Start using official Bazel worker helper.

This helper provides additional features like GC and worker multiplexing - though they are not yet enabled in this CL.

CL is temporarily forking the files until bazel_worker_java could be added as a dep for repo:
bazelbuild/bazel-worker-api#10

PiperOrigin-RevId: 733024990

transpiler/java/com/google/j2cl/common/bazel/BUILD

@@ -15,6 +15,7 @@ java_library(
     deps = [
         ":worker_protocol_java_proto",
         "//third_party:args4j",
+        "//third_party:error_prone_annotations",
         "//third_party:guava",
         "//transpiler/java/com/google/j2cl/common",
     ],

transpiler/java/com/google/j2cl/common/bazel/BazelWorker.java

@@ -21,13 +21,10 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.io.Files;
-import com.google.devtools.build.lib.worker.WorkerProtocol.WorkRequest;
-import com.google.devtools.build.lib.worker.WorkerProtocol.WorkResponse;
 import com.google.j2cl.common.Problems;
-import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
-import java.io.PrintStream;
+import java.io.PrintWriter;
 import java.util.List;
 import java.util.function.Supplier;
 import org.kohsuke.args4j.CmdLineException;
@@ -49,26 +46,22 @@ public abstract class BazelWorker {
    * Process the request described by the arguments. Note that you must output errors and warnings
    * via {@link Problems} to avoid interrupting the worker protocol which occurs over stdout.
    */
-  private int processRequest(List<String> args) {
+  private int processRequest(List<String> args, PrintWriter pw) {
     CmdLineParser parser = new CmdLineParser(this);
 
     try {
       parser.parseArgument(args);
     } catch (CmdLineException e) {
       problems.error("%s", e.getMessage());
-      return problems.reportAndGetExitCode(System.err);
+      return problems.reportAndGetExitCode(pw);
     }
 
     try {
       run();
     } catch (Problems.Exit e) {
       // Program aborted due to errors recorded in problems.
-    } catch (Throwable e) {
-      // Program crash.
-      e.printStackTrace(System.err);
-      return 1;
     }
-    return problems.reportAndGetExitCode(System.err);
+    return problems.reportAndGetExitCode(pw);
   }
 
   public static final void start(String[] args, Supplier<BazelWorker> workerSupplier)
@@ -83,35 +76,23 @@ public static final void start(String[] args, Supplier<BazelWorker> workerSuppli
   @SuppressWarnings("SystemExitOutsideMain")
   private static void runStandaloneWorker(Supplier<BazelWorker> workerSupplier, List<String> args) {
     // This is a single invocation of builder that exits after it processed the request.
-    int exitCode = workerSupplier.get().processRequest(args);
+    int exitCode =
+        workerSupplier
+            .get()
+            .processRequest(args, new PrintWriter(System.err, /* autoFlush= */ true));
     System.exit(exitCode);
   }
 
   private static void runPersistentWorker(Supplier<BazelWorker> workerSupplier) throws IOException {
-    PrintStream realStdOut = System.out;
-
-    // Ensure we capture stdout/sterr for potential debug/error messages.
-    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
-    PrintStream ps = new PrintStream(buffer, true);
-    System.setOut(ps);
-    System.setErr(ps);
-
-    while (true) {
-      WorkRequest request = WorkRequest.parseDelimitedFrom(System.in);
-
-      if (request == null) {
-        break;
-      }
-
-      int exitCode = workerSupplier.get().processRequest(request.getArgumentsList());
-      WorkResponse.newBuilder()
-          .setOutput(buffer.toString())
-          .setExitCode(exitCode)
-          .build()
-          .writeDelimitedTo(realStdOut);
-      realStdOut.flush();
-      buffer.reset();
-    }
+    WorkRequestHandler workerHandler =
+        new WorkRequestHandler.WorkRequestHandlerBuilder(
+                new WorkRequestHandler.WorkRequestCallback(
+                    (request, pw) ->
+                        workerSupplier.get().processRequest(request.getArgumentsList(), pw)),
+                System.err,
+                new ProtoWorkerMessageProcessor(System.in, System.out))
+            .build();
+    workerHandler.processRequests();
   }
 
   /**

transpiler/java/com/google/j2cl/common/bazel/ProtoWorkerMessageProcessor.java

@@ -0,0 +1,55 @@
+// Copyright 2020 The Bazel Authors. All rights reserved.
+//
+// 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.google.j2cl.common.bazel;
+
+import com.google.devtools.build.lib.worker.WorkerProtocol.WorkRequest;
+import com.google.devtools.build.lib.worker.WorkerProtocol.WorkResponse;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+// TODO(goktug): Remove this class after https://github.com/bazelbuild/bazel-worker-api/issues/10
+
+/** Implementation of the Worker Protocol using Proto to communicate with Bazel. */
+final class ProtoWorkerMessageProcessor implements WorkRequestHandler.WorkerMessageProcessor {
+
+  /** This worker's stdin. */
+  private final InputStream stdin;
+
+  /** This worker's stdout. Only {@link WorkRequest}s should be written here. */
+  private final OutputStream stdout;
+
+  /** Constructs a {@link WorkRequestHandler} that reads and writes Protocol Buffers. */
+  public ProtoWorkerMessageProcessor(InputStream stdin, OutputStream stdout) {
+    this.stdin = stdin;
+    this.stdout = stdout;
+  }
+
+  @Override
+  public WorkRequest readWorkRequest() throws IOException {
+    return WorkRequest.parseDelimitedFrom(stdin);
+  }
+
+  @Override
+  public void writeWorkResponse(WorkResponse workResponse) throws IOException {
+    try {
+      workResponse.writeDelimitedTo(stdout);
+    } finally {
+      stdout.flush();
+    }
+  }
+
+  @Override
+  public void close() {}
+}