# all files / lib/protocol/ stream.js

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82.42% Branches 150/182
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     var assert = require('assert');

    // The Stream class
    // ================

    // Stream is a [Duplex stream](https://nodejs.org/api/stream.html#stream_class_stream_duplex)
    // subclass that implements the [HTTP/2 Stream](https://tools.ietf.org/html/rfc7540#section-5)
    // concept. It has two 'sides': one that is used by the user to send/receive data (the `stream`
    // object itself) and one that is used by a Connection to read/write frames to/from the other peer
    // (`stream.upstream`).

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

    exports.Stream = Stream;

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

    // * **new Stream(log, connection)**: create a new Stream
    //
    // * **Event: 'headers' (headers)**: signals incoming headers
    //
    // * **Event: 'promise' (stream, headers)**: signals an incoming push promise
    //
    // * **Event: 'priority' (priority)**: signals a priority change. `priority` is a number between 0
    //     (highest priority) and 2^31-1 (lowest priority). Default value is 2^30.
    //
    // * **Event: 'error' (type)**: signals an error
    //
    // * **headers(headers)**: send headers
    //
    // * **promise(headers): Stream**: promise a stream
    //
    // * **priority(priority)**: set the priority of the stream. Priority can be changed by the peer
    //   too, but once it is set locally, it can not be changed remotely.
    //
    // * **reset(error)**: reset the stream with an error code
    //
    // * **upstream**: a [Flow](flow.js) that is used by the parent connection to write/read frames
    //   that are to be sent/arrived to/from the peer and are related to this stream.
    //
    // Headers are always in the [regular node.js header format][1].
    // [1]: https://nodejs.org/api/http.html#http_message_headers

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

    // The main aspects of managing the stream are:
    function Stream(log, connection) {
      Duplex.call(this);

      // * logging
      this._log = log.child({ component: 'stream', s: this });

      // * receiving and sending stream management commands
      this._initializeManagement();

      // * sending and receiving frames to/from the upstream connection
      this._initializeDataFlow();

      // * maintaining the state of the stream (idle, open, closed, etc.) and error detection
      this._initializeState();

      this.connection = connection;
    }

    Stream.prototype = Object.create(Duplex.prototype, { constructor: { value: Stream } });

    // Managing the stream
    // -------------------

    // the default stream priority is 2^30
    var DEFAULT_PRIORITY = Math.pow(2, 30);
    var MAX_PRIORITY = Math.pow(2, 31) - 1;

    // PUSH_PROMISE and HEADERS are forwarded to the user through events.
    Stream.prototype._initializeManagement = function _initializeManagement() {
      this._resetSent = false;
      this._priority = DEFAULT_PRIORITY;
      this._letPeerPrioritize = true;
    };

    Stream.prototype.promise = function promise(headers) {
      var stream = new Stream(this._log, this.connection);
      stream._priority = Math.min(this._priority + 1, MAX_PRIORITY);
      this._pushUpstream({
        type: 'PUSH_PROMISE',
        flags: {},
        stream: this.id,
        promised_stream: stream,
        headers: headers
      });
      return stream;
    };

    Stream.prototype._onPromise = function _onPromise(frame) {
      this.emit('promise', frame.promised_stream, frame.headers);
    };

    Stream.prototype.headers = function headers(headers) {
      this._pushUpstream({
        type: 'HEADERS',
        flags: {},
        stream: this.id,
        headers: headers
      });
    };

    Stream.prototype._onHeaders = function _onHeaders(frame) {
      Iif (frame.priority !== undefined) {
        this.priority(frame.priority, true);
      }
      this.emit('headers', frame.headers);
    };

    Stream.prototype.priority = function priority(priority, peer) {
      if ((peer && this._letPeerPrioritize) || !peer) {
        if (!peer) {
          this._letPeerPrioritize = false;

          var lastFrame = this.upstream.getLastQueuedFrame();
          if (lastFrame && ((lastFrame.type === 'HEADERS') || (lastFrame.type === 'PRIORITY'))) {
            lastFrame.priority = priority;
          } else {
            this._pushUpstream({
              type: 'PRIORITY',
              flags: {},
              stream: this.id,
              priority: priority
            });
          }
        }

        this._log.debug({ priority: priority }, 'Changing priority');
        this.emit('priority', priority);
        this._priority = priority;
      }
    };

