Class: EventMachine::RTMP::Header

Inherits:
Object
  • Object
show all
Defined in:
lib/em-rtmp/header.rb

Constant Summary collapse

HEADER_DEFAULTS = 
{
  header_length: 12,
  timestamp: 0,
  channel_id: 3,
  message_type_id: 0,
  message_stream_id: 0
}
HEADER_LENGTHS =

RTMP has a variable length header The keys below are binary values which correspond to expected byte lengths (0b00 in header length field would result in an expected 12 byte header)

{
  0b00 => 12,
  0b01 => 8,
  0b10 => 4,
  0b11 => 1
}
MESSAGE_TYPES =

RTMP uses a single byte to represent the message type These are the known values.

{
  0x00 => :none,
  0x01 => :chunk_size,
  0x02 => :abort,
  0x03 => :ack,
  0x04 => :ping,
  0x05 => :ack_size,
  0x06 => :bandwidth,
  0x08 => :audio,
  0x09 => :video,
  0x0f => :flex, # aka AMF3 data
  0x10 => :amf3_shared_object, # documented as kMsgContainer=16
  0x11 => :amf3,
  0x12 => :invoke, # aka AMF0 data
  0x13 => :amf0_shared_object, # documented as kMsgContainer=19
  0x14 => :amf0,
  0x16 => :flv # documented as aggregate
}

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(attrs = {}) ⇒ Header

Initialize and set instance variables

attrs - Hash of instance variables

Returns nothing



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# File 'lib/em-rtmp/header.rb', line 65

def initialize(attrs={})
  attrs.each {|k,v| send("#{k}=", v)}
end

Instance Attribute Details

#body_length ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def body_length
  @body_length
end

#channel_id ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def channel_id
  @channel_id
end

#header_length ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def header_length
  @header_length
end

#message_stream_id ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def message_stream_id
  @message_stream_id
end

#message_type_id ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def message_type_id
  @message_type_id
end

#timestamp ⇒ Object

The packet header is read as follows:

The first byte (8 bits) is read into two values:

Header type (2 bits)
Stream ID (6 bits)

The header type determines a header length, from which the rest of the data may be read:

TYPE    BYTES    DESCRIPTION
0b11    1        Just the header
0b10    4        Above plus timestamp (uint24 big endian)
0b01    8        Above plus body length (uint24 big endian) and message id (uint8 big endian)
0b00    12       Above plus Message stream id (uint32 little endian)



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# File 'lib/em-rtmp/header.rb', line 18

def timestamp
  @timestamp
end

Class Method Details

.read_from_connection(stream) ⇒ Object

Read the header from a connection

connection - connection to use

Returns a new header instance



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# File 'lib/em-rtmp/header.rb', line 139

def self.read_from_connection(stream)
  header = new

  begin
    h_type, header.channel_id = stream.read_bitfield(2, 6)
  rescue => e
    raise HeaderError, "Unable to read header type byte from buffer: #{e}"
  end

  unless header.header_length = HEADER_LENGTHS[h_type]
    raise HeaderError, "invalid header type #{h_type}"
  end

  # Stream ID may occupy up to two more bytes depending on the
  # value of the channel_id we have read:
  # 0 - value is second byte + 64
  # 1 - value is third byte * 256 + second byte + 64
  # 2 - low level protocol message (ignore)

  if header.channel_id == 0x00
    header.channel_id = stream.read_uint8 + 64
  elsif header.channel_id == 0x01
    header.channel_id = stream.read_uint8 + 64 + (stream.read_uint8 * 256)
  end

  # The timestamp is a 3-byte uint24. If this matches 0xffffff we will use another 4 bytes
  # after the header as the real timestamp.
  if header.header_length >= 4
    header.timestamp = stream.read_uint24_be
  end

  # The next 3 bytes are the length of the object body, followed by a single byte
  # representing the content type
  if header.header_length >= 8
    header.body_length = stream.read_uint24_be
    header.message_type_id = stream.read_uint8
  end

  # The next 4 bytes are the stream ID
  if header.header_length >= 12
    header.message_stream_id = stream.read_uint32_le
  end

  # If the timestamp was 0xffffff, the next 4 bytes are the real timestamp
  if header.timestamp == 0xffffff
    header.timestamp = stream.read_uint32_be
  end

  header
end

Instance Method Details

#+(header) ⇒ Object

Inherit values from another header

h - other Header object

Returns self



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# File 'lib/em-rtmp/header.rb', line 74

def +(header)
  keys = %w[header_length body_length channel_id message_type_id message_stream_id timestamp]
  other_values = Hash[keys.map {|k| [k, header.instance_variable_get("@#{k}")]}]
  other_values.each do |k, v|
    unless v.nil?
      send("#{k}=", v) unless v.nil?
    end
  end
  self
end

#encode ⇒ Object

Encode the instantiated header to a buffer

io - IO destination to write to

Returns the buffer



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# File 'lib/em-rtmp/header.rb', line 106

def encode

  # Set defaults if necessary
  HEADER_DEFAULTS.each do |k, v|
    send("#{k}=", v) if instance_variable_get("@#{k}").nil?
  end

  h_type = HEADER_LENGTHS.invert[header_length]

  buffer = Buffer.new
  buffer.write_bitfield [h_type, 2], [channel_id, 6]

  if header_length >= 4
    buffer.write_uint24_be timestamp
  end

  if header_length >= 8
    buffer.write_uint24_be body_length
    buffer.write_uint8 message_type_id
  end

  if header_length == 12
    buffer.write_uint32_le message_stream_id
  end

  buffer.string
end

#message_type ⇒ Object

Retrieve the message type for our header

Returns a symbol or nil



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# File 'lib/em-rtmp/header.rb', line 88

def message_type
  MESSAGE_TYPES[message_type_id] || "unknown_type_#{message_type_id}".to_sym
end

#message_type=(type) ⇒ Object

Set message type as symbol

type - message type symbol

Returns the id set



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# File 'lib/em-rtmp/header.rb', line 97

def message_type=(type)
  self.message_type_id = MESSAGE_TYPES.invert[type]
end