PlugEarlyHints (plug_early_hints v0.1.0)

Convenience plug for sending HTTP 103 Early Hints.

This is useful for static resources that will be for sure required by the resulting page. For example you can use it for informing the client that you will need CSS later, so it can start fetching it right now.

Usage

plug PlugEarlyHints,
  # List all resources that will be needed later when rendering page
  paths: [
    # External resources that will be connected to as we will use
    # different resources from it. It will speedup as the TLS handshake
    # will be already ended, so we will be able to fetch resources
    # right away
    "https://gravatar.com/": [rel: "dns-prefetch"],
    "https://gravatar.com/": [rel: "preconnect"],
    # "Regular" resources. We need to set `:as` to inform the client
    # (browser) what kinf of resource it is, so it will be able to
    # properly connect them
    "/css/app.css": [rel: "preload", as: "style"],
    "/js/app.js": [rel: "preload", as: "script"],
    # Preloading fonts will require additional `:type` and `:crossorgin`
    # to allow CSS engine to properly detect when apply the resource as
    # well as to prevent double load.
    "/fonts/recursive.woff2": [
      rel: "preload",
      as: "font",
      crossorgin: :anonymous,
      type: "font/woff2"
    ]
  ]

For more information about available options check out MDN Link.

Options

• :paths - enumerable containing pairs in form of {path, options}.
• :callback - 2-ary function used for expanding path value from :paths. It is useful for example to expand static assets in Phoenix applications. Due to nature of the Plug it must be in form of &Module.function/2 (it cannot be &function/2 nor fn conn, path -> … end). 1st argument will be conn passed to the plug and 2nd argument will be current path. By default it return path unmodified.
• :enable - 1-ary function that will receive conn and should return boolean whether the early hints should be sent or not. You mostly want to do it only for requests returning HTML. The same rules as in :callback apply. By default uses function that alwayst return true.