Class: Protocol::HPACK::Context

Inherits:
Object
  • Object
show all
Defined in:
lib/protocol/hpack/context.rb

Overview

To decompress header blocks, a decoder only needs to maintain a dynamic table as a decoding context. No other state information is needed.

Constant Summary collapse

STATIC_TABLE =

Static header table. tools.ietf.org/html/rfc7541#appendix-A

[
	[":authority", ""],
	[":method", "GET"],
	[":method", "POST"],
	[":path", "/"],
	[":path", "/index.html"],
	[":scheme", "http"],
	[":scheme", "https"],
	[":status", "200"],
	[":status", "204"],
	[":status", "206"],
	[":status", "304"],
	[":status", "400"],
	[":status", "404"],
	[":status", "500"],
	["accept-charset", ""],
	["accept-encoding", "gzip, deflate"],
	["accept-language", ""],
	["accept-ranges", ""],
	["accept", ""],
	["access-control-allow-origin", ""],
	["age", ""],
	["allow", ""],
	["authorization", ""],
	["cache-control", ""],
	["content-disposition", ""],
	["content-encoding", ""],
	["content-language", ""],
	["content-length", ""],
	["content-location", ""],
	["content-range", ""],
	["content-type", ""],
	["cookie", ""],
	["date", ""],
	["etag", ""],
	["expect", ""],
	["expires", ""],
	["from", ""],
	["host", ""],
	["if-match", ""],
	["if-modified-since", ""],
	["if-none-match", ""],
	["if-range", ""],
	["if-unmodified-since", ""],
	["last-modified", ""],
	["link", ""],
	["location", ""],
	["max-forwards", ""],
	["proxy-authenticate", ""],
	["proxy-authorization", ""],
	["range", ""],
	["referer", ""],
	["refresh", ""],
	["retry-after", ""],
	["server", ""],
	["set-cookie", ""],
	["strict-transport-security", ""],
	["transfer-encoding", ""],
	["user-agent", ""],
	["vary", ""],
	["via", ""],
	["www-authenticate", ""],
].each(&:freeze).freeze
STATIC_EXACT_LOOKUP = 
{}
STATIC_NAME_LOOKUP = 
{}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(table = nil, huffman: :shorter, index: :all, table_size: 4096) ⇒ Context

Initializes compression context with appropriate client/server defaults and maximum size of the dynamic table.

Options Hash (huffman:):

  • One (Symbol) —

    of ‘:always`, `:never`, `:shorter`. Controls use of compression.

Options Hash (index:):

  • One (Symbol) —

    of ‘:all`, `:static`, `:never`. Controls use of static/dynamic tables.

Options Hash (table_size:):

  • The (Integer) —

    current maximum dynamic table size.



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# File 'lib/protocol/hpack/context.rb', line 119

def initialize(table = nil, huffman: :shorter, index: :all, table_size: 4096)
	@huffman = huffman
	@index = index
	
	@table_size = table_size
	
	@table = (table&.dup) || []
end

Instance Attribute Details

#huffman ⇒ Object (readonly)

Returns the value of attribute huffman.



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# File 'lib/protocol/hpack/context.rb', line 138

def huffman
  @huffman
end

#index ⇒ Object (readonly)

Returns the value of attribute index.



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# File 'lib/protocol/hpack/context.rb', line 139

def index
  @index
end

#table ⇒ Object (readonly)

Current table of header key-value pairs.



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# File 'lib/protocol/hpack/context.rb', line 136

def table
  @table
end

#table_size ⇒ Object

Returns the value of attribute table_size.



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# File 'lib/protocol/hpack/context.rb', line 141

def table_size
  @table_size
end

Instance Method Details

#add_command(name, value) ⇒ Hash

Emits command for a header. Prefer static table over dynamic table. Prefer exact match over name-only match.

@index controls whether to use the dynamic table, static table, or both.

:never   Do not use dynamic table or static table reference at all.
:static  Use static table only.
:all     Use all of them.



