What causes "invalid hostname: %q" in mislav/hub?

Fix the host string to a bare, valid hostname such as ghe.example.com (no scheme, no spaces, no path).

invalid hostname: %q

Error message

invalid hostname: %q

What it means

PromptForHost validates any non-GitHub.com host by parsing "https://" + host with net/url before looking it up in the config. If the URL parse fails, the hostname is malformed and this error is returned. Note it only catches structurally invalid hostnames (e.g. containing spaces or control characters), not DNS or reachability problems.

Source

Thrown at github/config.go:48

	User        string `toml:"user"`
	AccessToken string `toml:"access_token"`
	Protocol    string `toml:"protocol"`
	UnixSocket  string `toml:"unix_socket,omitempty"`
}

type Config struct {
	Hosts []*Host `toml:"hosts"`

	stdinScanner *bufio.Scanner
}

func (c *Config) PromptForHost(host string) (h *Host, err error) {
	token := c.DetectToken()
	tokenFromEnv := token != ""

	if host != GitHubHost {
		if _, e := url.Parse("https://" + host); e != nil {
			err = fmt.Errorf("invalid hostname: %q", host)
			return
		}
	}

	h = c.Find(host)
	if h != nil {
		if h.User == "" {
			utils.Check(CheckWriteable(configsFile()))
			// User is missing from the config: this is a broken config probably
			// because it was created with an old (broken) version of hub. Let's fix
			// it now. See issue #1007 for details.
			user := c.PromptForUser(host)
			if user == "" {
				utils.Check(fmt.Errorf("missing user"))
			}
			h.User = user
			err := newConfigService().Save(configsFile(), c)
			utils.Check(err)

View on GitHub (pinned to 5c547ed804)

Solutions

Fix the host string to a bare, valid hostname such as ghe.example.com (no scheme, no spaces, no path).
Unset or correct the GITHUB_HOST environment variable if it holds an invalid value.
Sanitize input before calling DefaultHost/DefaultHostNoPrompt (strip scheme, trim spaces).

Example fix

// before
host := os.Getenv("GITHUB_HOST") // "https://ghe.corp.example"
// after
host := strings.TrimPrefix(strings.TrimPrefix(os.Getenv("GITHUB_HOST"), "https://"), "http://")
c.PromptForHost(host)

Defensive patterns

Strategy: validation

Validate before calling

host := os.Getenv("GITHUB_HOST")
host = strings.TrimPrefix(strings.TrimPrefix(host, "https://"), "http://")
host = strings.TrimSpace(host)
if _, err := url.Parse("https://" + host); err != nil {
    log.Fatalf("GITHUB_HOST is not a valid hostname: %q", host)
}

Type guard

func validHost(host string) bool {
    if host == "github.com" {
        return true
    }
    _, err := url.Parse("https://" + host)
    return err == nil && host != ""
}

Try / catch

h, err := cfg.PromptForHost(host)
if err != nil && strings.HasPrefix(err.Error(), "invalid hostname") {
    return fmt.Errorf("bad host %q: %w", host, err)
}

Prevention

Store bare hostnames (no scheme, no path) in GITHUB_HOST and hub config
Trim whitespace and scheme prefixes from user-supplied host strings
Validate hostnames with url.Parse before passing to DefaultHost

When it happens

Trigger: Calling PromptForHost (indirectly via DefaultHost or DefaultHostNoPrompt) with a host string that is not exactly github.com and cannot be parsed as a URL host, e.g. "my host.example.com" or a host with illegal characters.

Common situations: Typo or paste error in GITHUB_HOST or in the host name during first-run interactive setup; leading/trailing whitespace or protocol prefix ("https://ghe.example.com") accidentally included in the host value.

Related errors

AI-assisted analysis of mislav/hub@5c547ed804 (2026-09-01). Data as JSON: /api/errors/8448d1b8747c8a73. Report an issue: GitHub.