http2: tune control flow defaults

The current defaults are unnecessarily conservative which makes http2 control flow over
high latency connections (such as public internet) unbearably slow.

Author: ronag

doc/api/http2.md

@@ -3544,10 +3544,10 @@ properties.
   permitted on the `Http2Session` instances. **Default:** `true`.
 * `initialWindowSize` {number} Specifies the _sender's_ initial window size in
   bytes for stream-level flow control. The minimum allowed value is 0. The
-  maximum allowed value is 2<sup>32</sup>-1. **Default:** `65535`.
+  maximum allowed value is 2<sup>32</sup>-1. **Default:** `262144`.
 * `maxFrameSize` {number} Specifies the size in bytes of the largest frame
   payload. The minimum allowed value is 16,384. The maximum allowed value is
-  2<sup>24</sup>-1. **Default:** `16384`.
+  2<sup>24</sup>-1. **Default:** `32768`.
 * `maxConcurrentStreams` {number} Specifies the maximum number of concurrent
   streams permitted on an `Http2Session`. There is no default value which
   implies, at least theoretically, 2<sup>32</sup>-1 streams may be open

lib/internal/http2/core.js

@@ -3302,14 +3302,18 @@ function connectionListener(socket) {
 
   socket[kServer] = this;
 
+  // NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE default is 64KB, but we want to allow more data to be
+  // buffered without applying backpressure.
+  session.setLocalWindowSize(512 * 1024);
+
   this.emit('session', session);
 }
 
 function initializeOptions(options) {
   assertIsObject(options, 'options');
   options = { ...options };
   assertIsObject(options.settings, 'options.settings');
-  options.settings = { ...options.settings };
+  options.settings = { ...getDefaultSettings(), ...options.settings };
 
   assertIsArray(options.remoteCustomSettings, 'options.remoteCustomSettings');
   if (options.remoteCustomSettings) {
@@ -3531,6 +3535,8 @@ function connect(authority, options, listener) {
 
   assertIsObject(options, 'options');
   options = { ...options };
+  assertIsObject(options.settings, 'options.settings');
+  options.settings = { ...getDefaultSettings(), ...options.settings };
 
   assertIsArray(options.remoteCustomSettings, 'options.remoteCustomSettings');
   if (options.remoteCustomSettings) {
@@ -3576,6 +3582,10 @@ function connect(authority, options, listener) {
 
   const session = new ClientHttp2Session(options, socket);
 
+  // NGHTTP2_INITIAL_CONNECTION_WINDOW_SIZE default is 64KB, but we want to allow more data to be
+  // buffered without applying backpressure.
+  session.setLocalWindowSize(512 * 1024);
+
   session[kAuthority] = `${options.servername || host}:${port}`;
   session[kProtocol] = protocol;
 

lib/internal/http2/util.js

@@ -364,6 +364,13 @@ function getDefaultSettings() {
       settingsBuffer[IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL] === 1;
   }
 
+  // NGHTTP2_INITIAL_WINDOW_SIZE default is 64KB, but we want to allow more data to be
+  // buffered without applying backpressure.
+  holder.initialWindowSize = MathMax(holder.initialWindowSize, 256 * 1024);
+
+  // Default is 16KB.
+  holder.maxFrameSize = MathMax(32 * 1024, holder.maxFrameSize);
+
   if (settingsBuffer[IDX_SETTINGS_FLAGS + 1]) holder.customSettings = addCustomSettingsToObj();
 
   return holder;

test/parallel/test-http2-binding.js

@@ -17,8 +17,8 @@ const settings = http2.getDefaultSettings();
 assert.strictEqual(settings.headerTableSize, 4096);
 assert.strictEqual(settings.enablePush, true);
 assert.strictEqual(settings.maxConcurrentStreams, 4294967295);
-assert.strictEqual(settings.initialWindowSize, 65535);
-assert.strictEqual(settings.maxFrameSize, 16384);
+assert.strictEqual(settings.initialWindowSize, 256 * 1024);
+assert.strictEqual(settings.maxFrameSize, 32 * 1024);
 
 assert.strictEqual(binding.nghttp2ErrorString(-517),
                    'GOAWAY has already been sent');