device.rb

require 'ffi'

module HidApi
  class Device < FFI::Pointer
    extend FFI::DataConverter
    native_type FFI::Type::POINTER

    def self.from_native(value, ctx)
      new(value)
    end

    def close
      HidApi.close(self)
    end

    def set_nonblocking(int)
      HidApi.hid_set_nonblocking self, int
    end

    def get_manufacturer_string
      get_buffered_string :manufacturer
    end

    def get_product_string
      get_buffered_string :product
    end

    def get_serial_number_string
      get_buffered_string :serial_number
    end

    def read(length)
      buffer = clear_buffer length
      with_hid_error_handling do
        HidApi.hid_read self, buffer, buffer.length
      end
      buffer
    end

    def read_timeout(length, timeout)
      buffer = clear_buffer length
      with_hid_error_handling do
        HidApi.hid_read_timeout self, buffer, buffer.length, timeout
      end
      buffer
    end

    def write(data)
      buffer = clear_buffer data.length
      case data
      when String then buffer.put_bytes 0, data
      when Array then buffer.put_array_of_char 0, data
      end

      with_hid_error_handling do
        HidApi.hid_write self, buffer, buffer.length
      end
    end

    def get_feature_report(data)
      buffer = clear_buffer data.length
      case data
      when String then buffer.put_bytes 0, data
      when Array then buffer.put_array_of_char 0, data
      end

      with_hid_error_handling do
        HidApi.hid_get_feature_report self, buffer, buffer.length
      end
    end

    def send_feature_report(data)
      buffer = clear_buffer data.length
      case data
      when String then buffer.put_bytes 0, data
      when Array then buffer.put_array_of_char 0, data
      end

      with_hid_error_handling do
        HidApi.hid_send_feature_report self, buffer, buffer.length
      end
    end

    def error
      # NOTE: hid_error is only implemented on Windows systems and returns nil
      # on other platforms
      HidApi.hid_error(self)
    end

    private
    def clear_buffer length
      b = FFI::Buffer.new(1, length)
      # FFI::Buffer doesn't clear the first byte if length < 8
      b.put_char 0, 0
      b
    end

    def get_buffered_string field
      buffer = clear_buffer 255
      HidApi.send "hid_get_#{field}_string", self, buffer, buffer.length
      buffer.read_wchar_string
    end

    def with_hid_error_handling
      raise ArgumentError, "Block required" unless block_given?
      yield.tap do |result|
        raise HidError, error if result == -1
      end
    end
  end
end