    Stream.prototype._onPriority = function _onPriority(frame) {
      this.priority(frame.priority, true);
    };

    // Resetting the stream. Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame for
    // any stream.
    Stream.prototype.reset = function reset(error) {
      if (!this._resetSent) {
        this._resetSent = true;
        this._pushUpstream({
          type: 'RST_STREAM',
          flags: {},
          stream: this.id,
          error: error
        });
      }
    };

    // Specify an alternate service for the origin of this stream
    Stream.prototype.altsvc = function altsvc(host, port, protocolID, maxAge, origin) {
        var stream;
        if (origin) {
            stream = 0;
        } else {
            stream = this.id;
        }
        this._pushUpstream({
            type: 'ALTSVC',
            flags: {},
            stream: stream,
            host: host,
            port: port,
            protocolID: protocolID,
            origin: origin,
            maxAge: maxAge
        });
    };

    // Data flow
    // ---------

    // The incoming and the generated outgoing frames are received/transmitted on the `this.upstream`
    // [Flow](flow.html). The [Connection](connection.html) object instantiating the stream will read
    // and write frames to/from it. The stream itself is a regular [Duplex stream][1], and is used by
    // the user to write or read the body of the request.
    // [1]: https://nodejs.org/api/stream.html#stream_class_stream_duplex

    //     upstream side                  stream                  user side
    //
    //                    +------------------------------------+
    //                    |                                    |
    //                    +------------------+                 |
    //                    |     upstream     |                 |
    //                    |                  |                 |
    //                    +--+               |              +--|
    //            read()  |  |  _send()      |    _write()  |  |  write(buf)
    //     <--------------|B |<--------------|--------------| B|<------------
    //                    |  |               |              |  |
    //            frames  +--+               |              +--|  buffers
    //                    |  |               |              |  |
    //     -------------->|B |---------------|------------->| B|------------>
    //      write(frame)  |  |  _receive()   |     _read()  |  |  read()
    //                    +--+               |              +--|
    //                    |                  |                 |
    //                    |                  |                 |
    //                    +------------------+                 |
    //                    |                                    |
    //                    +------------------------------------+
    //
    //     B: input or output buffer

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

    Stream.prototype._initializeDataFlow = function _initializeDataFlow() {
      this.id = undefined;

      this._ended = false;

      this.upstream = new Flow();
      this.upstream._log = this._log;
      this.upstream._send = this._send.bind(this);
      this.upstream._receive = this._receive.bind(this);
      this.upstream.write = this._writeUpstream.bind(this);
      this.upstream.on('error', this.emit.bind(this, 'error'));

      this.on('finish', this._finishing);
    };

    Stream.prototype._pushUpstream = function _pushUpstream(frame) {
      this.upstream.push(frame);
      this._transition(true, frame);
    };

    // Overriding the upstream's `write` allows us to act immediately instead of waiting for the input
    // queue to empty. This is important in case of control frames.
    Stream.prototype._writeUpstream = function _writeUpstream(frame) {
      this._log.debug({ frame: frame }, 'Receiving frame');

      var moreNeeded = Flow.prototype.write.call(this.upstream, frame);

      // * Transition to a new state if that's the effect of receiving the frame
      this._transition(false, frame);

      // * If it's a control frame. Call the appropriate handler method.
      if (frame.type === 'HEADERS') {
        Iif (this._processedHeaders && !frame.flags['END_STREAM']) {
          this.emit('error', 'PROTOCOL_ERROR');
        }
        this._processedHeaders = true;
        this._onHeaders(frame);
      } else if (frame.type === 'PUSH_PROMISE') {
        this._onPromise(frame);
      } else Iif (frame.type === 'PRIORITY') {
        this._onPriority(frame);
      } else Iif (frame.type === 'ALTSVC') {
        // TODO
      } else Iif (frame.type === 'BLOCKED') {
        // TODO
      }

