# all files / lib/protocol/ framer.js

88.56% Statements 418/472
71.43% Branches 140/196
93.33% Functions 42/45
88.56% Lines 418/472

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     // The framer consists of two [Transform Stream][1] subclasses that operate in [object mode][2]:
    // the Serializer and the Deserializer
    // [1]: https://nodejs.org/api/stream.html#stream_class_stream_transform
    // [2]: https://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 = (process !== 'undefined' && process.env !== 'undefined' && process.env.HTTP2_LOG_DATA);

    var MAX_PAYLOAD_SIZE = 16384;
    var WINDOW_UPDATE_PAYLOAD_SIZE = 4;

    // Serializer
    // ----------
    //
    //     Frame Objects
    //     * * * * * * * --+---------------------------
    //                     |                          |
    //                     v                          v           Buffers
    //      [] -----> Payload Ser. --[buffers]--> Header Ser. --> * * * *
    //     empty      adds payload                adds header
    //     array        buffers                     buffer

    function Serializer(log) {
      this._log = log.child({ component: 'serializer' });
      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);
      var length = Serializer.commonHeader(frame, buffers);

      assert(length <= MAX_PAYLOAD_SIZE, 'Frame too large!');

      for (var i = 0; i < buffers.length; i++) {
        Iif (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, role) {
      this._role = role;
      this._log = log.child({ component: 'deserializer' });
      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;

      Iif (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);
          Eif (payloadSize <= MAX_PAYLOAD_SIZE) {
            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) {
          Eif (this._frame.type) {
            var error = Deserializer[this._frame.type](this._buffer, this._frame, this._role);
            Iif (error) {
              this._log.error('Incoming frame parsing error: ' + error);
              this.emit('error', error);
            } else {
              this._log.trace({ frame: this._frame }, 'Incoming frame');
              this.push(this._frame);
            }
          } else {
            this._log.error('Unknown type incoming frame');
            // Ignore it other than logging
          }
          this._next(COMMON_HEADER_SIZE);
        }
      }

      done();
    };

    // [Frame Header](https://tools.ietf.org/html/rfc7540#section-4.1)
    // --------------------------------------------------------------
    //
    // HTTP/2 frames share a common base format consisting of a 9-byte header followed by 0 to 2^24 - 1
    // bytes of data.
    //
    // Additional size limits can be set by specific application uses. HTTP limits the frame size to
    // 16,384 octets by default, though this can be increased by a receiver.
    //
    //      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
    //     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //     |                 Length (24)                   |
    //     +---------------+---------------+---------------+
    //     |   Type (8)    |   Flags (8)   |
    //     +-+-----------------------------+---------------+---------------+
    //     |R|                 Stream Identifier (31)                      |
    //     +-+-------------------------------------------------------------+
    //     |                     Frame Data (0...)                       ...
    //     +---------------------------------------------------------------+
    //
    // The fields of the frame header are defined as:
    //
    // * Length:
    //   The length of the frame data expressed as an unsigned 24-bit integer. The 9 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 = 9;

    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.writeUInt8(0, 0);
      headerBuffer.writeUInt16BE(size, 1);

      var typeId = frameTypes.indexOf(frame.type);  // If we are here then the type is valid for sure
      headerBuffer.writeUInt8(typeId, 3);

      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, 4);

      assert((0 <= frame.stream) && (frame.stream < 0x7fffffff), frame.stream);
      headerBuffer.writeUInt32BE(frame.stream || 0, 5);

      buffers.unshift(headerBuffer);

      return size;
    };

    Deserializer.commonHeader = function readCommonHeader(buffer, frame) {
      Iif (buffer.length < 9) {
        return 'FRAME_SIZE_ERROR';
      }

      var totallyWastedByte = buffer.readUInt8(0);
      var length = buffer.readUInt16BE(1);
      // We do this just for sanity checking later on, to make sure no one sent us a
      // frame that's super large.
      length += totallyWastedByte << 16;

      frame.type = frameTypes[buffer.readUInt8(3)];
      Iif (!frame.type) {
        // We are required to ignore unknown frame types
        return length;
      }

      frame.flags = {};
      var flagByte = buffer.readUInt8(4);
      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(5) & 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](https://tools.ietf.org/html/rfc7540#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.
    // * PADDED (0x08):
    //   Bit 4 being set indicates that the Pad Length field is present.

