michael@0: var assert = require('assert');
michael@0: 
michael@0: // The Stream class
michael@0: // ================
michael@0: 
michael@0: // Stream is a [Duplex stream](http://nodejs.org/api/stream.html#stream_class_stream_duplex)
michael@0: // subclass that implements the [HTTP/2 Stream](http://http2.github.io/http2-spec/#rfc.section.3.4)
michael@0: // concept. It has two 'sides': one that is used by the user to send/receive data (the `stream`
michael@0: // object itself) and one that is used by a Connection to read/write frames to/from the other peer
michael@0: // (`stream.upstream`).
michael@0: 
michael@0: var Duplex = require('stream').Duplex;
michael@0: 
michael@0: exports.Stream = Stream;
michael@0: 
michael@0: // Public API
michael@0: // ----------
michael@0: 
michael@0: // * **new Stream(log)**: create a new Stream
michael@0: //
michael@0: // * **Event: 'headers' (headers)**: signals incoming headers
michael@0: //
michael@0: // * **Event: 'promise' (stream, headers)**: signals an incoming push promise
michael@0: //
michael@0: // * **Event: 'priority' (priority)**: signals a priority change. `priority` is a number between 0
michael@0: //     (highest priority) and 2^31-1 (lowest priority). Default value is 2^30.
michael@0: //
michael@0: // * **Event: 'error' (type)**: signals an error
michael@0: //
michael@0: // * **headers(headers)**: send headers
michael@0: //
michael@0: // * **promise(headers): Stream**: promise a stream
michael@0: //
michael@0: // * **priority(priority)**: set the priority of the stream. Priority can be changed by the peer
michael@0: //   too, but once it is set locally, it can not be changed remotely.
michael@0: //
michael@0: // * **reset(error)**: reset the stream with an error code
michael@0: //
michael@0: // * **upstream**: a [Flow](flow.js) that is used by the parent connection to write/read frames
michael@0: //   that are to be sent/arrived to/from the peer and are related to this stream.
michael@0: //
michael@0: // Headers are always in the [regular node.js header format][1].
michael@0: // [1]: http://nodejs.org/api/http.html#http_message_headers
michael@0: 
michael@0: // Constructor
michael@0: // -----------
michael@0: 
michael@0: // The main aspects of managing the stream are:
michael@0: function Stream(log) {
michael@0:   Duplex.call(this);
michael@0: 
michael@0:   // * logging
michael@0:   this._log = log.child({ component: 'stream', s: this });
michael@0: 
michael@0:   // * receiving and sending stream management commands
michael@0:   this._initializeManagement();
michael@0: 
michael@0:   // * sending and receiving frames to/from the upstream connection
michael@0:   this._initializeDataFlow();
michael@0: 
michael@0:   // * maintaining the state of the stream (idle, open, closed, etc.) and error detection
michael@0:   this._initializeState();
michael@0: }
michael@0: 
michael@0: Stream.prototype = Object.create(Duplex.prototype, { constructor: { value: Stream } });
michael@0: 
michael@0: // Managing the stream
michael@0: // -------------------
michael@0: 
michael@0: // the default stream priority is 2^30
michael@0: var DEFAULT_PRIORITY = Math.pow(2, 30);
michael@0: var MAX_PRIORITY = Math.pow(2, 31) - 1;
michael@0: 
michael@0: // PUSH_PROMISE and HEADERS are forwarded to the user through events.
