The Tor Browser / file revision

 // The framer consists of two [Transform Stream][1] subclasses that operate in [object mode][2]:

 // the Serializer and the Deserializer

 // [1]: http://nodejs.org/api/stream.html#stream_class_stream_transform

 // [2]: http://nodejs.org/api/stream.html#stream_new_stream_readable_options

 var assert = require('assert');

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

 exports.Serializer = Serializer;

 exports.Deserializer = Deserializer;

 var logData = Boolean(process.env.HTTP2_LOG_DATA);

 var MAX_PAYLOAD_SIZE = 16383;

 // Serializer

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

 //

 //     Frame Objects

 //     * * * * * * * --+---------------------------

 //                     |                          |

 //                     v                          v           Buffers

 //      [] -----> Payload Ser. --[buffers]--> Header Ser. --> * * * *

 //     empty      adds payload                adds header

 //     array        buffers                     buffer

 function Serializer(log, sizeLimit) {

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

   this._sizeLimit = sizeLimit || MAX_PAYLOAD_SIZE;

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

 }

 Serializer.prototype = Object.create(Transform.prototype, { constructor: { value: Serializer } });

 // When there's an incoming frame object, it first generates the frame type specific part of the

 // frame (payload), and then then adds the header part which holds fields that are common to all

 // frame types (like the length of the payload).

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

   this._log.trace({ frame: frame }, 'Outgoing frame');

   assert(frame.type in Serializer, 'Unknown frame type: ' + frame.type);

   var buffers = [];

   Serializer[frame.type](frame, buffers);

   Serializer.commonHeader(frame, buffers);

   assert(buffers[0].readUInt16BE(0) <= this._sizeLimit, 'Frame too large!');

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

     if (logData) {

       this._log.trace({ data: buffers[i] }, 'Outgoing data');

     }

     this.push(buffers[i]);

   }

   done();

 };

 // Deserializer

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

 //

 //     Buffers

 //     * * * * --------+-------------------------

 //                     |                        |

 //                     v                        v           Frame Objects

 //      {} -----> Header Des. --{frame}--> Payload Des. --> * * * * * * *

 //     empty      adds parsed              adds parsed

 //     object  header properties        payload properties

 function Deserializer(log, sizeLimit, role) {

   this._role = role;

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

   this._sizeLimit = sizeLimit || MAX_PAYLOAD_SIZE;

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

   this._next(COMMON_HEADER_SIZE);

 }

 Deserializer.prototype = Object.create(Transform.prototype, { constructor: { value: Deserializer } });

 // The Deserializer is stateful, and it's two main alternating states are: *waiting for header* and

 // *waiting for payload*. The state is stored in the boolean property `_waitingForHeader`.

 //

 // When entering a new state, a `_buffer` is created that will hold the accumulated data (header or

 // payload). The `_cursor` is used to track the progress.

 Deserializer.prototype._next = function(size) {

   this._cursor = 0;

   this._buffer = new Buffer(size);

   this._waitingForHeader = !this._waitingForHeader;

   if (this._waitingForHeader) {

     this._frame = {};

   }

 };

 // Parsing an incoming buffer is an iterative process because it can hold multiple frames if it's

 // large enough. A `cursor` is used to track the progress in parsing the incoming `chunk`.

 Deserializer.prototype._transform = function _transform(chunk, encoding, done) {

   var cursor = 0;

   if (logData) {

     this._log.trace({ data: chunk }, 'Incoming data');

   }

   while(cursor < chunk.length) {

     // The content of an incoming buffer is first copied to `_buffer`. If it can't hold the full

     // chunk, then only a part of it is copied.

     var toCopy = Math.min(chunk.length - cursor, this._buffer.length - this._cursor);

     chunk.copy(this._buffer, this._cursor, cursor, cursor + toCopy);

     this._cursor += toCopy;

     cursor += toCopy;

     // When `_buffer` is full, it's content gets parsed either as header or payload depending on

     // the actual state.

     // If it's header then the parsed data is stored in a temporary variable and then the

     // deserializer waits for the specified length payload.

     if ((this._cursor === this._buffer.length) && this._waitingForHeader) {

       var payloadSize = Deserializer.commonHeader(this._buffer, this._frame);

       if (payloadSize <= this._sizeLimit) {

         this._next(payloadSize);

       } else {

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

         return;

       }

     }

     // If it's payload then the the frame object is finalized and then gets pushed out.

