Caddy handlers for _headers and _redirects

Two Caddy HTTP handler modules that serve the _headers and _redirects files of a static site build, the formats popularised by Netlify and Cloudflare Pages. They let the redirects and response headers of docs.nine.ch live next to the site content instead of in the Caddyfile.

The files themselves are parsed by thde.io/rulefiles, which has no dependency on Caddy. This module only registers the handlers and wires them into the request lifecycle.

Usage

Build a Caddy binary with both handlers:

xcaddy build \
  --with thde.io/caddy-rulefiles/headersfile \
  --with thde.io/caddy-rulefiles/redirectsfile

Then point the directives at the files of the build:

:8080 {
	root * /srv

	headers_file * /srv/_headers
	redirects_file * /srv/_redirects

	try_files {path} /index.html
	file_server
}

Both directives take [<matcher>] <file...>. A leading argument starting with / is taken for a path matcher, so the catch-all matcher * has to be spelled out. Multiple files are loaded in order of precedence. Files are read once while provisioning; changing them requires a config reload.

The directives are ordered after header and redir respectively, so rules are matched against the path as it was requested, before try_files or a rewrite changes it.

File formats

_redirects holds one <source> <target> [<status>] rule per line, first match wins. _headers holds an unindented path pattern followed by indented <name>: <value> or ! <name> lines, and all matching rules apply.

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

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

See the rulefiles documentation for the full syntax and how it differs from Netlify. Parse errors of all lines are reported together and fail provisioning.

Caddy specifics

• A redirect rule always takes precedence over an existing file. Netlify needs a trailing ! for that; the marker is accepted and ignored. To give files precedence, use a matcher: @missing not file plus redirects_file @missing /srv/_redirects.
• A rewrite (200) hands the rewritten path to the next handler, so try_files and file_server serve it as if it had been requested.
• A status of 400 and above is returned as a Caddy error, which the handle_errors routes can answer.

Tests

go test ./...