michael@0: Stream.prototype._initializeManagement = function _initializeManagement() {
michael@0:   this._resetSent = false;
michael@0:   this._priority = DEFAULT_PRIORITY;
michael@0:   this._letPeerPrioritize = true;
michael@0: };
michael@0: 
michael@0: Stream.prototype.promise = function promise(headers) {
michael@0:   var stream = new Stream(this._log);
michael@0:   stream._priority = Math.min(this._priority + 1, MAX_PRIORITY);
michael@0:   this._pushUpstream({
michael@0:     type: 'PUSH_PROMISE',
michael@0:     flags: {},
michael@0:     stream: this.id,
michael@0:     promised_stream: stream,
michael@0:     headers: headers
michael@0:   });
michael@0:   return stream;
michael@0: };
michael@0: 
michael@0: Stream.prototype._onPromise = function _onPromise(frame) {
michael@0:   this.emit('promise', frame.promised_stream, frame.headers);
michael@0: };
michael@0: 
michael@0: Stream.prototype.headers = function headers(headers) {
michael@0:   this._pushUpstream({
michael@0:     type: 'HEADERS',
michael@0:     flags: {},
michael@0:     stream: this.id,
michael@0:     headers: headers
michael@0:   });
michael@0: };
michael@0: 
michael@0: Stream.prototype._onHeaders = function _onHeaders(frame) {
michael@0:   if (frame.priority !== undefined) {
michael@0:     this.priority(frame.priority, true);
michael@0:   }
michael@0:   this.emit('headers', frame.headers);
michael@0: };
michael@0: 
michael@0: Stream.prototype.priority = function priority(priority, peer) {
michael@0:   if ((peer && this._letPeerPrioritize) || !peer) {
michael@0:     if (!peer) {
michael@0:       this._letPeerPrioritize = false;
michael@0: 
michael@0:       var lastFrame = this.upstream.getLastQueuedFrame();
michael@0:       if (lastFrame && ((lastFrame.type === 'HEADERS') || (lastFrame.type === 'PRIORITY'))) {
michael@0:         lastFrame.priority = priority;
michael@0:       } else {
michael@0:         this._pushUpstream({
michael@0:           type: 'PRIORITY',
michael@0:           flags: {},
michael@0:           stream: this.id,
michael@0:           priority: priority
michael@0:         });
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     this._log.debug({ priority: priority }, 'Changing priority');
michael@0:     this.emit('priority', priority);
michael@0:     this._priority = priority;
michael@0:   }
michael@0: };
michael@0: 
michael@0: Stream.prototype._onPriority = function _onPriority(frame) {
michael@0:   this.priority(frame.priority, true);
michael@0: };
michael@0: 
michael@0: // Resetting the stream. Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame for
michael@0: // any stream.
michael@0: Stream.prototype.reset = function reset(error) {
michael@0:   if (!this._resetSent) {
michael@0:     this._resetSent = true;
michael@0:     this._pushUpstream({
michael@0:       type: 'RST_STREAM',
michael@0:       flags: {},
michael@0:       stream: this.id,
michael@0:       error: error
michael@0:     });
michael@0:   }
michael@0: };
michael@0: 
michael@0: // Data flow
michael@0: // ---------
michael@0: 
michael@0: // The incoming and the generated outgoing frames are received/transmitted on the `this.upstream`
michael@0: // [Flow](flow.html). The [Connection](connection.html) object instantiating the stream will read
michael@0: // and write frames to/from it. The stream itself is a regular [Duplex stream][1], and is used by
michael@0: // the user to write or read the body of the request.
michael@0: // [1]: http://nodejs.org/api/stream.html#stream_class_stream_duplex
michael@0: 
michael@0: //     upstream side                  stream                  user side
michael@0: //
michael@0: //                    +------------------------------------+
michael@0: //                    |                                    |
michael@0: //                    +------------------+                 |
michael@0: //                    |     upstream     |                 |
michael@0: //                    |                  |                 |
michael@0: //                    +--+               |              +--|
michael@0: //            read()  |  |  _send()      |    _write()  |  |  write(buf)
michael@0: //     <--------------|B |<--------------|--------------| B|<------------
michael@0: //                    |  |               |              |  |
michael@0: //            frames  +--+               |              +--|  buffers
michael@0: //                    |  |               |              |  |
michael@0: //     -------------->|B |---------------|------------->| B|------------>
michael@0: //      write(frame)  |  |  _receive()   |     _read()  |  |  read()
michael@0: //                    +--+               |              +--|
michael@0: //                    |                  |                 |
michael@0: //                    |                  |                 |
michael@0: //                    +------------------+                 |
michael@0: //                    |                                    |
michael@0: //                    +------------------------------------+
michael@0: //
michael@0: //     B: input or output buffer
michael@0: 
michael@0: var Flow = require('./flow').Flow;
michael@0: 
michael@0: Stream.prototype._initializeDataFlow = function _initializeDataFlow() {
michael@0:   this.id = undefined;
michael@0: 
michael@0:   this._ended = false;
michael@0: 
michael@0:   this.upstream = new Flow();
michael@0:   this.upstream._log = this._log;
michael@0:   this.upstream._send = this._send.bind(this);
michael@0:   this.upstream._receive = this._receive.bind(this);
michael@0:   this.upstream.write = this._writeUpstream.bind(this);
michael@0:   this.upstream.on('error', this.emit.bind(this, 'error'));
michael@0: 
michael@0:   this.on('finish', this._finishing);
michael@0: };
michael@0: 
michael@0: Stream.prototype._pushUpstream = function _pushUpstream(frame) {
michael@0:   this.upstream.push(frame);
michael@0:   this._transition(true, frame);
michael@0: };
michael@0: 
michael@0: // Overriding the upstream's `write` allows us to act immediately instead of waiting for the input
michael@0: // queue to empty. This is important in case of control frames.
