Class: HTTP2::Framer

Inherits:
Object
  • Object
show all
Includes:
Error
Defined in:
lib/http/2/framer.rb

Overview

Performs encoding, decoding, and validation of binary HTTP 2.0 frames.

Constant Summary collapse

MAX_PAYLOAD_SIZE =

Maximum frame size (65535 bytes)

2**16-1
MAX_STREAM_ID =

Maximum stream ID (2^31)

0x7fffffff
MAX_WINDOWINC =

Maximum window increment value (2^31)

0x7fffffff
FRAME_TYPES =

HTTP 2.0 frame type mapping as defined by the spec

{
  data:          0x0,
  headers:       0x1,
  priority:      0x2,
  rst_stream:    0x3,
  settings:      0x4,
  push_promise:  0x5,
  ping:          0x6,
  goaway:        0x7,
  window_update: 0x9,
  continuation:  0xa
}
FRAME_FLAGS =

Per frame flags as defined by the spec

{
  data: {
    end_stream:  0, reserved: 1
  },
  headers: {
    end_stream:  0, reserved: 1,
    end_headers: 2, priority: 3
  },
  priority:     {},
  rst_stream:   {},
  settings:     {},
  push_promise: { end_push_promise: 0 },
  ping:         { pong: 0 },
  goaway:       {},
  window_update:{},
  continuation: {
    end_stream: 0, end_headers: 1
  }
}
DEFINED_SETTINGS =

Default settings as defined by the spec

{
  settings_max_concurrent_streams: 4,
  settings_initial_window_size:    7,
  settings_flow_control_options:   10
}
DEFINED_ERRORS =

Default error types as defined by the spec

{
  no_error:           0,
  protocol_error:     1,
  internal_error:     2,
  flow_control_error: 3,
  stream_closed:      5,
  frame_too_large:    6,
  refused_stream:     7,
  cancel:             8,
  compression_error:  9
}

Instance Method Summary collapse

Instance Method Details

#commonHeader(frame) ⇒ String

Generates common 8-byte frame header.

Parameters:

  • frame (Hash)

Returns:

  • (String) 


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# File 'lib/http/2/framer.rb', line 84

def commonHeader(frame)
  header = []

  if !FRAME_TYPES[frame[:type]]
    raise CompressionError.new("Invalid frame type (#{frame[:type]})")
  end

  if frame[:length] > MAX_PAYLOAD_SIZE
    raise CompressionError.new("Frame size is too large: #{frame[:length]}")
  end

  if frame[:stream] > MAX_STREAM_ID
    raise CompressionError.new("Stream ID (#{frame[:stream]}) is too large")
  end

  if frame[:type] == :window_update && frame[:increment] > MAX_WINDOWINC
    raise CompressionError.new("Window increment (#{frame[:increment]}) is too large")
  end

  header << frame[:length]
  header << FRAME_TYPES[frame[:type]]
  header << frame[:flags].reduce(0) do |acc, f|
    position = FRAME_FLAGS[frame[:type]][f]
    if !position
      raise CompressionError.new("Invalid frame flag (#{f}) for #{frame[:type]}")
    end

    acc |= (1 << position)
    acc
  end

  header << frame[:stream]
  header.pack(HEADERPACK) # 16,8,8,32
end

#generate(frame) ⇒ Object

Generates encoded HTTP 2.0 frame.

Parameters:

  • frame (Hash) 


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# File 'lib/http/2/framer.rb', line 140

def generate(frame)
  bytes  = ''
  length = 0

  frame[:flags]  ||= []
  frame[:stream] ||= 0

  case frame[:type]
  when :data
    bytes  += frame[:payload]
    length += frame[:payload].bytesize

  when :headers
    if frame[:priority]
      frame[:flags] += [:priority] if !frame[:flags].include? :priority
    end

    if frame[:flags].include? :priority
      bytes  += [frame[:priority] & RBIT].pack(UINT32)
      length += 4
    end

    bytes  += frame[:payload]
    length += frame[:payload].bytesize

  when :priority
    bytes  += [frame[:priority] & RBIT].pack(UINT32)
    length += 4