    frameTypes[0x0] = 'DATA';

    frameFlags.DATA = ['END_STREAM', 'RESERVED2', 'RESERVED4', 'PADDED'];

    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.PADDED) {
        Iif (buffer.length < 1) {
          // We must have at least one byte for padding control, but we don't. Bad peer!
          return 'FRAME_SIZE_ERROR';
        }
        paddingLength = (buffer.readUInt8(dataOffset) & 0xff);
        dataOffset = 1;
      }

      if (paddingLength) {
        Iif (paddingLength >= (buffer.length - 1)) {
          // We don't have enough room for the padding advertised - bad peer!
          return 'FRAME_SIZE_ERROR';
        }
        frame.data = buffer.slice(dataOffset, -1 * paddingLength);
      } else {
        frame.data = buffer.slice(dataOffset);
      }
    };

    // [HEADERS](https://tools.ietf.org/html/rfc7540#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_HEADERS (0x4):
    //   The END_HEADERS bit indicates that this frame contains the entire payload necessary to provide
    //   a complete set of headers.
    // * PADDED (0x08):
    //   Bit 4 being set indicates that the Pad Length field is present.
    // * PRIORITY (0x20):
    //   Bit 6 being set indicates that the Exlusive Flag (E), Stream Dependency, and Weight fields are
    //   present.

    frameTypes[0x1] = 'HEADERS';

    frameFlags.HEADERS = ['END_STREAM', 'RESERVED2', 'END_HEADERS', 'PADDED', 'RESERVED5', 'PRIORITY'];

    typeSpecificAttributes.HEADERS = ['priorityDependency', 'priorityWeight', 'exclusiveDependency', '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
    //     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //     |Pad Length? (8)|
    //     +-+-------------+---------------+-------------------------------+
    //     |E|                 Stream Dependency? (31)                     |
    //     +-+-------------+-----------------------------------------------+
    //     |  Weight? (8)  |
    //     +-+-------------+-----------------------------------------------+
    //     |                   Header Block Fragment (*)                 ...
    //     +---------------------------------------------------------------+
    //     |                           Padding (*)                       ...
    //     +---------------------------------------------------------------+
    //
    // The payload of a HEADERS frame contains a Headers Block

    Serializer.HEADERS = function writeHeadersPriority(frame, buffers) {
      if (frame.flags.PRIORITY) {
        var buffer = new Buffer(5);
        assert((0 <= frame.priorityDependency) && (frame.priorityDependency <= 0x7fffffff), frame.priorityDependency);
        buffer.writeUInt32BE(frame.priorityDependency, 0);
        if (frame.exclusiveDependency) {
          buffer[0] |= 0x80;
        }
        assert((0 <= frame.priorityWeight) && (frame.priorityWeight <= 0xff), frame.priorityWeight);
        buffer.writeUInt8(frame.priorityWeight, 4);
        buffers.push(buffer);
      }
      buffers.push(frame.data);
    };

    Deserializer.HEADERS = function readHeadersPriority(buffer, frame) {
      var minFrameLength = 0;
      if (frame.flags.PADDED) {
        minFrameLength += 1;
      }
      if (frame.flags.PRIORITY) {
        minFrameLength += 5;
      }
      Iif (buffer.length < minFrameLength) {
        // Peer didn't send enough data - bad peer!
        return 'FRAME_SIZE_ERROR';
      }

      var dataOffset = 0;
      var paddingLength = 0;
      if (frame.flags.PADDED) {
        paddingLength = (buffer.readUInt8(dataOffset) & 0xff);
        dataOffset = 1;
      }

