The Tor Browser / file revision

 // The implementation of the [HTTP/2 Header Compression][http2-compression] spec is separated from

 // the 'integration' part which handles HEADERS and PUSH_PROMISE frames. The compression itself is

 // implemented in the first part of the file, and consists of three classes: `HeaderTable`,

 // `HeaderSetDecompressor` and `HeaderSetCompressor`. The two latter classes are

 // [Transform Stream][node-transform] subclasses that operate in [object mode][node-objectmode].

 // These transform chunks of binary data into `[name, value]` pairs and vice versa, and store their

 // state in `HeaderTable` instances.

 //

 // The 'integration' part is also implemented by two [Transform Stream][node-transform] subclasses

 // that operate in [object mode][node-objectmode]: the `Compressor` and the `Decompressor`. These

 // provide a layer between the [framer](framer.html) and the

 // [connection handling component](connection.html).

 //

 // [node-transform]: http://nodejs.org/api/stream.html#stream_class_stream_transform

 // [node-objectmode]: http://nodejs.org/api/stream.html#stream_new_stream_readable_options

 // [http2-compression]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05

 exports.HeaderTable = HeaderTable;

 exports.HuffmanTable = HuffmanTable;

 exports.HeaderSetCompressor = HeaderSetCompressor;

 exports.HeaderSetDecompressor = HeaderSetDecompressor;

 exports.Compressor = Compressor;

 exports.Decompressor = Decompressor;

 var TransformStream = require('stream').Transform;

 var assert = require('assert');

 var util = require('util');

 // Header compression

 // ==================

 // The HeaderTable class

 // ---------------------

 // The [Header Table] is a component used to associate headers to index values. It is basically an

 // ordered list of `[name, value]` pairs, so it's implemented as a subclass of `Array`.

 // In this implementation, the Header Table and the [Static Table] are handled as a single table.

 // [Header Table]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-3.1.2

 // [Static Table]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#appendix-B

 function HeaderTable(log, limit) {

   var self = HeaderTable.staticTable.map(entryFromPair);

   self._log = log;

   self._limit = limit || DEFAULT_HEADER_TABLE_LIMIT;

   self._staticLength = self.length;

   self._size = 0;

   self._enforceLimit = HeaderTable.prototype._enforceLimit;

   self.add = HeaderTable.prototype.add;

   self.setSizeLimit = HeaderTable.prototype.setSizeLimit;

   return self;

 }

 // There are few more sets that are needed for the compression/decompression process that are all

 // subsets of the Header Table, and are implemented as flags on header table entries:

 //

 // * [Reference Set][referenceset]: contains a group of headers used as a reference for the

 //   differential encoding of a new set of headers. (`reference` flag)

 // * Emitted headers: the headers that are already emitted as part of the current decompression

 //   process (not part of the spec, `emitted` flag)

 // * Headers to be kept: headers that should not be removed as the last step of the encoding process

 //   (not part of the spec, `keep` flag)

 //

 // [referenceset]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-3.1.3

 //

 // Relations of the sets:

 //

 //     ,----------------------------------.

 //     |           Header Table           |

 //     |                                  |

 //     |  ,----------------------------.  |

 //     |  |        Reference Set       |  |

 //     |  |                            |  |

 //     |  |  ,---------.  ,---------.  |  |

 //     |  |  |  Keep   |  | Emitted |  |  |

 //     |  |  |         |  |         |  |  |

 //     |  |  `---------'  `---------'  |  |

 //     |  `----------------------------'  |

 //     `----------------------------------'

 function entryFromPair(pair) {

   var entry = pair.slice();

   entry.reference = false;

   entry.emitted = false;

   entry.keep = false;

   entry._size = size(entry);

   return entry;

 }

 // The encoder decides how to update the header table and as such can control how much memory is

 // used by the header table.  To limit the memory requirements on the decoder side, the header table

 // size is bounded.

 //

 // * The default header table size limit is 4096 bytes.

 // * The size of an entry is defined as follows: the size of an entry is the sum of its name's

 //   length in bytes, of its value's length in bytes and of 32 bytes.

 // * The size of a header table is the sum of the size of its entries.

 var DEFAULT_HEADER_TABLE_LIMIT = 4096;

 function size(entry) {

   return (new Buffer(entry[0] + entry[1], 'utf8')).length + 32;

 }

 // The `add(index, entry)` can be used to [manage the header table][tablemgmt]:

 // [tablemgmt]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-3.3

 //

 // * it pushes the new `entry` at the beggining of the table

 // * before doing such a modification, it has to be ensured that the header table size will stay

 //   lower than or equal to the header table size limit. To achieve this, entries are evicted from

 //   the end of the header table until the size of the header table is less than or equal to

 //   `(this._limit - entry.size)`, or until the table is empty.

 //

 //              <----------  Index Address Space ---------->

 //              <-- Header  Table -->  <-- Static  Table -->

 //              +---+-----------+---+  +---+-----------+---+

 //              | 0 |    ...    | k |  |k+1|    ...    | n |

 //              +---+-----------+---+  +---+-----------+---+

 //              ^                   |

 //              |                   V

 //       Insertion Point       Drop Point

 HeaderTable.prototype._enforceLimit = function _enforceLimit(limit) {

   var droppedEntries = [];

   var dropPoint = this.length - this._staticLength;

   while ((this._size > limit) && (dropPoint > 0)) {

     dropPoint -= 1;

     var dropped = this.splice(dropPoint, 1)[0];

     this._size -= dropped._size;

     droppedEntries[dropPoint] = dropped;

   }

   return droppedEntries;

 };

