gorilla/mux · error

mux: route doesn't have a host

Error message

mux: route doesn't have a host

What it means

Returned by Route.URLHost (route.go:648-653) when building a URL but the route has no host matcher (r.regexp.host == nil). URLHost constructs only the host (and scheme), so a host matcher is mandatory. Route.URL() works without one and just returns the path.

Source

Thrown at route.go:653

		queries = append(queries, query)
	}
	return &url.URL{
		Scheme:   scheme,
		Host:     host,
		Path:     path,
		RawQuery: strings.Join(queries, "&"),
	}, nil
}

// URLHost builds the host part of the URL for a route. See Route.URL().
//
// The route must have a host defined.
func (r *Route) URLHost(pairs ...string) (*url.URL, error) {
	if r.err != nil {
		return nil, r.err
	}
	if r.regexp.host == nil {
		return nil, errors.New("mux: route doesn't have a host")
	}
	values, err := r.prepareVars(pairs...)
	if err != nil {
		return nil, err
	}
	host, err := r.regexp.host.url(values)
	if err != nil {
		return nil, err
	}
	u := &url.URL{
		Scheme: "http",
		Host:   host,
	}
	if r.buildScheme != "" {
		u.Scheme = r.buildScheme
	}
	return u, nil
}

View on GitHub (pinned to db9d1d0073)

Solutions

1. Use Route.URL() if you only need the path (it tolerates a missing host).
2. Add .Host(...) to the route definition before calling URLHost.
3. Probe with GetHostTemplate() first; if it errors, fall back to URL().

Example fix

// before
u, err := r.Get("x").URLHost() // route has no Host

// after
u, err := r.Get("x").URL() // returns a path-only url

if _, err := rt.GetHostTemplate(); err != nil {
    return rt.URL(pairs...) // path-only fallback
}

func hasHost(rt *mux.Route) bool { _, err := rt.GetHostTemplate(); return err == nil }

u, err := rt.URLHost(pairs...)
if err != nil {
    if strings.Contains(err.Error(), "host") {
        u, err = rt.URL(pairs...)
    }
}

When it happens

Trigger: r.NewRoute().Path("/x").Name("x"); then r.Get("x").URLHost(...) is called but Host() was never invoked on the route.

Common situations: Calling URLHost on a path-only route during link generation; refactor that removed a Host matcher but left URLHost callers; subrouter routes that inherit path but not host.

Related errors

• mux: route doesn't have a path
• key not found in metadata
• mux: duplicated route variable %q
• mux: number of parameters must be multiple of 2, got %v
• mux: route already has name %q, can't set %q

AI-assisted analysis of gorilla/mux@db9d1d0073 (2026-08-04). Data as JSON: /data/errors/52565a3794e3beea.json. Report an issue: GitHub.