     // Unknown frame types are ignored.

     //

     // Note: If we just finished the parsing of a header and the payload length is 0, this branch

     // will also run.

     if ((this._cursor === this._buffer.length) && !this._waitingForHeader) {

       if (this._frame.type) {

         var error = Deserializer[this._frame.type](this._buffer, this._frame, this._role);

         if (error) {

           this._log.error('Incoming frame parsing error: ' + error);

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

         } else {

           this._log.trace({ frame: this._frame }, 'Incoming frame');

           this.push(this._frame);

         }

       } else {

         this._log.error('Unknown type incoming frame');

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

       }

       this._next(COMMON_HEADER_SIZE);

     }

   }

   done();

 };

 // [Frame Header](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-4.1)

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

 //

 // HTTP/2.0 frames share a common base format consisting of an 8-byte header followed by 0 to 65535

 // bytes of data.

 //

 // Additional size limits can be set by specific application uses. HTTP limits the frame size to

 // 16,383 octets.

 //

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     | R |     Length (14)           |   Type (8)    |   Flags (8)   |

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

 //     |R|                 Stream Identifier (31)                      |

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

 //     |                     Frame Data (0...)                       ...

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

 //

 // The fields of the frame header are defined as:

 //

 // * R:

 //   A reserved 2-bit field. The semantics of these bits are undefined and the bits MUST remain

 //   unset (0) when sending and MUST be ignored when receiving.

 //

 // * Length:

 //   The length of the frame data expressed as an unsigned 14-bit integer. The 8 bytes of the frame

 //   header are not included in this value.

 //

 // * Type:

 //   The 8-bit type of the frame. The frame type determines how the remainder of the frame header

 //   and data are interpreted. Implementations MUST ignore unsupported and unrecognized frame types.

 //

 // * Flags:

 //   An 8-bit field reserved for frame-type specific boolean flags.

 //

 //   Flags are assigned semantics specific to the indicated frame type. Flags that have no defined

 //   semantics for a particular frame type MUST be ignored, and MUST be left unset (0) when sending.

 //

 // * R:

 //   A reserved 1-bit field. The semantics of this bit are undefined and the bit MUST remain unset

 //   (0) when sending and MUST be ignored when receiving.

 //

 // * Stream Identifier:

 //   A 31-bit stream identifier. The value 0 is reserved for frames that are associated with the

 //   connection as a whole as opposed to an individual stream.

 //

 // The structure and content of the remaining frame data is dependent entirely on the frame type.

 var COMMON_HEADER_SIZE = 8;

 var frameTypes = [];

 var frameFlags = {};

 var genericAttributes = ['type', 'flags', 'stream'];

 var typeSpecificAttributes = {};

 Serializer.commonHeader = function writeCommonHeader(frame, buffers) {

   var headerBuffer = new Buffer(COMMON_HEADER_SIZE);

   var size = 0;

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

     size += buffers[i].length;

   }

   headerBuffer.writeUInt16BE(size, 0);

   var typeId = frameTypes.indexOf(frame.type);  // If we are here then the type is valid for sure

   headerBuffer.writeUInt8(typeId, 2);

   var flagByte = 0;

   for (var flag in frame.flags) {

     var position = frameFlags[frame.type].indexOf(flag);

     assert(position !== -1, 'Unknown flag for frame type ' + frame.type + ': ' + flag);

     if (frame.flags[flag]) {

       flagByte |= (1 << position);

     }

   }

   headerBuffer.writeUInt8(flagByte, 3);

   assert((0 <= frame.stream) && (frame.stream < 0x7fffffff), frame.stream);

   headerBuffer.writeUInt32BE(frame.stream || 0, 4);

   buffers.unshift(headerBuffer);

 };

 Deserializer.commonHeader = function readCommonHeader(buffer, frame) {

   var length = buffer.readUInt16BE(0);

   frame.type = frameTypes[buffer.readUInt8(2)];

   frame.flags = {};

   var flagByte = buffer.readUInt8(3);

   var definedFlags = frameFlags[frame.type];

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

     frame.flags[definedFlags[i]] = Boolean(flagByte & (1 << i));