 HeaderTable.prototype.add = function(entry) {

   var limit = this._limit - entry._size;

   var droppedEntries = this._enforceLimit(limit);

   if (this._size <= limit) {

     this.unshift(entry);

     this._size += entry._size;

   }

   return droppedEntries;

 };

 // The table size limit can be changed externally. In this case, the same eviction algorithm is used

 HeaderTable.prototype.setSizeLimit = function setSizeLimit(limit) {

   this._limit = limit;

   this._enforceLimit(this._limit);

 };

 // [The Static Table](http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#appendix-B)

 // ------------------

 // [statictable]:http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#appendix-B

 // The table is generated with feeding the table from the spec to the following sed command:

 //

 //     sed -re "s/\s*\| [0-9]+\s*\| ([^ ]*)/  [ '\1'/g" -e "s/\|\s([^ ]*)/, '\1'/g" -e 's/ \|/],/g'

 HeaderTable.staticTable  = [

   [ ':authority'                  , ''            ],

   [ ':method'                     , 'GET'         ],

   [ ':method'                     , 'POST'        ],

   [ ':path'                       , '/'           ],

   [ ':path'                       , '/index.html' ],

   [ ':scheme'                     , 'http'        ],

   [ ':scheme'                     , 'https'       ],

   [ ':status'                     , '200'         ],

   [ ':status'                     , '500'         ],

   [ ':status'                     , '404'         ],

   [ ':status'                     , '403'         ],

   [ ':status'                     , '400'         ],

   [ ':status'                     , '401'         ],

   [ 'accept-charset'              , ''            ],

   [ 'accept-encoding'             , ''            ],

   [ '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'            , ''            ]

 ];

 // The HeaderSetDecompressor class

 // -------------------------------

 // A `HeaderSetDecompressor` instance is a transform stream that can be used to *decompress a

 // single header set*. Its input is a stream of binary data chunks and its output is a stream of

 // `[name, value]` pairs.

 //

 // Currently, it is not a proper streaming decompressor implementation, since it buffer its input

 // until the end os the stream, and then processes the whole header block at once.

 util.inherits(HeaderSetDecompressor, TransformStream);

 function HeaderSetDecompressor(log, table) {

   TransformStream.call(this, { objectMode: true });

   this._log = log.child({ component: 'compressor' });

   this._table = table;

   this._chunks = [];

 }

 // `_transform` is the implementation of the [corresponding virtual function][_transform] of the

 // TransformStream class. It collects the data chunks for later processing.

 // [_transform]: http://nodejs.org/api/stream.html#stream_transform_transform_chunk_encoding_callback

 HeaderSetDecompressor.prototype._transform = function _transform(chunk, encoding, callback) {

   this._chunks.push(chunk);

   callback();

 };

 // `execute(rep)` executes the given [header representation][representation].

 // [representation]: http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-3.1.4

 // The *JavaScript object representation* of a header representation:

 //

 //     {

 //       name: String || Integer,  // string literal or index

 //       value: String || Integer, // string literal or index

 //       index: Boolean            // with or without indexing

 //     }

 //

 // *Important:* to ease the indexing of the header table, indexes start at 0 instead of 1.

 //

 // Examples:

 //

 //     Indexed:

 //     { name: 2  , value: 2  , index: false }

 //     { name: -1 , value: -1 , index: false } // reference set emptying

 //     Literal:

 //     { name: 2  , value: 'X', index: false } // without indexing

 //     { name: 2  , value: 'Y', index: true  } // with indexing

 //     { name: 'A', value: 'Z', index: true  } // with indexing, literal name

 HeaderSetDecompressor.prototype._execute = function _execute(rep) {

   this._log.trace({ key: rep.name, value: rep.value, index: rep.index },

                   'Executing header representation');

   var entry, pair;

   // * An _indexed representation_ with an index value of 0 (in our representation, it means -1)

   //   entails the following actions:

   //   * If the following byte starts with a set bit, the reference set is emptied.

   //   * Else, reduce the size of the header table to the value encoded with a 7-bit prefix

   // * An _indexed representation_ corresponding to an entry _present_ in the reference set

   //   entails the following actions:

   //   * The entry is removed from the reference set.

   // * An _indexed representation_ corresponding to an entry _not present_ in the reference set

   //   entails the following actions:

   //   * If referencing an element of the static table:

   //     * The header field corresponding to the referenced entry is emitted

   //     * The referenced static entry is added to the header table

   //     * A reference to this new header table entry is added to the reference set (except if

   //       this new entry didn't fit in the header table)

   //   * If referencing an element of the header table:

   //     * The header field corresponding to the referenced entry is emitted

   //     * The referenced header table entry is added to the reference set

   if (typeof rep.value === 'number') {

     var index = rep.value;

     entry = this._table[index];

     if (index == -1) {

       if (rep.index) {

         for (var i = 0; i < this._table.length; i++) {

           this._table[i].reference = false;

         }

       } else {

         // Set a new maximum size

         this.setTableSizeLimit(rep.name);

       }

     }

     else if (entry.reference) {

       entry.reference = false;

     }

     else {

       pair = entry.slice();

       this.push(pair);

       if (index >= this._table.length - this._table._staticLength) {

         entry = entryFromPair(pair);

         this._table.add(entry);

       }

       entry.reference = true;

       entry.emitted = true;

     }

   }

   // * A _literal representation_ that is _not added_ to the header table entails the following

   //   action:

   //   * The header is emitted.

   // * A _literal representation_ that is _added_ to the header table entails the following further

   //   actions:

   //   * The header is added to the header table.

