http2: Initial proposal for addtl http/2 settings

Currently, node.js http/2 is limited in sending SETTINGs,
that are currently implemented by nghttp2.
However, nghttp2 has the ability to send arbitary SETTINGs,
that are not known beforehand.
This patch adds this feature including a fall back mechanism,
if a SETTING is implemented in a later nghttp2 or node version.

Fixes: nodejs#1337

lib/internal/http2/core.js

@@ -946,6 +946,9 @@ function pingCallback(cb) {
 // All settings are optional and may be left undefined
 const validateSettings = hideStackFrames((settings) => {
   if (settings === undefined) return;
+
+  assertIsObject('customSettings', settings.customSettings)
+
   assertWithinRange('headerTableSize',
                     settings.headerTableSize,
                     0, kMaxInt);

lib/internal/http2/util.js

@@ -192,6 +192,9 @@ const IDX_SETTINGS_MAX_HEADER_LIST_SIZE = 5;
 const IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL = 6;
 const IDX_SETTINGS_FLAGS = 7;
 
+// Maximum number of allowed additional settings
+const MAX_ADDITIONAL_SETTINGS = 10;
+
 const IDX_SESSION_STATE_EFFECTIVE_LOCAL_WINDOW_SIZE = 0;
 const IDX_SESSION_STATE_EFFECTIVE_RECV_DATA_LENGTH = 1;
 const IDX_SESSION_STATE_NEXT_STREAM_ID = 2;
@@ -350,6 +353,65 @@ function getSettings(session, remote) {
 
 function updateSettingsBuffer(settings) {
   let flags = 0;
+
+  if (typeof settings.customSettings === 'object') {
+    let customSettings = settings.customSettings;
+    let numCustomSettings = 0;
+    for (const setting in customSettings) {
+      const val = customSettings[setting];
+      if (typeof setting === 'number' && typeof val === 'number') {
+        let set = false
+        if (setting < IDX_SETTINGS_FLAGS) {
+          set = true
+          switch (setting) {
+            case IDX_SETTINGS_HEADER_TABLE_SIZE:
+              flags |= (1 << IDX_SETTINGS_HEADER_TABLE_SIZE);
+              settingsBuffer[IDX_SETTINGS_HEADER_TABLE_SIZE] =
+                val;
+              break;
+            case IDX_SETTINGS_ENABLE_PUSH:
+              flags |= (1 << IDX_SETTINGS_ENABLE_PUSH);
+              settingsBuffer[IDX_SETTINGS_ENABLE_PUSH] = val;
+              break;
+            case IDX_SETTINGS_INITIAL_WINDOW_SIZE:
+              flags |= (1 << IDX_SETTINGS_INITIAL_WINDOW_SIZE);
+              settingsBuffer[IDX_SETTINGS_INITIAL_WINDOW_SIZE] =
+                val;
+              break;
+            case IDX_SETTINGS_MAX_FRAME_SIZE:
+              flags |= (1 << IDX_SETTINGS_MAX_FRAME_SIZE);
+              settingsBuffer[IDX_SETTINGS_MAX_FRAME_SIZE] =
+                val;
+              break;
+            case IDX_SETTINGS_MAX_CONCURRENT_STREAMS:
+              flags |= (1 << IDX_SETTINGS_MAX_CONCURRENT_STREAMS);
+              settingsBuffer[IDX_SETTINGS_MAX_CONCURRENT_STREAMS] = val;
+              break;
+            case IDX_SETTINGS_MAX_HEADER_LIST_SIZE:
+              flags |= (1 << IDX_SETTINGS_MAX_HEADER_LIST_SIZE);
+              settingsBuffer[IDX_SETTINGS_MAX_HEADER_LIST_SIZE] =
+                val;
+              break;
+            case IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL:
+              flags |= (1 << IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL);
+              settingsBuffer[IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL] = val;
+              break;
+            default:
+              set = false;
+              break;
+          }
+        }
+        if (!set) { // not supported
+          if (numCustomSettings === MAX_ADDITIONAL_SETTINGS) throw new Error('Number of custom settings exceeds MAX_ADDITIONAL_SETTINGS');
+          settingsBuffer[IDX_SETTINGS_FLAGS + 1 + 2 * numCustomSettings] = setting;
+          settingsBuffer[IDX_SETTINGS_FLAGS + 1 + 2 * numCustomSettings + 1] = val;
+          numCustomSettings++;
+        }
+      }
+      settingsBuffer[IDX_SETTINGS_FLAGS + 1] = numCustomSettings;
+    }
+  }
+
   if (typeof settings.headerTableSize === 'number') {
     flags |= (1 << IDX_SETTINGS_HEADER_TABLE_SIZE);
     settingsBuffer[IDX_SETTINGS_HEADER_TABLE_SIZE] =

