grafana/k6 · error

unable to parse "expires" date string "%s": %w

Error message

unable to parse "expires" date string "%s": %w

What it means

In the http cookiejar Set method, an expires parameter that is non-empty must parse as time.RFC1123; this error wraps time.Parse's failure for a malformed date string (e.g. "tomorrow" or missing GMT). The cookie is not set and the error propagates to the script.

Source

Thrown at js/modules/k6/http/cookiejar.go:69

	}

	c := http.Cookie{Name: name, Value: value}
	paramsV := opts
	if !common.IsNullish(paramsV) {
		params := paramsV.ToObject(rt)
		for _, k := range params.Keys() {
			switch strings.ToLower(k) {
			case "path":
				c.Path = params.Get(k).String()
			case "domain":
				c.Domain = params.Get(k).String()
			case "expires":
				var t time.Time
				expires := params.Get(k).String()
				if expires != "" {
					t, err = time.Parse(time.RFC1123, expires)
					if err != nil {
						return false, fmt.Errorf(`unable to parse "expires" date string "%s": %w`, expires, err)
					}
				}
				c.Expires = t
			case "max_age":
				c.MaxAge = int(params.Get(k).ToInteger())
			case "secure":
				c.Secure = params.Get(k).ToBoolean()
			case "http_only":
				c.HttpOnly = params.Get(k).ToBoolean()
			}
		}
	}
	j.Jar.SetCookies(u, []*http.Cookie{&c})
	return true, nil
}

// Clear all cookies for a particular URL
func (j CookieJar) Clear(url string) error {

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Provide expires in RFC 1123 format, e.g. 'Wed, 21 Oct 2026 07:28:00 GMT'
2. Or pass a Date object / omit expires for a session cookie

When it happens

Trigger: Thrown at js/modules/k6/http/cookiejar.go:69 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/8990451fd0a359fb. Report an issue: GitHub.