   //   * The new entry is added to the reference set.

   else {

     if (typeof rep.name === 'number') {

       pair = [this._table[rep.name][0], rep.value];

     } else {

       pair = [rep.name, rep.value];

     }

     if (rep.index) {

       entry = entryFromPair(pair);

       entry.reference = true;

       entry.emitted = true;

       this._table.add(entry);

     }

     this.push(pair);

   }

 };

 // `_flush` is the implementation of the [corresponding virtual function][_flush] of the

 // TransformStream class. The whole decompressing process is done in `_flush`. It gets called when

 // the input stream is over.

 // [_flush]: http://nodejs.org/api/stream.html#stream_transform_flush_callback

 HeaderSetDecompressor.prototype._flush = function _flush(callback) {

   var buffer = concat(this._chunks);

   // * processes the header representations

   buffer.cursor = 0;

   while (buffer.cursor < buffer.length) {

     this._execute(HeaderSetDecompressor.header(buffer));

   }

   // * [emits the reference set](http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-3.2.2)

   for (var index = 0; index < this._table.length; index++) {

     var entry = this._table[index];

     if (entry.reference && !entry.emitted) {

       this.push(entry.slice());

     }

     entry.emitted = false;

   }

   callback();

 };

 // The HeaderSetCompressor class

 // -----------------------------

 // A `HeaderSetCompressor` instance is a transform stream that can be used to *compress a single

 // header set*. Its input is a stream of `[name, value]` pairs and its output is a stream of

 // binary data chunks.

 //

 // It is a real streaming compressor, since it does not wait until the header set is complete.

 //

 // The compression algorithm is (intentionally) not specified by the spec. Therefore, the current

 // compression algorithm can probably be improved in the future.

 util.inherits(HeaderSetCompressor, TransformStream);

 function HeaderSetCompressor(log, table) {

   TransformStream.call(this, { objectMode: true });

   this._log = log.child({ component: 'compressor' });

   this._table = table;

   this.push = TransformStream.prototype.push.bind(this);

 }

 HeaderSetCompressor.prototype.send = function send(rep) {

   this._log.trace({ key: rep.name, value: rep.value, index: rep.index },

                   'Emitting header representation');

   if (!rep.chunks) {

     rep.chunks = HeaderSetCompressor.header(rep);

   }

   rep.chunks.forEach(this.push);

 };

 // `_transform` is the implementation of the [corresponding virtual function][_transform] of the

 // TransformStream class. It processes the input headers one by one:

 // [_transform]: http://nodejs.org/api/stream.html#stream_transform_transform_chunk_encoding_callback

 HeaderSetCompressor.prototype._transform = function _transform(pair, encoding, callback) {

   var name = pair[0].toLowerCase();

   var value = pair[1];

   var entry, rep;

   // * tries to find full (name, value) or name match in the header table

   var nameMatch = -1, fullMatch = -1;

   for (var droppedIndex = 0; droppedIndex < this._table.length; droppedIndex++) {

     entry = this._table[droppedIndex];

     if (entry[0] === name) {

       if (entry[1] === value) {

         fullMatch = droppedIndex;

         break;

       } else if (nameMatch === -1) {

         nameMatch = droppedIndex;

       }

     }

   }

   // * if there's full match, it will be an indexed representation (or more than one) depending

   //   on its presence in the reference, the emitted and the keep set:

   //

   //   * If the entry is outside the reference set, then a single indexed representation puts the

   //     entry into it and emits the header. Note that if the matched entry is in the static table,

   //     then it has to be added to the header table.

   //

   //   * If it's already in the keep set, then 4 indexed representations are needed:

   //

   //     1. removes it from the reference set

   //     2. puts it back in the reference set and emits the header once

   //     3. removes it again

   //     4. puts it back and emits it again for the second time

   //

   //     It won't be emitted at the end of the decoding process since it's now in the emitted set.

   //

   //   * If it's in the emitted set, then 2 indexed representations are needed:

   //

   //     1. removes it from the reference set

   //     2. puts it back in the reference set and emits the header once

   //

   //   * If it's in the reference set, but outside the keep set and the emitted set, then this

   //     header is common with the previous header set, and is still untouched. We mark it to keep

   //     in the reference set (that means don't remove at the end of the encoding process).

   if (fullMatch !== -1) {

     rep = { name: fullMatch, value: fullMatch, index: false };

     if (!entry.reference) {

       if (fullMatch >= this._table.length - this._table._staticLength) {

         entry = entryFromPair(pair);

         this._table.add(entry);

       }

       this.send(rep);

       entry.reference = true;

       entry.emitted = true;

     }

     else if (entry.keep) {

       this.send(rep);

       this.send(rep);

       this.send(rep);

       this.send(rep);

       entry.keep = false;

       entry.emitted = true;

     }

     else if (entry.emitted) {

       this.send(rep);

       this.send(rep);

     }

     else {

       entry.keep = true;

     }

   }

   // * otherwise, it will be a literal representation (with a name index if there's a name match)

   else {

     entry = entryFromPair(pair);

     entry.emitted = true;

     var indexing = (entry._size < this._table._limit / 2);

     if (indexing) {

       entry.reference = true;

       var droppedEntries = this._table.add(entry);

       for (droppedIndex in droppedEntries) {

         droppedIndex = Number(droppedIndex)

         var dropped = droppedEntries[droppedIndex];

         if (dropped.keep) {

           rep = { name: droppedIndex, value: droppedIndex, index: false };

           this.send(rep);

           this.send(rep);

         }

       }

     }

     this.send({ name: (nameMatch !== -1) ? nameMatch : name, value: value, index: indexing });

   }

   callback();

 };

 // `_flush` is the implementation of the [corresponding virtual function][_flush] of the

 // TransformStream class. It gets called when there's no more header to compress. The final step:

