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var assert = require('assert');
// The Stream class
// ================
// 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].
// 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;
this.sentEndStream = false;
}
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.trailers = function trailers(trailers) {
this.sentEndStream = true;
this._pushUpstream({
type: 'HEADERS',
flags: {'END_STREAM': true},
stream: this.id,
headers: trailers
});
};
Stream.prototype._onHeaders = function _onHeaders(frame) {
if (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.
// 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') {
if (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 if (frame.type === 'PRIORITY') {
this._onPriority(frame);
} else if (frame.type === 'ALTSVC') {
// TODO
} else if (frame.type === 'ORIGIN') {
// TODO
}
// * If it's an invalid stream level frame, emit error
else if ((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);
if (!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
if (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() {
if (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.
if (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 = Buffer.alloc(0);
Stream.prototype._finishing = function _finishing() {
var endFrame = {
type: 'DATA',
flags: { END_STREAM: true },
stream: this.id,
data: emptyBuffer
};
if (this.sentEndStream) {
this._log.debug('Already sent END_STREAM, not sending again.');
return;
}
this.sentEndStream = true;
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);
}
};
// ----------------
//
// +--------+
// 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, ORIGIN = 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 'ORIGIN' : ORIGIN = 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 if (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 if (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 if (PRIORITY || ORIGIN) {
/* 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 (ORIGIN || 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 (ORIGIN || 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) ||
(receiving && WINDOW_UPDATE) ||
(receiving && this._closedByUs &&
(this._closedWithRst || RST_STREAM || ALTSVC || ORIGIN))) {
/* 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;
};