      if (frame.flags.PRIORITY) {
        var dependencyData = new Buffer(4);
        buffer.copy(dependencyData, 0, dataOffset, dataOffset + 4);
        dataOffset += 4;
        frame.exclusiveDependency = !!(dependencyData[0] & 0x80);
        dependencyData[0] &= 0x7f;
        frame.priorityDependency = dependencyData.readUInt32BE(0);
        frame.priorityWeight = buffer.readUInt8(dataOffset);
        dataOffset += 1;
      }

      if (paddingLength) {
        Iif ((buffer.length - dataOffset) < paddingLength) {
          // Not enough data left to satisfy the advertised padding - bad peer!
          return 'FRAME_SIZE_ERROR';
        }
        frame.data = buffer.slice(dataOffset, -1 * paddingLength);
      } else {
        frame.data = buffer.slice(dataOffset);
      }
    };

    // [PRIORITY](https://tools.ietf.org/html/rfc7540#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 = ['priorityDependency', 'priorityWeight', 'exclusiveDependency'];

    //      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
    //     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //     |E|                 Stream Dependency? (31)                     |
    //     +-+-------------+-----------------------------------------------+
    //     |  Weight? (8)  |
    //     +-+-------------+
    //
    // The payload of a PRIORITY frame contains an exclusive bit, a 31-bit dependency, and an 8-bit weight

    Serializer.PRIORITY = function writePriority(frame, buffers) {
      var buffer = new Buffer(5);
      assert((0 <= frame.priorityDependency) && (frame.priorityDependency <= 0x7fffffff), frame.priorityDependency);
      buffer.writeUInt32BE(frame.priorityDependency, 0);
      if (frame.exclusiveDependency) {
        buffer[0] |= 0x80;
      }
      assert((0 <= frame.priorityWeight) && (frame.priorityWeight <= 0xff), frame.priorityWeight);
      buffer.writeUInt8(frame.priorityWeight, 4);

      buffers.push(buffer);
    };

    Deserializer.PRIORITY = function readPriority(buffer, frame) {
      Iif (buffer.length < 5) {
        // PRIORITY frames are 5 bytes long. Bad peer!
        return 'FRAME_SIZE_ERROR';
      }
      var dependencyData = new Buffer(4);
      buffer.copy(dependencyData, 0, 0, 4);
      frame.exclusiveDependency = !!(dependencyData[0] & 0x80);
      dependencyData[0] &= 0x7f;
      frame.priorityDependency = dependencyData.readUInt32BE(0);
      frame.priorityWeight = buffer.readUInt8(4);
    };

    // [RST_STREAM](https://tools.ietf.org/html/rfc7540#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) {
      Iif (buffer.length < 4) {
        // RST_STREAM is 4 bytes long. Bad peer!
        return 'FRAME_SIZE_ERROR';
      }
      frame.error = errorCodes[buffer.readUInt32BE(0)];
      Iif (!frame.error) {
        // Unknown error codes are considered equivalent to INTERNAL_ERROR
        frame.error = 'INTERNAL_ERROR';
      }
    };

    // [SETTINGS](https://tools.ietf.org/html/rfc7540#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 a
    // 16-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(16)          |        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 * 6);
      for (var i = 0; i < settings.length; i++) {
        buffer.writeUInt16BE(settings[i].id & 0xffff, i*6);
        buffer.writeUInt32BE(settings[i].value, i*6 + 2);
      }

      buffers.push(buffer);
    };

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

      // Receipt of a SETTINGS frame with the ACK flag set and a length
      // field value other than 0 MUST be treated as a connection error
      // (Section 5.4.1) of type FRAME_SIZE_ERROR.
      Iif(frame.flags.ACK && buffer.length != 0) {
        return 'FRAME_SIZE_ERROR';
      }

      Iif (buffer.length % 6 !== 0) {
        return 'PROTOCOL_ERROR';
      }
      for (var i = 0; i < buffer.length / 6; i++) {
        var id = buffer.readUInt16BE(i*6) & 0xffff;
        var setting = definedSettings[id];
        Eif (setting) {
          Iif (role == 'CLIENT' && setting.name == 'SETTINGS_ENABLE_PUSH') {
            return 'SETTINGS frame on client got SETTINGS_ENABLE_PUSH';
          }
          var value = buffer.readUInt32BE(i*6 + 2);
          frame.settings[setting.name] = setting.flag ? Boolean(value & 0x1) : value;
        }
      }
    };

