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 header 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',            ''            ],
].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 header table.

Parameters:

  • options (Hash) —

    encoding options :table_size Integer maximum header 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 101

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 header 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 92

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 85

def table
  @table
end

Instance Method Details

#addcmd(header) ⇒ Hash

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

@options [:index] controls whether to use the header table, static table, or both.

:never   Do not use header 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 231

def addcmd(header)
  exact = nil
  name_only = nil

  if [: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 274

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 header 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 header 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 header table.

Returns:

  • (Array) —

    [key, value]



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# File 'lib/http/2/compressor.rb', line 135

def dereference(index)
  # NOTE: index is zero-based in this module.
  STATIC_TABLE[index] or
    @table[index - STATIC_TABLE.size] or
    raise CompressionError.new("Index too large")
end

#dup ⇒ EncodingContext

Duplicates current compression context

Returns:



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# File 'lib/http/2/compressor.rb', line 114

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

#encode(headers) ⇒ Array

Plan header compression according to @options [:index]

:never   Do not use header 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 = [:static, :never].include?(@options[:index])
  headers.each do |h|
    cmd = addcmd(h)
    if noindex && cmd[:type] == :incremental
      cmd[:type] = :noindex
    end
    commands << cmd
    process(cmd)
  end
  commands
end

#process(cmd) ⇒ Array

Header Block Processing

Parameters:

  • cmd (Hash) —

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

Returns:

  • (Array) —

    [name, value] header field that is added to the decoded header list



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

def process(cmd)
  emit = nil

  case cmd[:type]
  when :changetablesize
    set_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 header 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 header table
    # entails the following action:
    # o  The header field is added to the decoded header list.

    # A _literal representation_ that is _added_ to the header 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 header 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]]

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

  else
    raise CompressionError.new("Invalid type: #{cmd[:type]}")
  end

  emit
end

#set_table_size(size) ⇒ Object

Alter header table size.

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



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# File 'lib/http/2/compressor.rb', line 267

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