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http2: only call into JS when necessary for session events
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For some JS events, it only makes sense to call into JS when there
are listeners for the event in question.

The overhead is noticeable if a lot of these events are emitted during
the lifetime of a session. To reduce this overhead, keep track of
whether any/how many JS listeners are present, and if there are none,
skip calls into JS altogether.

This is part of performance improvements to mitigate CVE-2019-9513.

Backport-PR-URL: #29124
PR-URL: #29122
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
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@addaleax @BethGriggs
addaleax authored and BethGriggs committed Aug 15, 2019
1 parent 00f6846 commit dd60d35
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Showing 4 changed files with 163 additions and 10 deletions.
119 changes: 112 additions & 7 deletions lib/internal/http2/core.js
View file
Expand Up @@ -108,6 +108,7 @@ const kInit = Symbol('init');
const kInfoHeaders = Symbol('sent-info-headers');
const kMaybeDestroy = Symbol('maybe-destroy');
const kLocalSettings = Symbol('local-settings');
const kNativeFields = Symbol('kNativeFields');
const kOptions = Symbol('options');
const kOwner = Symbol('owner');
const kOrigin = Symbol('origin');
Expand All @@ -130,7 +131,15 @@ const {
paddingBuffer,
PADDING_BUF_FRAME_LENGTH,
PADDING_BUF_MAX_PAYLOAD_LENGTH,
PADDING_BUF_RETURN_VALUE
PADDING_BUF_RETURN_VALUE,
kBitfield,
kSessionPriorityListenerCount,
kSessionFrameErrorListenerCount,
kSessionUint8FieldCount,
kSessionHasRemoteSettingsListeners,
kSessionRemoteSettingsIsUpToDate,
kSessionHasPingListeners,
kSessionHasAltsvcListeners,
} = binding;

const {
Expand Down Expand Up @@ -305,6 +314,76 @@ function submitRstStream(code) {
}
}

// Keep track of the number/presence of JS event listeners. Knowing that there
// are no listeners allows the C++ code to skip calling into JS for an event.
function sessionListenerAdded(name) {
switch (name) {
case 'ping':
this[kNativeFields][kBitfield] |= 1 << kSessionHasPingListeners;
break;
case 'altsvc':
this[kNativeFields][kBitfield] |= 1 << kSessionHasAltsvcListeners;
break;
case 'remoteSettings':
this[kNativeFields][kBitfield] |= 1 << kSessionHasRemoteSettingsListeners;
break;
case 'priority':
this[kNativeFields][kSessionPriorityListenerCount]++;
break;
case 'frameError':
this[kNativeFields][kSessionFrameErrorListenerCount]++;
break;
}
}

function sessionListenerRemoved(name) {
switch (name) {
case 'ping':
if (this.listenerCount(name) > 0) return;
this[kNativeFields][kBitfield] &= ~(1 << kSessionHasPingListeners);
break;
case 'altsvc':
if (this.listenerCount(name) > 0) return;
this[kNativeFields][kBitfield] &= ~(1 << kSessionHasAltsvcListeners);
break;
case 'remoteSettings':
if (this.listenerCount(name) > 0) return;
this[kNativeFields][kBitfield] &=
~(1 << kSessionHasRemoteSettingsListeners);
break;
case 'priority':
this[kNativeFields][kSessionPriorityListenerCount]--;
break;
case 'frameError':
this[kNativeFields][kSessionFrameErrorListenerCount]--;
break;
}
}

// Also keep track of listeners for the Http2Stream instances, as some events
// are emitted on those objects.
function streamListenerAdded(name) {
switch (name) {
case 'priority':
this[kSession][kNativeFields][kSessionPriorityListenerCount]++;
break;
case 'frameError':
this[kSession][kNativeFields][kSessionFrameErrorListenerCount]++;
break;
}
}

function streamListenerRemoved(name) {
switch (name) {
case 'priority':
this[kSession][kNativeFields][kSessionPriorityListenerCount]--;
break;
case 'frameError':
this[kSession][kNativeFields][kSessionFrameErrorListenerCount]--;
break;
}
}

function onPing(payload) {
const session = this[kOwner];
if (session.destroyed)
Expand Down Expand Up @@ -394,7 +473,6 @@ function onSettings() {
return;
session[kUpdateTimer]();
debugSessionObj(session, 'new settings received');
session[kRemoteSettings] = undefined;
session.emit('remoteSettings', session.remoteSettings);
}

Expand Down Expand Up @@ -845,6 +923,10 @@ function setupHandle(socket, type, options) {
handle.consume(socket._handle._externalStream);

this[kHandle] = handle;
if (this[kNativeFields])
handle.fields.set(this[kNativeFields]);
else
this[kNativeFields] = handle.fields;

if (socket.encrypted) {
this[kAlpnProtocol] = socket.alpnProtocol;
Expand Down Expand Up @@ -886,6 +968,7 @@ function finishSessionDestroy(session, error) {
session[kProxySocket] = undefined;
session[kSocket] = undefined;
session[kHandle] = undefined;
session[kNativeFields] = new Uint8Array(kSessionUint8FieldCount);
socket[kSession] = undefined;
socket[kServer] = undefined;