   }

   frame.stream = buffer.readUInt32BE(4) & 0x7fffffff;

   return length;

 };

 // Frame types

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

 // Every frame type is registered in the following places:

 //

 // * `frameTypes`: a register of frame type codes (used by `commonHeader()`)

 // * `frameFlags`: a register of valid flags for frame types (used by `commonHeader()`)

 // * `typeSpecificAttributes`: a register of frame specific frame object attributes (used by

 //   logging code and also serves as documentation for frame objects)

 // [DATA Frames](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.1)

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

 //

 // DATA frames (type=0x0) convey arbitrary, variable-length sequences of octets associated with a

 // stream.

 //

 // The DATA frame defines the following flags:

 //

 // * END_STREAM (0x1):

 //   Bit 1 being set indicates that this frame is the last that the endpoint will send for the

 //   identified stream.

 // * END_SEGMENT (0x2):

 //   Bit 2 being set indicates that this frame is the last for the current segment. Intermediaries

 //   MUST NOT coalesce frames across a segment boundary and MUST preserve segment boundaries when

 //   forwarding frames.

 // * PAD_LOW (0x10):

 //   Bit 5 being set indicates that the Pad Low field is present.

 // * PAD_HIGH (0x20):

 //   Bit 6 being set indicates that the Pad High field is present. This bit MUST NOT be set unless

 //   the PAD_LOW flag is also set. Endpoints that receive a frame with PAD_HIGH set and PAD_LOW

 //   cleared MUST treat this as a connection error of type PROTOCOL_ERROR.

 frameTypes[0x0] = 'DATA';

 frameFlags.DATA = ['END_STREAM', 'END_SEGMENT', 'RESERVED4', 'RESERVED8', 'PAD_LOW', 'PAD_HIGH'];

 typeSpecificAttributes.DATA = ['data'];

 Serializer.DATA = function writeData(frame, buffers) {

   buffers.push(frame.data);

 };

 Deserializer.DATA = function readData(buffer, frame) {

   var dataOffset = 0;

   var paddingLength = 0;

   if (frame.flags.PAD_LOW) {

     if (frame.flags.PAD_HIGH) {

       paddingLength = (buffer.readUInt8(dataOffset) & 0xff) * 256;

       dataOffset += 1;

     }

     paddingLength += (buffer.readUInt8(dataOffset) & 0xff);

     dataOffset += 1;

   } else if (frame.flags.PAD_HIGH) {

     return 'DATA frame got PAD_HIGH without PAD_LOW';

   }

   if (paddingLength) {

     frame.data = buffer.slice(dataOffset, -1 * paddingLength);

   } else {

     frame.data = buffer.slice(dataOffset);

   }

 };

 // [HEADERS](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.2)

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

 //

 // The HEADERS frame (type=0x1) allows the sender to create a stream.

 //

 // The HEADERS frame defines the following flags:

 //

 // * END_STREAM (0x1):

 //   Bit 1 being set indicates that this frame is the last that the endpoint will send for the

 //   identified stream.

 // * END_SEGMENT (0x2):

 //   Bit 2 being set indicates that this frame is the last for the current segment. Intermediaries

 //   MUST NOT coalesce frames across a segment boundary and MUST preserve segment boundaries when

 //   forwarding frames.

 // * END_HEADERS (0x4):

 //   The END_HEADERS bit indicates that this frame contains the entire payload necessary to provide

 //   a complete set of headers.

 // * PRIORITY (0x8):

 //   Bit 4 being set indicates that the first four octets of this frame contain a single reserved

 //   bit and a 31-bit priority.

 // * PAD_LOW (0x10):

 //   Bit 5 being set indicates that the Pad Low field is present.

 // * PAD_HIGH (0x20):

 //   Bit 6 being set indicates that the Pad High field is present. This bit MUST NOT be set unless

 //   the PAD_LOW flag is also set. Endpoints that receive a frame with PAD_HIGH set and PAD_LOW

 //   cleared MUST treat this as a connection error of type PROTOCOL_ERROR.

 frameTypes[0x1] = 'HEADERS';

 frameFlags.HEADERS = ['END_STREAM', 'END_SEGMENT', 'END_HEADERS', 'PRIORITY', 'PAD_LOW', 'PAD_HIGH'];

 typeSpecificAttributes.HEADERS = ['priority', 'headers', 'data'];

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |X|               (Optional) Priority (31)                      |

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

 //     |                    Header Block (*)                         ...

