# all files / lib/protocol/ connection.js

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76.36% Branches 84/110
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     var assert = require('assert');

    // The Connection class
    // ====================

    // The Connection class manages HTTP/2 connections. Each instance corresponds to one transport
    // stream (TCP stream). It operates by sending and receiving frames and is implemented as a
    // [Flow](flow.html) subclass.

    var Flow = require('./flow').Flow;
    var timers = require('timers');

    exports.Connection = Connection;

    // Public API
    // ----------

    // * **new Connection(log, firstStreamId, settings)**: create a new Connection
    //
    // * **Event: 'error' (type)**: signals a connection level error made by the other end
    //
    // * **Event: 'peerError' (type)**: signals the receipt of a GOAWAY frame that contains an error
    //   code other than NO_ERROR
    //
    // * **Event: 'stream' (stream)**: signals that there's an incoming stream
    //
    // * **createStream(): stream**: initiate a new stream
    //
    // * **set(settings, callback)**: change the value of one or more settings according to the
    //   key-value pairs of `settings`. The callback is called after the peer acknowledged the changes.
    //
    // * **ping([callback])**: send a ping and call callback when the answer arrives
    //
    // * **close([error])**: close the stream with an error code

    // Constructor
    // -----------

    // The main aspects of managing the connection are:
    function Connection(log, firstStreamId, settings) {
      // * initializing the base class
      Flow.call(this, 0);

      // * logging: every method uses the common logger object
      this._log = log.child({ component: 'connection' });

      // * stream management
      this._initializeStreamManagement(firstStreamId);

      // * lifecycle management
      this._initializeLifecycleManagement();

      // * flow control
      this._initializeFlowControl();

      // * settings management
      this._initializeSettingsManagement(settings);

      // * multiplexing
      this._initializeMultiplexing();
    }
    Connection.prototype = Object.create(Flow.prototype, { constructor: { value: Connection } });

    // Overview
    // --------

    //              |    ^             |    ^
    //              v    |             v    |
    //         +--------------+   +--------------+
    //     +---|   stream1    |---|   stream2    |----      ....      ---+
    //     |   | +----------+ |   | +----------+ |                       |
    //     |   | | stream1. | |   | | stream2. | |                       |
    //     |   +-| upstream |-+   +-| upstream |-+                       |
    //     |     +----------+       +----------+                         |
    //     |       |     ^             |     ^                           |
    //     |       v     |             v     |                           |
    //     |       +-----+-------------+-----+--------      ....         |
    //     |       ^     |             |     |                           |
    //     |       |     v             |     |                           |
    //     |   +--------------+        |     |                           |
    //     |   |   stream0    |        |     |                           |
    //     |   |  connection  |        |     |                           |
    //     |   |  management  |     multiplexing                         |
    //     |   +--------------+     flow control                         |
    //     |                           |     ^                           |
    //     |                   _read() |     | _write()                  |
    //     |                           v     |                           |
    //     |                +------------+ +-----------+                 |
    //     |                |output queue| |input queue|                 |
    //     +----------------+------------+-+-----------+-----------------+
    //                                 |     ^
    //                          read() |     | write()
    //                                 v     |

    // Stream management
    // -----------------

    var Stream  = require('./stream').Stream;

    // Initialization:
    Connection.prototype._initializeStreamManagement = function _initializeStreamManagement(firstStreamId) {
      // * streams are stored in two data structures:
      //   * `_streamIds` is an id -> stream map of the streams that are allowed to receive frames.
      //   * `_streamPriorities` is a priority -> [stream] map of stream that allowed to send frames.
      this._streamIds = [];
      this._streamPriorities = [];

      // * The next outbound stream ID and the last inbound stream id
      this._nextStreamId = firstStreamId;
      this._lastIncomingStream = 0;

      // * Calling `_writeControlFrame` when there's an incoming stream with 0 as stream ID
      this._streamIds[0] = { upstream: { write: this._writeControlFrame.bind(this) } };

      // * By default, the number of concurrent outbound streams is not limited. The `_streamLimit` can
      //   be set by the SETTINGS_MAX_CONCURRENT_STREAMS setting.
      this._streamSlotsFree = Infinity;
      this._streamLimit = Infinity;
      this.on('RECEIVING_SETTINGS_MAX_CONCURRENT_STREAMS', this._updateStreamLimit);
    };

