crowdsecurity/crowdsec · error

invalid type for url: %T

Error message

invalid type for url: %T

What it means

HTTPGet is an expr helper whose arguments arrive as ...any. It asserts params[0] to string and returns this error when the URL argument is not a string, naming the actual Go type so you can see what was passed instead.

Source

Thrown at pkg/exprhelpers/http.go:74

	defer resp.Body.Close()

	b, err := io.ReadAll(io.LimitReader(resp.Body, exprHTTPMaxBodySize))
	if err != nil {
		return nil, err
	}

	return &HTTPResponse{
		StatusCode: resp.StatusCode,
		Body:       string(b),
		Headers:    resp.Header,
	}, nil
}

// HTTPGet(url string) (*HTTPResponse, error)
func HTTPGet(params ...any) (any, error) {
	uri, ok := params[0].(string)
	if !ok {
		return nil, fmt.Errorf("invalid type for url: %T", params[0])
	}

	return doHTTPRequest(http.MethodGet, uri, nil, nil)
}

// HTTPHead(url string) (*HTTPResponse, error)
func HTTPHead(params ...any) (any, error) {
	uri, ok := params[0].(string)
	if !ok {
		return nil, fmt.Errorf("invalid type for url: %T", params[0])
	}

	return doHTTPRequest(http.MethodHead, uri, nil, nil)
}

// HTTPPost(url string, contentType string, body string) (*HTTPResponse, error)
func HTTPPost(params ...any) (any, error) {
	uri, ok := params[0].(string)

View on GitHub (pinned to 909b515798)

Solutions

1. Ensure the argument is a string: use a quoted literal or a field known to hold a string URL
2. If the field may be nil/missing, wrap in a condition checking it before calling HTTPGet
3. Convert non-string values to string first (e.g. string(evt.port) is not a URL — build the full URL string)
4. Check the reported %T in the message to identify what type the field actually holds

Example fix

// before
HTTPGet(evt.target) // target is nil sometimes
// after
// guard in expr:
//   evt.target != nil ? HTTPGet(evt.target) : nil

// expr: evt.url != nil && type(evt.url) == string

func isString(v interface{}) bool { _, ok := v.(string); return ok }

When it happens

Trigger: Calling HTTPGet() in an expression with a non-string first argument, e.g. HTTPGet(evt.url_field) where the field is nil, a number, or an object; forgetting to wrap a literal in quotes.

Common situations: Event field is nil because the URL was absent from the log; numeric fields (port-only value) passed as URL; expression written with an unquoted identifier that resolves to a non-string variable.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• invalid type for contentType: %T
• invalid type for body: %T
• invalid type for method: %T
• invalid type for headers: %T
• AverageInterval expects a slice of times

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/a76ffbd6a9dafc93. Report an issue: GitHub.