class Protocol::HPACK::Context
To decompress header blocks, a decoder only needs to maintain a dynamic table as a decoding context. No other state information is needed.
Constants
- STATIC_TABLE
Static header table. tools.ietf.org/html/rfc7541#appendix-A
Attributes
Current table of header key-value pairs.
Public Class Methods
Initializes compression context with appropriate client/server defaults and maximum size of the dynamic table.
@param table [Array] Table of header key-value pairs. @option huffman [Symbol] One of `:always`, `:never`, `:shorter`. Controls use of compression. @option index [Symbol] One of `:all`, `:static`, `:never`. Controls use of static/dynamic tables. @option table_size
[Integer] The current maximum dynamic table size.
# File lib/protocol/hpack/context.rb, line 117 def initialize(table = nil, huffman: :shorter, index: :all, table_size: 4096) @huffman = huffman @index = index @table_size = table_size @table = (table&.dup) || [] end
Public Instance Methods
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.
@param header [Array] +[name, value]+ @return [Hash] command
# File lib/protocol/hpack/context.rb, line 251 def add_command(*header) exact = nil name_only = nil if [:all, :static].include?(@index) STATIC_TABLE.each_index do |i| if STATIC_TABLE[i] == header exact ||= i break elsif STATIC_TABLE[i].first == header.first name_only ||= i end end end if [:all].include?(@index) && !exact @table.each_index do |i| if @table[i] == header exact ||= i + STATIC_TABLE.size break elsif @table[i].first == header.first name_only ||= i + STATIC_TABLE.size end end end if exact {name: exact, type: :indexed} elsif name_only {name: name_only, value: header.last, type: :incremental} else {name: header.first, value: header.last, type: :incremental} end end
# File lib/protocol/hpack/context.rb, line 292 def change_table_size(size) self.table_size = size # The command to resize the table: return {type: :change_table_size, value: size} end
Returns current table size in octets @return [Integer]
# File lib/protocol/hpack/context.rb, line 301 def current_table_size @table.inject(0) {|r, (k, v)| r + k.bytesize + v.bytesize + 32} end
Header Block Processing
@param command [Hash] {type:, name:, value:, index:} @return [Array] +[name, value]+ header field that is added to the decoded header list
# File lib/protocol/hpack/context.rb, line 167 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
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.
@param index [Integer] zero-based index in the dynamic table. @return [Array] +[key, value]+
# File lib/protocol/hpack/context.rb, line 151 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
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.
@param headers [Array] +[[name, value], …]+ @return [Array] array of commands
# File lib/protocol/hpack/context.rb, line 222 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
# File lib/protocol/hpack/context.rb, line 126 def initialize_copy(other) super # This is the only mutable state: @table = @table.dup end
Alter dynamic table size.
When the size is reduced, some headers might be evicted.
# File lib/protocol/hpack/context.rb, line 287 def table_size= size @table_size = size size_check(nil) end
Private Instance Methods
Add a name-value pair to the dynamic table. Older entries might have been evicted so that the new entry fits in the dynamic table. The command and the component strings will be frozen.
@param command [Array] +[name, value]+
# File lib/protocol/hpack/context.rb, line 310 def add_to_table(command) return unless size_check(command) command.each(&:freeze) command.freeze @table.unshift(command) end
To keep the dynamic table size lower than or equal to @table_size, remove one or more entries at the end of the dynamic table.
@param command [Hash] @return [Boolean] whether command
fits in the dynamic table.
# File lib/protocol/hpack/context.rb, line 324 def size_check(command) cursize = current_table_size cmdsize = command.nil? ? 0 : command[0].bytesize + command[1].bytesize + 32 while cursize + cmdsize > @table_size break if @table.empty? e = @table.pop cursize -= e[0].bytesize + e[1].bytesize + 32 end cmdsize <= @table_size end