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

 //

 // The payload of a HEADERS frame contains a Headers Block

 Serializer.HEADERS = function writeHeadersPriority(frame, buffers) {

   if (frame.flags.PRIORITY) {

     var buffer = new Buffer(4);

     assert((0 <= frame.priority) && (frame.priority <= 0xffffffff), frame.priority);

     buffer.writeUInt32BE(frame.priority, 0);

     buffers.push(buffer);

   }

   buffers.push(frame.data);

 };

 Deserializer.HEADERS = function readHeadersPriority(buffer, frame) {

   var dataOffset = 0;

   var paddingLength = 0;

   if (frame.flags.PAD_LOW) {

     if (frame.flags.PAD_HIGH) {

       paddingLength = (buffer.readUInt8(dataOffset) & 0xff) * 256;

       dataOffset += 1;

     }

     paddingLength += (buffer.readUInt8(dataOffset) & 0xff);

     dataOffset += 1;

   } else if (frame.flags.PAD_HIGH) {

     return 'HEADERS frame got PAD_HIGH without PAD_LOW';

   }

   if (frame.flags.PRIORITY) {

     frame.priority = buffer.readUInt32BE(dataOffset) & 0x7fffffff;

     dataOffset += 4;

   }

   if (paddingLength) {

     frame.data = buffer.slice(dataOffset, -1 * paddingLength);

   } else {

     frame.data = buffer.slice(dataOffset);

   }

 };

 // [PRIORITY](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.3)

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

 //

 // The PRIORITY frame (type=0x2) specifies the sender-advised priority of a stream.

 //

 // The PRIORITY frame does not define any flags.

 frameTypes[0x2] = 'PRIORITY';

 frameFlags.PRIORITY = [];

 typeSpecificAttributes.PRIORITY = ['priority'];

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |X|                   Priority (31)                             |

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

 //

 // The payload of a PRIORITY frame contains a single reserved bit and a 31-bit priority.

 Serializer.PRIORITY = function writePriority(frame, buffers) {

   var buffer = new Buffer(4);

   buffer.writeUInt32BE(frame.priority, 0);

   buffers.push(buffer);

 };

 Deserializer.PRIORITY = function readPriority(buffer, frame) {

   frame.priority = buffer.readUInt32BE(0);

 };

 // [RST_STREAM](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.4)

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

 //

 // The RST_STREAM frame (type=0x3) allows for abnormal termination of a stream.

 //

 // No type-flags are defined.

 frameTypes[0x3] = 'RST_STREAM';

 frameFlags.RST_STREAM = [];

 typeSpecificAttributes.RST_STREAM = ['error'];

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |                         Error Code (32)                       |

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

 //

 // The RST_STREAM frame contains a single unsigned, 32-bit integer identifying the error

 // code (see Error Codes). The error code indicates why the stream is being terminated.

 Serializer.RST_STREAM = function writeRstStream(frame, buffers) {

   var buffer = new Buffer(4);

   var code = errorCodes.indexOf(frame.error);

   assert((0 <= code) && (code <= 0xffffffff), code);

   buffer.writeUInt32BE(code, 0);

   buffers.push(buffer);

 };

 Deserializer.RST_STREAM = function readRstStream(buffer, frame) {

   frame.error = errorCodes[buffer.readUInt32BE(0)];

 };

 // [SETTINGS](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.5)

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

 //

 // The SETTINGS frame (type=0x4) conveys configuration parameters that affect how endpoints

 // communicate.

 //

 // The SETTINGS frame defines the following flag:

 // * ACK (0x1):

 //   Bit 1 being set indicates that this frame acknowledges receipt and application of the peer's

 //   SETTINGS frame.

 frameTypes[0x4] = 'SETTINGS';

 frameFlags.SETTINGS = ['ACK'];

 typeSpecificAttributes.SETTINGS = ['settings'];

 // The payload of a SETTINGS frame consists of zero or more settings. Each setting consists of an

 // 8-bit identifier, and an unsigned 32-bit value.