      // * If it's an invalid stream level frame, emit error
      else Iif ((frame.type !== 'DATA') &&
               (frame.type !== 'WINDOW_UPDATE') &&
               (frame.type !== 'RST_STREAM')) {
        this._log.error({ frame: frame }, 'Invalid stream level frame');
        this.emit('error', 'PROTOCOL_ERROR');
      }

      return moreNeeded;
    };

    // The `_receive` method (= `upstream._receive`) gets called when there's an incoming frame.
    Stream.prototype._receive = function _receive(frame, ready) {
      // * If it's a DATA frame, then push the payload into the output buffer on the other side.
      //   Call ready when the other side is ready to receive more.
      if (!this._ended && (frame.type === 'DATA')) {
        var moreNeeded = this.push(frame.data);
        Iif (!moreNeeded) {
          this._receiveMore = ready;
        }
      }

      // * Any frame may signal the end of the stream with the END_STREAM flag
      if (!this._ended && (frame.flags.END_STREAM || (frame.type === 'RST_STREAM'))) {
        this.push(null);
        this._ended = true;
      }

      // * Postpone calling `ready` if `push()` returned a falsy value
      Eif (this._receiveMore !== ready) {
        ready();
      }
    };

    // The `_read` method is called when the user side is ready to receive more data. If there's a
    // pending write on the upstream, then call its pending ready callback to receive more frames.
    Stream.prototype._read = function _read() {
      Iif (this._receiveMore) {
        var receiveMore = this._receiveMore;
        delete this._receiveMore;
        receiveMore();
      }
    };

    // The `write` method gets called when there's a write request from the user.
    Stream.prototype._write = function _write(buffer, encoding, ready) {
      // * Chunking is done by the upstream Flow.
      var moreNeeded = this._pushUpstream({
        type: 'DATA',
        flags: {},
        stream: this.id,
        data: buffer
      });

      // * Call ready when upstream is ready to receive more frames.
      Iif (moreNeeded) {
        ready();
      } else {
        this._sendMore = ready;
      }
    };

    // The `_send` (= `upstream._send`) method is called when upstream is ready to receive more frames.
    // If there's a pending write on the user side, then call its pending ready callback to receive more
    // writes.
    Stream.prototype._send = function _send() {
      if (this._sendMore) {
        var sendMore = this._sendMore;
        delete this._sendMore;
        sendMore();
      }
    };

    // When the stream is finishing (the user calls `end()` on it), then we have to set the `END_STREAM`
    // flag on the last frame. If there's no frame in the queue, or if it doesn't support this flag,
    // then we create a 0 length DATA frame. We could do this all the time, but putting the flag on an
    // existing frame is a nice optimization.
    var emptyBuffer = new Buffer(0);
    Stream.prototype._finishing = function _finishing() {
      var endFrame = {
        type: 'DATA',
        flags: { END_STREAM: true },
        stream: this.id,
        data: emptyBuffer
      };
      var lastFrame = this.upstream.getLastQueuedFrame();
      if (lastFrame && ((lastFrame.type === 'DATA') || (lastFrame.type === 'HEADERS'))) {
        this._log.debug({ frame: lastFrame }, 'Marking last frame with END_STREAM flag.');
        lastFrame.flags.END_STREAM = true;
        this._transition(true, endFrame);
      } else {
        this._pushUpstream(endFrame);
      }
    };

    // [Stream States](https://tools.ietf.org/html/rfc7540#section-5.1)
    // ----------------
    //
    //                           +--------+
    //                     PP    |        |    PP
    //                  ,--------|  idle  |--------.
    //                 /         |        |         \
    //                v          +--------+          v
    //         +----------+          |           +----------+
    //         |          |          | H         |          |
    //     ,---| reserved |          |           | reserved |---.
    //     |   | (local)  |          v           | (remote) |   |
    //     |   +----------+      +--------+      +----------+   |
    //     |      |          ES  |        |  ES          |      |
    //     |      | H    ,-------|  open  |-------.      | H    |
    //     |      |     /        |        |        \     |      |
    //     |      v    v         +--------+         v    v      |
    //     |   +----------+          |           +----------+   |
    //     |   |   half   |          |           |   half   |   |
    //     |   |  closed  |          | R         |  closed  |   |
    //     |   | (remote) |          |           | (local)  |   |
    //     |   +----------+          |           +----------+   |
    //     |        |                v                 |        |
    //     |        |  ES / R    +--------+  ES / R    |        |
    //     |        `----------->|        |<-----------'        |
    //     |  R                  | closed |                  R  |
    //     `-------------------->|        |<--------------------'
    //                           +--------+

