基於Yocto交叉編譯gRPC的步驟簡介

版本適配：gRPC=v1.21.0, Protobuf=v3.5.0

交叉編譯之前，請先編譯安裝本地版本的gRPC和Protobuf，注意版本適配。

第一步：初始化Yocto的交叉編譯環境

source Yocto 的環境變量 environment-setup-cortexa9hf-vfp-neon-poky-linux-gnueabi

第二步：編譯安裝Protobuf

cd third_party/protobuf/
git submodule update --init --recursive #修改本地源方法如前文，更新第三方源碼
./autogen.sh
./configure --prefix=/usr --host=arm-poky-linux-gnueabi --with-protoc=/usr/local/bin/protoc
make -j2
make DESTDIR=~/rootfs install

注意：其中DESTDIR指定交叉編譯環境的安裝目錄，而不是本地系統環境。

第三步：配置gRPC的環境變量

注意：先修改Makefile文件，後面還需要再修改一次
prefix ?= /usr

export GRPC_CROSS_COMPILE=true
export LDXX=$CXX
export LD=$CXX
export PROTOBUF_CONFIG_OPTS="--host=arm-poky-linux-gnueabi --with-protoc=/usr/local/bin/protoc"
export GRPC_CROSS_LDOPTS=$LDFLAGS
export GRPC_CROSS_AROPTS=rc
export USE_BUILT_PROTOC=true

第四步：執行make命令並解決一些問題

問題1：src/compiler/ruby_generator.cc和src/cpp/server/channelz/channelz_service.cc依賴了Protobuf 3.6.0的頭文件

解決1：替換源文件爲舊版本，內容較多放在文章最後面。

問題2：

[GRPC]    Generating gRPC's protobuf service CC file from src/proto/grpc/channelz/channelz.proto
/home/help/RPC/grpc/bins/opt/grpc_cpp_plugin: program not found or is not executable
--grpc_out: protoc-gen-grpc: Plugin failed with status code 1.
Makefile:2590: recipe for target '/home/help/RPC/grpc/gens/src/proto/grpc/channelz/channelz.grpc.pb.cc' failed
make: *** [/home/help/RPC/grpc/gens/src/proto/grpc/channelz/channelz.grpc.pb.cc] Error 1

解決2：修改Makefile文件，找到變量PROTOC_PLUGINS_DIR ，覆蓋所有變量賦值：PROTOC_PLUGINS_DIR = /usr/local/bin

問題3：如何交叉編譯的安裝？

解決3：修改Makefile文件，設置變量爲： prefix ?= ~/rootfs

第五步：執行make install安裝

以上，已經安裝完成。

附件：

src/compiler/ruby_generator.cc

/*
 *
 * Copyright 2015 gRPC authors.
 *
 * 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 <cctype>
#include <map>
#include <vector>

#include "src/compiler/config.h"
#include "src/compiler/ruby_generator.h"
#include "src/compiler/ruby_generator_helpers-inl.h"
#include "src/compiler/ruby_generator_map-inl.h"
#include "src/compiler/ruby_generator_string-inl.h"

using grpc::protobuf::FileDescriptor;
using grpc::protobuf::MethodDescriptor;
using grpc::protobuf::ServiceDescriptor;
using grpc::protobuf::io::Printer;
using grpc::protobuf::io::StringOutputStream;
using std::map;
using std::vector;

namespace grpc_ruby_generator {
namespace {

// Prints out the method using the ruby gRPC DSL.
void PrintMethod(const MethodDescriptor* method, const grpc::string& package,
                 Printer* out) {
  grpc::string input_type =
      RubyTypeOf(method->input_type()->full_name(), package);
  if (method->client_streaming()) {
    input_type = "stream(" + input_type + ")";
  }
  grpc::string output_type =
      RubyTypeOf(method->output_type()->full_name(), package);
  if (method->server_streaming()) {
    output_type = "stream(" + output_type + ")";
  }
  std::map<grpc::string, grpc::string> method_vars = ListToDict({
      "mth.name",
      method->name(),
      "input.type",
      input_type,
      "output.type",
      output_type,
  });
  out->Print(GetRubyComments(method, true).c_str());
  out->Print(method_vars, "rpc :$mth.name$, $input.type$, $output.type$\n");
  out->Print(GetRubyComments(method, false).c_str());
}

// Prints out the service using the ruby gRPC DSL.
void PrintService(const ServiceDescriptor* service, const grpc::string& package,
                  Printer* out) {
  if (service->method_count() == 0) {
    return;
  }

  // Begin the service module
  std::map<grpc::string, grpc::string> module_vars = ListToDict({
      "module.name",
      Modularize(service->name()),
  });
  out->Print(module_vars, "module $module.name$\n");
  out->Indent();

  out->Print(GetRubyComments(service, true).c_str());
  out->Print("class Service\n");

