caddyserver/caddy · error

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

Error message

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

What it means

AddOperation enforces maxPatternLength (1000 characters) on the rawRegexp argument. It mirrors the Validate() length cap so that programmatically merged filters cannot bypass the config-time limit.

Source

Thrown at modules/logging/filters.go:1008

		}
	}
	return result
}

// AddOperation adds a single regexp operation to the filter with validation.
// This is used when merging multiple RegexpFilter instances.
func (f *MultiRegexpFilter) AddOperation(rawRegexp, value string) error {
	// Security checks
	if len(f.Operations) >= maxRegexpOperations {
		return fmt.Errorf("cannot add operation: maximum %d operations allowed", maxRegexpOperations)
	}

	if rawRegexp == "" {
		return fmt.Errorf("regexp pattern cannot be empty")
	}

	if len(rawRegexp) > maxPatternLength {
		return fmt.Errorf("regexp pattern too long: %d characters (maximum %d)", len(rawRegexp), maxPatternLength)
	}

	f.Operations = append(f.Operations, regexpFilterOperation{
		RawRegexp: rawRegexp,
		Value:     value,
	})
	return nil
}

// RenameFilter is a Caddy log field filter that
// renames the field's key with the indicated name.
type RenameFilter struct {
	Name string `json:"name,omitempty"`
}

// CaddyModule returns the Caddy module information.
func (RenameFilter) CaddyModule() caddy.ModuleInfo {
	return caddy.ModuleInfo{

View on GitHub (pinned to 50e54ee279)

Solutions

1. Split the long pattern into multiple operations (respecting the 50-op cap)
2. Shorten with grouping/character classes, or use a purpose-built filter (hash_query, delete) for redaction
3. Add a length assertion in the generator so oversized patterns never reach AddOperation

Example fix

// before
mf.AddOperation(hugePattern, "REDACTED") // len(hugePattern) > 1000

// after
for _, p := range splitPattern(hugePattern, 1000) {
    if err := mf.AddOperation(p, "REDACTED"); err != nil {
        return err
    }
}

if len(rawRegexp) > 1000 {
    return fmt.Errorf("pattern too long: split it across operations")
}

When it happens

Trigger: Calling AddOperation with a pattern longer than 1000 characters, typically in code that merges or generates regexp filter operations.

Common situations: Generated alternation lists of redaction tokens; concatenating patterns with | while merging filters; embedding large literals into the expression.

Related errors

• cannot add operation: maximum %d operations allowed
• regexp pattern cannot be empty
• server %s: logger name must not have a port: %s
• provisioning fallback encoder module: %v
• loading wrapped encoder module: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/3e47a0766a701011. Report an issue: GitHub.