caddyserver/caddy · error

compiling regular expression

Error message

compiling regular expression %s in query rewrite replace operation: %v

What it means

Wrapper error produced while provisioning the query-rewrite section of the rewrite handler. It surfaces when any query replace operation's Provision fails; the %s shows the operation's SearchRegexp so you can identify which regex is broken. The underlying cause is almost always the nested 'replacement for query field' regexp compile error.

Solutions

1. Note the search_regexp printed in the message and validate it with Go's RE2 syntax
2. Fix or remove the invalid search_regexp for that query key
3. Escape backslashes correctly in JSON
4. Run 'caddy validate' after editing

Example fix

// before
"query": { "replace": [{ "key": "q", "search_regexp": "[", "replace": "x" }] }

// after
"query": { "replace": [{ "key": "q", "search_regexp": "\\[\\d+\\]", "replace": "x" }] }

for _, op := range rewriteCfg.Query.Replace {
    if op.SearchRegexp != "" {
        if _, err := regexp.Compile(op.SearchRegexp); err != nil {
            return fmt.Errorf("query replace for %q has invalid regex: %w", op.Key, err)
        }
    }
}

When it happens

Trigger: Config with rewrite.query.replace[] where search_regexp is set to an invalid RE2 pattern, e.g. "[" or "(?i" (unterminated).

Common situations: Adding query-parameter rewriting with copy-pasted regexes from other tools, or JSON escaping issues that corrupt the pattern.

Related errors

• compiling regular expression
• path_regexp find cannot be empty
• replacement for query field
• compiling matcher regexp
• compiling regexp for mapping

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/119f155b4fe7beea. Report an issue: GitHub.

Appendix: source

Thrown at modules/caddyhttp/rewrite/rewrite.go:124

// Provision sets up rewr.
func (rewr *Rewrite) Provision(ctx caddy.Context) error {
	rewr.logger = ctx.Logger()

	for i, rep := range rewr.PathRegexp {
		if rep.Find == "" {
			return fmt.Errorf("path_regexp find cannot be empty")
		}
		re, err := regexp.Compile(rep.Find)
		if err != nil {
			return fmt.Errorf("compiling regular expression %d: %v", i, err)
		}
		rep.re = re
	}
	if rewr.Query != nil {
		for _, replacementOp := range rewr.Query.Replace {
			err := replacementOp.Provision(ctx)
			if err != nil {
				return fmt.Errorf("compiling regular expression %s in query rewrite replace operation: %v", replacementOp.SearchRegexp, err)
			}
		}
	}

	return nil
}

func (rewr Rewrite) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
	repl := r.Context().Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
	const message = "rewrote request"

	c := rewr.logger.Check(zap.DebugLevel, message)
	if c == nil {
		rewr.Rewrite(r, repl)
		return next.ServeHTTP(w, r)
	}

	changed := rewr.Rewrite(r, repl)

View on GitHub (pinned to 50e54ee279)