gocolly/colly · warning

ErrNoPattern

ErrNoPattern

Error message

No pattern defined in LimitRule

What it means

ErrNoPattern is returned by LimitRule.Init() when a LimitRule has no URL pattern defined. Limit rules use regexp patterns to match which URLs a rate limit applies to; a rule without DomainRegexp, Domain, or URLRegexp/Path cannot be compiled, so Init fails and the collector cannot start limiting.

Source

Thrown at colly.go:240

	// a domain which is not allowed in AllowedDomains
	ErrForbiddenDomain = errors.New("Forbidden domain")
	// ErrMissingURL is the error type for missing URL errors
	ErrMissingURL = errors.New("Missing URL")
	// ErrMaxDepth is the error type for exceeding max depth
	ErrMaxDepth = errors.New("Max depth limit reached")
	// ErrForbiddenURL is the error thrown if visiting
	// a URL which is not allowed by URLFilters
	ErrForbiddenURL = errors.New("ForbiddenURL")

	// ErrNoURLFiltersMatch is the error thrown if visiting
	// a URL which is not allowed by URLFilters
	ErrNoURLFiltersMatch = errors.New("No URLFilters match")
	// ErrRobotsTxtBlocked is the error type for robots.txt errors
	ErrRobotsTxtBlocked = errors.New("URL blocked by robots.txt")
	// ErrNoCookieJar is the error type for missing cookie jar
	ErrNoCookieJar = errors.New("Cookie jar is not available")
	// ErrNoPattern is the error type for LimitRules without patterns
	ErrNoPattern = errors.New("No pattern defined in LimitRule")
	// ErrEmptyProxyURL is the error type for empty Proxy URL list
	ErrEmptyProxyURL = errors.New("Proxy URL list is empty")
	// ErrAbortedAfterHeaders is the error returned when OnResponseHeaders aborts the transfer.
	ErrAbortedAfterHeaders = errors.New("Aborted after receiving response headers")
	// ErrAbortedBeforeRequest is the error returned when OnResponseHeaders aborts the transfer.
	ErrAbortedBeforeRequest = errors.New("Aborted before Do Request")
	// ErrQueueFull is the error returned when the queue is full
	ErrQueueFull = errors.New("Queue MaxSize reached")
	// ErrMaxRequests is the error returned when exceeding max requests
	ErrMaxRequests = errors.New("Max Requests limit reached")
	// ErrRetryBodyUnseekable is the error when retry with not seekable body
	ErrRetryBodyUnseekable = errors.New("Retry Body Unseekable")
)

var envMap = map[string]func(*Collector, string){
	"ALLOWED_DOMAINS": func(c *Collector, val string) {
		c.AllowedDomains = strings.Split(val, ",")
	},

View on GitHub (pinned to 17d1d6ca92)

Solutions

1. Set a pattern on the rule: Domain, DomainRegexp, or URLRegexp must be non-empty
2. Validate rule config at startup before calling c.LimitRule
3. Skip empty rules in generated config instead of passing them to LimitRule
4. Double-check field names — pattern fields are DomainRegexp/DomainGlob/URLRegexp etc., not "Pattern"

Example fix

// before
rule := &colly.LimitRule{Delay: 2 * time.Second, RandomDelay: time.Second}
err := c.LimitRule(rule) // ErrNoPattern: no pattern defined
// after
rule := &colly.LimitRule{DomainRegexp: "example\.com", Delay: 2 * time.Second, RandomDelay: time.Second}
err := c.LimitRule(rule)

for _, r := range rules {
    if r.Domain == "" && r.DomainRegexp == "" && r.DomainGlob == "" && r.URLRegexp == "" {
        return fmt.Errorf("limit rule %+v has no pattern", r)
    }
}
for _, r := range rules {
    if err := c.LimitRule(r); err != nil { return err }
}

if err := c.LimitRule(rule); err != nil {
    if errors.Is(err, colly.ErrNoPattern) {
        return fmt.Errorf("rule %v missing Domain/DomainRegexp/URLRegexp: %w", rule, err)
    }
    return err
}

When it happens

Trigger: Calling c.LimitRule(&colly.LimitRule{DomainRegexp: "...", Delay: ...}) with a rule missing any pattern fields; constructing rules dynamically where the pattern string ends up empty; c.Limit/rules initialization loops where one entry forgot its pattern.

Common situations: Building LimitRules from config/JSON where the pattern key is absent or empty; copy-pasting a rule and deleting the Domain/DomainRegexp line; programmatically generating rules for multiple domains where one domain string is blank.

Related errors

• ErrEmptyProxyURL
• ErrForbiddenDomain
• ErrMissingURL
• ErrMaxDepth
• ErrForbiddenURL

AI-assisted analysis of gocolly/colly@17d1d6ca92 (2026-08-30). Data as JSON: /api/errors/c6d4d6b7f44998be. Report an issue: GitHub.