 //

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |  Identifier(8)  |                  Value (32)                 |

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

 //     ...Value          |

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

 //

 // Each setting in a SETTINGS frame replaces the existing value for that setting.  Settings are

 // processed in the order in which they appear, and a receiver of a SETTINGS frame does not need to

 // maintain any state other than the current value of settings.  Therefore, the value of a setting

 // is the last value that is seen by a receiver. This permits the inclusion of the same settings

 // multiple times in the same SETTINGS frame, though doing so does nothing other than waste

 // connection capacity.

 Serializer.SETTINGS = function writeSettings(frame, buffers) {

   var settings = [], settingsLeft = Object.keys(frame.settings);

   definedSettings.forEach(function(setting, id) {

     if (setting.name in frame.settings) {

       settingsLeft.splice(settingsLeft.indexOf(setting.name), 1);

       var value = frame.settings[setting.name];

       settings.push({ id: id, value: setting.flag ? Boolean(value) : value });

     }

   });

   assert(settingsLeft.length === 0, 'Unknown settings: ' + settingsLeft.join(', '));

   var buffer = new Buffer(settings.length * 5);

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

     buffer.writeUInt8(settings[i].id & 0xff, i*5);

     buffer.writeUInt32BE(settings[i].value, i*5 + 1);

   }

   buffers.push(buffer);

 };

 Deserializer.SETTINGS = function readSettings(buffer, frame, role) {

   frame.settings = {};

   if (buffer.length % 5 !== 0) {

     return 'Invalid SETTINGS frame';

   }

   for (var i = 0; i < buffer.length / 5; i++) {

     var id = buffer.readUInt8(i*5) & 0xff;

     var setting = definedSettings[id];

     if (setting) {

       if (role == 'CLIENT' && setting.name == 'SETTINGS_ENABLE_PUSH') {

         return 'SETTINGS frame on client got SETTINGS_ENABLE_PUSH';

       }

       var value = buffer.readUInt32BE(i*5 + 1);

       frame.settings[setting.name] = setting.flag ? Boolean(value & 0x1) : value;

     } else {

       /* Unknown setting, protocol error */

       return 'SETTINGS frame got unknown setting type';

     }

   }

 };

 // The following settings are defined:

 var definedSettings = [];

 // * SETTINGS_HEADER_TABLE_SIZE (1):

 //   Allows the sender to inform the remote endpoint of the size of the header compression table

 //   used to decode header blocks.

 definedSettings[1] = { name: 'SETTINGS_HEADER_TABLE_SIZE', flag: false };

 // * SETTINGS_ENABLE_PUSH (2):

 //   This setting can be use to disable server push. An endpoint MUST NOT send a PUSH_PROMISE frame

 //   if it receives this setting set to a value of 0. The default value is 1, which indicates that

 //   push is permitted.

 definedSettings[2] = { name: 'SETTINGS_ENABLE_PUSH', flag: true };

 // * SETTINGS_MAX_CONCURRENT_STREAMS (4):

 //   indicates the maximum number of concurrent streams that the sender will allow.

 definedSettings[3] = { name: 'SETTINGS_MAX_CONCURRENT_STREAMS', flag: false };

 // * SETTINGS_INITIAL_WINDOW_SIZE (7):

 //   indicates the sender's initial stream window size (in bytes) for new streams.

 definedSettings[4] = { name: 'SETTINGS_INITIAL_WINDOW_SIZE', flag: false };

 // [PUSH_PROMISE](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.6)

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

 //

 // The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint in advance of streams the

 // sender intends to initiate.

 //

 // The PUSH_PROMISE frame defines the following flags:

 //

 // * END_PUSH_PROMISE (0x4):

 //   The END_PUSH_PROMISE bit indicates that this frame contains the entire payload necessary to

 //   provide a complete set of headers.

 frameTypes[0x5] = 'PUSH_PROMISE';

 frameFlags.PUSH_PROMISE = ['RESERVED1', 'RESERVED2', 'END_PUSH_PROMISE'];

 typeSpecificAttributes.PUSH_PROMISE = ['promised_stream', 'headers', 'data'];

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |X|                Promised-Stream-ID (31)                      |

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

 //     |                    Header Block (*)                         ...

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

 //

 // The PUSH_PROMISE frame includes the unsigned 31-bit identifier of

 // the stream the endpoint plans to create along with a minimal set of headers that provide

 // additional context for the stream.