    // Streams begin in the IDLE state and transitions happen when there's an incoming or outgoing frame
    Stream.prototype._initializeState = function _initializeState() {
      this.state = 'IDLE';
      this._initiated = undefined;
      this._closedByUs = undefined;
      this._closedWithRst = undefined;
      this._processedHeaders = false;
    };

    // Only `_setState` should change `this.state` directly. It also logs the state change and notifies
    // interested parties using the 'state' event.
    Stream.prototype._setState = function transition(state) {
      assert(this.state !== state);
      this._log.debug({ from: this.state, to: state }, 'State transition');
      this.state = state;
      this.emit('state', state);
    };

    // A state is 'active' if the stream in that state counts towards the concurrency limit. Streams
    // that are in the "open" state, or either of the "half closed" states count toward this limit.
    function activeState(state) {
      return ((state === 'HALF_CLOSED_LOCAL') || (state === 'HALF_CLOSED_REMOTE') || (state === 'OPEN'));
    }

    // `_transition` is called every time there's an incoming or outgoing frame. It manages state
    // transitions, and detects stream errors. A stream error is always caused by a frame that is not
    // allowed in the current state.
    Stream.prototype._transition = function transition(sending, frame) {
      var receiving = !sending;
      var connectionError;
      var streamError;

      var DATA = false, HEADERS = false, PRIORITY = false, ALTSVC = false, BLOCKED = false;
      var RST_STREAM = false, PUSH_PROMISE = false, WINDOW_UPDATE = false;
      switch(frame.type) {
        case 'DATA'         : DATA          = true; break;
        case 'HEADERS'      : HEADERS       = true; break;
        case 'PRIORITY'     : PRIORITY      = true; break;
        case 'RST_STREAM'   : RST_STREAM    = true; break;
        case 'PUSH_PROMISE' : PUSH_PROMISE  = true; break;
        case 'WINDOW_UPDATE': WINDOW_UPDATE = true; break;
        case 'ALTSVC'       : ALTSVC        = true; break;
        case 'BLOCKED'      : BLOCKED       = true; break;
      }

      var previousState = this.state;

      switch (this.state) {
        // All streams start in the **idle** state. In this state, no frames have been exchanged.
        //
        // * Sending or receiving a HEADERS frame causes the stream to become "open".
        //
        // When the HEADERS frame contains the END_STREAM flags, then two state transitions happen.
        case 'IDLE':
          if (HEADERS) {
            this._setState('OPEN');
            if (frame.flags.END_STREAM) {
              this._setState(sending ? 'HALF_CLOSED_LOCAL' : 'HALF_CLOSED_REMOTE');
            }
            this._initiated = sending;
          } else if (sending && RST_STREAM) {
            this._setState('CLOSED');
          } else Iif (PRIORITY) {
            /* No state change */
          } else {
            connectionError = 'PROTOCOL_ERROR';
          }
          break;

        // A stream in the **reserved (local)** state is one that has been promised by sending a
        // PUSH_PROMISE frame.
        //
        // * The endpoint can send a HEADERS frame. This causes the stream to open in a "half closed
        //   (remote)" state.
        // * Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This
        //   releases the stream reservation.
        // * An endpoint may receive PRIORITY frame in this state.
        // * An endpoint MUST NOT send any other type of frame in this state.
        case 'RESERVED_LOCAL':
          if (sending && HEADERS) {
            this._setState('HALF_CLOSED_REMOTE');
          } else if (RST_STREAM) {
            this._setState('CLOSED');
          } else Iif (PRIORITY) {
            /* No state change */
          } else {
            connectionError = 'PROTOCOL_ERROR';
          }
          break;

