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

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 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

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/header/encoding_context.rb', line 97

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 90

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/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

#current_table_size ⇒ Integer

Returns current table size in octets

Returns:

  • (Integer) 


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# File 'lib/http/2/header/encoding_context.rb', line 295

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/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

#dup ⇒ EncodingContext

Duplicates current compression context

Returns:



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# File 'lib/http/2/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

#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 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

#listen_on_table ⇒ Object 



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# File 'lib/http/2/header/encoding_context.rb', line 299

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 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

#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 288

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