransformQuery,
+		actPreview,
+		actChangePreview,
+		actExecute,
+		actExecuteSilent,
+		actExecuteMulti,
+		actReload,
+		actReloadSync,
+		actBecome:
+		return true
+	}
+	return false
+}
+
 type placeholderFlags struct {
 	plus          bool
 	preserveSpace bool
@@ -661,6 +682,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 		padding:            opts.Padding,
 		unicode:            opts.Unicode,
 		listenAddr:         opts.ListenAddr,
+		listenUnsafe:       opts.Unsafe,
 		borderShape:        opts.BorderShape,
 		borderWidth:        1,
 		borderLabel:        nil,
@@ -3088,8 +3110,18 @@ func (t *Terminal) Loop() {
 			select {
 			case event = <-t.eventChan:
 				needBarrier = !event.Is(tui.Load, tui.One, tui.Zero)
-			case actions = <-t.serverInputChan:
+			case serverActions := <-t.serverInputChan:
 				event = tui.Invalid.AsEvent()
+				if t.listenAddr == nil || t.listenAddr.IsLocal() || t.listenUnsafe {
+					actions = serverActions
+				} else {
+					for _, action := range serverActions {
+						if !processExecution(action.t) {
+							actions = append(actions, action)
+						}
+					}
+				}
+
 				needBarrier = false
 			}
 		}