michael@0: Stream.prototype._writeUpstream = function _writeUpstream(frame) {
michael@0:   this._log.debug({ frame: frame }, 'Receiving frame');
michael@0: 
michael@0:   var moreNeeded = Flow.prototype.write.call(this.upstream, frame);
michael@0: 
michael@0:   // * Transition to a new state if that's the effect of receiving the frame
michael@0:   this._transition(false, frame);
michael@0: 
michael@0:   // * If it's a control frame. Call the appropriate handler method.
michael@0:   if (frame.type === 'HEADERS') {
michael@0:     this._onHeaders(frame);
michael@0:   } else if (frame.type === 'PUSH_PROMISE') {
michael@0:     this._onPromise(frame);
michael@0:   } else if (frame.type === 'PRIORITY') {
michael@0:     this._onPriority(frame);
michael@0:   }
michael@0: 
michael@0:   // * If it's an invalid stream level frame, emit error
michael@0:   else if ((frame.type !== 'DATA') &&
michael@0:            (frame.type !== 'WINDOW_UPDATE') &&
michael@0:            (frame.type !== 'RST_STREAM')) {
michael@0:     this._log.error({ frame: frame }, 'Invalid stream level frame');
michael@0:     this.emit('error', 'PROTOCOL_ERROR');
michael@0:   }
michael@0: 
michael@0:   return moreNeeded;
michael@0: };
michael@0: 
michael@0: // The `_receive` method (= `upstream._receive`) gets called when there's an incoming frame.
michael@0: Stream.prototype._receive = function _receive(frame, ready) {
michael@0:   // * If it's a DATA frame, then push the payload into the output buffer on the other side.
michael@0:   //   Call ready when the other side is ready to receive more.
michael@0:   if (!this._ended && (frame.type === 'DATA')) {
michael@0:     var moreNeeded = this.push(frame.data);
michael@0:     if (!moreNeeded) {
michael@0:       this._receiveMore = ready;
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   // * Any frame may signal the end of the stream with the END_STREAM flag
michael@0:   if (!this._ended && (frame.flags.END_STREAM || (frame.type === 'RST_STREAM'))) {
michael@0:     this.push(null);
michael@0:     this._ended = true;
michael@0:   }
michael@0: 
michael@0:   // * Postpone calling `ready` if `push()` returned a falsy value
michael@0:   if (this._receiveMore !== ready) {
michael@0:     ready();
michael@0:   }
michael@0: };
michael@0: 
michael@0: // The `_read` method is called when the user side is ready to receive more data. If there's a
michael@0: // pending write on the upstream, then call its pending ready callback to receive more frames.
michael@0: Stream.prototype._read = function _read() {
michael@0:   if (this._receiveMore) {
michael@0:     var receiveMore = this._receiveMore;
michael@0:     delete this._receiveMore;
michael@0:     receiveMore();
michael@0:   }
michael@0: };
michael@0: 
michael@0: // The `write` method gets called when there's a write request from the user.
michael@0: Stream.prototype._write = function _write(buffer, encoding, ready) {
michael@0:   // * Chunking is done by the upstream Flow.
michael@0:   var moreNeeded = this._pushUpstream({
michael@0:     type: 'DATA',
michael@0:     flags: {},
michael@0:     stream: this.id,
michael@0:     data: buffer
michael@0:   });
michael@0: 
michael@0:   // * Call ready when upstream is ready to receive more frames.
michael@0:   if (moreNeeded) {
michael@0:     ready();
michael@0:   } else {
michael@0:     this._sendMore = ready;
michael@0:   }
michael@0: };
michael@0: 
michael@0: // The `_send` (= `upstream._send`) method is called when upstream is ready to receive more frames.