    // 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 (3):
    //   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 (4):
    //   indicates the sender's initial stream window size (in bytes) for new streams.
    definedSettings[4] = { name: 'SETTINGS_INITIAL_WINDOW_SIZE', flag: false };

    // * SETTINGS_MAX_FRAME_SIZE (5):
    //   indicates the maximum size of a frame the receiver will allow.
    definedSettings[5] = { name: 'SETTINGS_MAX_FRAME_SIZE', flag: false };

    // [PUSH_PROMISE](https://tools.ietf.org/html/rfc7540#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', 'PADDED'];

    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
    //     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //     |Pad Length? (8)|
    //     +-+-------------+-----------------------------------------------+
    //     |X|                Promised-Stream-ID (31)                      |
    //     +-+-------------------------------------------------------------+
    //     |                 Header Block Fragment (*)                   ...
    //     +---------------------------------------------------------------+
    //     |                         Padding (*)                         ...
    //     +---------------------------------------------------------------+
    //
    // 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) {
      Iif (buffer.length < 4) {
        return 'FRAME_SIZE_ERROR';
      }
      var dataOffset = 0;
      var paddingLength = 0;
      if (frame.flags.PADDED) {
        Iif (buffer.length < 5) {
          return 'FRAME_SIZE_ERROR';
        }
        paddingLength = (buffer.readUInt8(dataOffset) & 0xff);
        dataOffset = 1;
      }
      frame.promised_stream = buffer.readUInt32BE(dataOffset) & 0x7fffffff;
      dataOffset += 4;
      if (paddingLength) {
        Iif ((buffer.length - dataOffset) < paddingLength) {
          return 'FRAME_SIZE_ERROR';
        }
        frame.data = buffer.slice(dataOffset, -1 * paddingLength);
      } else {
        frame.data = buffer.slice(dataOffset);
      }
    };

    // [PING](https://tools.ietf.org/html/rfc7540#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) {
      Iif (buffer.length !== 8) {
        return 'FRAME_SIZE_ERROR';
      }
      frame.data = buffer;
    };

    // [GOAWAY](https://tools.ietf.org/html/rfc7540#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)                          |
    //     +---------------------------------------------------------------+
    //     |                  Additional Debug Data (*)                    |
    //     +---------------------------------------------------------------+
    //
    // 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) {
      Iif (buffer.length < 8) {
        // GOAWAY must have at least 8 bytes
        return 'FRAME_SIZE_ERROR';
      }
      frame.last_stream = buffer.readUInt32BE(0) & 0x7fffffff;
      frame.error = errorCodes[buffer.readUInt32BE(4)];
      Iif (!frame.error) {
        // Unknown error types are to be considered equivalent to INTERNAL ERROR
        frame.error = 'INTERNAL_ERROR';
      }
      // Read remaining data into "debug_data"
      // https://http2.github.io/http2-spec/#GOAWAY
      //   Endpoints MAY append opaque data to the payload of any GOAWAY frame
      Iif (buffer.length > 8) {
        frame.debug_data = buffer.slice(8);
      }
    };

    // [WINDOW_UPDATE](https://tools.ietf.org/html/rfc7540#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) {
      Iif (buffer.length !== WINDOW_UPDATE_PAYLOAD_SIZE) {
        return 'FRAME_SIZE_ERROR';
      }
      frame.window_size = buffer.readUInt32BE(0) & 0x7fffffff;
      Iif (frame.window_size === 0) {
        return 'PROTOCOL_ERROR';
      }
    };

    // [CONTINUATION](https://tools.ietf.org/html/rfc7540#section-6.10)
    // ------------------------------------------------------------
    //
    // The CONTINUATION frame (type=0x9) 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.

    frameTypes[0x9] = 'CONTINUATION';

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

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

    Serializer.CONTINUATION = function writeContinuation(frame, buffers) {
      buffers.push(frame.data);
    };

