lib: http2 compatibility error with connection header

Ignoring the connection header and disable the
`ERR_HTTP2_INVALID_CONNECTION_HEADERS` error.

Added a warning log on the compatibility.

Fixes: nodejs#23748

lib/internal/http2/util.js

@@ -246,43 +246,43 @@ function getDefaultSettings() {
   const flags = settingsBuffer[IDX_SETTINGS_FLAGS];
 
   if ((flags & (1 << IDX_SETTINGS_HEADER_TABLE_SIZE)) ===
-      (1 << IDX_SETTINGS_HEADER_TABLE_SIZE)) {
+    (1 << IDX_SETTINGS_HEADER_TABLE_SIZE)) {
     holder.headerTableSize =
       settingsBuffer[IDX_SETTINGS_HEADER_TABLE_SIZE];
   }
 
   if ((flags & (1 << IDX_SETTINGS_ENABLE_PUSH)) ===
-      (1 << IDX_SETTINGS_ENABLE_PUSH)) {
+    (1 << IDX_SETTINGS_ENABLE_PUSH)) {
     holder.enablePush =
       settingsBuffer[IDX_SETTINGS_ENABLE_PUSH] === 1;
   }
 
   if ((flags & (1 << IDX_SETTINGS_INITIAL_WINDOW_SIZE)) ===
-      (1 << IDX_SETTINGS_INITIAL_WINDOW_SIZE)) {
+    (1 << IDX_SETTINGS_INITIAL_WINDOW_SIZE)) {
     holder.initialWindowSize =
       settingsBuffer[IDX_SETTINGS_INITIAL_WINDOW_SIZE];
   }
 
   if ((flags & (1 << IDX_SETTINGS_MAX_FRAME_SIZE)) ===
-      (1 << IDX_SETTINGS_MAX_FRAME_SIZE)) {
+    (1 << IDX_SETTINGS_MAX_FRAME_SIZE)) {
     holder.maxFrameSize =
       settingsBuffer[IDX_SETTINGS_MAX_FRAME_SIZE];
   }
 
   if ((flags & (1 << IDX_SETTINGS_MAX_CONCURRENT_STREAMS)) ===
-      (1 << IDX_SETTINGS_MAX_CONCURRENT_STREAMS)) {
+    (1 << IDX_SETTINGS_MAX_CONCURRENT_STREAMS)) {
     holder.maxConcurrentStreams =
       settingsBuffer[IDX_SETTINGS_MAX_CONCURRENT_STREAMS];
   }
 
   if ((flags & (1 << IDX_SETTINGS_MAX_HEADER_LIST_SIZE)) ===
-      (1 << IDX_SETTINGS_MAX_HEADER_LIST_SIZE)) {
+    (1 << IDX_SETTINGS_MAX_HEADER_LIST_SIZE)) {
     holder.maxHeaderListSize =
       settingsBuffer[IDX_SETTINGS_MAX_HEADER_LIST_SIZE];
   }
 
   if ((flags & (1 << IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL)) ===
-      (1 << IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL)) {
+    (1 << IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL)) {
     holder.enableConnectProtocol =
       settingsBuffer[IDX_SETTINGS_ENABLE_CONNECT_PROTOCOL];
   }
@@ -387,7 +387,6 @@ function getStreamState(stream) {
 
 function isIllegalConnectionSpecificHeader(name, value) {
   switch (name) {
-    case HTTP2_HEADER_CONNECTION:
     case HTTP2_HEADER_UPGRADE:
     case HTTP2_HEADER_HOST:
     case HTTP2_HEADER_HTTP2_SETTINGS:
@@ -425,7 +424,7 @@ function assertValidPseudoHeaderTrailer(key) {
 }
 
 function mapToHeaders(map,
-                      assertValuePseudoHeader = assertValidPseudoHeader) {
+  assertValuePseudoHeader = assertValidPseudoHeader) {
   let ret = '';
   let count = 0;
   const keys = Object.keys(map);
@@ -470,15 +469,22 @@ function mapToHeaders(map,
         throw err;
       ret = `${key}\0${value}\0${ret}`;
       count++;
-      continue;
-    }
-    if (isIllegalConnectionSpecificHeader(key, value)) {
-      throw new ERR_HTTP2_INVALID_CONNECTION_HEADERS(key);
-    }
-    if (isArray) {
-      for (var k = 0; k < value.length; k++) {
-        const val = String(value[k]);
-        ret += `${key}\0${val}\0`;
+    } else {
+      if (isIllegalConnectionSpecificHeader(key, value)) {
+        return new ERR_HTTP2_INVALID_CONNECTION_HEADERS(key);
+      }
+      if (isArray) {
+        for (var k = 0; k < value.length; k++) {
+          const val = String(value[k]);
+          ret += `${key}\0${val}\0`;
+        }
+        count += value.length;
+      }
+      else if (key === HTTP2_HEADER_CONNECTION) {
+        headerMessageWarn(key);
+      } else {
+        ret += `${key}\0${value}\0`;
+        count++;
       }
       count += value.length;
       continue;
@@ -501,9 +507,9 @@ class NghttpError extends Error {
 
 function assertIsObject(value, name, types = 'Object') {
   if (value !== undefined &&
-      (value === null ||
-       typeof value !== 'object' ||
-       Array.isArray(value))) {
+    (value === null ||
+      typeof value !== 'object' ||
+      Array.isArray(value))) {
     const err = new ERR_INVALID_ARG_TYPE(name, types, value);
     Error.captureStackTrace(err, assertIsObject);
     throw err;
@@ -512,7 +518,7 @@ function assertIsObject(value, name, types = 'Object') {
 
 function assertWithinRange(name, value, min = 0, max = Infinity) {
   if (value !== undefined &&
-      (typeof value !== 'number' || value < min || value > max)) {
+    (typeof value !== 'number' || value < min || value > max)) {
     const err = new ERR_HTTP2_INVALID_SETTING_VALUE.RangeError(name, value);
     err.min = min;
     err.max = max;
@@ -581,6 +587,14 @@ function sessionName(type) {
   }
 }
 
+function headerMessageWarn(key) {
+  process.emitWarning(
+    `The provided header "${key}" is not valid, ` +
+    'and is supported only for compatibility.',
+    'UnsupportedWarning'
+  );
+}
+
 module.exports = {
   assertIsObject,
   assertValidPseudoHeaderResponse,