thanos-io/thanos · error

create request

Error message

create %s request

What it means

In promclient's req2xx helper, http.NewRequest failed while building the outgoing API request. The error wraps the underlying reason (bad method, unparseable URL, invalid body) with the message "create <method> request". No network traffic has happened yet.

Solutions

1. Validate the base URL with url.Parse and require a scheme before calling the client
2. URL-encode query values (url.Values.Encode) instead of string concatenation
3. Use only valid HTTP method constants
4. Log/inspect the wrapped error to see which URL component failed

Example fix

// before
u, _ := url.Parse(baseURL + "/api/v1/query?query=" + query)
// after
u, err := url.Parse(baseURL)
if err != nil { return err }
u.Path = "/api/v1/query"
u.RawQuery = url.Values{"query": []string{query}}.Encode()

u, err := url.Parse(promURL)
if err != nil || u.Scheme == "" || u.Host == "" {
    return fmt.Errorf("invalid prometheus URL %q", promURL)
}

func isValidURL(raw string) bool {
    u, err := url.Parse(raw)
    return err == nil && (u.Scheme == "http" || u.Scheme == "https") && u.Host != ""
}

flags, _, err := client.BuildVersion(ctx, promURL)
if err != nil && strings.Contains(err.Error(), "create request") {
    // malformed URL/method: fix config, do not retry
    return err
}

When it happens

Trigger: Calling any client wrapper (ExternalLabels, QueryInstant, QueryRange, AlertmanagerAlerts, BuildVersion) with a URL that fails url.Parse or an invalid HTTP method, e.g. a malformed promURL containing spaces or bad characters.

Common situations: Misconfigured --prometheus.url flag with typos or unencoded characters; programmatically built URLs missing scheme ("localhost:9090" without http://); empty base URL.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

• creating request to downstream URL
• expected 2xx response, got
• create request
• unable to create request
• setup downstream roundtripper

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/de804b0e4fdc589e. Report an issue: GitHub.

Appendix: source

Thrown at pkg/promclient/promclient.go:120

		httpClient,
		logger,
		userAgent,
	)
}

// req2xx sends a request to the given url.URL. If method is http.MethodPost then
// the raw query is encoded in the body and the appropriate Content-Type is set.
func (c *Client) req2xx(ctx context.Context, u *url.URL, method string, headers http.Header) (_ []byte, _ int, err error) {
	var b io.Reader
	if method == http.MethodPost {
		rq := u.RawQuery
		b = strings.NewReader(rq)
		u.RawQuery = ""
	}

	req, err := http.NewRequest(method, u.String(), b)
	if err != nil {
		return nil, 0, errors.Wrapf(err, "create %s request", method)
	}
	if headers != nil {
		req.Header = headers
	}

	if c.userAgent != "" {
		req.Header.Set("User-Agent", c.userAgent)
	}
	if method == http.MethodPost {
		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	}

	resp, err := c.Do(req.WithContext(ctx))
	if err != nil {
		return nil, 0, errors.Wrapf(err, "perform %s request against %s", method, u.String())
	}
	defer runutil.ExhaustCloseWithErrCapture(&err, resp.Body, "%s: close body", req.URL.String())

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