protoc extensions supported.

jprotoc/README.md

@@ -130,4 +130,45 @@ Using the Jdk8 Protoc generator
 3. Reference the java 8 client stubs like this:
     ```java
     MyServiceGrpc8.GreeterCompletableFutureStub stub = MyServiceGrpc8.newCompletableFutureStub(channel);
-    ```
+    ```
+
+Implementing Custom Protoc Options
+==================================
+1. Create a custom option as per https://developers.google.com/protocol-buffers/docs/reference/java-generated#extension.
+For example:
+
+    ```
+    syntax = "proto3";
+
+    package com.example.proto.options;
+
+    import "google/protobuf/descriptor.proto";
+
+    option java_multiple_files = true;
+    option java_outer_classname = "ServerOptionsProto";
+    option java_package = "com.example.proto.options";
+
+    extend google.protobuf.FileOptions {
+        ServerOptions server = 50621;
+    }
+
+    message ServerOptions {
+        // Java classname
+        string name = 1;
+    }
+    ```
+
+2. Run the Protoc generator on the Extension proto.
+
+3. Use `ProtocPlugin.generate(List<Generator> generators, List<GeneratedExtension> extensions)` so
+that the option gets registered:
+
+    ```
+    class Generator extends com.salesforce.jprotoc.Generator {
+      public static void main(String[] args) {
+        ProtocPlugin.generate([new Generator()], [com.example.proto.options.ServerOptionsProto.server]);
+      }
+
+      // ?
+    }
+    ```

jprotoc/src/main/java/com/salesforce/jprotoc/ProtocPlugin.java

@@ -9,13 +9,14 @@
 
 import com.google.common.base.Preconditions;
 import com.google.common.io.ByteStreams;
+import com.google.protobuf.ExtensionRegistry;
+import com.google.protobuf.GeneratedMessage.GeneratedExtension;
 import com.google.protobuf.compiler.PluginProtos;
-
-import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
+import javax.annotation.Nonnull;
 
 /**
  * ProtocPlugin is the main entry point for running one or more java-base protoc plugins. This class handles
@@ -40,13 +41,34 @@ public static void generate(@Nonnull Generator generator) {
      * @param generators The list of generators to run.
      */
     public static void generate(@Nonnull List<Generator> generators) {
+        generate(generators, Collections.emptyList());
+    }
+
+    /**
+     * Apply multiple generators to the parsed proto descriptor, aggregating their results.
+     * Also register the given extensions so they may be processed by the generator.
+     *
+     * @param generators The list of generators to run.
+     * @param extensions The list of extensions to register.
+     */
+    public static void generate(
+            @Nonnull List<Generator> generators, List<GeneratedExtension> extensions) {
         Preconditions.checkNotNull(generators, "generators");
         Preconditions.checkArgument(!generators.isEmpty(), "generators.isEmpty()");
+        Preconditions.checkNotNull(extensions, "extensions");
+
+        // As per https://developers.google.com/protocol-buffers/docs/reference/java-generated#extension,
+        // extensions must be registered in order to be processed.
+        ExtensionRegistry extensionRegistry = ExtensionRegistry.newInstance();
+        for (GeneratedExtension extension : extensions) {
+            extensionRegistry.add(extension);
+        }
 
         try {
             // Parse the input stream to extract the generator request
             byte[] generatorRequestBytes = ByteStreams.toByteArray(System.in);
-            PluginProtos.CodeGeneratorRequest request = PluginProtos.CodeGeneratorRequest.parseFrom(generatorRequestBytes);
+            PluginProtos.CodeGeneratorRequest request = PluginProtos.CodeGeneratorRequest.parseFrom(
+                    generatorRequestBytes, extensionRegistry);
 
             // Run each file generator, collecting the output
             List<PluginProtos.CodeGeneratorResponse.File> outputFiles = generators