 // [_flush]: http://nodejs.org/api/stream.html#stream_transform_flush_callback

 HeaderSetCompressor.prototype._flush = function _flush(callback) {

   // * removing entries from the header set that are not marked to be kept or emitted

   for (var index = 0; index < this._table.length; index++) {

     var entry = this._table[index];

     if (entry.reference && !entry.keep && !entry.emitted) {

       this.send({ name: index, value: index, index: false });

       entry.reference = false;

     }

     entry.keep = false;

     entry.emitted = false;

   }

   callback();

 };

 // [Detailed Format](http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-05#section-4)

 // -----------------

 // ### Integer representation ###

 //

 // The algorithm to represent an integer I is as follows:

 //

 // 1. If I < 2^N - 1, encode I on N bits

 // 2. Else, encode 2^N - 1 on N bits and do the following steps:

 //    1. Set I to (I - (2^N - 1)) and Q to 1

 //    2. While Q > 0

 //       1. Compute Q and R, quotient and remainder of I divided by 2^7

 //       2. If Q is strictly greater than 0, write one 1 bit; otherwise, write one 0 bit

 //       3. Encode R on the next 7 bits

 //       4. I = Q

 HeaderSetCompressor.integer = function writeInteger(I, N) {

   var limit = Math.pow(2,N) - 1;

   if (I < limit) {

     return [new Buffer([I])];

   }

   var bytes = [];

   if (N !== 0) {

     bytes.push(limit);

   }

   I -= limit;

   var Q = 1, R;

   while (Q > 0) {

     Q = Math.floor(I / 128);

     R = I % 128;

     if (Q > 0) {

       R += 128;

     }

     bytes.push(R);

     I = Q;

   }

   return [new Buffer(bytes)];

 };

 // The inverse algorithm:

 //

 // 1. Set I to the number coded on the lower N bits of the first byte

 // 2. If I is smaller than 2^N - 1 then return I

 // 2. Else the number is encoded on more than one byte, so do the following steps:

 //    1. Set M to 0

 //    2. While returning with I

 //       1. Let B be the next byte (the first byte if N is 0)

 //       2. Read out the lower 7 bits of B and multiply it with 2^M

 //       3. Increase I with this number

 //       4. Increase M by 7

 //       5. Return I if the most significant bit of B is 0

 HeaderSetDecompressor.integer = function readInteger(buffer, N) {

   var limit = Math.pow(2,N) - 1;

   var I = buffer[buffer.cursor] & limit;

   if (N !== 0) {

     buffer.cursor += 1;

   }

   if (I === limit) {

     var M = 0;

     do {

       I += (buffer[buffer.cursor] & 127) << M;

       M += 7;

       buffer.cursor += 1;

     } while (buffer[buffer.cursor - 1] & 128);

   }

   return I;

 };

 // ### Huffman Encoding ###

 function HuffmanTable(table) {

   function createTree(codes, position) {

     if (codes.length === 1) {

       return [table.indexOf(codes[0])];

     }

     else {

       position = position || 0;

       var zero = [];

       var one = [];

       for (var i = 0; i < codes.length; i++) {

         var string = codes[i];

         if (string[position] === '0') {

           zero.push(string);

         } else {

           one.push(string);

         }

       }

       return [createTree(zero, position + 1), createTree(one, position + 1)];

     }

   }

   this.tree = createTree(table);

   this.codes = table.map(function(bits) {

     return parseInt(bits, 2);

   });

   this.lengths = table.map(function(bits) {

     return bits.length;

   });

 }

 HuffmanTable.prototype.encode = function encode(buffer) {

   var result = [];

   var space = 8;

   function add(data) {

     if (space === 8) {

       result.push(data);

     } else {

       result[result.length - 1] |= data;

     }

   }

   for (var i = 0; i < buffer.length; i++) {

     var byte = buffer[i];

     var code = this.codes[byte];

     var length = this.lengths[byte];

     while (length !== 0) {

       if (space >= length) {

         add(code << (space - length));

         code = 0;

         space -= length;

         length = 0;

       } else {

         var shift = length - space;

         var msb = code >> shift;

         add(msb);

         code -= msb << shift;

         length -= space;

         space = 0;

       }

       if (space === 0) {

         space = 8;

       }

     }

   }

   if (space !== 8) {

     add(this.codes[256] >> (this.lengths[256] - space));

   }

   return new Buffer(result);

 }

 HuffmanTable.prototype.decode = function decode(buffer) {

   var result = [];

   var subtree = this.tree;

   for (var i = 0; i < buffer.length; i++) {

     var byte = buffer[i];

     for (var j = 0; j < 8; j++) {

       var bit = (byte & 128) ? 1 : 0;

       byte = byte << 1;

       subtree = subtree[bit];

       if (subtree.length === 1) {

         result.push(subtree[0]);

         subtree = this.tree;

       }

     }

   }

   return new Buffer(result);

 }

 // The initializer arrays for the Huffman tables are generated with feeding the tables from the

 // spec to this sed command:

 //

 //     sed -e "s/^.* [|]//g" -e "s/|//g" -e "s/ .*//g" -e "s/^/  '/g" -e "s/$/',/g"