 Serializer.PUSH_PROMISE = function writePushPromise(frame, buffers) {

   var buffer = new Buffer(4);

   var promised_stream = frame.promised_stream;

   assert((0 <= promised_stream) && (promised_stream <= 0x7fffffff), promised_stream);

   buffer.writeUInt32BE(promised_stream, 0);

   buffers.push(buffer);

   buffers.push(frame.data);

 };

 Deserializer.PUSH_PROMISE = function readPushPromise(buffer, frame) {

   frame.promised_stream = buffer.readUInt32BE(0) & 0x7fffffff;

   frame.data = buffer.slice(4);

 };

 // [PING](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.7)

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

 //

 // The PING frame (type=0x6) is a mechanism for measuring a minimal round-trip time from the

 // sender, as well as determining whether an idle connection is still functional.

 //

 // The PING frame defines one type-specific flag:

 //

 // * ACK (0x1):

 //   Bit 1 being set indicates that this PING frame is a PING response.

 frameTypes[0x6] = 'PING';

 frameFlags.PING = ['ACK'];

 typeSpecificAttributes.PING = ['data'];

 // In addition to the frame header, PING frames MUST contain 8 additional octets of opaque data.

 Serializer.PING = function writePing(frame, buffers) {

   buffers.push(frame.data);

 };

 Deserializer.PING = function readPing(buffer, frame) {

   if (buffer.length !== 8) {

     return 'Invalid size PING frame';

   }

   frame.data = buffer;

 };

 // [GOAWAY](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.8)

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

 //

 // The GOAWAY frame (type=0x7) informs the remote peer to stop creating streams on this connection.

 //

 // The GOAWAY frame does not define any flags.

 frameTypes[0x7] = 'GOAWAY';

 frameFlags.GOAWAY = [];

 typeSpecificAttributes.GOAWAY = ['last_stream', 'error'];

 //      0                   1                   2                   3

 //      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

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

 //     |X|                  Last-Stream-ID (31)                        |

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

 //     |                      Error Code (32)                          |

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

 //

 // The last stream identifier in the GOAWAY frame contains the highest numbered stream identifier

 // for which the sender of the GOAWAY frame has received frames on and might have taken some action

 // on.

 //

 // The GOAWAY frame also contains a 32-bit error code (see Error Codes) that contains the reason for

 // closing the connection.

 Serializer.GOAWAY = function writeGoaway(frame, buffers) {

   var buffer = new Buffer(8);

   var last_stream = frame.last_stream;

   assert((0 <= last_stream) && (last_stream <= 0x7fffffff), last_stream);

   buffer.writeUInt32BE(last_stream, 0);

   var code = errorCodes.indexOf(frame.error);

   assert((0 <= code) && (code <= 0xffffffff), code);

   buffer.writeUInt32BE(code, 4);

   buffers.push(buffer);

 };

 Deserializer.GOAWAY = function readGoaway(buffer, frame) {

   frame.last_stream = buffer.readUInt32BE(0) & 0x7fffffff;

   frame.error = errorCodes[buffer.readUInt32BE(4)];

 };

 // [WINDOW_UPDATE](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.9)

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

 //

 // The WINDOW_UPDATE frame (type=0x8) is used to implement flow control.

 //

 // The WINDOW_UPDATE frame does not define any flags.

 frameTypes[0x8] = 'WINDOW_UPDATE';

 frameFlags.WINDOW_UPDATE = [];

 typeSpecificAttributes.WINDOW_UPDATE = ['window_size'];

 // The payload of a WINDOW_UPDATE frame is a 32-bit value indicating the additional number of bytes

 // that the sender can transmit in addition to the existing flow control window. The legal range

 // for this field is 1 to 2^31 - 1 (0x7fffffff) bytes; the most significant bit of this value is

 // reserved.

 Serializer.WINDOW_UPDATE = function writeWindowUpdate(frame, buffers) {

   var buffer = new Buffer(4);

   var window_size = frame.window_size;

   assert((0 <= window_size) && (window_size <= 0x7fffffff), window_size);

   buffer.writeUInt32BE(window_size, 0);

   buffers.push(buffer);

 };

 Deserializer.WINDOW_UPDATE = function readWindowUpdate(buffer, frame) {

   frame.window_size = buffer.readUInt32BE(0) & 0x7fffffff;

 };

 // [CONTINUATION](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-6.10)

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

 //

 // The CONTINUATION frame (type=0xA) is used to continue a sequence of header block fragments.

