grpc/src/compiler/java_generator.cc

/*
 * Copyright 2016 Google Inc. 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.
 */

#include "src/compiler/java_generator.h"

#include <algorithm>
#include <iostream>
#include <iterator>
#include <map>
#include <utility>
#include <vector>

#include "flatbuffers/util.h"
#define to_string flatbuffers::NumToString

// Stringify helpers used solely to cast GRPC_VERSION
#ifndef STR
#  define STR(s) #  s
#endif

#ifndef XSTR
#  define XSTR(s) STR(s)
#endif

typedef grpc_generator::Printer Printer;
typedef std::map<grpc::string, grpc::string> VARS;
typedef grpc_generator::Service ServiceDescriptor;
typedef grpc_generator::CommentHolder
    DescriptorType;  // base class of all 'descriptors'
typedef grpc_generator::Method MethodDescriptor;

namespace grpc_java_generator {
typedef std::string string;
namespace {
// Generates imports for the service
static void GenerateImports(grpc_generator::File *file,
                     grpc_generator::Printer *printer, VARS &vars) {
  vars["filename"] = file->filename();
  printer->Print(vars,
                 "//Generated by flatc compiler (version $flatc_version$)\n");
  printer->Print("//If you make any local changes, they will be lost\n");
  printer->Print(vars, "//source: $filename$.fbs\n\n");
  printer->Print(vars, "package $Package$;\n\n");
  vars["Package"] = vars["Package"] + ".";
  if (!file->additional_headers().empty()) {
    printer->Print(file->additional_headers().c_str());
    printer->Print("\n\n");
  }
}

// Adjust a method name prefix identifier to follow the JavaBean spec:
//   - decapitalize the first letter
//   - remove embedded underscores & capitalize the following letter
static string MixedLower(const string &word) {
  string w;
  w += static_cast<string::value_type>(tolower(word[0]));
  bool after_underscore = false;
  for (size_t i = 1; i < word.length(); ++i) {
    if (word[i] == '_') {
      after_underscore = true;
    } else {
      w += after_underscore ? static_cast<string::value_type>(toupper(word[i]))
                            : word[i];
      after_underscore = false;
    }
  }
  return w;
}

// Converts to the identifier to the ALL_UPPER_CASE format.
//   - An underscore is inserted where a lower case letter is followed by an
//     upper case letter.
//   - All letters are converted to upper case
static string ToAllUpperCase(const string &word) {
  string w;
  for (size_t i = 0; i < word.length(); ++i) {
    w += static_cast<string::value_type>(toupper(word[i]));
    if ((i < word.length() - 1) && islower(word[i]) && isupper(word[i + 1])) {
      w += '_';
    }
  }
  return w;
}

static inline string LowerMethodName(const MethodDescriptor *method) {
  return MixedLower(method->name());
}

static inline string MethodPropertiesFieldName(const MethodDescriptor *method) {
  return "METHOD_" + ToAllUpperCase(method->name());
}

static inline string MethodPropertiesGetterName(
    const MethodDescriptor *method) {
  return MixedLower("get_" + method->name() + "_method");
}

static inline string MethodIdFieldName(const MethodDescriptor *method) {
  return "METHODID_" + ToAllUpperCase(method->name());
}

static inline string JavaClassName(VARS &vars, const string &name) {
  // string name = google::protobuf::compiler::java::ClassName(desc);
  return vars["Package"] + name;
}

static inline string ServiceClassName(const string &service_name) {
  return service_name + "Grpc";
}

// TODO(nmittler): Remove once protobuf includes javadoc methods in
// distribution.
template<typename ITR>
static void GrpcSplitStringToIteratorUsing(const string &full,
                                           const char *delim, ITR &result) {
  // Optimize the common case where delim is a single character.
  if (delim[0] != '\0' && delim[1] == '\0') {
    char c = delim[0];
    const char *p = full.data();
    const char *end = p + full.size();
    while (p != end) {
      if (*p == c) {
        ++p;
      } else {
        const char *start = p;
        while (++p != end && *p != c)
          ;
        *result++ = string(start, p - start);
      }
    }
    return;
  }

  string::size_type begin_index, end_index;
  begin_index = full.find_first_not_of(delim);
  while (begin_index != string::npos) {
    end_index = full.find_first_of(delim, begin_index);
    if (end_index == string::npos) {
      *result++ = full.substr(begin_index);
      return;
    }
    *result++ = full.substr(begin_index, (end_index - begin_index));
    begin_index = full.find_first_not_of(delim, end_index);
  }
}

static void GrpcSplitStringUsing(const string &full, const char *delim,
                                 std::vector<string> *result) {
  std::back_insert_iterator<std::vector<string>> it(*result);
  GrpcSplitStringToIteratorUsing(full, delim, it);
}

static std::vector<string> GrpcSplit(const string &full, const char *delim) {
  std::vector<string> result;
  GrpcSplitStringUsing(full, delim, &result);
  return result;
}

