Collect FaaS info during handshake (#1156)

JAVA-4761

Author: katcharov

driver-core/src/main/com/mongodb/MongoDriverInformation.java

@@ -167,7 +167,7 @@ private List<String> prependToList(final List<String> stringList, final String v
         }
 
         private Builder() {
-            List<String> immutableEmptyList = Collections.unmodifiableList(Collections.emptyList());
+            List<String> immutableEmptyList = Collections.emptyList();
             driverInformation = new MongoDriverInformation(immutableEmptyList, immutableEmptyList, immutableEmptyList);
         }
 

driver-core/src/main/com/mongodb/internal/connection/ClientMetadataHelper.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2008-present MongoDB, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.mongodb.client;
+
+import com.mongodb.lang.Nullable;
+
+import java.lang.reflect.Field;
+import java.util.Map;
+
+import static java.lang.System.getenv;
+
+@FunctionalInterface
+public interface WithWrapper {
+
+    void run(Runnable r);
+
+    static WithWrapper withWrapper() {
+        return r -> r.run();
+    }
+
+    default WithWrapper withEnvironmentVariable(final String name, @Nullable final String value) {
+        return runnable -> {
+            Map<String, String> innerMap = getEnvInnerMap();
+            String original = innerMap.get(name);
+            if (value == null) {
+                innerMap.remove(name);
+            } else {
+                innerMap.put(name, value);
+            }
+            try {
+                this.run(runnable);
+            } finally {
+                if (original == null) {
+                    innerMap.remove(name);
+                } else {
+                    innerMap.put(name, original);
+                }
+            }
+        };
+    }
+
+    default WithWrapper withSystemProperty(final String name, final String value) {
+        return runnable -> {
+            String original = System.getProperty(name);
+            System.setProperty(name, value);
+            try {
+                this.run(runnable);
+            } finally {
+                System.setProperty(name, original);
+            }
+        };
+    }
+
+    static Map<String, String> getEnvInnerMap() {
+        try {
+            Map<String, String> env = getenv();
+            Field field = env.getClass().getDeclaredField("m");
+            field.setAccessible(true);
+            @SuppressWarnings("unchecked")
+            Map<String, String> result = (Map<String, String>) field.get(env);
+            return result;
+        } catch (IllegalAccessException | NoSuchFieldException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}