rulefiles

Go parsers for the _headers and _redirects files of a static site build, the formats popularised by Netlify and Cloudflare Pages.

Package	File	Purpose	Documentation
header	_headers	Response header fields for a path	pkg.go.dev/thde.io/rulefiles/header
redirect	_redirects	URL redirects, rewrites, and errors	pkg.go.dev/thde.io/rulefiles/redirect

go get thde.io/rulefiles@latest

Quick Start

NewHandler reads a rules file and wraps an http.Handler. Handlers compose with header innermost (around the static file server) and redirect outermost, so that header rules apply to the rewritten destination of a redirect:

site, err := header.NewHandler(headersFile, http.FileServerFS(build))
if err != nil {
	return err
}

site, err = redirect.NewHandler(redirectsFile, site)
if err != nil {
	return err
}

For callers that need to inspect or act on rules directly without middleware, both packages also export Parse and Resolve functions. See the package documentation for details.

File Formats

_redirects

_redirects holds one <source> <target> [<status>] rule per line, as documented by Netlify and Cloudflare Pages. The status defaults to 301. A status of 200 rewrites the request internally instead of redirecting. Query parameters of the request are preserved unless the target defines them.

/old/path        /new/path
/docs/:id/*      /articles/:id/:splat  302
/gone            /                     410

_headers

_headers holds an unindented path pattern followed by indented <name>: <value> or ! <name> lines, as documented by Netlify and Cloudflare Pages. All matching rules apply in the order declared; a field set by more than one rule is joined with a comma. Field names are case insensitive.

/*
  X-Robots-Tag: noindex
/static/*
  Cache-Control: public, max-age=31536000, immutable
  ! X-Robots-Tag

Path Patterns & Placeholders

Both formats share pattern syntax:

• Patterns match against the decoded request path and are case sensitive.
• Named placeholders (:name) capture individual path segments.
• A trailing * captures the remainder of the path as :splat.
• Placeholders expand into the target path, query, and fragment separately with proper escaping. Placeholders cannot introduce directory traversals (..).
• Comments start with # at the start of a line or after whitespace.

Differences from Netlify and Cloudflare Pages

• Matching on a scheme, host, query string, country, language, role, or cookie is not supported. Proxying to another host is supported via redirect.WithProxying and redirect.WithProxy.
• A trailing ! on a redirect status (e.g. 301!) forces a rule to apply even if a file of the same name exists, reported as Rule.Force (enabled with redirect.WithExists).
• A rule that omits the status redirects with 301 (Netlify default). Cloudflare defaults to 302; use redirect.WithDefaultStatus to configure.
• By default a trailing slash is ignored on both sides (Netlify default). Use WithExactTrailingSlash() to match trailing slashes exactly (Cloudflare default).
• * is only supported as the last segment of a pattern.
• Special characters in source paths may be URL-encoded or written as literals.
• Header fields that frame the response (Content-Length, Transfer-Encoding, Connection, Upgrade, etc.) are rejected with ErrUnsupported.
• A field declared more than once is joined with ", " (Cloudflare behavior). Set-Cookie values are retained as separate header lines.
• Lines longer than 1 MiB are rejected to bound allocation.

Documentation

Full API documentation, options, and examples are available via go doc or pkg.go.dev:

• thde.io/rulefiles: Root module overview, architecture, and pipeline composition.
• thde.io/rulefiles/header: Header rule parsing, resolution, and response writer middleware.
• thde.io/rulefiles/redirect: Redirect rule parsing, resolution, proxying, and middleware.

Tests

go test ./...

Both parsers include fuzz tests verifying round-trip encoding and safe resolution:

go test ./redirect -run '^$' -fuzz FuzzResolve
go test ./header -run '^$' -fuzz FuzzResolve