// TODO(nmittler): Remove once protobuf includes javadoc methods in
// distribution.
static string GrpcEscapeJavadoc(const string &input) {
  string result;
  result.reserve(input.size() * 2);

  char prev = '*';

  for (string::size_type i = 0; i < input.size(); i++) {
    char c = input[i];
    switch (c) {
      case '*':
        // Avoid "/*".
        if (prev == '/') {
          result.append("&#42;");
        } else {
          result.push_back(c);
        }
        break;
      case '/':
        // Avoid "*/".
        if (prev == '*') {
          result.append("&#47;");
        } else {
          result.push_back(c);
        }
        break;
      case '@':
        // '@' starts javadoc tags including the @deprecated tag, which will
        // cause a compile-time error if inserted before a declaration that
        // does not have a corresponding @Deprecated annotation.
        result.append("&#64;");
        break;
      case '<':
        // Avoid interpretation as HTML.
        result.append("&lt;");
        break;
      case '>':
        // Avoid interpretation as HTML.
        result.append("&gt;");
        break;
      case '&':
        // Avoid interpretation as HTML.
        result.append("&amp;");
        break;
      case '\\':
        // Java interprets Unicode escape sequences anywhere!
        result.append("&#92;");
        break;
      default: result.push_back(c); break;
    }

    prev = c;
  }

  return result;
}

static std::vector<string> GrpcGetDocLines(const string &comments) {
  if (!comments.empty()) {
    // TODO(kenton):  Ideally we should parse the comment text as Markdown and
    //   write it back as HTML, but this requires a Markdown parser.  For now
    //   we just use <pre> to get fixed-width text formatting.

    // If the comment itself contains block comment start or end markers,
    // HTML-escape them so that they don't accidentally close the doc comment.
    string escapedComments = GrpcEscapeJavadoc(comments);

    std::vector<string> lines = GrpcSplit(escapedComments, "\n");
    while (!lines.empty() && lines.back().empty()) { lines.pop_back(); }
    return lines;
  }
  return std::vector<string>();
}

static std::vector<string> GrpcGetDocLinesForDescriptor(
    const DescriptorType *descriptor) {
  return descriptor->GetAllComments();
  // return GrpcGetDocLines(descriptor->GetLeadingComments("///"));
}

static void GrpcWriteDocCommentBody(Printer *printer, VARS &vars,
                                    const std::vector<string> &lines,
                                    bool surroundWithPreTag) {
  if (!lines.empty()) {
    if (surroundWithPreTag) { printer->Print(" * <pre>\n"); }

    for (size_t i = 0; i < lines.size(); i++) {
      // Most lines should start with a space.  Watch out for lines that start
      // with a /, since putting that right after the leading asterisk will
      // close the comment.
      vars["line"] = lines[i];
      if (!lines[i].empty() && lines[i][0] == '/') {
        printer->Print(vars, " * $line$\n");
      } else {
        printer->Print(vars, " *$line$\n");
      }
    }

    if (surroundWithPreTag) { printer->Print(" * </pre>\n"); }
  }
}

static void GrpcWriteDocComment(Printer *printer, VARS &vars,
                                const string &comments) {
  printer->Print("/**\n");
  std::vector<string> lines = GrpcGetDocLines(comments);
  GrpcWriteDocCommentBody(printer, vars, lines, false);
  printer->Print(" */\n");
}

static void GrpcWriteServiceDocComment(Printer *printer, VARS &vars,
                                       const ServiceDescriptor *service) {
  printer->Print("/**\n");
  std::vector<string> lines = GrpcGetDocLinesForDescriptor(service);
  GrpcWriteDocCommentBody(printer, vars, lines, true);
  printer->Print(" */\n");
}

static void GrpcWriteMethodDocComment(Printer *printer, VARS &vars,
                               const MethodDescriptor *method) {
  printer->Print("/**\n");
  std::vector<string> lines = GrpcGetDocLinesForDescriptor(method);
  GrpcWriteDocCommentBody(printer, vars, lines, true);
  printer->Print(" */\n");
}

// outputs static singleton extractor for type stored in "extr_type" and
// "extr_type_name" vars
static void PrintTypeExtractor(Printer *p, VARS &vars) {
  p->Print(vars,
           "private static volatile FlatbuffersUtils.FBExtactor<$extr_type$> "
           "extractorOf$extr_type_name$;\n"
           "private static FlatbuffersUtils.FBExtactor<$extr_type$> "
           "getExtractorOf$extr_type_name$() {\n"
           "    if (extractorOf$extr_type_name$ != null) return "
           "extractorOf$extr_type_name$;\n"
           "    synchronized ($service_class_name$.class) {\n"
           "        if (extractorOf$extr_type_name$ != null) return "
           "extractorOf$extr_type_name$;\n"
           "        extractorOf$extr_type_name$ = new "
           "FlatbuffersUtils.FBExtactor<$extr_type$>() {\n"
           "            public $extr_type$ extract (ByteBuffer buffer) {\n"
           "                return "
           "$extr_type$.getRootAs$extr_type_name$(buffer);\n"
           "            }\n"
           "        };\n"
           "        return extractorOf$extr_type_name$;\n"
           "    }\n"
           "}\n\n");
}
static void PrintMethodFields(Printer *p, VARS &vars,
                              const ServiceDescriptor *service) {
  p->Print("// Static method descriptors that strictly reflect the proto.\n");
  vars["service_name"] = service->name();

