Class: HTTP2::Header::EncodingContext

Inherits:
Object
  • Object
show all
Includes:
Error
Defined in:
lib/http/2/header/encoding_context.rb

Constant Summary collapse

UPPER = 
/[[:upper:]]/.freeze
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(&:freeze).freeze
STATIC_TABLE_BY_FIELD = 
STATIC_TABLE
.each_with_object({})
.with_index { |((field, value), hs), idx| (hs[field] ||= []) << [idx, value].freeze }
.each_value(&:freeze)
.freeze
STATIC_TABLE_SIZE = 
STATIC_TABLE.size
DEFAULT_OPTIONS = 
{
  huffman: :shorter,
  index: :all,
  table_size: 4096
}.freeze
STATIC_ALL = 
%i[all static].freeze
STATIC_NEVER = 
%i[never static].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) (defaults to: {}) —

    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/header/encoding_context.rb', line 119

def initialize(options = {})
  @table = []
  @table_by_field = Hash.new { |hs, k| hs[k] = [] }
  @unshifts = 0
  @options = DEFAULT_OPTIONS.merge(options)
  @limit = @options[:table_size]
  @_table_updated = false
  @current_table_size = 0
end

Instance Attribute Details

#current_table_size ⇒ Object (readonly)

Current table size in octets



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# File 'lib/http/2/header/encoding_context.rb', line 110

def current_table_size
  @current_table_size
end

#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/header/encoding_context.rb', line 107

def options
  @options
end

#table ⇒ Object (readonly)

Current table of header key-value pairs.



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# File 'lib/http/2/header/encoding_context.rb', line 100

def table
  @table
end

Instance Method Details

#addcmd(field, value) ⇒ 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:

  • field (String) —

    the header field

  • value (String) —

    the header value

Returns:

  • (Hash) —

    command



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# File 'lib/http/2/header/encoding_context.rb', line 270

def addcmd(field, value)
  # @type var exact: Integer?
  exact = nil
  # @type var name_only: Integer?
  name_only = nil

  index_type = @options[:index]

  if STATIC_ALL.include?(index_type) &&
     STATIC_TABLE_BY_FIELD.key?(field)
    STATIC_TABLE_BY_FIELD[field].each do |i, svalue|
      name_only ||= i
      if value == svalue
        exact = i
        break
      end
    end
  end

  if index_type == :all && !exact
    field_entries = @table_by_field[field]

    field_entries&.each do |hvalue, unshift_id|
      abs_index = (@unshifts - unshift_id) + STATIC_TABLE_SIZE
      name_only ||= abs_index
      if value == hvalue
        exact = abs_index
        break
      end
    end
  end

  if exact
    { name: exact, type: :indexed }
  else
    { name: name_only || field, value: value, type: :incremental }
  end
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/header/encoding_context.rb', line 156

def dereference(index)
  # NOTE: index is zero-based in this module.
  return STATIC_TABLE[index] if index < STATIC_TABLE_SIZE

  idx = index - STATIC_TABLE_SIZE

  raise CompressionError, "Index too large" if idx >= @table.size

  @table[index - STATIC_TABLE_SIZE]
end

#dup ⇒ EncodingContext

Duplicates current compression context

Returns:



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# File 'lib/http/2/header/encoding_context.rb', line 131

def dup
  other = EncodingContext.new(@options)
  t = @table
  tbf = @table_by_field.transform_values(&:dup)
  unshifts = @unshifts
  l = @limit
  other.instance_eval do
    @table = t.dup # shallow copy
    @table_by_field = tbf
    @unshifts = unshifts
    @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/header/encoding_context.rb', line 241

def encode(headers)
  # 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 if UPPER.match?(field)
    value = "/" if field == ":path" && value.empty?
    cmd = addcmd(field, value)
    cmd[:type] = :noindex if noindex && cmd[:type] == :incremental
    process(cmd)
    yield cmd
  end
end

#listen_on_table ⇒ Object 



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# File 'lib/http/2/header/encoding_context.rb', line 316

def listen_on_table
  yield
ensure
  @_table_updated = false
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/header/encoding_context.rb', line 173

def process(cmd)
  type = cmd[:type]
  name = cmd[:name]
  value = cmd[:value]

  case 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 && value > @limit

    self.table_size = value

    nil
  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.
    dereference(name)
  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 name
    when Integer
      name, v = dereference(name)

      value ||= v
    when UPPER
      raise ProtocolError, "Invalid uppercase key: #{name}"
    end

    emit = [name, value]

    # add to table
    if type == :incremental && size_check?(name.bytesize + value.bytesize + 32)
      @table.unshift(emit)
      @unshifts += 1
      @table_by_field[name].unshift([value, @unshifts])
      @current_table_size += name.bytesize + value.bytesize + 32
      @_table_updated = true
    end

    emit
  else
    raise CompressionError, "Invalid type: #{type}"
  end
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/header/encoding_context.rb', line 311

def table_size=(size)
  @limit = size
  resize_table(0)
end