    // `_writeControlFrame` is called when there's an incoming frame in the `_control` stream. It
    // broadcasts the message by creating an event on it.
    Connection.prototype._writeControlFrame = function _writeControlFrame(frame) {
      Eif ((frame.type === 'SETTINGS') || (frame.type === 'PING') ||
          (frame.type === 'GOAWAY') || (frame.type === 'WINDOW_UPDATE') ||
          (frame.type === 'ALTSVC')) {
        this._log.debug({ frame: frame }, 'Receiving connection level frame');
        this.emit(frame.type, frame);
      } else {
        this._log.error({ frame: frame }, 'Invalid connection level frame');
        this.emit('error', 'PROTOCOL_ERROR');
      }
    };

    // Methods to manage the stream slot pool:
    Connection.prototype._updateStreamLimit = function _updateStreamLimit(newStreamLimit) {
      var wakeup = (this._streamSlotsFree === 0) && (newStreamLimit > this._streamLimit);
      this._streamSlotsFree += newStreamLimit - this._streamLimit;
      this._streamLimit = newStreamLimit;
      Iif (wakeup) {
        this.emit('wakeup');
      }
    };

    Connection.prototype._changeStreamCount = function _changeStreamCount(change) {
      if (change) {
        this._log.trace({ free: this._streamSlotsFree, change: change },
                        'Changing active stream count.');
        var wakeup = (this._streamSlotsFree === 0) && (change < 0);
        this._streamSlotsFree -= change;
        Iif (wakeup) {
          this.emit('wakeup');
        }
      }
    };

    // Creating a new *inbound or outbound* stream with the given `id` (which is undefined in case of
    // an outbound stream) consists of three steps:
    //
    // 1. var stream = new Stream(this._log, this);
    // 2. this._allocateId(stream, id);
    // 2. this._allocatePriority(stream);

    // Allocating an ID to a stream
    Connection.prototype._allocateId = function _allocateId(stream, id) {
      // * initiated stream without definite ID
      if (id === undefined) {
        id = this._nextStreamId;
        this._nextStreamId += 2;
      }

      // * incoming stream with a legitim ID (larger than any previous and different parity than ours)
      else Eif ((id > this._lastIncomingStream) && ((id - this._nextStreamId) % 2 !== 0)) {
        this._lastIncomingStream = id;
      }

      // * incoming stream with invalid ID
      else {
        this._log.error({ stream_id: id, lastIncomingStream: this._lastIncomingStream },
                        'Invalid incoming stream ID.');
        this.emit('error', 'PROTOCOL_ERROR');
        return undefined;
      }

      assert(!(id in this._streamIds));

      // * adding to `this._streamIds`
      this._log.trace({ s: stream, stream_id: id }, 'Allocating ID for stream.');
      this._streamIds[id] = stream;
      stream.id = id;
      this.emit('new_stream', stream, id);

      // * forwarding connection errors from streams
      stream.on('connectionError', this.emit.bind(this, 'error'));

      return id;
    };

    // Allocating a priority to a stream, and managing priority changes
    Connection.prototype._allocatePriority = function _allocatePriority(stream) {
      this._log.trace({ s: stream }, 'Allocating priority for stream.');
      this._insert(stream, stream._priority);
      stream.on('priority', this._reprioritize.bind(this, stream));
      stream.upstream.on('readable', this.emit.bind(this, 'wakeup'));
      this.emit('wakeup');
    };

    Connection.prototype._insert = function _insert(stream, priority) {
      if (priority in this._streamPriorities) {
        this._streamPriorities[priority].push(stream);
      } else {
        this._streamPriorities[priority] = [stream];
      }
    };

    Connection.prototype._reprioritize = function _reprioritize(stream, priority) {
      this._removePrioritisedStream(stream);
      this._insert(stream, priority);
    };

    Connection.prototype._removePrioritisedStream = function _removePrioritisedStream(stream) {
      var bucket = this._streamPriorities[stream._priority];
      var index = bucket.indexOf(stream);
      assert(index !== -1);
      bucket.splice(index, 1);
      if (bucket.length === 0) {
        delete this._streamPriorities[stream._priority];
      }
    };

    // Creating an *inbound* stream with the given ID. It is called when there's an incoming frame to
    // a previously nonexistent stream.
    Connection.prototype._createIncomingStream = function _createIncomingStream(id) {
      this._log.debug({ stream_id: id }, 'New incoming stream.');

      var stream = new Stream(this._log, this);
      this._allocateId(stream, id);
      this._allocatePriority(stream);
      this.emit('stream', stream, id);

      return stream;
    };