  when :rst_stream
    bytes  += pack_error frame[:error]
    length += 4

  when :settings
    if frame[:stream] != 0
      raise CompressionError.new("Invalid stream ID (#{frame[:stream]})")
    end

    frame[:payload].each do |(k,v)|
      if !k.is_a? Integer
        k = DEFINED_SETTINGS[k]

        if k.nil?
          raise CompressionError.new("Unknown settings ID for #{k}")
        end
      end

      bytes  += [k & RBYTE].pack(UINT32)
      bytes  += [v].pack(UINT32)
      length += 8
    end

  when :push_promise
    bytes  += [frame[:promise_stream] & RBIT].pack(UINT32)
    bytes  += frame[:payload]
    length += 4 + frame[:payload].bytesize

  when :ping
    if frame[:payload].bytesize != 8
      raise CompressionError.new("Invalid payload size \
                                (#{frame[:payload].size} != 8 bytes)")
    end
    bytes  += frame[:payload]
    length += 8

  when :goaway
    bytes  += [frame[:last_stream] & RBIT].pack(UINT32)
    bytes  += pack_error frame[:error]
    length += 8

    if frame[:payload]
      bytes  += frame[:payload]
      length += frame[:payload].bytesize
    end

  when :window_update
    bytes  += [frame[:increment] & RBIT].pack(UINT32)
    length += 4

  when :continuation
    bytes  += frame[:payload]
    length += frame[:payload].bytesize
  end

  frame[:length] = length
  commonHeader(frame) + bytes
end

#parse(buf) ⇒ Object

Decodes complete HTTP 2.0 frame from provided buffer. If the buffer does not contain enough data, no further work is performed.

Parameters:

  • buf (String) 


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# File 'lib/http/2/framer.rb', line 232

def parse(buf)
  return nil if buf.size < 8
  frame = readCommonHeader(buf)
  return nil if buf.size < 8 + frame[:length]

  buf.read(8)
  payload = buf.read(frame[:length])

  case frame[:type]
  when :data
    frame[:payload] = payload.read(frame[:length])
  when :headers
    if frame[:flags].include? :priority
      frame[:priority] = payload.read(4).unpack(UINT32).first & RBIT
    end
    frame[:payload] = payload.read(frame[:length])
  when :priority
    frame[:priority] = payload.read(4).unpack(UINT32).first & RBIT
  when :rst_stream
    frame[:error] = unpack_error payload.read(4).unpack(UINT32).first

  when :settings
    frame[:payload] = {}
    (frame[:length] / 8).times do
      id  = payload.read(4).unpack(UINT32).first & RBYTE
      val = payload.read(4).unpack(UINT32).first

      name, _ = DEFINED_SETTINGS.select { |name, v| v == id }.first
      frame[:payload][name || id] = val
    end
  when :push_promise
    frame[:promise_stream] = payload.read(4).unpack(UINT32).first & RBIT
    frame[:payload] = payload.read(frame[:length])
  when :ping
    frame[:payload] = payload.read(frame[:length])
  when :goaway
    frame[:last_stream] = payload.read(4).unpack(UINT32).first & RBIT
    frame[:error] = unpack_error payload.read(4).unpack(UINT32).first

    size = frame[:length] - 8
    frame[:payload] = payload.read(size) if size > 0
  when :window_update
    frame[:increment] = payload.read(4).unpack(UINT32).first & RBIT
  when :continuation
    frame[:payload] = payload.read(frame[:length])
  end

  frame
end

#readCommonHeader(buf) ⇒ Object

Decodes common 8-byte header.

Parameters:

  • buf (String) 


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# File 'lib/http/2/framer.rb', line 122

def readCommonHeader(buf)
  frame = {}
  frame[:length], type, flags, stream = buf.slice(0,8).unpack(HEADERPACK)

  frame[:type], _ = FRAME_TYPES.select { |t,pos| type == pos }.first
  frame[:flags] = FRAME_FLAGS[frame[:type]].reduce([]) do |acc, (name, pos)|
    acc << name if (flags & (1 << pos)) > 0
    acc
  end

  frame[:stream] = stream & RBIT
  frame
end