fix: centralize ttdy host

tty.go

@@ -16,6 +16,8 @@ import (
 	"os/exec"
 )
 
+const ttyHost = "127.0.0.1"
+
 // randomPort returns a random port number that is not in use.
 func randomPort() int {
 	addr, _ := net.Listen("tcp", ":0") //nolint:gosec,noctx
@@ -27,7 +29,7 @@ func randomPort() int {
 func buildTtyCmd(port int, shell Shell) *exec.Cmd {
 	args := []string{ //nolint:prealloc
 		fmt.Sprintf("--port=%d", port),
-		"--interface", "127.0.0.1",
+		"--interface", ttyHost,
 		"-t", "rendererType=canvas",
 		"-t", "disableResizeOverlay=true",
 		"-t", "enableSixel=true",

vhs.go

@@ -143,7 +143,7 @@ func (vhs *VHS) Start() error {
 		return fmt.Errorf("could not launch browser: %w", err)
 	}
 	browser := rod.New().ControlURL(u).MustConnect()
-	page, err := browser.Page(proto.TargetCreateTarget{URL: fmt.Sprintf("http://localhost:%d", port)})
+	page, err := browser.Page(proto.TargetCreateTarget{URL: ttyURL(port)})
 	if err != nil {
 		return fmt.Errorf("could not open ttyd: %w", err)
 	}
@@ -155,6 +155,10 @@ func (vhs *VHS) Start() error {
 	return nil
 }
 
+func ttyURL(port int) string {
+	return fmt.Sprintf("http://%s:%d", ttyHost, port)
+}
+
 // Setup sets up the VHS instance and performs the necessary actions to reflect
 // the options that are default and set by the user.
 func (vhs *VHS) Setup() {

vhs_test.go

@@ -0,0 +1,25 @@
+package main
+
+import "testing"
+
+func TestTtyHostMatchesBrowserURL(t *testing.T) {
+	const port = 19760
+
+	cmd := buildTtyCmd(port, Shell{Command: []string{"sh"}})
+	iface := ""
+	for i, arg := range cmd.Args {
+		if arg == "--interface" && i+1 < len(cmd.Args) {
+			iface = cmd.Args[i+1]
+			break
+		}
+	}
+
+	if iface != ttyHost {
+		t.Fatalf("expected ttyd to bind to %q, got %q", ttyHost, iface)
+	}
+
+	wantURL := "http://" + iface + ":19760"
+	if gotURL := ttyURL(port); gotURL != wantURL {
+		t.Fatalf("expected browser URL %q, got %q", wantURL, gotURL)
+	}
+}