    // Creating an *outbound* stream
    Connection.prototype.createStream = function createStream() {
      this._log.trace('Creating new outbound stream.');

      // * Receiving is enabled immediately, and an ID gets assigned to the stream
      var stream = new Stream(this._log, this);
      this._allocatePriority(stream);

      stream.on('end', this._removeStream.bind(this, stream));

      return stream;
    };

    Connection.prototype._removeStream = function _removeStream(stream) {
      this._log.trace('Removing outbound stream.');

      delete this._streamIds[stream.id];
      this._removePrioritisedStream(stream);
    };

    // Multiplexing
    // ------------

    Connection.prototype._initializeMultiplexing = function _initializeMultiplexing() {
      this.on('window_update', this.emit.bind(this, 'wakeup'));
      this._sendScheduled = false;
      this._firstFrameReceived = false;
    };

    // The `_send` method is a virtual method of the [Flow class](flow.html) that has to be implemented
    // by child classes. It reads frames from streams and pushes them to the output buffer.
    Connection.prototype._send = function _send(immediate) {
      // * Do not do anything if the connection is already closed
      if (this._closed) {
        return;
      }

      // * Collapsing multiple calls in a turn into a single deferred call
      if (immediate) {
        this._sendScheduled = false;
      } else {
        if (!this._sendScheduled) {
          this._sendScheduled = true;
            timers.setImmediate(this._send.bind(this, true));
        }
        return;
      }

      this._log.trace('Starting forwarding frames from streams.');

      // * Looping through priority `bucket`s in priority order.
    priority_loop:
      for (var priority in this._streamPriorities) {
        var bucket = this._streamPriorities[priority];
        var nextBucket = [];

        // * Forwarding frames from buckets with round-robin scheduling.
        //   1. pulling out frame
        //   2. if there's no frame, skip this stream
        //   3. if forwarding this frame would make `streamCount` greater than `streamLimit`, skip
        //      this stream
        //   4. adding stream to the bucket of the next round unless it has ended
        //   5. assigning an ID to the frame (allocating an ID to the stream if there isn't already)
        //   6. if forwarding a PUSH_PROMISE, allocate ID to the promised stream
        //   7. forwarding the frame, changing `streamCount` as appropriate
        //   8. stepping to the next stream if there's still more frame needed in the output buffer
        //   9. switching to the bucket of the next round
        while (bucket.length > 0) {
          for (var index = 0; index < bucket.length; index++) {
            var stream = bucket[index];
            Iif(!stream || !stream.upstream) continue;
            var frame = stream.upstream.read((this._window > 0) ? this._window : -1);

            if (!frame) {
              continue;
            } else Iif (frame.count_change > this._streamSlotsFree) {
              stream.upstream.unshift(frame);
              continue;
            }

            if (!stream._ended) {
              nextBucket.push(stream);
            } else {
              delete this._streamIds[stream.id];
            }

            if (frame.stream === undefined) {
              frame.stream = stream.id || this._allocateId(stream);
            }

            if (frame.type === 'PUSH_PROMISE') {
              this._allocatePriority(frame.promised_stream);
              frame.promised_stream = this._allocateId(frame.promised_stream);
            }

            this._log.trace({ s: stream, frame: frame }, 'Forwarding outgoing frame');
            var moreNeeded = this.push(frame);
            this._changeStreamCount(frame.count_change);

            Iif (!moreNeeded) {
              break priority_loop;
            }
          }

          bucket = nextBucket;
          nextBucket = [];
        }
      }

      // * if we couldn't forward any frame, then sleep until window update, or some other wakeup event
      if (moreNeeded === undefined) {
        this.once('wakeup', this._send.bind(this));
      }

      this._log.trace({ moreNeeded: moreNeeded }, 'Stopping forwarding frames from streams.');
    };

    // The `_receive` method is another virtual method of the [Flow class](flow.html) that has to be
    // implemented by child classes. It forwards the given frame to the appropriate stream:
    Connection.prototype._receive = function _receive(frame, done) {
      this._log.trace({ frame: frame }, 'Forwarding incoming frame');