        // A stream in the **reserved (remote)** state has been reserved by a remote peer.
        //
        // * Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This
        //   releases the stream reservation.
        // * Receiving a HEADERS frame causes the stream to transition to "half closed (local)".
        // * An endpoint MAY send PRIORITY frames in this state to reprioritize the stream.
        // * Receiving any other type of frame MUST be treated as a stream error of type PROTOCOL_ERROR.
        case 'RESERVED_REMOTE':
          if (RST_STREAM) {
            this._setState('CLOSED');
          } else if (receiving && HEADERS) {
            this._setState('HALF_CLOSED_LOCAL');
          } else Iif (BLOCKED || PRIORITY) {
            /* No state change */
          } else {
            connectionError = 'PROTOCOL_ERROR';
          }
          break;

        // The **open** state is where both peers can send frames. In this state, sending peers observe
        // advertised stream level flow control limits.
        //
        // * From this state either endpoint can send a frame with a END_STREAM flag set, which causes
        //   the stream to transition into one of the "half closed" states: an endpoint sending a
        //   END_STREAM flag causes the stream state to become "half closed (local)"; an endpoint
        //   receiving a END_STREAM flag causes the stream state to become "half closed (remote)".
        // * Either endpoint can send a RST_STREAM frame from this state, causing it to transition
        //   immediately to "closed".
        case 'OPEN':
          if (frame.flags.END_STREAM) {
            this._setState(sending ? 'HALF_CLOSED_LOCAL' : 'HALF_CLOSED_REMOTE');
          } else if (RST_STREAM) {
            this._setState('CLOSED');
          } else {
            /* No state change */
          }
          break;

        // A stream that is **half closed (local)** cannot be used for sending frames.
        //
        // * A stream transitions from this state to "closed" when a frame that contains a END_STREAM
        //   flag is received, or when either peer sends a RST_STREAM frame.
        // * An endpoint MAY send or receive PRIORITY frames in this state to reprioritize the stream.
        // * WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the END_STREAM flag.
        case 'HALF_CLOSED_LOCAL':
          if (RST_STREAM || (receiving && frame.flags.END_STREAM)) {
            this._setState('CLOSED');
          } else if (BLOCKED || ALTSVC || receiving || PRIORITY || (sending && WINDOW_UPDATE)) {
            /* No state change */
          } else {
            connectionError = 'PROTOCOL_ERROR';
          }
          break;

        // A stream that is **half closed (remote)** is no longer being used by the peer to send frames.
        // In this state, an endpoint is no longer obligated to maintain a receiver flow control window
        // if it performs flow control.
        //
        // * If an endpoint receives additional frames for a stream that is in this state it MUST
        //   respond with a stream error of type STREAM_CLOSED.
        // * A stream can transition from this state to "closed" by sending a frame that contains a
        //   END_STREAM flag, or when either peer sends a RST_STREAM frame.
        // * An endpoint MAY send or receive PRIORITY frames in this state to reprioritize the stream.
        // * A receiver MAY receive a WINDOW_UPDATE frame on a "half closed (remote)" stream.
        case 'HALF_CLOSED_REMOTE':
          if (RST_STREAM || (sending && frame.flags.END_STREAM)) {
            this._setState('CLOSED');
          } else if (BLOCKED || ALTSVC || sending || PRIORITY || (receiving && WINDOW_UPDATE)) {
            /* No state change */
          } else {
            connectionError = 'PROTOCOL_ERROR';
          }
          break;