 HuffmanTable.huffmanTable = new HuffmanTable([

   '111111111111111111110111010',

   '111111111111111111110111011',

   '111111111111111111110111100',

   '111111111111111111110111101',

   '111111111111111111110111110',

   '111111111111111111110111111',

   '111111111111111111111000000',

   '111111111111111111111000001',

   '111111111111111111111000010',

   '111111111111111111111000011',

   '111111111111111111111000100',

   '111111111111111111111000101',

   '111111111111111111111000110',

   '111111111111111111111000111',

   '111111111111111111111001000',

   '111111111111111111111001001',

   '111111111111111111111001010',

   '111111111111111111111001011',

   '111111111111111111111001100',

   '111111111111111111111001101',

   '111111111111111111111001110',

   '111111111111111111111001111',

   '111111111111111111111010000',

   '111111111111111111111010001',

   '111111111111111111111010010',

   '111111111111111111111010011',

   '111111111111111111111010100',

   '111111111111111111111010101',

   '111111111111111111111010110',

   '111111111111111111111010111',

   '111111111111111111111011000',

   '111111111111111111111011001',

   '11101000',

   '111111111100',

   '11111111111010',

   '111111111111100',

   '111111111111101',

   '100100',

   '1101110',

   '111111111111110',

   '11111111010',

   '11111111011',

   '1111111010',

   '11111111100',

   '11101001',

   '100101',

   '00100',

   '0000',

   '00101',

   '00110',

   '00111',

   '100110',

   '100111',

   '101000',

   '101001',

   '101010',

   '101011',

   '101100',

   '111101100',

   '11101010',

   '111111111111111110',

   '101101',

   '11111111111111100',

   '111101101',

   '11111111111011',

   '1101111',

   '11101011',

   '11101100',

   '11101101',

   '11101110',

   '1110000',

   '111101110',

   '111101111',

   '111110000',

   '111110001',

   '1111111011',

   '111110010',

   '11101111',

   '111110011',

   '111110100',

   '111110101',

   '111110110',

   '111110111',

   '11110000',

   '11110001',

   '111111000',

   '111111001',

   '111111010',

   '111111011',

   '111111100',

   '1111111100',

   '11111111111100',

   '111111111111111111111011010',

   '1111111111100',

   '11111111111101',

   '101110',

   '1111111111111111110',

   '01000',

   '101111',

   '01001',

   '110000',

   '0001',

   '110001',

   '110010',

   '110011',

   '01010',

   '1110001',

   '1110010',

   '01011',

   '110100',

   '01100',

   '01101',

   '01110',

   '11110010',

   '01111',

   '10000',

   '10001',

   '110101',

   '1110011',

   '110110',

   '11110011',

   '11110100',

   '11110101',

   '11111111111111101',

   '11111111101',

   '11111111111111110',

   '111111111101',

   '111111111111111111111011011',

   '111111111111111111111011100',

   '111111111111111111111011101',

   '111111111111111111111011110',

   '111111111111111111111011111',

   '111111111111111111111100000',

   '111111111111111111111100001',

   '111111111111111111111100010',

   '111111111111111111111100011',

   '111111111111111111111100100',

   '111111111111111111111100101',

   '111111111111111111111100110',

   '111111111111111111111100111',

   '111111111111111111111101000',

   '111111111111111111111101001',

   '111111111111111111111101010',

   '111111111111111111111101011',

   '111111111111111111111101100',

   '111111111111111111111101101',

   '111111111111111111111101110',

   '111111111111111111111101111',

   '111111111111111111111110000',

   '111111111111111111111110001',

   '111111111111111111111110010',

   '111111111111111111111110011',

   '111111111111111111111110100',

   '111111111111111111111110101',

   '111111111111111111111110110',

   '111111111111111111111110111',

   '111111111111111111111111000',

   '111111111111111111111111001',

   '111111111111111111111111010',

   '111111111111111111111111011',

   '111111111111111111111111100',

   '111111111111111111111111101',

   '111111111111111111111111110',

   '111111111111111111111111111',

   '11111111111111111110000000',

   '11111111111111111110000001',

   '11111111111111111110000010',

   '11111111111111111110000011',

   '11111111111111111110000100',

   '11111111111111111110000101',

   '11111111111111111110000110',

   '11111111111111111110000111',

   '11111111111111111110001000',

   '11111111111111111110001001',

   '11111111111111111110001010',

   '11111111111111111110001011',

   '11111111111111111110001100',

   '11111111111111111110001101',

   '11111111111111111110001110',

   '11111111111111111110001111',

   '11111111111111111110010000',

   '11111111111111111110010001',

   '11111111111111111110010010',

   '11111111111111111110010011',

   '11111111111111111110010100',

   '11111111111111111110010101',

   '11111111111111111110010110',

   '11111111111111111110010111',

   '11111111111111111110011000',

   '11111111111111111110011001',

   '11111111111111111110011010',

   '11111111111111111110011011',

   '11111111111111111110011100',

   '11111111111111111110011101',

   '11111111111111111110011110',

   '11111111111111111110011111',

   '11111111111111111110100000',

   '11111111111111111110100001',

   '11111111111111111110100010',

   '11111111111111111110100011',

   '11111111111111111110100100',

   '11111111111111111110100101',

   '11111111111111111110100110',

   '11111111111111111110100111',

   '11111111111111111110101000',

   '11111111111111111110101001',

   '11111111111111111110101010',

   '11111111111111111110101011',

   '11111111111111111110101100',

   '11111111111111111110101101',

   '11111111111111111110101110',

   '11111111111111111110101111',

   '11111111111111111110110000',

   '11111111111111111110110001',

   '11111111111111111110110010',

   '11111111111111111110110011',

   '11111111111111111110110100',