  // set of names of rpc input- and output- types that were already encountered.
  // this is needed to avoid duplicating type extractor since it's possible that
  // the same type is used as an input or output type of more than a single RPC
  // method
  std::set<std::string> encounteredTypes;

  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    vars["arg_in_id"] = to_string(2L * i);  // trying to make msvc 10 happy
    vars["arg_out_id"] = to_string(2L * i + 1);
    vars["method_name"] = method->name();
    vars["input_type_name"] = method->get_input_type_name();
    vars["output_type_name"] = method->get_output_type_name();
    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
    vars["method_field_name"] = MethodPropertiesFieldName(method.get());
    vars["method_new_field_name"] = MethodPropertiesGetterName(method.get());
    vars["method_method_name"] = MethodPropertiesGetterName(method.get());
    bool client_streaming =
        method->ClientStreaming() || method->BidiStreaming();
    bool server_streaming =
        method->ServerStreaming() || method->BidiStreaming();
    if (client_streaming) {
      if (server_streaming) {
        vars["method_type"] = "BIDI_STREAMING";
      } else {
        vars["method_type"] = "CLIENT_STREAMING";
      }
    } else {
      if (server_streaming) {
        vars["method_type"] = "SERVER_STREAMING";
      } else {
        vars["method_type"] = "UNARY";
      }
    }

    p->Print(
        vars,
        "@$ExperimentalApi$(\"https://github.com/grpc/grpc-java/issues/"
        "1901\")\n"
        "@$Deprecated$ // Use {@link #$method_method_name$()} instead. \n"
        "public static final $MethodDescriptor$<$input_type$,\n"
        "    $output_type$> $method_field_name$ = $method_method_name$();\n"
        "\n"
        "private static volatile $MethodDescriptor$<$input_type$,\n"
        "    $output_type$> $method_new_field_name$;\n"
        "\n");

    if (encounteredTypes.insert(vars["input_type_name"]).second) {
      vars["extr_type"] = vars["input_type"];
      vars["extr_type_name"] = vars["input_type_name"];
      PrintTypeExtractor(p, vars);
    }

    if (encounteredTypes.insert(vars["output_type_name"]).second) {
      vars["extr_type"] = vars["output_type"];
      vars["extr_type_name"] = vars["output_type_name"];
      PrintTypeExtractor(p, vars);
    }

    p->Print(
        vars,
        "@$ExperimentalApi$(\"https://github.com/grpc/grpc-java/issues/"
        "1901\")\n"
        "public static $MethodDescriptor$<$input_type$,\n"
        "    $output_type$> $method_method_name$() {\n"
        "  $MethodDescriptor$<$input_type$, $output_type$> "
        "$method_new_field_name$;\n"
        "  if (($method_new_field_name$ = "
        "$service_class_name$.$method_new_field_name$) == null) {\n"
        "    synchronized ($service_class_name$.class) {\n"
        "      if (($method_new_field_name$ = "
        "$service_class_name$.$method_new_field_name$) == null) {\n"
        "        $service_class_name$.$method_new_field_name$ = "
        "$method_new_field_name$ = \n"
        "            $MethodDescriptor$.<$input_type$, "
        "$output_type$>newBuilder()\n"
        "            .setType($MethodType$.$method_type$)\n"
        "            .setFullMethodName(generateFullMethodName(\n"
        "                \"$Package$$service_name$\", \"$method_name$\"))\n"
        "            .setSampledToLocalTracing(true)\n"
        "            .setRequestMarshaller(FlatbuffersUtils.marshaller(\n"
        "                $input_type$.class, "
        "getExtractorOf$input_type_name$()))\n"
        "            .setResponseMarshaller(FlatbuffersUtils.marshaller(\n"
        "                $output_type$.class, "
        "getExtractorOf$output_type_name$()))\n");

    //            vars["proto_method_descriptor_supplier"] = service->name() +
    //            "MethodDescriptorSupplier";
    p->Print(vars, "                .setSchemaDescriptor(null)\n");
    //"                .setSchemaDescriptor(new
    //$proto_method_descriptor_supplier$(\"$method_name$\"))\n");

    p->Print(vars, "                .build();\n");
    p->Print(vars,
             "        }\n"
             "      }\n"
             "   }\n"
             "   return $method_new_field_name$;\n"
             "}\n");

    p->Print("\n");
  }
}
enum StubType {
  ASYNC_INTERFACE = 0,
  BLOCKING_CLIENT_INTERFACE = 1,
  FUTURE_CLIENT_INTERFACE = 2,
  BLOCKING_SERVER_INTERFACE = 3,
  ASYNC_CLIENT_IMPL = 4,
  BLOCKING_CLIENT_IMPL = 5,
  FUTURE_CLIENT_IMPL = 6,
  ABSTRACT_CLASS = 7,
};

enum CallType { ASYNC_CALL = 0, BLOCKING_CALL = 1, FUTURE_CALL = 2 };

static void PrintBindServiceMethodBody(Printer *p, VARS &vars,
                                       const ServiceDescriptor *service);