        // The **closed** state is the terminal state.
        //
        // * An endpoint MUST NOT send frames on a closed stream. An endpoint that receives a frame
        //   after receiving a RST_STREAM or a frame containing a END_STREAM flag on that stream MUST
        //   treat that as a stream error of type STREAM_CLOSED.
        // * WINDOW_UPDATE, PRIORITY or RST_STREAM frames can be received in this state for a short
        //   period after a frame containing an END_STREAM flag is sent.  Until the remote peer receives
        //   and processes the frame bearing the END_STREAM flag, it might send either frame type.
        //   Endpoints MUST ignore WINDOW_UPDATE frames received in this state, though endpoints MAY
        //   choose to treat WINDOW_UPDATE frames that arrive a significant time after sending
        //   END_STREAM as a connection error of type PROTOCOL_ERROR.
        // * If this state is reached as a result of sending a RST_STREAM frame, the peer that receives
        //   the RST_STREAM might have already sent - or enqueued for sending - frames on the stream
        //   that cannot be withdrawn. An endpoint that sends a RST_STREAM frame MUST ignore frames that
        //   it receives on closed streams after it has sent a RST_STREAM frame. An endpoint MAY choose
        //   to limit the period over which it ignores frames and treat frames that arrive after this
        //   time as being in error.
        // * An endpoint might receive a PUSH_PROMISE frame after it sends RST_STREAM. PUSH_PROMISE
        //   causes a stream to become "reserved". If promised streams are not desired, a RST_STREAM
        //   can be used to close any of those streams.
        case 'CLOSED':
          if (PRIORITY || (sending && RST_STREAM) ||
              (sending && this._closedWithRst) ||
              (receiving && WINDOW_UPDATE) ||
              (receiving && this._closedByUs &&
               (this._closedWithRst || RST_STREAM || ALTSVC))) {
            /* No state change */
          } else {
            streamError = 'STREAM_CLOSED';
          }
          break;
      }

      // Noting that the connection was closed by the other endpoint. It may be important in edge cases.
      // For example, when the peer tries to cancel a promised stream, but we already sent every data
      // on it, then the stream is in CLOSED state, yet we want to ignore the incoming RST_STREAM.
      if ((this.state === 'CLOSED') && (previousState !== 'CLOSED')) {
        this._closedByUs = sending;
        this._closedWithRst = RST_STREAM;
      }

      // Sending/receiving a PUSH_PROMISE
      //
      // * Sending a PUSH_PROMISE frame marks the associated stream for later use. The stream state
      //   for the reserved stream transitions to "reserved (local)".
      // * Receiving a PUSH_PROMISE frame marks the associated stream as reserved by the remote peer.
      //   The state of the stream becomes "reserved (remote)".
      if (PUSH_PROMISE && !connectionError && !streamError) {
        /* This assertion must hold, because _transition is called immediately when a frame is written
           to the stream. If it would be called when a frame gets out of the input queue, the state
           of the reserved could have been changed by then. */
        assert(frame.promised_stream.state === 'IDLE', frame.promised_stream.state);
        frame.promised_stream._setState(sending ? 'RESERVED_LOCAL' : 'RESERVED_REMOTE');
        frame.promised_stream._initiated = sending;
      }

      // Signaling how sending/receiving this frame changes the active stream count (-1, 0 or +1)
      if (this._initiated) {
        var change = (activeState(this.state) - activeState(previousState));
        if (sending) {
          frame.count_change = change;
        } else {
          frame.count_change(change);
        }
      } else if (sending) {
        frame.count_change = 0;
      }

      // Common error handling.
      if (connectionError || streamError) {
        var info = {
          error: connectionError,
          frame: frame,
          state: this.state,
          closedByUs: this._closedByUs,
          closedWithRst: this._closedWithRst
        };

        // * When sending something invalid, throwing an exception, since it is probably a bug.
        if (sending) {
          this._log.error(info, 'Sending illegal frame.');
          return this.emit('error', new Error('Sending illegal frame (' + frame.type + ') in ' + this.state + ' state.'));
        }

        // * In case of a serious problem, emitting and error and letting someone else handle it
        //   (e.g. closing the connection)
        // * When receiving something invalid, sending an RST_STREAM using the `reset` method.
        //   This will automatically cause a transition to the CLOSED state.
        else {
          this._log.error(info, 'Received illegal frame.');
          if (connectionError) {
            this.emit('connectionError', connectionError);
          } else {
            this.reset(streamError);
            this.emit('error', streamError);
          }
        }
      }
    };

    // Bunyan serializers
    // ------------------

    exports.serializers = {};

    var nextId = 0;
    exports.serializers.s = function(stream) {
      if (!('_id' in stream)) {
        stream._id = nextId;
        nextId += 1;
      }
      return stream._id;
    };