michael@0: // If there's a pending write on the user side, then call its pending ready callback to receive more
michael@0: // writes.
michael@0: Stream.prototype._send = function _send() {
michael@0:   if (this._sendMore) {
michael@0:     var sendMore = this._sendMore;
michael@0:     delete this._sendMore;
michael@0:     sendMore();
michael@0:   }
michael@0: };
michael@0: 
michael@0: // When the stream is finishing (the user calls `end()` on it), then we have to set the `END_STREAM`
michael@0: // flag on the last frame. If there's no frame in the queue, or if it doesn't support this flag,
michael@0: // then we create a 0 length DATA frame. We could do this all the time, but putting the flag on an
michael@0: // existing frame is a nice optimization.
michael@0: var emptyBuffer = new Buffer(0);
michael@0: Stream.prototype._finishing = function _finishing() {
michael@0:   var endFrame = {
michael@0:     type: 'DATA',
michael@0:     flags: { END_STREAM: true },
michael@0:     stream: this.id,
michael@0:     data: emptyBuffer
michael@0:   };
michael@0:   var lastFrame = this.upstream.getLastQueuedFrame();
michael@0:   if (lastFrame && ((lastFrame.type === 'DATA') || (lastFrame.type === 'HEADERS'))) {
michael@0:     this._log.debug({ frame: lastFrame }, 'Marking last frame with END_STREAM flag.');
michael@0:     lastFrame.flags.END_STREAM = true;
michael@0:     this._transition(true, endFrame);
michael@0:   } else {
michael@0:     this._pushUpstream(endFrame);
michael@0:   }
michael@0: };
michael@0: 
michael@0: // [Stream States](http://tools.ietf.org/html/draft-ietf-httpbis-http2-10#section-5.1)
michael@0: // ----------------
michael@0: //
michael@0: //                           +--------+
michael@0: //                     PP    |        |    PP
michael@0: //                  ,--------|  idle  |--------.
michael@0: //                 /         |        |         \
michael@0: //                v          +--------+          v
michael@0: //         +----------+          |           +----------+
michael@0: //         |          |          | H         |          |
michael@0: //     ,---| reserved |          |           | reserved |---.
michael@0: //     |   | (local)  |          v           | (remote) |   |
michael@0: //     |   +----------+      +--------+      +----------+   |
michael@0: //     |      |          ES  |        |  ES          |      |
michael@0: //     |      | H    ,-------|  open  |-------.      | H    |
michael@0: //     |      |     /        |        |        \     |      |
michael@0: //     |      v    v         +--------+         v    v      |
michael@0: //     |   +----------+          |           +----------+   |
michael@0: //     |   |   half   |          |           |   half   |   |
michael@0: //     |   |  closed  |          | R         |  closed  |   |
michael@0: //     |   | (remote) |          |           | (local)  |   |
michael@0: //     |   +----------+          |           +----------+   |
michael@0: //     |        |                v                 |        |
michael@0: //     |        |  ES / R    +--------+  ES / R    |        |
michael@0: //     |        `----------->|        |<-----------'        |
michael@0: //     |  R                  | closed |                  R  |
michael@0: //     `-------------------->|        |<--------------------'
michael@0: //                           +--------+
michael@0: 
michael@0: // Streams begin in the IDLE state and transitions happen when there's an incoming or outgoing frame
michael@0: Stream.prototype._initializeState = function _initializeState() {
michael@0:   this.state = 'IDLE';
michael@0:   this._initiated = undefined;
michael@0:   this._closedByUs = undefined;
michael@0:   this._closedWithRst = undefined;
michael@0: };
michael@0: 
michael@0: // Only `_setState` should change `this.state` directly. It also logs the state change and notifies
michael@0: // interested parties using the 'state' event.
michael@0: Stream.prototype._setState = function transition(state) {
michael@0:   assert(this.state !== state);
michael@0:   this._log.debug({ from: this.state, to: state }, 'State transition');
michael@0:   this.state = state;
michael@0:   this.emit('state', state);
michael@0: };
michael@0: 
michael@0: // A state is 'active' if the stream in that state counts towards the concurrency limit. Streams
michael@0: // that are in the "open" state, or either of the "half closed" states count toward this limit.