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

    // [ALTSVC](https://tools.ietf.org/html/rfc7838#section-4)
    // ------------------------------------------------------------
    //
    // The ALTSVC frame (type=0xA) advertises the availability of an alternative service to the client.
    //
    // The ALTSVC frame does not define any flags.

    frameTypes[0xA] = 'ALTSVC';

    frameFlags.ALTSVC = [];

    //     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
    //    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //    |         Origin-Len (16)       | Origin? (*)                 ...
    //    +-------------------------------+----------------+--------------+
    //    |                   Alt-Svc-Field-Value (*)                   ...
    //    +---------------------------------------------------------------+
    //
    // The ALTSVC frame contains the following fields:
    //
    // Origin-Len: An unsigned, 16-bit integer indicating the length, in
    //    octets, of the Origin field.
    //
    // Origin: An OPTIONAL sequence of characters containing ASCII
    //    serialisation of an origin ([RFC6454](https://tools.ietf.org/html/rfc6454),
    //    Section 6.2) that the alternate service is applicable to.
    //
    // Alt-Svc-Field-Value: A sequence of octets (length determined by
    //    subtracting the length of all preceding fields from the frame
    //    length) containing a value identical to the Alt-Svc field value
    //    defined in (Section 3)[https://tools.ietf.org/html/rfc7838#section-3]
    //    (ABNF production "Alt-Svc").

    typeSpecificAttributes.ALTSVC = ['maxAge', 'port', 'protocolID', 'host',
                                     'origin'];

    function istchar(c) {
      return ('!#$&\'*+-.^_`|~1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.indexOf(c) > -1);
    }

    function hexencode(s) {
      var t = '';
      for (var i = 0; i < s.length; i++) {
        Iif (!istchar(s[i])) {
          t += '%';
          t += new Buffer(s[i]).toString('hex');
        } else {
          t += s[i];
        }
      }
      return t;
    }

    Serializer.ALTSVC = function writeAltSvc(frame, buffers) {
      var buffer = new Buffer(2);
      buffer.writeUInt16BE(frame.origin.length, 0);
      buffers.push(buffer);
      buffers.push(new Buffer(frame.origin, 'ascii'));

      var fieldValue = hexencode(frame.protocolID) + '="' + frame.host + ':' + frame.port + '"';
      Eif (frame.maxAge !== 86400) { // 86400 is the default
        fieldValue += "; ma=" + frame.maxAge;
      }

      buffers.push(new Buffer(fieldValue, 'ascii'));
    };

    function stripquotes(s) {
      var start = 0;
      var end = s.length;
      while ((start < end) && (s[start] === '"')) {
        start++;
      }
      while ((end > start) && (s[end - 1] === '"')) {
        end--;
      }
      Iif (start >= end) {
        return "";
      }
      return s.substring(start, end);
    }

    function splitNameValue(nvpair) {
      var eq = -1;
      var inQuotes = false;

      for (var i = 0; i < nvpair.length; i++) {
        Iif (nvpair[i] === '"') {
          inQuotes = !inQuotes;
          continue;
        }
        Iif (inQuotes) {
          continue;
        }
        if (nvpair[i] === '=') {
          eq = i;
          break;
        }
      }

      Iif (eq === -1) {
        return {'name': nvpair, 'value': null};
      }

      var name = stripquotes(nvpair.substring(0, eq).trim());
      var value = stripquotes(nvpair.substring(eq + 1).trim());
      return {'name': name, 'value': value};
    }

    function splitHeaderParameters(hv) {
      return parseHeaderValue(hv, ';', splitNameValue);
    }

    function parseHeaderValue(hv, separator, callback) {
      var start = 0;
      var inQuotes = false;
      var values = [];

      for (var i = 0; i < hv.length; i++) {
        if (hv[i] === '"') {
          inQuotes = !inQuotes;
          continue;
        }
        if (inQuotes) {
          // Just skip this
          continue;
        }
        if (hv[i] === separator) {
          var newValue = hv.substring(start, i).trim();
          Eif (newValue.length > 0) {
            newValue = callback(newValue);
            values.push(newValue);
          }
          start = i + 1;
        }
      }