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# File 'lib/protocol/hpack/context.rb', line 254

def add_command(name, value)
	exact = nil
	name_only = nil

	if @index == :all || @index == :static
		if (values_and_indices = STATIC_EXACT_LOOKUP[name])
			values_and_indices.each do |known_value, index|
				if value == known_value
					exact = index
					break
				end
			end
			
			needs_name_lookup = exact.nil?
		else
			needs_name_lookup = true
		end

		if needs_name_lookup && (static_value = STATIC_NAME_LOOKUP[name])
			name_only = static_value
		end
	end

	if @index == :all && !exact
		@table.each_index do |i|
			entry = @table[i]
			if entry.first == name
				if entry.last == value
					exact ||= i + STATIC_TABLE.size
					break
				else
					name_only ||= i + STATIC_TABLE.size
				end
			end
		end
	end

	if exact
		{name: exact, type: :indexed}
	elsif name_only
		{name: name_only, value: value, type: :incremental}
	else
		{name: name, value: value, type: :incremental}
	end
end

#change_table_size(size) ⇒ Object 



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# File 'lib/protocol/hpack/context.rb', line 307

def change_table_size(size)
	self.table_size = size
	
	# The command to resize the table:
	return {type: :change_table_size, value: size}
end

#compute_current_table_size ⇒ Integer

Returns current table size in octets



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# File 'lib/protocol/hpack/context.rb', line 316

def compute_current_table_size
	@table.sum { |k, v| k.bytesize + v.bytesize + 32 }
end

#decode(command) ⇒ Array

Header Block Processing



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# File 'lib/protocol/hpack/context.rb', line 169

def decode(command)
	emit = nil

	case command[:type]
	when :change_table_size
		self.table_size = command[:value]

	when :indexed
		# Indexed Representation
		# An _indexed representation_ entails the following actions:
		# o  The header field corresponding to the referenced entry in either
		# the static table or dynamic table is added to the decoded header
		# list.
		idx = command[:name]

		k, v = dereference(idx)
		emit = [k, v]

	when :incremental, :no_index, :never_indexed
		# A _literal representation_ that is _not added_ to the dynamic table
		# entails the following action:
		# o  The header field is added to the decoded header list.

		# A _literal representation_ that is _added_ to the dynamic table
		# entails the following actions:
		# o  The header field is added to the decoded header list.
		# o  The header field is inserted at the beginning of the dynamic table.

		if command[:name].is_a? Integer
			k, v = dereference(command[:name])

			command = command.dup
			command[:index] ||= command[:name]
			command[:value] ||= v
			command[:name] = k
		end

		emit = [command[:name], command[:value]]

		add_to_table(emit) if command[:type] == :incremental

	else
		raise CompressionError, "Invalid type: #{command[:type]}"
	end

	return emit
end

#dereference(index) ⇒ Array

Finds an entry in current dynamic table by index. Note that index is zero-based in this module.

If the index is greater than the last index in the static table, an entry in the dynamic table is dereferenced.

If the index is greater than the last header index, an error is raised.



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# File 'lib/protocol/hpack/context.rb', line 153

def dereference(index)
	# NOTE: index is zero-based in this module.
	value = STATIC_TABLE[index] || @table[index - STATIC_TABLE.size]
	
	if value.nil?
		raise CompressionError, "Index #{index} too large!"
	end
	
	return value
end

#encode(headers) ⇒ Array

Plan header compression according to @index

:never   Do not use dynamic table or static table reference at all.
:static  Use static table only.
:all     Use all of them.



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# File 'lib/protocol/hpack/context.rb', line 224

def encode(headers)
	commands = []
	
	# Literals commands are marked with :no_index when index is not used
	no_index = [:static, :never].include?(@index)
	
	headers.each do |field, value|
		command = add_command(field, value)
		command[:type] = :no_index if no_index && command[:type] == :incremental
		commands << command
		
		decode(command)
	end
	
	return commands
end

#initialize_copy(other) ⇒ Object 



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# File 'lib/protocol/hpack/context.rb', line 128

def initialize_copy(other)
	super
	
	# This is the only mutable state:
	@table = @table.dup
end