      // * first frame needs to be checked by the `_onFirstFrameReceived` method
      if (!this._firstFrameReceived) {
        this._firstFrameReceived = true;
        this._onFirstFrameReceived(frame);
      }

      // Do some sanity checking here before we create a stream
      Iif ((frame.type == 'SETTINGS' ||
           frame.type == 'PING' ||
           frame.type == 'GOAWAY') &&
          frame.stream != 0) {
        // Got connection-level frame on a stream - EEP!
        this.close('PROTOCOL_ERROR');
        return;
      } else Iif ((frame.type == 'DATA' ||
                  frame.type == 'HEADERS' ||
                  frame.type == 'PRIORITY' ||
                  frame.type == 'RST_STREAM' ||
                  frame.type == 'PUSH_PROMISE' ||
                  frame.type == 'CONTINUATION') &&
                 frame.stream == 0) {
        // Got stream-level frame on connection - EEP!
        this.close('PROTOCOL_ERROR');
        return;
      }
      // WINDOW_UPDATE can be on either stream or connection

      // * gets the appropriate stream from the stream registry
      var stream = this._streamIds[frame.stream];

      // * or creates one if it's not in `this.streams`
      if (!stream) {
        stream = this._createIncomingStream(frame.stream);
      }

      // * in case of PUSH_PROMISE, replaces the promised stream id with a new incoming stream
      if (frame.type === 'PUSH_PROMISE') {
        frame.promised_stream = this._createIncomingStream(frame.promised_stream);
      }

      frame.count_change = this._changeStreamCount.bind(this);

      // * and writes it to the `stream`'s `upstream`
      stream.upstream.write(frame);

      done();
    };

    // Settings management
    // -------------------

    var defaultSettings = {
    };

    // Settings management initialization:
    Connection.prototype._initializeSettingsManagement = function _initializeSettingsManagement(settings) {
      // * Setting up the callback queue for setting acknowledgements
      this._settingsAckCallbacks = [];

      // * Sending the initial settings.
      this._log.debug({ settings: settings },
                      'Sending the first SETTINGS frame as part of the connection header.');
      this.set(settings || defaultSettings);

      // * Forwarding SETTINGS frames to the `_receiveSettings` method
      this.on('SETTINGS', this._receiveSettings);
      this.on('RECEIVING_SETTINGS_MAX_FRAME_SIZE', this._sanityCheckMaxFrameSize);
    };

    // * Checking that the first frame the other endpoint sends is SETTINGS
    Connection.prototype._onFirstFrameReceived = function _onFirstFrameReceived(frame) {
      Eif ((frame.stream === 0) && (frame.type === 'SETTINGS')) {
        this._log.debug('Receiving the first SETTINGS frame as part of the connection header.');
      } else {
        this._log.fatal({ frame: frame }, 'Invalid connection header: first frame is not SETTINGS.');
        this.emit('error', 'PROTOCOL_ERROR');
      }
    };

    // Handling of incoming SETTINGS frames.
    Connection.prototype._receiveSettings = function _receiveSettings(frame) {
      // * If it's an ACK, call the appropriate callback
      if (frame.flags.ACK) {
        var callback = this._settingsAckCallbacks.shift();
        Eif (callback) {
          callback();
        }
      }

      // * If it's a setting change request, then send an ACK and change the appropriate settings
      else {
        if (!this._closed) {
          this.push({
            type: 'SETTINGS',
            flags: { ACK: true },
            stream: 0,
            settings: {}
          });
        }
        for (var name in frame.settings) {
          this.emit('RECEIVING_' + name, frame.settings[name]);
        }
      }
    };

    Connection.prototype._sanityCheckMaxFrameSize = function _sanityCheckMaxFrameSize(value) {
      if ((value < 0x4000) || (value >= 0x01000000)) {
        this._log.fatal('Received invalid value for max frame size: ' + value);
        this.emit('error');
      }
    };

    // Changing one or more settings value and sending out a SETTINGS frame
    Connection.prototype.set = function set(settings, callback) {
      // * Calling the callback and emitting event when the change is acknowledges
      var self = this;
      this._settingsAckCallbacks.push(function() {
        for (var name in settings) {
          self.emit('ACKNOWLEDGED_' + name, settings[name]);
        }
        Iif (callback) {
          callback();
        }
      });