// Prints a client interface or implementation class, or a server interface.
static void PrintStub(Printer *p, VARS &vars, const ServiceDescriptor *service,
                      StubType type) {
  const string service_name = service->name();
  vars["service_name"] = service_name;
  vars["abstract_name"] = service_name + "ImplBase";
  string stub_name = service_name;
  string client_name = service_name;
  CallType call_type = ASYNC_CALL;
  bool impl_base = false;
  bool interface = false;
  switch (type) {
    case ABSTRACT_CLASS:
      call_type = ASYNC_CALL;
      impl_base = true;
      break;
    case ASYNC_CLIENT_IMPL:
      call_type = ASYNC_CALL;
      stub_name += "Stub";
      break;
    case BLOCKING_CLIENT_INTERFACE:
      interface = true;
      FLATBUFFERS_FALLTHROUGH();  // fall thru
    case BLOCKING_CLIENT_IMPL:
      call_type = BLOCKING_CALL;
      stub_name += "BlockingStub";
      client_name += "BlockingClient";
      break;
    case FUTURE_CLIENT_INTERFACE:
      interface = true;
      FLATBUFFERS_FALLTHROUGH();  // fall thru
    case FUTURE_CLIENT_IMPL:
      call_type = FUTURE_CALL;
      stub_name += "FutureStub";
      client_name += "FutureClient";
      break;
    case ASYNC_INTERFACE:
      call_type = ASYNC_CALL;
      interface = true;
      break;
    default:
      GRPC_CODEGEN_FAIL << "Cannot determine class name for StubType: " << type;
  }
  vars["stub_name"] = stub_name;
  vars["client_name"] = client_name;

  // Class head
  if (!interface) { GrpcWriteServiceDocComment(p, vars, service); }
  if (impl_base) {
    p->Print(vars,
             "public static abstract class $abstract_name$ implements "
             "$BindableService$ {\n");
  } else {
    p->Print(vars,
             "public static final class $stub_name$ extends "
             "$AbstractStub$<$stub_name$> {\n");
  }
  p->Indent();

  // Constructor and build() method
  if (!impl_base && !interface) {
    p->Print(vars, "private $stub_name$($Channel$ channel) {\n");
    p->Indent();
    p->Print("super(channel);\n");
    p->Outdent();
    p->Print("}\n\n");
    p->Print(vars,
             "private $stub_name$($Channel$ channel,\n"
             "    $CallOptions$ callOptions) {\n");
    p->Indent();
    p->Print("super(channel, callOptions);\n");
    p->Outdent();
    p->Print("}\n\n");
    p->Print(vars,
             "@$Override$\n"
             "protected $stub_name$ build($Channel$ channel,\n"
             "    $CallOptions$ callOptions) {\n");
    p->Indent();
    p->Print(vars, "return new $stub_name$(channel, callOptions);\n");
    p->Outdent();
    p->Print("}\n");
  }

  // RPC methods
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
    vars["lower_method_name"] = LowerMethodName(&*method);
    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
    bool client_streaming =
        method->ClientStreaming() || method->BidiStreaming();
    bool server_streaming =
        method->ServerStreaming() || method->BidiStreaming();

    if (call_type == BLOCKING_CALL && client_streaming) {
      // Blocking client interface with client streaming is not available
      continue;
    }

    if (call_type == FUTURE_CALL && (client_streaming || server_streaming)) {
      // Future interface doesn't support streaming.
      continue;
    }

    // Method signature
    p->Print("\n");
    // TODO(nmittler): Replace with WriteMethodDocComment once included by the
    // protobuf distro.
    if (!interface) { GrpcWriteMethodDocComment(p, vars, &*method); }
    p->Print("public ");
    switch (call_type) {
      case BLOCKING_CALL:
        GRPC_CODEGEN_CHECK(!client_streaming)
            << "Blocking client interface with client streaming is unavailable";
        if (server_streaming) {
          // Server streaming
          p->Print(vars,
                   "$Iterator$<$output_type$> $lower_method_name$(\n"
                   "    $input_type$ request)");
        } else {
          // Simple RPC
          p->Print(vars,
                   "$output_type$ $lower_method_name$($input_type$ request)");
        }
        break;
      case ASYNC_CALL:
        if (client_streaming) {
          // Bidirectional streaming or client streaming
          p->Print(vars,
                   "$StreamObserver$<$input_type$> $lower_method_name$(\n"
                   "    $StreamObserver$<$output_type$> responseObserver)");
        } else {
          // Server streaming or simple RPC
          p->Print(vars,
                   "void $lower_method_name$($input_type$ request,\n"
                   "    $StreamObserver$<$output_type$> responseObserver)");
        }
        break;
      case FUTURE_CALL:
        GRPC_CODEGEN_CHECK(!client_streaming && !server_streaming)
            << "Future interface doesn't support streaming. "
            << "client_streaming=" << client_streaming << ", "
            << "server_streaming=" << server_streaming;
        p->Print(vars,
                 "$ListenableFuture$<$output_type$> $lower_method_name$(\n"
                 "    $input_type$ request)");
        break;
    }

