caddyserver/caddy · error

regexp pattern %d too long: %d characters (maximum %d)

Error message

regexp pattern %d too long: %d characters (maximum %d)

What it means

Error "regexp pattern %d too long: %d characters (maximum %d)" thrown in caddyserver/caddy.

Source

Thrown at modules/logging/filters.go:914

	return nil
}

// Provision compiles all regexp patterns with security validation.
func (f *MultiRegexpFilter) Provision(ctx caddy.Context) error {
	// Security check: validate operation count
	if len(f.Operations) > maxRegexpOperations {
		return fmt.Errorf("too many regexp operations: %d (maximum %d allowed)", len(f.Operations), maxRegexpOperations)
	}

	if len(f.Operations) == 0 {
		return fmt.Errorf("multi_regexp filter requires at least one operation")
	}

	for i := range f.Operations {
		// Security validation: pattern length check
		if len(f.Operations[i].RawRegexp) > maxPatternLength {
			return fmt.Errorf("regexp pattern %d too long: %d characters (maximum %d)", i, len(f.Operations[i].RawRegexp), maxPatternLength)
		}

		// Security validation: empty pattern check
		if f.Operations[i].RawRegexp == "" {
			return fmt.Errorf("regexp pattern %d cannot be empty", i)
		}

		// Compile and validate the pattern (uses RE2 engine - safe from ReDoS)
		r, err := regexp.Compile(f.Operations[i].RawRegexp)
		if err != nil {
			return fmt.Errorf("compiling regexp pattern %d (%s): %v", i, f.Operations[i].RawRegexp, err)
		}
		f.Operations[i].regexp = r
	}
	return nil
}

// Validate ensures the filter is properly configured with security checks.

View on GitHub (pinned to 50e54ee279)

Solutions

1. Shorten the regexp pattern to fit within the maximum allowed length.

When it happens

Trigger: Thrown at modules/logging/filters.go:914 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/6102cf6c152e4ad5. Report an issue: GitHub.