module HTTP2::FlowBuffer

Implementation of stream and connection DATA flow control: frames may be split and / or may be buffered based on current flow control window.

Public Instance Methods

buffered_amount() click to toggle source

Amount of buffered data. Only DATA payloads are subject to flow stream and connection flow control.

@return [Integer]

# File lib/http/2/flow_buffer.rb, line 10
def buffered_amount
  @send_buffer.map { |f| f[:length] }.reduce(:+) || 0
end

Private Instance Methods

calculate_window_update(window_max_size) click to toggle source
# File lib/http/2/flow_buffer.rb, line 22
def calculate_window_update(window_max_size)
  # If DATA frame is received with length > 0 and
  # current received window size + delta length is strictly larger than
  # local window size, it throws a flow control error.
  #
  error(:flow_control_error) if @local_window < 0

  # Send WINDOW_UPDATE if the received window size goes over
  # the local window size / 2.
  #
  # The HTTP/2 spec mandates that every DATA frame received
  # generates a WINDOW_UPDATE to send. In some cases however,
  # (ex: DATA frames with short payloads),
  # the noise generated by flow control frames creates enough
  # congestion for this to be deemed very inefficient.
  #
  # This heuristic was inherited from nghttp, which delays the
  # WINDOW_UPDATE until at least half the window is exhausted.
  # This works because the sender doesn't need those increments
  # until the receiver window is exhausted, after which he'll be
  # waiting for the WINDOW_UPDATE frame.
  return unless @local_window <= (window_max_size / 2)
  window_update(window_max_size - @local_window)
end
process_window_update(frame) click to toggle source
# File lib/http/2/flow_buffer.rb, line 94
def process_window_update(frame)
  return if frame[:ignore]
  @remote_window += frame[:increment]
  send_data
end
send_data(frame = nil, encode = false) click to toggle source

Buffers outgoing DATA frames and applies flow control logic to split and emit DATA frames based on current flow control window. If the window is large enough, the data is sent immediately. Otherwise, the data is buffered until the flow control window is updated.

Buffered DATA frames are emitted in FIFO order.

@param frame [Hash] @param encode [Boolean] set to true by co

# File lib/http/2/flow_buffer.rb, line 56
def send_data(frame = nil, encode = false)
  @send_buffer.push frame unless frame.nil?

  # FIXME: Frames with zero length with the END_STREAM flag set (that
  # is, an empty DATA frame) MAY be sent if there is no available space
  # in either flow control window.
  while @remote_window > 0 && !@send_buffer.empty?
    frame = @send_buffer.shift

    sent, frame_size = 0, frame[:payload].bytesize

    if frame_size > @remote_window
      payload = frame.delete(:payload)
      chunk   = frame.dup

      # Split frame so that it fits in the window
      # TODO: consider padding!
      frame[:payload] = payload.slice!(0, @remote_window)
      chunk[:length]  = payload.bytesize
      chunk[:payload] = payload

      # if no longer last frame in sequence...
      frame[:flags] -= [:end_stream] if frame[:flags].include? :end_stream

      @send_buffer.unshift chunk
      sent = @remote_window
    else
      sent = frame_size
    end

    manage_state(frame) do
      frames = encode ? encode(frame) : [frame]
      frames.each { |f| emit(:frame, f) }
      @remote_window -= sent
    end
  end
end
update_local_window(frame) click to toggle source
# File lib/http/2/flow_buffer.rb, line 16
def update_local_window(frame)
  frame_size = frame[:payload].bytesize
  frame_size += frame[:padding] || 0
  @local_window -= frame_size
end