michael@0: function activeState(state) {
michael@0:   return ((state === 'HALF_CLOSED_LOCAL') || (state === 'HALF_CLOSED_REMOTE') || (state === 'OPEN'));
michael@0: }
michael@0: 
michael@0: // `_transition` is called every time there's an incoming or outgoing frame. It manages state
michael@0: // transitions, and detects stream errors. A stream error is always caused by a frame that is not
michael@0: // allowed in the current state.
michael@0: Stream.prototype._transition = function transition(sending, frame) {
michael@0:   var receiving = !sending;
michael@0:   var error = undefined;
michael@0: 
michael@0:   var DATA = false, HEADERS = false, PRIORITY = false;
michael@0:   var RST_STREAM = false, PUSH_PROMISE = false, WINDOW_UPDATE = false;
michael@0:   switch(frame.type) {
michael@0:     case 'DATA'         : DATA          = true; break;
michael@0:     case 'HEADERS'      : HEADERS       = true; break;
michael@0:     case 'PRIORITY'     : PRIORITY      = true; break;
michael@0:     case 'RST_STREAM'   : RST_STREAM    = true; break;
michael@0:     case 'PUSH_PROMISE' : PUSH_PROMISE  = true; break;
michael@0:     case 'WINDOW_UPDATE': WINDOW_UPDATE = true; break;
michael@0:   }
michael@0: 
michael@0:   var previousState = this.state;
michael@0: 
michael@0:   switch (this.state) {
michael@0:     // All streams start in the **idle** state. In this state, no frames have been exchanged.
michael@0:     //
michael@0:     // * Sending or receiving a HEADERS frame causes the stream to become "open".
michael@0:     //
michael@0:     // When the HEADERS frame contains the END_STREAM flags, then two state transitions happen.
michael@0:     case 'IDLE':
michael@0:       if (HEADERS) {
michael@0:         this._setState('OPEN');
michael@0:         if (frame.flags.END_STREAM) {
michael@0:           this._setState(sending ? 'HALF_CLOSED_LOCAL' : 'HALF_CLOSED_REMOTE');
michael@0:         }
michael@0:         this._initiated = sending;
michael@0:       } else if (sending && RST_STREAM) {
michael@0:         this._setState('CLOSED');
michael@0:       } else {
michael@0:         error = 'PROTOCOL_ERROR';
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // A stream in the **reserved (local)** state is one that has been promised by sending a
michael@0:     // PUSH_PROMISE frame.
michael@0:     //
michael@0:     // * The endpoint can send a HEADERS frame. This causes the stream to open in a "half closed
michael@0:     //   (remote)" state.
michael@0:     // * Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This
michael@0:     //   releases the stream reservation.
michael@0:     // * An endpoint may receive PRIORITY frame in this state.
michael@0:     // * An endpoint MUST NOT send any other type of frame in this state.
michael@0:     case 'RESERVED_LOCAL':
michael@0:       if (sending && HEADERS) {
michael@0:         this._setState('HALF_CLOSED_REMOTE');
michael@0:       } else if (RST_STREAM) {
michael@0:         this._setState('CLOSED');
michael@0:       } else if (receiving && PRIORITY) {
michael@0:         /* No state change */
michael@0:       } else {
michael@0:         error = 'PROTOCOL_ERROR';
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // A stream in the **reserved (remote)** state has been reserved by a remote peer.
michael@0:     //
michael@0:     // * Either endpoint can send a RST_STREAM frame to cause the stream to become "closed". This
michael@0:     //   releases the stream reservation.
michael@0:     // * Receiving a HEADERS frame causes the stream to transition to "half closed (local)".
michael@0:     // * An endpoint MAY send PRIORITY frames in this state to reprioritize the stream.
michael@0:     // * Receiving any other type of frame MUST be treated as a stream error of type PROTOCOL_ERROR.
michael@0:     case 'RESERVED_REMOTE':
michael@0:       if (RST_STREAM) {
michael@0:         this._setState('CLOSED');
michael@0:       } else if (receiving && HEADERS) {
michael@0:         this._setState('HALF_CLOSED_LOCAL');
michael@0:       } else if (sending && PRIORITY) {
michael@0:         /* No state change */
michael@0:       } else {
michael@0:         error = 'PROTOCOL_ERROR';
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // The **open** state is where both peers can send frames. In this state, sending peers observe
michael@0:     // advertised stream level flow control limits.
