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settings_frame.rb
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settings_frame.rb
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# frozen_string_literal: true
# Released under the MIT License.
# Copyright, 2019-2023, by Samuel Williams.
require_relative 'ping_frame'
module Protocol
module HTTP2
class Settings
HEADER_TABLE_SIZE = 0x1
ENABLE_PUSH = 0x2
MAXIMUM_CONCURRENT_STREAMS = 0x3
INITIAL_WINDOW_SIZE = 0x4
MAXIMUM_FRAME_SIZE = 0x5
MAXIMUM_HEADER_LIST_SIZE = 0x6
ENABLE_CONNECT_PROTOCOL = 0x8
ASSIGN = [
nil,
:header_table_size=,
:enable_push=,
:maximum_concurrent_streams=,
:initial_window_size=,
:maximum_frame_size=,
:maximum_header_list_size=,
nil,
:enable_connect_protocol=,
]
# Allows the sender to inform the remote endpoint of the maximum size of the header compression table used to decode header blocks, in octets.
attr_accessor :header_table_size
# This setting can be used to disable server push. An endpoint MUST NOT send a PUSH_PROMISE frame if it receives this parameter set to a value of 0.
attr :enable_push
def enable_push= value
if value == 0 or value == 1
@enable_push = value
else
raise ProtocolError, "Invalid value for enable_push: #{value}"
end
end
def enable_push?
@enable_push == 1
end
# Indicates the maximum number of concurrent streams that the sender will allow.
attr_accessor :maximum_concurrent_streams
# Indicates the sender's initial window size (in octets) for stream-level flow control.
attr :initial_window_size
def initial_window_size= value
if value <= MAXIMUM_ALLOWED_WINDOW_SIZE
@initial_window_size = value
else
raise ProtocolError, "Invalid value for initial_window_size: #{value} > #{MAXIMUM_ALLOWED_WINDOW_SIZE}"
end
end
# Indicates the size of the largest frame payload that the sender is willing to receive, in octets.
attr :maximum_frame_size
def maximum_frame_size= value
if value > MAXIMUM_ALLOWED_FRAME_SIZE
raise ProtocolError, "Invalid value for maximum_frame_size: #{value} > #{MAXIMUM_ALLOWED_FRAME_SIZE}"
elsif value < MINIMUM_ALLOWED_FRAME_SIZE
raise ProtocolError, "Invalid value for maximum_frame_size: #{value} < #{MINIMUM_ALLOWED_FRAME_SIZE}"
else
@maximum_frame_size = value
end
end
# This advisory setting informs a peer of the maximum size of header list that the sender is prepared to accept, in octets.
attr_accessor :maximum_header_list_size
attr :enable_connect_protocol
def enable_connect_protocol= value
if value == 0 or value == 1
@enable_connect_protocol = value
else
raise ProtocolError, "Invalid value for enable_connect_protocol: #{value}"
end
end
def enable_connect_protocol?
@enable_connect_protocol == 1
end
def initialize
# These limits are taken from the RFC:
# https://tools.ietf.org/html/rfc7540#section-6.5.2
@header_table_size = 4096
@enable_push = 1
@maximum_concurrent_streams = 0xFFFFFFFF
@initial_window_size = 0xFFFF # 2**16 - 1
@maximum_frame_size = 0x4000 # 2**14
@maximum_header_list_size = 0xFFFFFFFF
@enable_connect_protocol = 0
end
def update(changes)
changes.each do |key, value|
if name = ASSIGN[key]
self.send(name, value)
end
end
end
def difference(other)
changes = []
if @header_table_size != other.header_table_size
changes << [HEADER_TABLE_SIZE, @header_table_size]
end
if @enable_push != other.enable_push
changes << [ENABLE_PUSH, @enable_push]
end
if @maximum_concurrent_streams != other.maximum_concurrent_streams
changes << [MAXIMUM_CONCURRENT_STREAMS, @maximum_concurrent_streams]
end
if @initial_window_size != other.initial_window_size
changes << [INITIAL_WINDOW_SIZE, @initial_window_size]
end
if @maximum_frame_size != other.maximum_frame_size
changes << [MAXIMUM_FRAME_SIZE, @maximum_frame_size]
end
if @maximum_header_list_size != other.maximum_header_list_size
changes << [MAXIMUM_HEADER_LIST_SIZE, @maximum_header_list_size]
end
if @enable_connect_protocol != other.enable_connect_protocol
changes << [ENABLE_CONNECT_PROTOCOL, @enable_connect_protocol]
end
return changes
end
end
class PendingSettings
def initialize(current = Settings.new)
@current = current
@pending = current.dup
@queue = []
end
attr :current
attr :pending
def append(changes)
@queue << changes
@pending.update(changes)
end
def acknowledge
if changes = @queue.shift
@current.update(changes)
return changes
else
raise ProtocolError, "Cannot acknowledge settings, no changes pending"
end
end
def header_table_size
@current.header_table_size
end
def enable_push
@current.enable_push
end
def maximum_concurrent_streams
@current.maximum_concurrent_streams
end
def initial_window_size
@current.initial_window_size
end
def maximum_frame_size
@current.maximum_frame_size
end
def maximum_header_list_size
@current.maximum_header_list_size
end
def enable_connect_protocol
@current.enable_connect_protocol
end
end
# The SETTINGS frame conveys configuration parameters that affect how endpoints communicate, such as preferences and constraints on peer behavior. The SETTINGS frame is also used to acknowledge the receipt of those parameters. Individually, a SETTINGS parameter can also be referred to as a "setting".
#
# +-------------------------------+
# | Identifier (16) |
# +-------------------------------+-------------------------------+
# | Value (32) |
# +---------------------------------------------------------------+
#
class SettingsFrame < Frame
TYPE = 0x4
FORMAT = "nN".freeze
include Acknowledgement
def connection?
true
end
def unpack
if buffer = super
# TODO String#each_slice, or #each_unpack would be nice.
buffer.scan(/....../m).map{|s| s.unpack(FORMAT)}
else
[]
end
end
def pack(settings = [])
super(settings.map{|s| s.pack(FORMAT)}.join)
end
def apply(connection)
connection.receive_settings(self)
end
def read_payload(stream)
super
if @stream_id != 0
raise ProtocolError, "Settings apply to connection only, but stream_id was given"
end
if acknowledgement? and @length != 0
raise FrameSizeError, "Settings acknowledgement must not contain payload: #{@payload.inspect}"
end
if (@length % 6) != 0
raise FrameSizeError, "Invalid frame length"
end
end
end
end
end