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 =
[
  [':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.


97
98
99
100
101
102
103
104
105
106
# File 'lib/http/2/compressor.rb', line 97

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

#optionsObject (readonly)

Current encoding options

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

88
89
90
# File 'lib/http/2/compressor.rb', line 88

def options
  @options
end

#tableObject (readonly)

Current table of header key-value pairs.


81
82
83
# File 'lib/http/2/compressor.rb', line 81

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.

227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
# File 'lib/http/2/compressor.rb', line 227

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_sizeInteger

Returns current table size in octets


270
271
272
# File 'lib/http/2/compressor.rb', line 270

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.


131
132
133
134
135
136
# File 'lib/http/2/compressor.rb', line 131

def dereference(index)
  # NOTE: index is zero-based in this module.
  value = STATIC_TABLE[index] || @table[index - STATIC_TABLE.size]
  fail CompressionError, 'Index too large' unless value
  value
end

#dupEncodingContext

Duplicates current compression context


110
111
112
113
114
115
116
117
118
119
# File 'lib/http/2/compressor.rb', line 110

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.

198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
# File 'lib/http/2/compressor.rb', line 198

def encode(headers)
  commands = []
  # Literals commands are marked with :noindex when index is not used
  noindex = [: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


143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
# File 'lib/http/2/compressor.rb', line 143

def process(cmd)
  emit = nil

  case cmd[:type]
  when :changetablesize
    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
    fail 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.

263
264
265
266
# File 'lib/http/2/compressor.rb', line 263

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