Class: HTTP2::Header::EncodingContext

Inherits:
Object
  • Object
show all
Includes:
Error
Defined in:
lib/http/2/compressor.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 table

[
  [':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 { |pair| pair.each(&:freeze).freeze }.freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(**options) ⇒ EncodingContext

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

Parameters:

  • options (Hash) —

    encoding options :table_size Integer maximum dynamic table size in bytes :huffman Symbol :always, :never, :shorter :index Symbol :all, :static, :never



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# File 'lib/http/2/compressor.rb', line 99

def initialize(**options)
  default_options = {
    huffman: :shorter,
    index: :all,
    table_size: 4096
  }
  @table = []
  @options = default_options.merge(options)
  @limit = @options[:table_size]
end

Instance Attribute Details

#options ⇒ Object (readonly)

Current encoding options

:table_size  Integer  maximum dynamic table size in bytes
:huffman     Symbol   :always, :never, :shorter
:index       Symbol   :all, :static, :never



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# File 'lib/http/2/compressor.rb', line 90

def options
  @options
end

#table ⇒ Object (readonly)

Current table of header key-value pairs.



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# File 'lib/http/2/compressor.rb', line 83

def table
  @table
end

Instance Method Details

#addcmd(*header) ⇒ Hash

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.

Parameters:

  • header (Array) —

    [name, value]

Returns:

  • (Hash) —

    command



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# File 'lib/http/2/compressor.rb', line 233

def addcmd(*header)
  exact = nil
  name_only = nil

  if i[all static].include?(@options[: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?(@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

#current_table_size ⇒ Integer

Returns current table size in octets

Returns:

  • (Integer) 


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# File 'lib/http/2/compressor.rb', line 276

def current_table_size
  @table.inject(0) { |r, (k, v)| r + k.bytesize + v.bytesize + 32 }
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.

Parameters:

  • index (Integer) —

    zero-based index in the dynamic table.

Returns:

  • (Array) —

    [key, value]

Raises:



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# File 'lib/http/2/compressor.rb', line 133

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

#dup ⇒ EncodingContext

Duplicates current compression context

Returns:



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# File 'lib/http/2/compressor.rb', line 112

def dup
  other = EncodingContext.new(@options)
  t = @table
  l = @limit
  other.instance_eval do
    @table = t.dup # shallow copy
    @limit = l
  end
  other
end

#encode(headers) ⇒ Array

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.

Parameters:

  • headers (Array) —

    [[name, value], …]

Returns:

  • (Array) —

    array of commands



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# File 'lib/http/2/compressor.rb', line 204

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
    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

#process(cmd) ⇒ Array?

Header Block Processing

Parameters:

  • cmd (Hash) —

    { type:, name:, value:, index: }

Returns:

  • (Array, nil) —

    [name, value] header field that is added to the decoded header list, or nil if cmd[:type] is :changetablesize



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# File 'lib/http/2/compressor.rb', line 147

def process(cmd)
  emit = nil

  case cmd[:type]
  when :changetablesize
    raise CompressionError, 'dynamic table size update exceed limit' if 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.

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

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

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

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

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

  emit
end

#table_size=(size) ⇒ Object

Alter dynamic table size.

When the size is reduced, some headers might be evicted.



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# File 'lib/http/2/compressor.rb', line 269

def table_size=(size)
  @limit = size
  size_check(nil)
end