   '11111111111111111110110101',

   '11111111111111111110110110',

   '11111111111111111110110111',

   '11111111111111111110111000',

   '11111111111111111110111001',

   '11111111111111111110111010',

   '11111111111111111110111011',

   '11111111111111111110111100',

   '11111111111111111110111101',

   '11111111111111111110111110',

   '11111111111111111110111111',

   '11111111111111111111000000',

   '11111111111111111111000001',

   '11111111111111111111000010',

   '11111111111111111111000011',

   '11111111111111111111000100',

   '11111111111111111111000101',

   '11111111111111111111000110',

   '11111111111111111111000111',

   '11111111111111111111001000',

   '11111111111111111111001001',

   '11111111111111111111001010',

   '11111111111111111111001011',

   '11111111111111111111001100',

   '11111111111111111111001101',

   '11111111111111111111001110',

   '11111111111111111111001111',

   '11111111111111111111010000',

   '11111111111111111111010001',

   '11111111111111111111010010',

   '11111111111111111111010011',

   '11111111111111111111010100',

   '11111111111111111111010101',

   '11111111111111111111010110',

   '11111111111111111111010111',

   '11111111111111111111011000',

   '11111111111111111111011001',

   '11111111111111111111011010',

   '11111111111111111111011011',

   '11111111111111111111011100'

 ]);

 // ### String literal representation ###

 //

 // Literal **strings** can represent header names or header values. There's two variant of the

 // string encoding:

 //

 // String literal with Huffman encoding:

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 1 |  Value Length Prefix (7)  |

 //     +---+---+---+---+---+---+---+---+

 //     |   Value Length (0-N bytes)    |

 //     +---+---+---+---+---+---+---+---+

 //     ...

 //     +---+---+---+---+---+---+---+---+

 //     | Huffman Encoded Data  |Padding|

 //     +---+---+---+---+---+---+---+---+

 //

 // String literal without Huffman encoding:

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 0 |  Value Length Prefix (7)  |

 //     +---+---+---+---+---+---+---+---+

 //     |   Value Length (0-N bytes)    |

 //     +---+---+---+---+---+---+---+---+

 //     ...

 //     +---+---+---+---+---+---+---+---+

 //     |  Field Bytes Without Encoding |

 //     +---+---+---+---+---+---+---+---+

 HeaderSetCompressor.string = function writeString(str) {

   str = new Buffer(str, 'utf8');

   var huffman = HuffmanTable.huffmanTable.encode(str);

   if (huffman.length < str.length) {

     var length = HeaderSetCompressor.integer(huffman.length, 7)

     length[0][0] |= 128;

     return length.concat(huffman);

   }

   else {

     length = HeaderSetCompressor.integer(str.length, 7)

     return length.concat(str);

   }

 };

 HeaderSetDecompressor.string = function readString(buffer) {

   var huffman = buffer[buffer.cursor] & 128;

   var length = HeaderSetDecompressor.integer(buffer, 7);

   var encoded = buffer.slice(buffer.cursor, buffer.cursor + length);

   buffer.cursor += length;

   return (huffman ? HuffmanTable.huffmanTable.decode(encoded) : encoded).toString('utf8');

 };

 // ### Header represenations ###

 // The JavaScript object representation is described near the

 // `HeaderSetDecompressor.prototype._execute()` method definition.

 //

 // **All binary header representations** start with a prefix signaling the representation type and

 // an index represented using prefix coded integers:

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 1 |        Index (7+)         |  Indexed Representation

 //     +---+---------------------------+

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 0 | 1 |      Index (6+)       |

 //     +---+---+---+-------------------+  Literal w/o Indexing

 //     |       Value Length (8+)       |

 //     +-------------------------------+  w/ Indexed Name

 //     | Value String (Length octets)  |

 //     +-------------------------------+

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 0 | 1 |           0           |

 //     +---+---+---+-------------------+

 //     |       Name Length (8+)        |

 //     +-------------------------------+  Literal w/o Indexing

 //     |  Name String (Length octets)  |

 //     +-------------------------------+  w/ New Name

 //     |       Value Length (8+)       |

 //     +-------------------------------+

 //     | Value String (Length octets)  |

 //     +-------------------------------+

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 0 | 0 |      Index (6+)       |

 //     +---+---+---+-------------------+  Literal w/ Incremental Indexing

 //     |       Value Length (8+)       |

 //     +-------------------------------+  w/ Indexed Name

 //     | Value String (Length octets)  |

 //     +-------------------------------+

 //

 //       0   1   2   3   4   5   6   7

 //     +---+---+---+---+---+---+---+---+

 //     | 0 | 0 |           0           |

 //     +---+---+---+-------------------+

 //     |       Name Length (8+)        |

 //     +-------------------------------+  Literal w/ Incremental Indexing

 //     |  Name String (Length octets)  |

 //     +-------------------------------+  w/ New Name

 //     |       Value Length (8+)       |

 //     +-------------------------------+

 //     | Value String (Length octets)  |

 //     +-------------------------------+

 //

 // The **Indexed Representation** consists of the 1-bit prefix and the Index that is represented as

 // a 7-bit prefix coded integer and nothing else.

 //

 // After the first bits, **all literal representations** specify the header name, either as a

 // pointer to the Header Table (Index) or a string literal. When the string literal representation

 // is used, the Index is set to 0 and the string literal starts at the second byte.

