From b7311df34f75353b342974b8714c48a18109a6cd Mon Sep 17 00:00:00 2001
From: Oliver Chen <oliverxchen@gmail.com>
Date: Mon, 11 May 2026 13:46:37 +0800
Subject: [PATCH] fix: centralize ttdy host

- ttyd binds to 127.0.0.1 but vhs.go was opening Chrome at
  http://localhost:<port>. This fails when Chrome choose IPv6 first.
- This fix centralizes the ttdy host in `ttyHost`, uses it for both the
  ttyd --interface and the browser URL, and adds `vhs_test.go` to ensure
  they stay aligned.
---
 tty.go      |  4 +++-
 vhs.go      |  6 +++++-
 vhs_test.go | 25 +++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 vhs_test.go

diff --git a/tty.go b/tty.go
index c8af5dea..6a75263f 100644
--- a/tty.go
+++ b/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",
diff --git a/vhs.go b/vhs.go
index 235e7b42..bb226b83 100644
--- a/vhs.go
+++ b/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() {
diff --git a/vhs_test.go b/vhs_test.go
new file mode 100644
index 00000000..6405415c
--- /dev/null
+++ b/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)
+	}
+}