src/node_http2.cc

@@ -228,6 +228,16 @@ size_t Http2Settings::Init(
   HTTP2_SETTINGS(V)
 #undef V
 
+  uint32_t numAddSettings = buffer[IDX_SETTINGS_COUNT + 1];
+  if (numAddSettings > 0) {
+    uint32_t offset = IDX_SETTINGS_COUNT + 1 + 1;
+    for (uint32_t i = 0; i < numAddSettings; i++) {
+      uint32_t key = buffer[offset + i * 2 + 0];
+      uint32_t val = buffer[offset + i * 2 + 1];
+      entries[count++] = nghttp2_settings_entry{(int32_t)key, val};
+    }
+  }
+
   return count;
 }
 #undef GRABSETTING
@@ -262,7 +272,7 @@ Local<Value> Http2Settings::Pack() {
 }
 
 Local<Value> Http2Settings::Pack(Http2State* state) {
-  nghttp2_settings_entry entries[IDX_SETTINGS_COUNT];
+  nghttp2_settings_entry entries[IDX_SETTINGS_COUNT + MAX_ADDITIONAL_SETTINGS];
   size_t count = Init(state, entries);
   return Pack(state->env(), count, entries);
 }
@@ -298,6 +308,8 @@ void Http2Settings::Update(Http2Session* session, get_setting fn) {
       fn(session->session(), NGHTTP2_SETTINGS_ ## name);
   HTTP2_SETTINGS(V)
 #undef V
+  buffer[IDX_SETTINGS_COUNT + 1] =
+      0;  // no additional settings are coming, clear them
 }
 
 // Initializes the shared TypedArray with the default settings values.
@@ -314,6 +326,7 @@ void Http2Settings::RefreshDefaults(Http2State* http2_state) {
 #undef V
 
   buffer[IDX_SETTINGS_COUNT] = flags;
+  buffer[IDX_SETTINGS_COUNT + 1] = 0; // no additional settings
 }
 
 

src/node_http2.h

@@ -1035,7 +1035,7 @@ class Http2Settings : public AsyncWrap {
   v8::Global<v8::Function> callback_;
   uint64_t startTime_;
   size_t count_ = 0;
-  nghttp2_settings_entry entries_[IDX_SETTINGS_COUNT];
+  nghttp2_settings_entry entries_[IDX_SETTINGS_COUNT + MAX_ADDITIONAL_SETTINGS];
 };
 
 class Origins {

src/node_http2_state.h

@@ -21,6 +21,9 @@ namespace http2 {
     IDX_SETTINGS_COUNT
   };
 
+ // number of max additional settings, thus settings not implemente by nghttp2
+  const size_t MAX_ADDITIONAL_SETTINGS = 10;
+
   enum Http2SessionStateIndex {
     IDX_SESSION_STATE_EFFECTIVE_LOCAL_WINDOW_SIZE,
     IDX_SESSION_STATE_EFFECTIVE_RECV_DATA_LENGTH,
@@ -110,7 +113,8 @@ class Http2State : public BaseObject {
                        root_buffer),
         settings_buffer(realm->isolate(),
                         offsetof(http2_state_internal, settings_buffer),
-                        IDX_SETTINGS_COUNT + 1,
+                        IDX_SETTINGS_COUNT + 1 + 1 +
+                             2 * MAX_ADDITIONAL_SETTINGS,
                         root_buffer) {}
 
   AliasedUint8Array root_buffer;
@@ -135,7 +139,8 @@ class Http2State : public BaseObject {
     double stream_stats_buffer[IDX_STREAM_STATS_COUNT];
     double session_stats_buffer[IDX_SESSION_STATS_COUNT];
     uint32_t options_buffer[IDX_OPTIONS_FLAGS + 1];
-    uint32_t settings_buffer[IDX_SETTINGS_COUNT + 1];
+    uint32_t settings_buffer[IDX_SETTINGS_COUNT + 1 + 1 +
+                             2 * MAX_ADDITIONAL_SETTINGS];
   };
 };