 //

 // For **all literal representations**, the specification of the header value comes next. It is

 // always represented as a string.

 var representations = {

   indexed             : { prefix: 7, pattern: 0x80 },

   literal             : { prefix: 6, pattern: 0x40 },

   literalIncremental  : { prefix: 6, pattern: 0x00 }

 };

 HeaderSetCompressor.header = function writeHeader(header) {

   var representation, buffers = [];

   if (typeof header.value === 'number') {

     representation = representations.indexed;

   } else if (header.index) {

     representation = representations.literalIncremental;

   } else {

     representation = representations.literal;

   }

   if (representation === representations.indexed) {

     buffers.push(HeaderSetCompressor.integer(header.value + 1, representation.prefix));

     if (header.value == -1) {

       if (header.index) {

         buffers.push(HeaderSetCompressor.integer(0x80, 8));

       } else {

         buffers.push(HeaderSetCompressor.integer(header.name, 7));

       }

     }

   }

   else {

     if (typeof header.name === 'number') {

       buffers.push(HeaderSetCompressor.integer(header.name + 1, representation.prefix));

     } else {

       buffers.push(HeaderSetCompressor.integer(0, representation.prefix));

       buffers.push(HeaderSetCompressor.string(header.name));

     }

     buffers.push(HeaderSetCompressor.string(header.value));

   }

   buffers[0][0][0] |= representation.pattern;

   return Array.prototype.concat.apply([], buffers); // array of arrays of buffers -> array of buffers

 };

 HeaderSetDecompressor.header = function readHeader(buffer) {

   var representation, header = {};

   var firstByte = buffer[buffer.cursor];

   if (firstByte & 0x80) {

     representation = representations.indexed;

   } else if (firstByte & 0x40) {

     representation = representations.literal;

   } else {

     representation = representations.literalIncremental;

   }

   if (representation === representations.indexed) {

     header.value = header.name = HeaderSetDecompressor.integer(buffer, representation.prefix) - 1;

     header.index = false;

     if (header.value === -1) {

       if (buffer[buffer.cursor] & 0x80) {

         header.index = true;

         buffer.cursor += 1;

       } else {

         header.name = HeaderSetDecompressor.integer(buffer, 7);

       }

     }

   }

   else {

     header.name = HeaderSetDecompressor.integer(buffer, representation.prefix) - 1;

     if (header.name === -1) {

       header.name = HeaderSetDecompressor.string(buffer);

     }

     header.value = HeaderSetDecompressor.string(buffer);

     header.index = (representation === representations.literalIncremental);

   }

   return header;

 };

 // Integration with HTTP/2

 // =======================

 // This section describes the interaction between the compressor/decompressor and the rest of the

 // HTTP/2 implementation. The `Compressor` and the `Decompressor` makes up a layer between the

 // [framer](framer.html) and the [connection handling component](connection.html). They let most

 // frames pass through, except HEADERS and PUSH_PROMISE frames. They convert the frames between

 // these two representations:

 //

 //     {                                   {

 //      type: 'HEADERS',                    type: 'HEADERS',

 //      flags: {},                          flags: {},

 //      stream: 1,               <===>      stream: 1,

 //      headers: {                          data: Buffer

 //       N1: 'V1',                         }

 //       N2: ['V1', 'V2', ...],

 //       // ...

 //      }

 //     }

 //

 // There are possibly several binary frame that belong to a single non-binary frame.

 var MAX_HTTP_PAYLOAD_SIZE = 16383;

 // The Compressor class

 // --------------------

 // The Compressor transform stream is basically stateless.

 util.inherits(Compressor, TransformStream);

 function Compressor(log, type) {

   TransformStream.call(this, { objectMode: true });

   this._log = log.child({ component: 'compressor' });

   assert((type === 'REQUEST') || (type === 'RESPONSE'));

   this._table = new HeaderTable(this._log);

 }

 // Changing the header table size

 Compressor.prototype.setTableSizeLimit = function setTableSizeLimit(size) {

   this._table.setSizeLimit(size);

 };

 // `compress` takes a header set, and compresses it using a new `HeaderSetCompressor` stream

 // instance. This means that from now on, the advantages of streaming header encoding are lost,

 // but the API becomes simpler.

 Compressor.prototype.compress = function compress(headers) {

   var compressor = new HeaderSetCompressor(this._log, this._table);

   for (var name in headers) {

     var value = headers[name];

     name = String(name).toLowerCase();

     // * To allow for better compression efficiency, the Cookie header field MAY be split into

     //   separate header fields, each with one or more cookie-pairs.

     if (name == 'cookie') {

       if (!(value instanceof Array)) {

         value = [value]

       }

       value = Array.prototype.concat.apply([], value.map(function(cookie) {

         return String(cookie).split(';').map(trim)

       }));

     }

     // * To preserve the order of a comma-separated list, the ordered values for a single header

     //   field name appearing in different header fields are concatenated into a single value.

     //   A zero-valued octet (0x0) is used to delimit multiple values.

     // * Header fields containing multiple values MUST be concatenated into a single value unless

     //   the ordering of that header field is known to be not significant.

     // * Currently, only the Cookie header is considered to be order-insensitive.

     if ((value instanceof Array) && (name !== 'cookie')) {

       value = value.join('\0');

     }

     if (value instanceof Array) {

       for (var i = 0; i < value.length; i++) {

         compressor.write([name, String(value[i])]);

       }

     } else {

       compressor.write([name, String(value)]);

     }

   }

   compressor.end();

   var chunk, chunks = [];

   while (chunk = compressor.read()) {

     chunks.push(chunk);

   }

   return concat(chunks);

 };

 // When a `frame` arrives

 Compressor.prototype._transform = function _transform(frame, encoding, done) {

   // * and it is a HEADERS or PUSH_PROMISE frame

   //   * it generates a header block using the compress method

   //   * cuts the header block into `chunks` that are not larger than `MAX_HTTP_PAYLOAD_SIZE`

   //   * for each chunk, it pushes out a chunk frame that is identical to the original, except

   //     the `data` property which holds the given chunk, the type of the frame which is always

   //     CONTINUATION except for the first frame, and the END_HEADERS/END_PUSH_STREAM flag that