    if (interface) {
      p->Print(";\n");
      continue;
    }
    // Method body.
    p->Print(" {\n");
    p->Indent();
    if (impl_base) {
      switch (call_type) {
          // NB: Skipping validation of service methods. If something is wrong,
          // we wouldn't get to this point as compiler would return errors when
          // generating service interface.
        case ASYNC_CALL:
          if (client_streaming) {
            p->Print(vars,
                     "return "
                     "asyncUnimplementedStreamingCall($method_method_name$(), "
                     "responseObserver);\n");
          } else {
            p->Print(vars,
                     "asyncUnimplementedUnaryCall($method_method_name$(), "
                     "responseObserver);\n");
          }
          break;
        default: break;
      }
    } else if (!interface) {
      switch (call_type) {
        case BLOCKING_CALL:
          GRPC_CODEGEN_CHECK(!client_streaming)
              << "Blocking client streaming interface is not available";
          if (server_streaming) {
            vars["calls_method"] = "blockingServerStreamingCall";
            vars["params"] = "request";
          } else {
            vars["calls_method"] = "blockingUnaryCall";
            vars["params"] = "request";
          }
          p->Print(vars,
                   "return $calls_method$(\n"
                   "    getChannel(), $method_method_name$(), "
                   "getCallOptions(), $params$);\n");
          break;
        case ASYNC_CALL:
          if (server_streaming) {
            if (client_streaming) {
              vars["calls_method"] = "asyncBidiStreamingCall";
              vars["params"] = "responseObserver";
            } else {
              vars["calls_method"] = "asyncServerStreamingCall";
              vars["params"] = "request, responseObserver";
            }
          } else {
            if (client_streaming) {
              vars["calls_method"] = "asyncClientStreamingCall";
              vars["params"] = "responseObserver";
            } else {
              vars["calls_method"] = "asyncUnaryCall";
              vars["params"] = "request, responseObserver";
            }
          }
          vars["last_line_prefix"] = client_streaming ? "return " : "";
          p->Print(vars,
                   "$last_line_prefix$$calls_method$(\n"
                   "    getChannel().newCall($method_method_name$(), "
                   "getCallOptions()), $params$);\n");
          break;
        case FUTURE_CALL:
          GRPC_CODEGEN_CHECK(!client_streaming && !server_streaming)
              << "Future interface doesn't support streaming. "
              << "client_streaming=" << client_streaming << ", "
              << "server_streaming=" << server_streaming;
          vars["calls_method"] = "futureUnaryCall";
          p->Print(vars,
                   "return $calls_method$(\n"
                   "    getChannel().newCall($method_method_name$(), "
                   "getCallOptions()), request);\n");
          break;
      }
    }
    p->Outdent();
    p->Print("}\n");
  }

  if (impl_base) {
    p->Print("\n");
    p->Print(
        vars,
        "@$Override$ public final $ServerServiceDefinition$ bindService() {\n");
    vars["instance"] = "this";
    PrintBindServiceMethodBody(p, vars, service);
    p->Print("}\n");
  }

  p->Outdent();
  p->Print("}\n\n");
}

static bool CompareMethodClientStreaming(
    const std::unique_ptr<const grpc_generator::Method> &method1,
    const std::unique_ptr<const grpc_generator::Method> &method2) {
  return method1->ClientStreaming() < method2->ClientStreaming();
}

// Place all method invocations into a single class to reduce memory footprint
// on Android.
static void PrintMethodHandlerClass(Printer *p, VARS &vars,
                                    const ServiceDescriptor *service) {
  // Sort method ids based on ClientStreaming() so switch tables are compact.
  std::vector<std::unique_ptr<const grpc_generator::Method>> sorted_methods(
      service->method_count());
  for (int i = 0; i < service->method_count(); ++i) {
    sorted_methods[i] = service->method(i);
  }
  stable_sort(sorted_methods.begin(), sorted_methods.end(),
              CompareMethodClientStreaming);
  for (size_t i = 0; i < sorted_methods.size(); i++) {
    auto &method = sorted_methods[i];
    vars["method_id"] = to_string(i);
    vars["method_id_name"] = MethodIdFieldName(&*method);
    p->Print(vars,
             "private static final int $method_id_name$ = $method_id$;\n");
  }
  p->Print("\n");
  vars["service_name"] = service->name() + "ImplBase";
  p->Print(vars,
           "private static final class MethodHandlers<Req, Resp> implements\n"
           "    io.grpc.stub.ServerCalls.UnaryMethod<Req, Resp>,\n"
           "    io.grpc.stub.ServerCalls.ServerStreamingMethod<Req, Resp>,\n"
           "    io.grpc.stub.ServerCalls.ClientStreamingMethod<Req, Resp>,\n"
           "    io.grpc.stub.ServerCalls.BidiStreamingMethod<Req, Resp> {\n"
           "  private final $service_name$ serviceImpl;\n"
           "  private final int methodId;\n"
           "\n"
           "  MethodHandlers($service_name$ serviceImpl, int methodId) {\n"
           "    this.serviceImpl = serviceImpl;\n"
           "    this.methodId = methodId;\n"
           "  }\n\n");
  p->Indent();
  p->Print(vars,
           "@$Override$\n"
           "@java.lang.SuppressWarnings(\"unchecked\")\n"
           "public void invoke(Req request, $StreamObserver$<Resp> "
           "responseObserver) {\n"
           "  switch (methodId) {\n");
  p->Indent();
  p->Indent();

