runtime/java/v17/lib/src/Launcher.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

 import java.io.*;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import com.google.gson.*;
 import java.security.Permission;
 import java.lang.reflect.InvocationTargetException;

 class Launcher {

     private static String mainClassName = "Main";
     private static String mainMethodName = "main";
     private static Class mainClass = null;
     private static Method mainMethod = null;

     @SuppressWarnings({ "unchecked", "rawtypes" })
     private static void augmentEnv(Map<String, String> newEnv) {
         try {
             for (Class cl : Collections.class.getDeclaredClasses()) {
                 if ("java.util.Collections$UnmodifiableMap".equals(cl.getName())) {
                     Field field = cl.getDeclaredField("m");
                     field.setAccessible(true);
                     Object obj = field.get(System.getenv());
                     Map<String, String> map = (Map<String, String>) obj;
                     map.putAll(newEnv);
                 }
             }
         } catch (Exception e) {}
     }

     private static void initMain(String[] args) throws Exception {
         if(args.length > 0)
             mainClassName = args[0];
         int pos = mainClassName.indexOf("#");
         if(pos != -1) {
             if(pos + 1 != mainClassName.length())
                 mainMethodName = args[0].substring(pos+1);
             mainClassName = args[0].substring(0,pos);
         }

         mainClass = Class.forName(mainClassName);
         Method[] methods = mainClass.getDeclaredMethods();
         Boolean existMain = false;
         for(Method method: methods) {
             if (method.getName().equals(mainMethodName)) {
                 existMain = true;
                 break;
             }
         }
         if (!existMain) {
             throw new NoSuchMethodException(mainMethodName);
         }
     }

     private static Object invokeMain(JsonElement arg, Map<String, String> env) throws Exception {
         augmentEnv(env);
         return mainMethod.invoke(null, arg);
     }


     /*
     Use of SecurityManager has been Deprrecated from JDK17. Alternatives to prevent System.exit() are not yet available.

     private static SecurityManager defaultSecurityManager = null;
     private static void installSecurityManager() {
         defaultSecurityManager = System.getSecurityManager();
         System.setSecurityManager(new SecurityManager() {
             @Override
             public void checkPermission(Permission p) {
                 // Not throwing means accepting anything.
             }

             @Override
             public void checkPermission(Permission p, Object ctx) {
                 // Not throwing means accepting anything.
             }

             @Override
             public void checkExit(int status) {
                 super.checkExit(status);
                 throw new SecurityException("System.exit(" + status + ") called from within an action.");
             }
         });
     }

     private static void uninstallSecurityManager() {
         if(defaultSecurityManager != null) {
             System.setSecurityManager(defaultSecurityManager);
         }
     }
     */

     public static void main(String[] args) throws Exception {

         initMain(args);

         // exit after main class loading if "exit" specified
         // used to check healthy launch after init
         if(args.length >1 && args[1] == "-exit")
             System.exit(0);

         // install a security manager to prevent exit
         //installSecurityManager();

         BufferedReader in = new BufferedReader(
                 new InputStreamReader(System.in, StandardCharsets.UTF_8));
         PrintWriter out = new PrintWriter(
                 new OutputStreamWriter(
                         new FileOutputStream("/dev/fd/3"), StandardCharsets.UTF_8));
         JsonParser json = new JsonParser();
         JsonObject emptyForJsonObject = json.parse("{}").getAsJsonObject();
         JsonArray emptyForJsonArray = json.parse("[]").getAsJsonArray();
         Boolean isJsonObjectParam = true;
         String input = "";
         while (true) {
             try {
                 input = in.readLine();
                 if (input == null)
                     break;
                 JsonElement element = json.parse(input);
                 JsonObject payloadForJsonObject = emptyForJsonObject.deepCopy();
                 JsonArray payloadForJsonArray = emptyForJsonArray.deepCopy();
                 Map<String, String> env = new HashMap<>();
                 if (element.isJsonObject()) {
                     // collect payload and environment
                     for (Map.Entry<String, JsonElement> entry : element.getAsJsonObject().entrySet()) {
                         if (entry.getKey().equals("value")) {
                             if (entry.getValue().isJsonObject())
                                 payloadForJsonObject = entry.getValue().getAsJsonObject();
                             else {
                                 payloadForJsonArray = entry.getValue().getAsJsonArray();
                                 isJsonObjectParam = false;
                             }
                         } else {
                             env.put(String.format("__OW_%s", entry.getKey().toUpperCase()),
                                     entry.getValue().getAsString());
                         }
                     }
                     augmentEnv(env);
                 }

                 Method m = null;
                 if (isJsonObjectParam) {
                     m = mainClass.getMethod(mainMethodName, new Class[] { JsonObject.class });
                 } else {
                     m = mainClass.getMethod(mainMethodName, new Class[] { JsonArray.class });
                 }
                 m.setAccessible(true);
                 int modifiers = m.getModifiers();
                 if ((m.getReturnType() != JsonObject.class && m.getReturnType() != JsonArray.class) || !Modifier.isStatic(modifiers) || !Modifier.isPublic(modifiers)) {
                     throw new NoSuchMethodException(mainMethodName);
                 }
                 mainMethod = m;

                 Object response;
                 if (isJsonObjectParam) {
                     response = invokeMain(payloadForJsonObject, env);
                 } else {
                     response = invokeMain(payloadForJsonArray, env);
                 }
                 out.println(response.toString());
             } catch(NullPointerException npe) {
                 System.out.println("the action returned null");
                 npe.printStackTrace(System.err);
                 JsonObject error = new JsonObject();
                 error.addProperty("error", "the action returned null");
                 out.println(error.toString());
                 out.flush();
             } catch(InvocationTargetException ite) {
                 Throwable ex = ite;
                 if(ite.getCause() != null)
                     ex = ite.getCause();
                 ex.printStackTrace(System.err);
                 JsonObject error = new JsonObject();
                 error.addProperty("error", ex.getMessage());
                 out.println(error.toString());
                 out.flush();
             } catch (Exception ex) {
                 ex.printStackTrace(System.err);
                 JsonObject error = new JsonObject();
                 error.addProperty("error", ex.getMessage());
                 out.println(error.toString());
                 out.flush();
             }
             out.flush();
             System.out.flush();
             System.err.flush();
         }
         //uninstallSecurityManager();
     }
 }