class HTTP2Next::Header::EncodingContext
Constants
- STATIC_TABLE
@private Static table
- STATIC_TABLE_BY_FIELD
- STATIC_TABLE_SIZE
- UPPER
Attributes
Current encoding options
:table_size Integer maximum dynamic table size in bytes :huffman Symbol :always, :never, :shorter :index Symbol :all, :static, :never
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 options [Hash] encoding options
:table_size Integer maximum dynamic table size in bytes :huffman Symbol :always, :never, :shorter :index Symbol :all, :static, :never
# File lib/http/2/next/header/encoding_context.rb, line 106 def initialize(options = {}) default_options = { huffman: :shorter, index: :all, table_size: 4096 } @table = [] @options = default_options.merge(options) @limit = @options[:table_size] @_table_updated = false end
Public Instance Methods
Emits command for a header. Prefer static table over dynamic table. Prefer exact match over name-only match.
+@options [: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/http/2/next/header/encoding_context.rb, line 250 def addcmd(*header) exact = nil name_only = nil if %i[all static].include?(@options[:index]) field, value = header if (svalues = STATIC_TABLE_BY_FIELD[field]) svalues.each do |i, svalue| name_only ||= i if svalue == value exact = i break end end end end if [:all].include?(@options[: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
Returns current table size in octets @return [Integer]
# File lib/http/2/next/header/encoding_context.rb, line 295 def current_table_size @table.inject(0) { |r, (k, v)| r + k.bytesize + v.bytesize + 32 } 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/http/2/next/header/encoding_context.rb, line 141 def dereference(index) # NOTE: index is zero-based in this module. value = STATIC_TABLE[index] || @table[index - STATIC_TABLE_SIZE] raise CompressionError, "Index too large" unless value value end
Duplicates current compression context @return [EncodingContext]
# File lib/http/2/next/header/encoding_context.rb, line 120 def dup other = EncodingContext.new(@options) t = @table l = @limit other.instance_eval do @table = t.dup # shallow copy @limit = l end other end
Plan header compression according to +@options [: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/http/2/next/header/encoding_context.rb, line 221 def encode(headers) commands = [] # Literals commands are marked with :noindex when index is not used noindex = %i[static never].include?(@options[:index]) headers.each do |field, value| # Literal header names MUST be translated to lowercase before # encoding and transmission. field = field.downcase if UPPER.match?(field) value = "/" if field == ":path" && value.empty? cmd = addcmd(field, value) cmd[:type] = :noindex if noindex && cmd[:type] == :incremental commands << cmd process(cmd) end commands end
# File lib/http/2/next/header/encoding_context.rb, line 299 def listen_on_table yield ensure @_table_updated = false end
Header
Block Processing
@param cmd [Hash] { type:, name:, value:, index: } @return [Array, nil] +[name, value]+ header field that is added to the decoded header list,
or nil if +cmd[:type]+ is +:changetablesize+
# File lib/http/2/next/header/encoding_context.rb, line 155 def process(cmd) emit = nil case cmd[:type] when :changetablesize raise CompressionError, "tried to change table size after adding elements to table" if @_table_updated # we can receive multiple table size change commands inside a header frame. However, # we should blow up if we receive another frame where the new table size is bigger. table_size_updated = @limit != @options[:table_size] raise CompressionError, "dynamic table size update exceed limit" if !table_size_updated && cmd[:value] > @limit self.table_size = cmd[: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 = cmd[:name] k, v = dereference(idx) emit = [k, v] when :incremental, :noindex, :neverindexed # 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. case cmd[:name] when Integer k, v = dereference(cmd[:name]) cmd = cmd.dup cmd[:index] ||= cmd[:name] cmd[:value] ||= v cmd[:name] = k when UPPER raise ProtocolError, "Invalid uppercase key: #{cmd[:name]}" end emit = [cmd[:name], cmd[:value]] add_to_table(emit) if cmd[:type] == :incremental else raise CompressionError, "Invalid type: #{cmd[:type]}" end emit end
Alter dynamic table size.
When the size is reduced, some headers might be evicted.
# File lib/http/2/next/header/encoding_context.rb, line 288 def table_size=(size) @limit = 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.
@param cmd [Array] +[name, value]+
# File lib/http/2/next/header/encoding_context.rb, line 312 def add_to_table(cmd) return unless size_check(cmd) @table.unshift(cmd) @_table_updated = true end
To keep the dynamic table size lower than or equal to @limit, remove one or more entries at the end of the dynamic table.
@param cmd [Hash] @return [Boolean] whether cmd
fits in the dynamic table.
# File lib/http/2/next/header/encoding_context.rb, line 324 def size_check(cmd) cursize = current_table_size cmdsize = cmd.nil? ? 0 : cmd[0].bytesize + cmd[1].bytesize + 32 while cursize + cmdsize > @limit break if @table.empty? e = @table.pop cursize -= e[0].bytesize + e[1].bytesize + 32 end cmdsize <= @limit end