Expand Down Expand Up @@ -963,6 +1046,7 @@ class Http2Session extends EventEmitter {
this[kType] = type;
this[kProxySocket] = null;
this[kSocket] = socket;
this[kHandle] = undefined;

// Do not use nagle's algorithm
if (typeof socket.setNoDelay === 'function')
Expand All @@ -981,6 +1065,11 @@ class Http2Session extends EventEmitter {
setupFn();
}

if (!this[kNativeFields])
this[kNativeFields] = new Uint8Array(kSessionUint8FieldCount);
this.on('newListener', sessionListenerAdded);
this.on('removeListener', sessionListenerRemoved);

debugSession(type, 'created');
}

Expand Down Expand Up @@ -1136,13 +1225,18 @@ class Http2Session extends EventEmitter {

// The settings currently in effect for the remote peer.
get remoteSettings() {
const settings = this[kRemoteSettings];
if (settings !== undefined)
return settings;
if (this[kNativeFields][kBitfield] &
(1 << kSessionRemoteSettingsIsUpToDate)) {
const settings = this[kRemoteSettings];
if (settings !== undefined) {
return settings;
}
}

if (this.destroyed || this.connecting)
return {};

this[kNativeFields][kBitfield] |= (1 << kSessionRemoteSettingsIsUpToDate);
return this[kRemoteSettings] = getSettings(this[kHandle], true); // Remote
}

Expand Down Expand Up @@ -1330,6 +1424,12 @@ class ServerHttp2Session extends Http2Session {
constructor(options, socket, server) {
super(NGHTTP2_SESSION_SERVER, options, socket);
this[kServer] = server;
// This is a bit inaccurate because it does not reflect changes to
// number of listeners made after the session was created. This should
// not be an issue in practice. Additionally, the 'priority' event on
// server instances (or any other object) is fully undocumented.
this[kNativeFields][kSessionPriorityListenerCount] =
server.listenerCount('priority');
}

get server() {
Expand Down Expand Up @@ -1668,6 +1768,9 @@ class Http2Stream extends Duplex {
};

this.on('pause', streamOnPause);

this.on('newListener', streamListenerAdded);
this.on('removeListener', streamListenerRemoved);
}

[kUpdateTimer]() {
Expand Down Expand Up @@ -2620,7 +2723,7 @@ function sessionOnPriority(stream, parent, weight, exclusive) {
}

function sessionOnError(error) {
if (this[kServer])
if (this[kServer] !== undefined)
this[kServer].emit('sessionError', error, this);
}

Expand Down Expand Up @@ -2669,8 +2772,10 @@ function connectionListener(socket) {
const session = new ServerHttp2Session(options, socket, this);

session.on('stream', sessionOnStream);
session.on('priority', sessionOnPriority);
session.on('error', sessionOnError);
// Don't count our own internal listener.
session.on('priority', sessionOnPriority);
session[kNativeFields][kSessionPriorityListenerCount]--;

if (this.timeout)
session.setTimeout(this.timeout, sessionOnTimeout);
Expand Down
1 change: 1 addition & 0 deletions src/env.h
View file
Expand Up @@ -161,6 +161,7 @@ class ModuleWrap;
V(family_string, "family") \
V(fatal_exception_string, "_fatalException") \
V(fd_string, "fd") \
V(fields_string, "fields") \
V(file_string, "file") \
V(fingerprint_string, "fingerprint") \
V(flags_string, "flags") \
Expand Down
33 changes: 30 additions & 3 deletions src/node_http2.cc
View file
Expand Up @@ -20,6 +20,7 @@ using v8::ObjectTemplate;
using v8::String;
using v8::Uint32;
using v8::Uint32Array;
using v8::Uint8Array;
using v8::Undefined;

using node::performance::PerformanceEntry;
Expand Down Expand Up @@ -667,6 +668,15 @@ Http2Session::Http2Session(Environment* env,

outgoing_storage_.reserve(4096);
outgoing_buffers_.reserve(32);

{
// Make the js_fields_ property accessible to JS land.
Local<ArrayBuffer> ab =
ArrayBuffer::New(env->isolate(), js_fields_, kSessionUint8FieldCount);
Local<Uint8Array> uint8_arr =
Uint8Array::New(ab, 0, kSessionUint8FieldCount);
/*USE*/(wrap->Set(env->context(), env->fields_string(), uint8_arr));
}
}

void Http2Session::Unconsume() {
Expand Down Expand Up @@ -1090,7 +1100,8 @@ inline int Http2Session::OnFrameNotSent(nghttp2_session* handle,
// Do not report if the frame was not sent due to the session closing
if (error_code == NGHTTP2_ERR_SESSION_CLOSING ||
error_code == NGHTTP2_ERR_STREAM_CLOSED ||
error_code == NGHTTP2_ERR_STREAM_CLOSING) {
error_code == NGHTTP2_ERR_STREAM_CLOSING ||
session->js_fields_[kSessionFrameErrorListenerCount] == 0) {
return 0;
}