michael@0:     //
michael@0:     // * From this state either endpoint can send a frame with a END_STREAM flag set, which causes
michael@0:     //   the stream to transition into one of the "half closed" states: an endpoint sending a
michael@0:     //   END_STREAM flag causes the stream state to become "half closed (local)"; an endpoint
michael@0:     //   receiving a END_STREAM flag causes the stream state to become "half closed (remote)".
michael@0:     // * Either endpoint can send a RST_STREAM frame from this state, causing it to transition
michael@0:     //   immediately to "closed".
michael@0:     case 'OPEN':
michael@0:       if (frame.flags.END_STREAM) {
michael@0:         this._setState(sending ? 'HALF_CLOSED_LOCAL' : 'HALF_CLOSED_REMOTE');
michael@0:       } else if (RST_STREAM) {
michael@0:         this._setState('CLOSED');
michael@0:       } else {
michael@0:         /* No state change */
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // A stream that is **half closed (local)** cannot be used for sending frames.
michael@0:     //
michael@0:     // * A stream transitions from this state to "closed" when a frame that contains a END_STREAM
michael@0:     //   flag is received, or when either peer sends a RST_STREAM frame.
michael@0:     // * An endpoint MAY send or receive PRIORITY frames in this state to reprioritize the stream.
michael@0:     // * WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the END_STREAM flag.
michael@0:     case 'HALF_CLOSED_LOCAL':
michael@0:       if (RST_STREAM || (receiving && frame.flags.END_STREAM)) {
michael@0:         this._setState('CLOSED');
michael@0:       } else if (receiving || (sending && (PRIORITY || WINDOW_UPDATE))) {
michael@0:         /* No state change */
michael@0:       } else {
michael@0:         error = 'PROTOCOL_ERROR';
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // A stream that is **half closed (remote)** is no longer being used by the peer to send frames.
michael@0:     // In this state, an endpoint is no longer obligated to maintain a receiver flow control window
michael@0:     // if it performs flow control.
michael@0:     //
michael@0:     // * If an endpoint receives additional frames for a stream that is in this state it MUST
michael@0:     //   respond with a stream error of type STREAM_CLOSED.
michael@0:     // * A stream can transition from this state to "closed" by sending a frame that contains a
michael@0:     //   END_STREAM flag, or when either peer sends a RST_STREAM frame.
michael@0:     // * An endpoint MAY send or receive PRIORITY frames in this state to reprioritize the stream.
michael@0:     // * A receiver MAY receive a WINDOW_UPDATE frame on a "half closed (remote)" stream.
michael@0:     case 'HALF_CLOSED_REMOTE':
michael@0:       if (RST_STREAM || (sending && frame.flags.END_STREAM)) {
michael@0:         this._setState('CLOSED');
michael@0:       } else if (sending || (receiving && (WINDOW_UPDATE || PRIORITY))) {
michael@0:         /* No state change */
michael@0:       } else {
michael@0:         error = 'PROTOCOL_ERROR';
michael@0:       }
michael@0:       break;
michael@0: 
michael@0:     // The **closed** state is the terminal state.
michael@0:     //
michael@0:     // * An endpoint MUST NOT send frames on a closed stream. An endpoint that receives a frame
michael@0:     //   after receiving a RST_STREAM or a frame containing a END_STREAM flag on that stream MUST
michael@0:     //   treat that as a stream error of type STREAM_CLOSED.
michael@0:     // * WINDOW_UPDATE, PRIORITY or RST_STREAM frames can be received in this state for a short
michael@0:     //   period after a frame containing an END_STREAM flag is sent.  Until the remote peer receives
michael@0:     //   and processes the frame bearing the END_STREAM flag, it might send either frame type.
michael@0:     //   Endpoints MUST ignore WINDOW_UPDATE frames received in this state, though endpoints MAY
michael@0:     //   choose to treat WINDOW_UPDATE frames that arrive a significant time after sending
michael@0:     //   END_STREAM as a connection error of type PROTOCOL_ERROR.
michael@0:     // * If this state is reached as a result of sending a RST_STREAM frame, the peer that receives
michael@0:     //   the RST_STREAM might have already sent - or enqueued for sending - frames on the stream
michael@0:     //   that cannot be withdrawn. An endpoint that sends a RST_STREAM frame MUST ignore frames that
michael@0:     //   it receives on closed streams after it has sent a RST_STREAM frame. An endpoint MAY choose
michael@0:     //   to limit the period over which it ignores frames and treat frames that arrive after this
michael@0:     //   time as being in error.