  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    if (method->ClientStreaming() || method->BidiStreaming()) { continue; }
    vars["method_id_name"] = MethodIdFieldName(&*method);
    vars["lower_method_name"] = LowerMethodName(&*method);
    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
    p->Print(vars,
             "case $method_id_name$:\n"
             "  serviceImpl.$lower_method_name$(($input_type$) request,\n"
             "      ($StreamObserver$<$output_type$>) responseObserver);\n"
             "  break;\n");
  }
  p->Print(
      "default:\n"
      "  throw new AssertionError();\n");

  p->Outdent();
  p->Outdent();
  p->Print(
      "  }\n"
      "}\n\n");

  p->Print(vars,
           "@$Override$\n"
           "@java.lang.SuppressWarnings(\"unchecked\")\n"
           "public $StreamObserver$<Req> invoke(\n"
           "    $StreamObserver$<Resp> responseObserver) {\n"
           "  switch (methodId) {\n");
  p->Indent();
  p->Indent();

  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    if (!(method->ClientStreaming() || method->BidiStreaming())) { continue; }
    vars["method_id_name"] = MethodIdFieldName(&*method);
    vars["lower_method_name"] = LowerMethodName(&*method);
    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
    p->Print(
        vars,
        "case $method_id_name$:\n"
        "  return ($StreamObserver$<Req>) serviceImpl.$lower_method_name$(\n"
        "      ($StreamObserver$<$output_type$>) responseObserver);\n");
  }
  p->Print(
      "default:\n"
      "  throw new AssertionError();\n");

  p->Outdent();
  p->Outdent();
  p->Print(
      "  }\n"
      "}\n");

  p->Outdent();
  p->Print("}\n\n");
}

static void PrintGetServiceDescriptorMethod(Printer *p, VARS &vars,
                                            const ServiceDescriptor *service) {
  vars["service_name"] = service->name();
  //        vars["proto_base_descriptor_supplier"] = service->name() +
  //        "BaseDescriptorSupplier"; vars["proto_file_descriptor_supplier"] =
  //        service->name() + "FileDescriptorSupplier";
  //        vars["proto_method_descriptor_supplier"] = service->name() +
  //        "MethodDescriptorSupplier"; vars["proto_class_name"] =
  //        google::protobuf::compiler::java::ClassName(service->file());
  //        p->Print(
  //                 vars,
  //                 "private static abstract class
  //                 $proto_base_descriptor_supplier$\n" "    implements
  //                 $ProtoFileDescriptorSupplier$,
  //                 $ProtoServiceDescriptorSupplier$ {\n" "
  //                 $proto_base_descriptor_supplier$() {}\n"
  //                 "\n"
  //                 "  @$Override$\n"
  //                 "  public com.google.protobuf.Descriptors.FileDescriptor
  //                 getFileDescriptor() {\n" "    return
  //                 $proto_class_name$.getDescriptor();\n" "  }\n"
  //                 "\n"
  //                 "  @$Override$\n"
  //                 "  public com.google.protobuf.Descriptors.ServiceDescriptor
  //                 getServiceDescriptor() {\n" "    return
  //                 getFileDescriptor().findServiceByName(\"$service_name$\");\n"
  //                 "  }\n"
  //                 "}\n"
  //                 "\n"
  //                 "private static final class
  //                 $proto_file_descriptor_supplier$\n" "    extends
  //                 $proto_base_descriptor_supplier$ {\n" "
  //                 $proto_file_descriptor_supplier$() {}\n"
  //                 "}\n"
  //                 "\n"
  //                 "private static final class
  //                 $proto_method_descriptor_supplier$\n" "    extends
  //                 $proto_base_descriptor_supplier$\n" "    implements
  //                 $ProtoMethodDescriptorSupplier$ {\n" "  private final
  //                 String methodName;\n"
  //                 "\n"
  //                 "  $proto_method_descriptor_supplier$(String methodName)
  //                 {\n" "    this.methodName = methodName;\n" "  }\n"
  //                 "\n"
  //                 "  @$Override$\n"
  //                 "  public com.google.protobuf.Descriptors.MethodDescriptor
  //                 getMethodDescriptor() {\n" "    return
  //                 getServiceDescriptor().findMethodByName(methodName);\n" "
  //                 }\n"
  //                 "}\n\n");