      // * Sending out the SETTINGS frame
      this.push({
        type: 'SETTINGS',
        flags: { ACK: false },
        stream: 0,
        settings: settings
      });
      for (var name in settings) {
        this.emit('SENDING_' + name, settings[name]);
      }
    };

    // Lifecycle management
    // --------------------

    // The main responsibilities of lifecycle management code:
    //
    // * keeping the connection alive by
    //   * sending PINGs when the connection is idle
    //   * answering PINGs
    // * ending the connection

    Connection.prototype._initializeLifecycleManagement = function _initializeLifecycleManagement() {
      this._pings = {};
      this.on('PING', this._receivePing);
      this.on('GOAWAY', this._receiveGoaway);
      this._closed = false;
    };

    // Generating a string of length 16 with random hexadecimal digits
    Connection.prototype._generatePingId = function _generatePingId() {
      do {
        var id = '';
        for (var i = 0; i < 16; i++) {
          id += Math.floor(Math.random()*16).toString(16);
        }
      } while(id in this._pings);
      return id;
    };

    // Sending a ping and calling `callback` when the answer arrives
    Connection.prototype.ping = function ping(callback) {
      var id = this._generatePingId();
      var data = new Buffer(id, 'hex');
      this._pings[id] = callback;

      this._log.debug({ data: data }, 'Sending PING.');
      this.push({
        type: 'PING',
        flags: {
          ACK: false
        },
        stream: 0,
        data: data
      });
    };

    // Answering pings
    Connection.prototype._receivePing = function _receivePing(frame) {
      if (frame.flags.ACK) {
        var id = frame.data.toString('hex');
        Eif (id in this._pings) {
          this._log.debug({ data: frame.data }, 'Receiving answer for a PING.');
          var callback = this._pings[id];
          Eif (callback) {
            callback();
          }
          delete this._pings[id];
        } else {
          this._log.warn({ data: frame.data }, 'Unsolicited PING answer.');
        }

      } else {
        this._log.debug({ data: frame.data }, 'Answering PING.');
        this.push({
          type: 'PING',
          flags: {
            ACK: true
          },
          stream: 0,
          data: frame.data
        });
      }
    };

    // Terminating the connection
    Connection.prototype.close = function close(error) {
      Iif (this._closed) {
        this._log.warn('Trying to close an already closed connection');
        return;
      }

      this._log.debug({ error: error }, 'Closing the connection');
      this.push({
        type: 'GOAWAY',
        flags: {},
        stream: 0,
        last_stream: this._lastIncomingStream,
        error: error || 'NO_ERROR'
      });
      this.push(null);
      this._closed = true;
    };

    Connection.prototype._receiveGoaway = function _receiveGoaway(frame) {
      this._log.debug({ error: frame.error }, 'Other end closed the connection');
      this.push(null);
      this._closed = true;
      Iif (frame.error !== 'NO_ERROR') {
        this.emit('peerError', frame.error);
      }
    };

    // Flow control
    // ------------

    Connection.prototype._initializeFlowControl = function _initializeFlowControl() {
      // Handling of initial window size of individual streams.
      this._initialStreamWindowSize = INITIAL_STREAM_WINDOW_SIZE;
      this.on('new_stream', function(stream) {
        stream.upstream.setInitialWindow(this._initialStreamWindowSize);
      });
      this.on('RECEIVING_SETTINGS_INITIAL_WINDOW_SIZE', this._setInitialStreamWindowSize);
      this._streamIds[0].upstream.setInitialWindow = function noop() {};
    };

    // The initial connection flow control window is 65535 bytes.
    var INITIAL_STREAM_WINDOW_SIZE = 65535;

    // A SETTINGS frame can alter the initial flow control window size for all current streams. When the
    // value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust the window size of all
    // stream by calling the `setInitialStreamWindowSize` method. The window size has to be modified by
    // the difference between the new value and the old value.
    Connection.prototype._setInitialStreamWindowSize = function _setInitialStreamWindowSize(size) {
      Iif ((this._initialStreamWindowSize === Infinity) && (size !== Infinity)) {
        this._log.error('Trying to manipulate initial flow control window size after flow control was turned off.');
        this.emit('error', 'FLOW_CONTROL_ERROR');
      } else {
        this._log.debug({ size: size }, 'Changing stream initial window size.');
        this._initialStreamWindowSize = size;
        this._streamIds.forEach(function(stream) {
          stream.upstream.setInitialWindow(size);
        });
      }
    };