   //     marks the last frame and the END_STREAM flag which is always false before the end

   if (frame.type === 'HEADERS' || frame.type === 'PUSH_PROMISE') {

     var buffer = this.compress(frame.headers);

     var chunks = cut(buffer, MAX_HTTP_PAYLOAD_SIZE);

     for (var i = 0; i < chunks.length; i++) {

       var chunkFrame;

       var first = (i === 0);

       var last = (i === chunks.length - 1);

       if (first) {

         chunkFrame = util._extend({}, frame);

         chunkFrame.flags = util._extend({}, frame.flags);

         chunkFrame.flags['END_' + frame.type] = last;

       } else {

         chunkFrame = {

           type: 'CONTINUATION',

           flags: { END_HEADERS: last },

           stream: frame.stream

         };

       }

       chunkFrame.data = chunks[i];

       this.push(chunkFrame);

     }

   }

   // * otherwise, the frame is forwarded without taking any action

   else {

     this.push(frame);

   }

   done();

 };

 // The Decompressor class

 // ----------------------

 // The Decompressor is a stateful transform stream, since it has to collect multiple frames first,

 // and the decoding comes after unifying the payload of those frames.

 //

 // If there's a frame in progress, `this._inProgress` is `true`. The frames are collected in

 // `this._frames`, and the type of the frame and the stream identifier is stored in `this._type`

 // and `this._stream` respectively.

 util.inherits(Decompressor, TransformStream);

 function Decompressor(log, type) {

   TransformStream.call(this, { objectMode: true });

   this._log = log.child({ component: 'compressor' });

   assert((type === 'REQUEST') || (type === 'RESPONSE'));

   this._table = new HeaderTable(this._log);

   this._inProgress = false;

   this._base = undefined;

 }

 // Changing the header table size

 Decompressor.prototype.setTableSizeLimit = function setTableSizeLimit(size) {

   this._table.setSizeLimit(size);

 };

 // `decompress` takes a full header block, and decompresses it using a new `HeaderSetDecompressor`

 // stream instance. This means that from now on, the advantages of streaming header decoding are

 // lost, but the API becomes simpler.

 Decompressor.prototype.decompress = function decompress(block) {

   var decompressor = new HeaderSetDecompressor(this._log, this._table);

   decompressor.end(block);

   var headers = {};

   var pair;

   while (pair = decompressor.read()) {

     var name = pair[0];

     // * After decompression, header fields that have values containing zero octets (0x0) MUST be

     //   split into multiple header fields before being processed.

     var values = pair[1].split('\0');

     for (var i = 0; i < values.length; i++) {

       var value = values[i];

       if (name in headers) {

         if (headers[name] instanceof Array) {

           headers[name].push(value);

         } else {

           headers[name] = [headers[name], value];

         }

       } else {

         headers[name] = value;

       }

     }

   }

   // * If there are multiple Cookie header fields after decompression, these MUST be concatenated

   //   into a single octet string using the two octet delimiter of 0x3B, 0x20 (the ASCII

   //   string "; ").

   if (('cookie' in headers) && (headers['cookie'] instanceof Array)) {

     headers['cookie'] = headers['cookie'].join('; ')

   }

   return headers;

 };

 // When a `frame` arrives

 Decompressor.prototype._transform = function _transform(frame, encoding, done) {

   // * and the collection process is already `_inProgress`, the frame is simply stored, except if

   //   it's an illegal frame

   if (this._inProgress) {

     if ((frame.type !== 'CONTINUATION') || (frame.stream !== this._base.stream)) {

       this._log.error('A series of HEADER frames were not continuous');

       this.emit('error', 'PROTOCOL_ERROR');

       return;

     }

     this._frames.push(frame);

   }

   // * and the collection process is not `_inProgress`, but the new frame's type is HEADERS or

   //   PUSH_PROMISE, a new collection process begins

   else if ((frame.type === 'HEADERS') || (frame.type === 'PUSH_PROMISE')) {

     this._inProgress = true;

     this._base = util._extend({}, frame);

     this._frames = [frame];

   }

   // * otherwise, the frame is forwarded without taking any action

   else {

     this.push(frame);

   }

   // * When the frame signals that it's the last in the series, the header block chunks are

   //   concatenated, the headers are decompressed, and a new frame gets pushed out with the

   //   decompressed headers.

   if (this._inProgress && (frame.flags.END_HEADERS || frame.flags.END_PUSH_PROMISE)) {

     var buffer = concat(this._frames.map(function(frame) {

       return frame.data;

     }));

     try {

       var headers = this.decompress(buffer);

     } catch(error) {

       this._log.error({ err: error }, 'Header decompression error');

       this.emit('error', 'COMPRESSION_ERROR');

       return;

     }

     this.push(util._extend(this._base, { headers: headers }));

     this._inProgress = false;

   }

   done();

 };

 // Helper functions

 // ================

 // Concatenate an array of buffers into a new buffer

 function concat(buffers) {

   var size = 0;

   for (var i = 0; i < buffers.length; i++) {

     size += buffers[i].length;

   }

   var concatenated = new Buffer(size);

   for (var cursor = 0, j = 0; j < buffers.length; cursor += buffers[j].length, j++) {

     buffers[j].copy(concatenated, cursor);

   }

   return concatenated;

 }

 // Cut `buffer` into chunks not larger than `size`

 function cut(buffer, size) {

   var chunks = [];

   var cursor = 0;

   do {

     var chunkSize = Math.min(size, buffer.length - cursor);

     chunks.push(buffer.slice(cursor, cursor + chunkSize));

     cursor += chunkSize;

   } while(cursor < buffer.length);

   return chunks;

 }

 function trim(string) {

   return string.trim()

 }