Domain pattern ' ' has parts, which exceeds the maximum of

Error message

Domain pattern '%s' has %d parts, which exceeds the maximum of %d

What it means

parseDomainPattern splits the pattern on '.' and rejects any pattern with more than maxDomainParts labels to prevent DoS via pathological patterns (each label is processed and matched per request). This is a defensive cap on pattern complexity.

Solutions

Reduce the number of dot-separated labels below maxDomainParts (check the constant in domain.go for the exact cap).
Validate segment count before registering: if len(strings.Split(p, ".")) > cap { return error }.
Collapse redundant subdomains or use a wildcard parameter label.

Example fix

// before
pattern := strings.Join(segments, ".")  // segments has 200 entries
app.Domain(pattern)

// after
if len(segments) > maxDomainParts { return fmt.Errorf("too many domain labels") }
app.Domain(strings.Join(segments, "."))

Defensive patterns

Strategy: validation

Validate before calling

// Reject patterns with too many labels before registration
func validateDomainParts(p string, max int) error {
    n := strings.Count(p, ".") + 1
    if n > max { return fmt.Errorf("too many domain labels: %d > %d", n, max) }
    return nil
}

Prevention

Bound the number of segments when composing patterns from lists.
Document the maxDomainParts cap for your team.
Use wildcard parameter labels to absorb redundant subdomains.

When it happens

Trigger: Passing a pattern like a.b.c.d....z with more labels than maxDomainParts allows; or a pattern constructed by joining many tokens without limit.

Common situations: Building a domain pattern from a list of user-supplied segments; copy-paste of a deep subdomain chain; misconfigured wildcard expansion.

Related errors

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/fc980bccbcebcf02. Report an issue: GitHub.

Appendix: source

Thrown at domain.go:76

	// consistent with Fiber's own host normalization in Subdomains().
	pattern = utils.TrimRight(pattern, '.')

	// Validate pattern is not empty after trimming
	if pattern == "" {
		panic("Domain pattern cannot be empty")
	}

	// Enforce RFC 1035 total length limit on patterns
	if len(pattern) > 253 {
		panic(fmt.Sprintf("Domain pattern '%s' exceeds RFC 1035 maximum of 253 characters (%d chars)",
			pattern, len(pattern)))
	}

	parts := strings.Split(pattern, ".")

	// Prevent DoS from patterns with excessive label counts
	if len(parts) > maxDomainParts {
		panic(fmt.Sprintf("Domain pattern '%s' has %d parts, which exceeds the maximum of %d",
			pattern, len(parts), maxDomainParts))
	}

	m := domainMatcher{
		parts:    make([]string, len(parts)),
		numParts: len(parts),
	}

	for i, part := range parts {
		// Validate no empty labels (e.g., "example..com" is invalid)
		if part == "" {
			panic(fmt.Sprintf("Domain pattern '%s' contains empty label at position %d", pattern, i))
		}

		if part[0] == ':' {
			// Validate parameter name is not empty
			if len(part) == 1 {
				panic(fmt.Sprintf("Domain pattern '%s' contains empty parameter name at position %d", pattern, i))

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