brotli_decompression_middleware.rb

require 'brotli'

module FeedRs
  class BrotliDecompressionMiddleware < Faraday::Middleware
    ACCEPT_ENCODING = 'Accept-Encoding'.freeze
    CONTENT_ENCODING = 'Content-Encoding'.freeze
    CONTENT_LENGTH = 'Content-Length'.freeze
    SUPPORTED_ENCODINGS = 'br'.freeze

    def call(env)
      env[:request_headers][ACCEPT_ENCODING] = SUPPORTED_ENCODINGS

      @app.call(env).on_complete do |response_env|
        if response_env[:body].empty?
          reset_body(response_env, &method(:raw_body))
        else
          case response_env[:response_headers][CONTENT_ENCODING]
          when 'br'
            reset_body(response_env, &method(:brotli_inflate))
          else
            reset_body(response_env, &method(:raw_body))
          end
        end
      end
    end

    def reset_body(env)
      env[:body] = yield(env[:body])
      env[:response_headers].delete(CONTENT_ENCODING)
      env[:response_headers][CONTENT_LENGTH] = env[:body].length
    end

    def brotli_inflate(body)
      Brotli.inflate(body)
    end

    def raw_body(body)
      body
    end

    Faraday::Response.register_middleware(brotli: -> { BrotliDecompressionMiddleware })
  end
end