 //

 // The CONTINUATION frame defines the following flag:

 //

 // * END_HEADERS (0x4):

 //   The END_HEADERS bit indicates that this frame ends the sequence of header block fragments

 //   necessary to provide a complete set of headers.

 // * PAD_LOW (0x10):

 //   Bit 5 being set indicates that the Pad Low field is present.

 // * PAD_HIGH (0x20):

 //   Bit 6 being set indicates that the Pad High field is present. This bit MUST NOT be set unless

 //   the PAD_LOW flag is also set. Endpoints that receive a frame with PAD_HIGH set and PAD_LOW

 //   cleared MUST treat this as a connection error of type PROTOCOL_ERROR.

 frameTypes[0x9] = 'CONTINUATION';

 frameFlags.CONTINUATION = ['RESERVED1', 'RESERVED2', 'END_HEADERS', 'RESERVED8', 'PAD_LOW', 'PAD_HIGH'];

 typeSpecificAttributes.CONTINUATION = ['headers', 'data'];

 Serializer.CONTINUATION = function writeContinuation(frame, buffers) {

   buffers.push(frame.data);

 };

 Deserializer.CONTINUATION = function readContinuation(buffer, frame) {

   var dataOffset = 0;

   var paddingLength = 0;

   if (frame.flags.PAD_LOW) {

     if (frame.flags.PAD_HIGH) {

       paddingLength = (buffer.readUInt8(dataOffset) & 0xff) * 256;

       dataOffset += 1;

     }

     paddingLength += (buffer.readUInt8(dataOffset) & 0xff);

     dataOffset += 1;

   } else if (frame.flags.PAD_HIGH) {

     return 'CONTINUATION frame got PAD_HIGH without PAD_LOW';

   }

   if (paddingLength) {

     frame.data = buffer.slice(dataOffset, -1 * paddingLength);

   } else {

     frame.data = buffer.slice(dataOffset);

   }

 };

 // [Error Codes](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-7)

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

 var errorCodes = [

   'NO_ERROR',

   'PROTOCOL_ERROR',

   'INTERNAL_ERROR',

   'FLOW_CONTROL_ERROR',

   'SETTINGS_TIMEOUT',

   'STREAM_CLOSED',

   'FRAME_SIZE_ERROR',

   'REFUSED_STREAM',

   'CANCEL',

   'COMPRESSION_ERROR',

   'CONNECT_ERROR'

 ];

 errorCodes[420] = 'ENHANCE_YOUR_CALM';

 // Logging

 // -------

 // [Bunyan serializers](https://github.com/trentm/node-bunyan#serializers) to improve logging output

 // for debug messages emitted in this component.

 exports.serializers = {};

 // * `frame` serializer: it transforms data attributes from Buffers to hex strings and filters out

 //   flags that are not present.

 var frameCounter = 0;

 exports.serializers.frame = function(frame) {

   if (!frame) {

     return null;

   }

   if ('id' in frame) {

     return frame.id;

   }

   frame.id = frameCounter;

   frameCounter += 1;

   var logEntry = { id: frame.id };

   genericAttributes.concat(typeSpecificAttributes[frame.type]).forEach(function(name) {

     logEntry[name] = frame[name];

   });

   if (frame.data instanceof Buffer) {

     if (logEntry.data.length > 50) {

       logEntry.data = frame.data.slice(0, 47).toString('hex') + '...';

     } else {

       logEntry.data = frame.data.toString('hex');

     }

     if (!('length' in logEntry)) {

       logEntry.length = frame.data.length;

     }

   }

   if (frame.promised_stream instanceof Object) {

     logEntry.promised_stream = 'stream-' + frame.promised_stream.id;

   }

   logEntry.flags = Object.keys(frame.flags || {}).filter(function(name) {

     return frame.flags[name] === true;

   });

   return logEntry;

 };

 // * `data` serializer: it simply transforms a buffer to a hex string.

 exports.serializers.data = function(data) {

   return data.toString('hex');

 };