  p->Print(
      vars,
      "private static volatile $ServiceDescriptor$ serviceDescriptor;\n\n");

  p->Print(vars,
           "public static $ServiceDescriptor$ getServiceDescriptor() {\n");
  p->Indent();
  p->Print(vars, "$ServiceDescriptor$ result = serviceDescriptor;\n");
  p->Print("if (result == null) {\n");
  p->Indent();
  p->Print(vars, "synchronized ($service_class_name$.class) {\n");
  p->Indent();
  p->Print("result = serviceDescriptor;\n");
  p->Print("if (result == null) {\n");
  p->Indent();

  p->Print(vars,
           "serviceDescriptor = result = "
           "$ServiceDescriptor$.newBuilder(SERVICE_NAME)");
  p->Indent();
  p->Indent();
  p->Print(vars, "\n.setSchemaDescriptor(null)");
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
    p->Print(vars, "\n.addMethod($method_method_name$())");
  }
  p->Print("\n.build();\n");
  p->Outdent();
  p->Outdent();

  p->Outdent();
  p->Print("}\n");
  p->Outdent();
  p->Print("}\n");
  p->Outdent();
  p->Print("}\n");
  p->Print("return result;\n");
  p->Outdent();
  p->Print("}\n");
}

static void PrintBindServiceMethodBody(Printer *p, VARS &vars,
                                       const ServiceDescriptor *service) {
  vars["service_name"] = service->name();
  p->Indent();
  p->Print(vars,
           "return "
           "$ServerServiceDefinition$.builder(getServiceDescriptor())\n");
  p->Indent();
  p->Indent();
  for (int i = 0; i < service->method_count(); ++i) {
    auto method = service->method(i);
    vars["lower_method_name"] = LowerMethodName(&*method);
    vars["method_method_name"] = MethodPropertiesGetterName(&*method);
    vars["input_type"] = JavaClassName(vars, method->get_input_type_name());
    vars["output_type"] = JavaClassName(vars, method->get_output_type_name());
    vars["method_id_name"] = MethodIdFieldName(&*method);
    bool client_streaming =
        method->ClientStreaming() || method->BidiStreaming();
    bool server_streaming =
        method->ServerStreaming() || method->BidiStreaming();
    if (client_streaming) {
      if (server_streaming) {
        vars["calls_method"] = "asyncBidiStreamingCall";
      } else {
        vars["calls_method"] = "asyncClientStreamingCall";
      }
    } else {
      if (server_streaming) {
        vars["calls_method"] = "asyncServerStreamingCall";
      } else {
        vars["calls_method"] = "asyncUnaryCall";
      }
    }
    p->Print(vars, ".addMethod(\n");
    p->Indent();
    p->Print(vars,
             "$method_method_name$(),\n"
             "$calls_method$(\n");
    p->Indent();
    p->Print(vars,
             "new MethodHandlers<\n"
             "  $input_type$,\n"
             "  $output_type$>(\n"
             "    $instance$, $method_id_name$)))\n");
    p->Outdent();
    p->Outdent();
  }
  p->Print(".build();\n");
  p->Outdent();
  p->Outdent();
  p->Outdent();
}

static void PrintService(Printer *p, VARS &vars,
                         const ServiceDescriptor *service,
                         bool disable_version) {
  vars["service_name"] = service->name();
  vars["service_class_name"] = ServiceClassName(service->name());
  vars["grpc_version"] = "";
#ifdef GRPC_VERSION
  if (!disable_version) {
    vars["grpc_version"] = " (version " XSTR(GRPC_VERSION) ")";
  }
#else
  (void)disable_version;
#endif
  // TODO(nmittler): Replace with WriteServiceDocComment once included by
  // protobuf distro.
  GrpcWriteServiceDocComment(p, vars, service);
  p->Print(vars,
           "@$Generated$(\n"
           "    value = \"by gRPC proto compiler$grpc_version$\",\n"
           "    comments = \"Source: $file_name$.fbs\")\n"
           "public final class $service_class_name$ {\n\n");
  p->Indent();
  p->Print(vars, "private $service_class_name$() {}\n\n");

  p->Print(vars,
           "public static final String SERVICE_NAME = "
           "\"$Package$$service_name$\";\n\n");

  PrintMethodFields(p, vars, service);

  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
  // distro.
  GrpcWriteDocComment(
      p, vars,
      " Creates a new async stub that supports all call types for the service");
  p->Print(vars,
           "public static $service_name$Stub newStub($Channel$ channel) {\n");
  p->Indent();
  p->Print(vars, "return new $service_name$Stub(channel);\n");
  p->Outdent();
  p->Print("}\n\n");