michael@0:     // * An endpoint might receive a PUSH_PROMISE frame after it sends RST_STREAM. PUSH_PROMISE
michael@0:     //   causes a stream to become "reserved". If promised streams are not desired, a RST_STREAM
michael@0:     //   can be used to close any of those streams.
michael@0:     case 'CLOSED':
michael@0:       if ((sending && RST_STREAM) ||
michael@0:           (receiving && this._closedByUs &&
michael@0:            (this._closedWithRst || WINDOW_UPDATE || PRIORITY || RST_STREAM))) {
michael@0:         /* No state change */
michael@0:       } else {
michael@0:         error = 'STREAM_CLOSED';
michael@0:       }
michael@0:       break;
michael@0:   }
michael@0: 
michael@0:   // Noting that the connection was closed by the other endpoint. It may be important in edge cases.
michael@0:   // For example, when the peer tries to cancel a promised stream, but we already sent every data
michael@0:   // on it, then the stream is in CLOSED state, yet we want to ignore the incoming RST_STREAM.
michael@0:   if ((this.state === 'CLOSED') && (previousState !== 'CLOSED')) {
michael@0:     this._closedByUs = sending;
michael@0:     this._closedWithRst = RST_STREAM;
michael@0:   }
michael@0: 
michael@0:   // Sending/receiving a PUSH_PROMISE
michael@0:   //
michael@0:   // * Sending a PUSH_PROMISE frame marks the associated stream for later use. The stream state
michael@0:   //   for the reserved stream transitions to "reserved (local)".
michael@0:   // * Receiving a PUSH_PROMISE frame marks the associated stream as reserved by the remote peer.
michael@0:   //   The state of the stream becomes "reserved (remote)".
michael@0:   if (PUSH_PROMISE && !error) {
michael@0:     /* This assertion must hold, because _transition is called immediately when a frame is written
michael@0:        to the stream. If it would be called when a frame gets out of the input queue, the state
michael@0:        of the reserved could have been changed by then. */
michael@0:     assert(frame.promised_stream.state === 'IDLE', frame.promised_stream.state);
michael@0:     frame.promised_stream._setState(sending ? 'RESERVED_LOCAL' : 'RESERVED_REMOTE');
michael@0:     frame.promised_stream._initiated = sending;
michael@0:   }
michael@0: 
michael@0:   // Signaling how sending/receiving this frame changes the active stream count (-1, 0 or +1)
michael@0:   if (this._initiated) {
michael@0:     var change = (activeState(this.state) - activeState(previousState));
michael@0:     if (sending) {
michael@0:       frame.count_change = change;
michael@0:     } else {
michael@0:       frame.count_change(change);
michael@0:     }
michael@0:   } else if (sending) {
michael@0:     frame.count_change = 0;
michael@0:   }
michael@0: 
michael@0:   // Common error handling.
michael@0:   if (error) {
michael@0:     var info = {
michael@0:       error: error,
michael@0:       frame: frame,
michael@0:       state: this.state,
michael@0:       closedByUs: this._closedByUs,
michael@0:       closedWithRst: this._closedWithRst
michael@0:     };
michael@0: 
michael@0:     // * When sending something invalid, throwing an exception, since it is probably a bug.
michael@0:     if (sending) {
michael@0:       this._log.error(info, 'Sending illegal frame.');
michael@0:       throw new Error('Sending illegal frame (' + frame.type + ') in ' + this.state + ' state.');
michael@0:     }
michael@0: 
michael@0:     // * When receiving something invalid, sending an RST_STREAM using the `reset` method.
michael@0:     //   This will automatically cause a transition to the CLOSED state.
michael@0:     else {
michael@0:       this._log.error(info, 'Received illegal frame.');
michael@0:       this.emit('error', error);
michael@0:     }
michael@0:   }
michael@0: };
michael@0: 
michael@0: // Bunyan serializers
michael@0: // ------------------
michael@0: 
michael@0: exports.serializers = {};
michael@0: 
michael@0: var nextId = 0;
michael@0: exports.serializers.s = function(stream) {
michael@0:   if (!('_id' in stream)) {
michael@0:     stream._id = nextId;
michael@0:     nextId += 1;
michael@0:   }
michael@0:   return stream._id;
michael@0: };