Let users opt-in for app initialization failures without native libs (#…

…2006)

Motivation:

#1979 fails app initialization if native transport libs can not be
loaded. This is too aggressive. Instead, keep warning users and let
them opt-in for the enforced behavior.

Modifications:

- Fail initialization only if users explicitly opt-it for this using
`-Dio.servicetalk.transport.netty.requireNativeLibs=true`;
- Improve exception and log messages;

Result:

Users can enforce requirement for native libs if they need.

servicetalk-transport-netty-internal/src/main/java/io/servicetalk/transport/netty/internal/NativeTransportUtils.java

@@ -40,6 +40,8 @@
 final class NativeTransportUtils {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(NativeTransportUtils.class);
+    private static final String REQUIRE_NATIVE_LIBS_NAME = "io.servicetalk.transport.netty.requireNativeLibs";
+    private static final boolean REQUIRE_NATIVE_LIBS = getBoolean(REQUIRE_NATIVE_LIBS_NAME);
     private static final String NETTY_NO_NATIVE_NAME = "io.netty.transport.noNative";
     private static final boolean NETTY_NO_NATIVE = getBoolean(NETTY_NO_NATIVE_NAME);
 
@@ -63,16 +65,30 @@ private NativeTransportUtils() {
     }
 
     private static void reactOnUnavailability(final String transport, final String os, final Throwable cause) {
+        if (REQUIRE_NATIVE_LIBS) {
+            throw new IllegalStateException("Can not load required \"io.netty:netty-transport-native-" + transport +
+                    ":$nettyVersion:" + os + '-' + normalizedArch() + "\", it may impact responsiveness, " +
+                    "reliability, and performance of the application. Fix the deployment to make sure the native " +
+                    "libraries are packaged and can be loaded. Otherwise, unset \"-D" + REQUIRE_NATIVE_LIBS_NAME +
+                    "=true\" system property to let the application start without native libraries and set \"-D" +
+                    NETTY_NO_NATIVE_NAME + "=true\" if running without native libs is intentional. " +
+                    "For more information, see https://netty.io/wiki/native-transports.html", cause);
+        }
         if (NETTY_NO_NATIVE) {
             LOGGER.info("io.netty:netty-transport-native-{} is explicitly disabled with \"-D{}=true\". Note that it " +
-                    "may impact responsiveness, reliability, and performance of the application. For more information" +
-                    ", see https://netty.io/wiki/native-transports.html", transport, NETTY_NO_NATIVE_NAME);
-            return;
+                    "may impact responsiveness, reliability, and performance of the application. ServiceTalk " +
+                    "recommends always running with native libraries. Consider using \"-D{}=true\" to fail " +
+                    "application initialization without native libs. For more information, see " +
+                    "https://netty.io/wiki/native-transports.html",
+                    transport, NETTY_NO_NATIVE_NAME, REQUIRE_NATIVE_LIBS_NAME);
+        } else {
+            LOGGER.warn("Can not load \"io.netty:netty-transport-native-{}:$nettyVersion:{}-{}\", it may impact " +
+                    "responsiveness, reliability, and performance of the application. ServiceTalk recommends always " +
+                    "running with native libraries. Consider using \"-D{}=true\" to fail application initialization " +
+                    "without native libraries. If this is intentional, let netty know about it using \"-D{}=true\". " +
+                    "For more information, see https://netty.io/wiki/native-transports.html",
+                    transport, os, normalizedArch(), REQUIRE_NATIVE_LIBS_NAME, NETTY_NO_NATIVE_NAME);
         }
-        throw new IllegalStateException("Can not load \"io.netty:netty-transport-native-" + transport +
-                ":$nettyVersion:" + os + '-' + normalizedArch() + "\", it may impact responsiveness, reliability, " +
-                "and performance of the application. Explicitly set \"-D" + NETTY_NO_NATIVE_NAME + "=true\" if this " +
-                "is intentional. For more information, see https://netty.io/wiki/native-transports.html", cause);
     }
 
     /**