Defines the Phoenix.Digester.Compressor behaviour for implementing static file compressors.

A custom compressor expects 2 functions to be implemented.

By default, Phoenix uses only Phoenix.Digester.Gzip to compress static files, but additional compressors can be defined and added to the digest process.

Example

If you wanted to compress files using an external brotli compression library, you could define a new module implementing the behaviour and add the module to the list of configured Phoenix static compressors.

defmodule MyApp.BrotliCompressor do
  @behaviour Phoenix.Digester.Compressor

  def compress_file(file_path, content) do
    valid_extension = Path.extname(file_path) in Application.fetch_env!(:phoenix, :gzippable_exts)
    compressed_content = :brotli.encode(content)

    if valid_extension && byte_size(compressed_content) < byte_size(content) do
      {:ok, compressed_content}
    else
      :error
    end
  end

  def file_extensions do
    [".br"]
  end
end

# config/config.exs
config :phoenix,
  static_compressors: [Phoenix.Digester.Gzip, MyApp.BrotliCompressor],
  # ...