class EventMachine::FileStreamer

Streams a file over a given connection. Streaming begins once the object is instantiated. Typically FileStreamer instances are not reused.

Streaming uses buffering for files larger than 16K and uses so-called fast file reader (a C++ extension) if available (it is part of eventmachine gem itself).

@example

module FileSender
  def post_init
    streamer = EventMachine::FileStreamer.new(self, '/tmp/bigfile.tar')
    streamer.callback{
      # file was sent successfully
      close_connection_after_writing
    }
  end
end

@author Francis Cianfrocca

Constants

BackpressureLevel

Wait until next tick to send more data when 50k is still in the outgoing buffer

ChunkSize

Send 16k chunks at a time

MappingThreshold

Use mapped streamer for files bigger than 16k

Public Class Methods

new(connection, filename, args = {}) click to toggle source

@param [EventMachine::Connection] connection @param [String] filename File path

@option args [Boolean] :http_chunks (false) Use HTTP 1.1 style chunked-encoding semantics.

# File lib/em/streamer.rb, line 36
def initialize connection, filename, args = {}
  @connection = connection
  @http_chunks = args[:http_chunks]

  if File.exist?(filename)
    @size = File.size(filename)
    if @size <= MappingThreshold
      stream_without_mapping filename
    else
      stream_with_mapping filename
    end
  else
    fail "file not found"
  end
end

Public Instance Methods

stream_one_chunk() click to toggle source

Used internally to stream one chunk at a time over multiple reactor ticks @private

# File lib/em/streamer.rb, line 77
def stream_one_chunk
  loop {
    if @position < @size
      if @connection.get_outbound_data_size > BackpressureLevel
        EventMachine::next_tick {stream_one_chunk}
        break
      else
        len = @size - @position
        len = ChunkSize if (len > ChunkSize)

        @connection.send_data( "#{len.to_s(16)}\r\n" ) if @http_chunks
        @connection.send_data( @mapping.get_chunk( @position, len ))
        @connection.send_data("\r\n") if @http_chunks

        @position += len
      end
    else
      @connection.send_data "0\r\n\r\n" if @http_chunks
      @mapping.close
      succeed
      break
    end
  }
end

Private Instance Methods

ensure_mapping_extension_is_present() click to toggle source

We use an outboard extension class to get memory-mapped files. It’s outboard to avoid polluting the core distro, but that means there’s a “hidden” dependency on it. The first time we get here in any run, try to load up the dependency extension. User code will see a LoadError if it’s not available, but code that doesn’t require mapped files will work fine without it. This is a somewhat difficult compromise between usability and proper modularization.

@private

# File lib/em/streamer.rb, line 112
def ensure_mapping_extension_is_present
  @@fastfilereader ||= (require 'fastfilereaderext')
end
stream_with_mapping(filename) click to toggle source

@private

# File lib/em/streamer.rb, line 66
def stream_with_mapping filename
  ensure_mapping_extension_is_present

  @position = 0
  @mapping = EventMachine::FastFileReader::Mapper.new filename
  stream_one_chunk
end
stream_without_mapping(filename) click to toggle source

@private

# File lib/em/streamer.rb, line 53
def stream_without_mapping filename
  if @http_chunks
    @connection.send_data "#{@size.to_s(16)}\r\n"
    @connection.send_file_data filename
    @connection.send_data "\r\n0\r\n\r\n"
  else
    @connection.send_file_data filename
  end
  succeed
end