Expand Down Expand Up @@ -1346,7 +1357,8 @@ inline void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
// received. Notifies JS land about the priority change. Note that priorities
// are considered advisory only, so this has no real effect other than to
// simply let user code know that the priority has changed.
inline void Http2Session::HandlePriorityFrame(const nghttp2_frame* frame) {
void Http2Session::HandlePriorityFrame(const nghttp2_frame* frame) {
if (js_fields_[kSessionPriorityListenerCount] == 0) return;
Isolate* isolate = env()->isolate();
HandleScope scope(isolate);
Local<Context> context = env()->context();
Expand Down Expand Up @@ -1413,7 +1425,8 @@ inline void Http2Session::HandleGoawayFrame(const nghttp2_frame* frame) {
}

// Called by OnFrameReceived when a complete ALTSVC frame has been received.
inline void Http2Session::HandleAltSvcFrame(const nghttp2_frame* frame) {
void Http2Session::HandleAltSvcFrame(const nghttp2_frame* frame) {
if (!(js_fields_[kBitfield] & (1 << kSessionHasAltsvcListeners))) return;
Isolate* isolate = env()->isolate();
HandleScope scope(isolate);
Local<Context> context = env()->context();
Expand Down Expand Up @@ -1499,6 +1512,7 @@ inline void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
return;
}

if (!(js_fields_[kBitfield] & (1 << kSessionHasPingListeners))) return;
// Notify the session that a ping occurred
arg = Buffer::Copy(env(),
reinterpret_cast<const char*>(frame->ping.opaque_data),
Expand All @@ -1510,6 +1524,9 @@ inline void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
inline void Http2Session::HandleSettingsFrame(const nghttp2_frame* frame) {
bool ack = frame->hd.flags & NGHTTP2_FLAG_ACK;
if (!ack) {
js_fields_[kBitfield] &= ~(1 << kSessionRemoteSettingsIsUpToDate);
if (!(js_fields_[kBitfield] & (1 << kSessionHasRemoteSettingsListeners)))
return;
// This is not a SETTINGS acknowledgement, notify and return
MakeCallback(env()->onsettings_string(), 0, nullptr);
return;
Expand Down Expand Up @@ -3135,6 +3152,16 @@ void Initialize(Local<Object> target,
NODE_DEFINE_CONSTANT(target, PADDING_BUF_MAX_PAYLOAD_LENGTH);
NODE_DEFINE_CONSTANT(target, PADDING_BUF_RETURN_VALUE);

NODE_DEFINE_CONSTANT(target, kBitfield);
NODE_DEFINE_CONSTANT(target, kSessionPriorityListenerCount);
NODE_DEFINE_CONSTANT(target, kSessionFrameErrorListenerCount);
NODE_DEFINE_CONSTANT(target, kSessionUint8FieldCount);

NODE_DEFINE_CONSTANT(target, kSessionHasRemoteSettingsListeners);
NODE_DEFINE_CONSTANT(target, kSessionRemoteSettingsIsUpToDate);
NODE_DEFINE_CONSTANT(target, kSessionHasPingListeners);
NODE_DEFINE_CONSTANT(target, kSessionHasAltsvcListeners);

// Method to fetch the nghttp2 string description of an nghttp2 error code
env->SetMethod(target, "nghttp2ErrorString", HttpErrorString);

Expand Down
20 changes: 20 additions & 0 deletions src/node_http2.h
View file
Expand Up @@ -735,6 +735,23 @@ class Http2Stream::Provider::Stream : public Http2Stream::Provider {
void* user_data);
};

// Indices for js_fields_, which serves as a way to communicate data with JS
// land fast. In particular, we store information about the number/presence
// of certain event listeners in JS, and skip calls from C++ into JS if they
// are missing.
enum SessionUint8Fields {
kBitfield, // See below
kSessionPriorityListenerCount,
kSessionFrameErrorListenerCount,
kSessionUint8FieldCount
};

enum SessionBitfieldFlags {
kSessionHasRemoteSettingsListeners,
kSessionRemoteSettingsIsUpToDate,
kSessionHasPingListeners,
kSessionHasAltsvcListeners
};

class Http2Session : public AsyncWrap {
public:
Expand Down Expand Up @@ -1016,6 +1033,9 @@ class Http2Session : public AsyncWrap {
// The underlying nghttp2_session handle
nghttp2_session* session_;

// JS-accessible numeric fields, as indexed by SessionUint8Fields.
uint8_t js_fields_[kSessionUint8FieldCount] = {};

// The session type: client or server
nghttp2_session_type session_type_;

Expand Down

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