  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
  // distro.
  GrpcWriteDocComment(
      p, vars,
      " Creates a new blocking-style stub that supports unary and streaming "
      "output calls on the service");
  p->Print(vars,
           "public static $service_name$BlockingStub newBlockingStub(\n"
           "    $Channel$ channel) {\n");
  p->Indent();
  p->Print(vars, "return new $service_name$BlockingStub(channel);\n");
  p->Outdent();
  p->Print("}\n\n");

  // TODO(nmittler): Replace with WriteDocComment once included by protobuf
  // distro.
  GrpcWriteDocComment(
      p, vars,
      " Creates a new ListenableFuture-style stub that supports unary calls "
      "on the service");
  p->Print(vars,
           "public static $service_name$FutureStub newFutureStub(\n"
           "    $Channel$ channel) {\n");
  p->Indent();
  p->Print(vars, "return new $service_name$FutureStub(channel);\n");
  p->Outdent();
  p->Print("}\n\n");

  PrintStub(p, vars, service, ABSTRACT_CLASS);
  PrintStub(p, vars, service, ASYNC_CLIENT_IMPL);
  PrintStub(p, vars, service, BLOCKING_CLIENT_IMPL);
  PrintStub(p, vars, service, FUTURE_CLIENT_IMPL);

  PrintMethodHandlerClass(p, vars, service);
  PrintGetServiceDescriptorMethod(p, vars, service);
  p->Outdent();
  p->Print("}\n");
}

static void PrintStaticImports(Printer *p) {
  p->Print(
      "import java.nio.ByteBuffer;\n"
      "import static "
      "io.grpc.MethodDescriptor.generateFullMethodName;\n"
      "import static "
      "io.grpc.stub.ClientCalls.asyncBidiStreamingCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.asyncClientStreamingCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.asyncServerStreamingCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.asyncUnaryCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.blockingServerStreamingCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.blockingUnaryCall;\n"
      "import static "
      "io.grpc.stub.ClientCalls.futureUnaryCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncBidiStreamingCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncClientStreamingCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncServerStreamingCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncUnaryCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncUnimplementedStreamingCall;\n"
      "import static "
      "io.grpc.stub.ServerCalls.asyncUnimplementedUnaryCall;\n\n");
}

static void GenerateService(const grpc_generator::Service *service,
                     grpc_generator::Printer *printer, VARS &vars,
                     bool disable_version) {
  // All non-generated classes must be referred by fully qualified names to
  // avoid collision with generated classes.
  vars["String"] = "java.lang.String";
  vars["Deprecated"] = "java.lang.Deprecated";
  vars["Override"] = "java.lang.Override";
  vars["Channel"] = "io.grpc.Channel";
  vars["CallOptions"] = "io.grpc.CallOptions";
  vars["MethodType"] = "io.grpc.MethodDescriptor.MethodType";
  vars["ServerMethodDefinition"] = "io.grpc.ServerMethodDefinition";
  vars["BindableService"] = "io.grpc.BindableService";
  vars["ServerServiceDefinition"] = "io.grpc.ServerServiceDefinition";
  vars["ServiceDescriptor"] = "io.grpc.ServiceDescriptor";
  vars["ProtoFileDescriptorSupplier"] =
      "io.grpc.protobuf.ProtoFileDescriptorSupplier";
  vars["ProtoServiceDescriptorSupplier"] =
      "io.grpc.protobuf.ProtoServiceDescriptorSupplier";
  vars["ProtoMethodDescriptorSupplier"] =
      "io.grpc.protobuf.ProtoMethodDescriptorSupplier";
  vars["AbstractStub"] = "io.grpc.stub.AbstractStub";
  vars["MethodDescriptor"] = "io.grpc.MethodDescriptor";
  vars["NanoUtils"] = "io.grpc.protobuf.nano.NanoUtils";
  vars["StreamObserver"] = "io.grpc.stub.StreamObserver";
  vars["Iterator"] = "java.util.Iterator";
  vars["Generated"] = "javax.annotation.Generated";
  vars["ListenableFuture"] =
      "com.google.common.util.concurrent.ListenableFuture";
  vars["ExperimentalApi"] = "io.grpc.ExperimentalApi";

  PrintStaticImports(printer);

  PrintService(printer, vars, service, disable_version);
}
} // namespace

grpc::string GenerateServiceSource(
    grpc_generator::File *file, const grpc_generator::Service *service,
    grpc_java_generator::Parameters *parameters) {
  grpc::string out;
  auto printer = file->CreatePrinter(&out);
  VARS vars;
  vars["flatc_version"] = grpc::string(
      FLATBUFFERS_STRING(FLATBUFFERS_VERSION_MAJOR) "." FLATBUFFERS_STRING(
          FLATBUFFERS_VERSION_MINOR) "." FLATBUFFERS_STRING(FLATBUFFERS_VERSION_REVISION));

  vars["file_name"] = file->filename();

  if (!parameters->package_name.empty()) {
    vars["Package"] = parameters->package_name;  // ServiceJavaPackage(service);
  }
  GenerateImports(file, &*printer, vars);
  GenerateService(service, &*printer, vars, false);
  return out;
}

}  // namespace grpc_java_generator