      var newValue = hv.substring(start).trim();
      Eif (newValue.length > 0) {
        newValue = callback(newValue);
        values.push(newValue);
      }

      return values;
    }

    function rsplit(s, delim, count) {
      var nsplits = 0;
      var end = s.length;
      var rval = [];
      for (var i = s.length - 1; i >= 0; i--) {
        if (s[i] === delim) {
          var t = s.substring(i + 1, end);
          end = i;
          rval.unshift(t);
          nsplits++;
          Eif (nsplits === count) {
            break;
          }
        }
      }
      Eif (end !== 0) {
        rval.unshift(s.substring(0, end));
      }
      return rval;
    }

    function ishex(c) {
      return ('0123456789ABCDEFabcdef'.indexOf(c) > -1);
    }

    function unescape(s) {
      var i = 0;
      var t = '';
      while (i < s.length) {
        Eif (s[i] != '%' || !ishex(s[i + 1]) || !ishex(s[i + 2])) {
          t += s[i];
        } else {
          ++i;
          var hexvalue = '';
          if (i < s.length) {
            hexvalue += s[i];
            ++i;
          }
          if (i < s.length) {
            hexvalue += s[i];
          }
          if (hexvalue.length > 0) {
            t += new Buffer(hexvalue, 'hex').toString();
          } else {
            t += '%';
          }
        }

        ++i;
      }
      return t;
    }

    Deserializer.ALTSVC = function readAltSvc(buffer, frame) {
      Iif (buffer.length < 2) {
        return 'FRAME_SIZE_ERROR';
      }
      var originLength = buffer.readUInt16BE(0);
      Iif ((buffer.length - 2) < originLength) {
        return 'FRAME_SIZE_ERROR';
      }
      frame.origin = buffer.toString('ascii', 2, 2 + originLength);
      var fieldValue = buffer.toString('ascii', 2 + originLength);
      var values = parseHeaderValue(fieldValue, ',', splitHeaderParameters);
      Iif (values.length > 1) {
        // TODO - warn that we only use one here
      }
      Iif (values.length === 0) {
        // Well that's a malformed frame. Just ignore it.
        return;
      }

      var chosenAltSvc = values[0];
      frame.maxAge = 86400; // Default
      for (var i = 0; i < chosenAltSvc.length; i++) {
        if (i === 0) {
          // This corresponds to the protocolID="<host>:<port>" item
          frame.protocolID = unescape(chosenAltSvc[i].name);
          var hostport = rsplit(chosenAltSvc[i].value, ':', 1);
          frame.host = hostport[0];
          frame.port = parseInt(hostport[1], 10);
        } else Eif (chosenAltSvc[i].name == 'ma') {
          frame.maxAge = parseInt(chosenAltSvc[i].value, 10);
        }
        // Otherwise, we just ignore this
      }
    };

    // BLOCKED
    // ------------------------------------------------------------
    //
    // The BLOCKED frame (type=0xB) indicates that the sender is unable to send data
    // due to a closed flow control window.
    //
    // The BLOCKED frame does not define any flags and contains no payload.

    frameTypes[0xB] = 'BLOCKED';

    frameFlags.BLOCKED = [];

    typeSpecificAttributes.BLOCKED = [];

    Serializer.BLOCKED = function writeBlocked(frame, buffers) {
    };

    Deserializer.BLOCKED = function readBlocked(buffer, frame) {
    };

    // [Error Codes](https://tools.ietf.org/html/rfc7540#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',
      'ENHANCE_YOUR_CALM',
      'INADEQUATE_SECURITY',
      'HTTP_1_1_REQUIRED'
    ];

    // 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) {
      Iif (!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) {
        Iif (logEntry.data.length > 50) {
          logEntry.data = frame.data.slice(0, 47).toString('hex') + '...';
        } else {
          logEntry.data = frame.data.toString('hex');
        }

        Eif (!('length' in logEntry)) {
          logEntry.length = frame.data.length;
        }
      }

      Iif (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');
    };