yudai/gotty · error

failed to compile regular expression of Websocket Origin: %s

Error message

failed to compile regular expression of Websocket Origin: %s

What it means

New() validates the WSOrigin option by compiling it as a Go regular expression. If the pattern is syntactically invalid, regexp.Compile fails and the error is wrapped with the offending pattern so you can see exactly which string was rejected. The compiled matcher is later used to check the Origin header of WebSocket connections.

Source

Thrown at server/server.go:64

		if err != nil {
			return nil, errors.Wrapf(err, "failed to read custom index file at `%s`", path)
		}
	}
	indexTemplate, err := template.New("index").Parse(string(indexData))
	if err != nil {
		panic("index template parse failed") // must be valid
	}

	titleTemplate, err := noesctmpl.New("title").Parse(options.TitleFormat)
	if err != nil {
		return nil, errors.Wrapf(err, "failed to parse window title format `%s`", options.TitleFormat)
	}

	var originChekcer func(r *http.Request) bool
	if options.WSOrigin != "" {
		matcher, err := regexp.Compile(options.WSOrigin)
		if err != nil {
			return nil, errors.Wrapf(err, "failed to compile regular expression of Websocket Origin: %s", options.WSOrigin)
		}
		originChekcer = func(r *http.Request) bool {
			return matcher.MatchString(r.Header.Get("Origin"))
		}
	}

	return &Server{
		factory: factory,
		options: options,

		upgrader: &websocket.Upgrader{
			ReadBufferSize:  1024,
			WriteBufferSize: 1024,
			Subprotocols:    webtty.Protocols,
			CheckOrigin:     originChekcer,
		},
		indexTemplate: indexTemplate,
		titleTemplate: titleTemplate,

View on GitHub (pinned to a080c85cbc)

Solutions

1. Fix the WSOrigin regex syntax in your options/config (escape dots, use .* not *, balance parens)
2. Test the pattern with Go regexp (or a regex tester with RE2 semantics) before launching
3. If you meant a plain origin match, escape metacharacters: https://example\.com

Example fix

// before
options.WSOrigin = "*.example.com"
// after
options.WSOrigin = ".*\.example\.com"

if _, err := regexp.Compile(opts.WSOrigin); err != nil {
    return fmt.Errorf("invalid WSOrigin %q: %w", opts.WSOrigin, err)
}

srv, err := server.New(factory, opts)
if err != nil {
    log.Fatalf("WSOrigin regex invalid: %v", err)
}

When it happens

Trigger: Calling server.New() with Options.WSOrigin set to a string that is not a valid regular expression (e.g. "*.example.com", "(foo", "[a-z").

Common situations: Putting glob-style wildcards in WSOrigin instead of regex syntax; copying a shell-quoted value with stray backslashes; unbalanced parentheses when listing multiple origins like "(a.com|b.com".

Related errors

• failed to setup an HTTP server
• failed to setup TLS configuration
• could not open CA crt file %s
• Error: No command given.
• invalid bool expression: %v, use true/false

AI-assisted analysis of yudai/gotty@a080c85cbc (2026-09-02). Data as JSON: /api/errors/f581befd8a612d8e. Report an issue: GitHub.