The Tor Browser: testing/xpcshell/node-http2/node_modules/http2-protocol/lib/compressor.js@6474c204b198 (annotated)

testing/xpcshell/node-http2/node_modules/http2-protocol/lib/compressor.js@6474c204b198 (annotated)

testing/xpcshell/node-http2/node_modules/http2-protocol/lib/compressor.js

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 // 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()
 }