  // Write the indented class body.
  out->Indent();
  out->Print("\n");
  out->Print("include GRPC::GenericService\n");
  out->Print("\n");
  out->Print("self.marshal_class_method = :encode\n");
  out->Print("self.unmarshal_class_method = :decode\n");
  std::map<grpc::string, grpc::string> pkg_vars =
      ListToDict({"service_full_name", service->full_name()});
  out->Print(pkg_vars, "self.service_name = '$service_full_name$'\n");
  out->Print("\n");
  for (int i = 0; i < service->method_count(); ++i) {
    PrintMethod(service->method(i), package, out);
  }
  out->Outdent();

  out->Print("end\n");
  out->Print("\n");
  out->Print("Stub = Service.rpc_stub_class\n");

  // End the service module
  out->Outdent();
  out->Print("end\n");
  out->Print(GetRubyComments(service, false).c_str());
}

}  // namespace

// The following functions are copied directly from the source for the protoc
// ruby generator
// to ensure compatibility (with the exception of int and string type changes).
// See
// https://github.com/google/protobuf/blob/master/src/google/protobuf/compiler/ruby/ruby_generator.cc#L250
// TODO: keep up to date with protoc code generation, though this behavior isn't
// expected to change
bool IsLower(char ch) { return ch >= 'a' && ch <= 'z'; }

char ToUpper(char ch) { return IsLower(ch) ? (ch - 'a' + 'A') : ch; }

// Package names in protobuf are snake_case by convention, but Ruby module
// names must be PascalCased.
//
//   foo_bar_baz -> FooBarBaz
grpc::string PackageToModule(const grpc::string& name) {
  bool next_upper = true;
  grpc::string result;
  result.reserve(name.size());

  for (grpc::string::size_type i = 0; i < name.size(); i++) {
    if (name[i] == '_') {
      next_upper = true;
    } else {
      if (next_upper) {
        result.push_back(ToUpper(name[i]));
      } else {
        result.push_back(name[i]);
      }
      next_upper = false;
    }
  }

  return result;
}
// end copying of protoc generator for ruby code

grpc::string GetServices(const FileDescriptor* file) {
  grpc::string output;
  {
    // Scope the output stream so it closes and finalizes output to the string.

    StringOutputStream output_stream(&output);
    Printer out(&output_stream, '$');

    // Don't write out any output if there no services, to avoid empty service
    // files being generated for proto files that don't declare any.
    if (file->service_count() == 0) {
      return output;
    }

    // Write out a file header.
    std::map<grpc::string, grpc::string> header_comment_vars = ListToDict({
        "file.name",
        file->name(),
        "file.package",
        file->package(),
    });
    out.Print("# Generated by the protocol buffer compiler.  DO NOT EDIT!\n");
    out.Print(header_comment_vars,
              "# Source: $file.name$ for package '$file.package$'\n");

    grpc::string leading_comments = GetRubyComments(file, true);
    if (!leading_comments.empty()) {
      out.Print("# Original file comments:\n");
      out.PrintRaw(leading_comments.c_str());
    }

    out.Print("\n");
    out.Print("require 'grpc'\n");
    // Write out require statemment to import the separately generated file
    // that defines the messages used by the service. This is generated by the
    // main ruby plugin.
    std::map<grpc::string, grpc::string> dep_vars = ListToDict({
        "dep.name",
        MessagesRequireName(file),
    });
    out.Print(dep_vars, "require '$dep.name$'\n");

    // Write out services within the modules
    out.Print("\n");
    std::vector<grpc::string> modules = Split(file->package(), '.');
    for (size_t i = 0; i < modules.size(); ++i) {
      std::map<grpc::string, grpc::string> module_vars = ListToDict({
          "module.name",
          PackageToModule(modules[i]),
      });
      out.Print(module_vars, "module $module.name$\n");
      out.Indent();
    }
    for (int i = 0; i < file->service_count(); ++i) {
      auto service = file->service(i);
      PrintService(service, file->package(), &out);
    }
    for (size_t i = 0; i < modules.size(); ++i) {
      out.Outdent();
      out.Print("end\n");
    }

    out.Print(GetRubyComments(file, false).c_str());
  }
  return output;
}

}  // namespace grpc_ruby_generator

src/cpp/server/channelz/channelz_service.cc

/*
 *
 * Copyright 2018 gRPC authors.
 *
 * 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 <grpc/support/port_platform.h>

#include "src/cpp/server/channelz/channelz_service.h"

#include <grpc/grpc.h>
#include <grpc/support/alloc.h>

namespace grpc {

Status ChannelzService::GetTopChannels(
    ServerContext* unused, const channelz::v1::GetTopChannelsRequest* request,
    channelz::v1::GetTopChannelsResponse* response) {
  char* json_str = grpc_channelz_get_top_channels(request->start_channel_id());
  if (json_str == nullptr) {
    return Status(StatusCode::INTERNAL,
                  "grpc_channelz_get_top_channels returned null");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetServers(
    ServerContext* unused, const channelz::v1::GetServersRequest* request,
    channelz::v1::GetServersResponse* response) {
  char* json_str = grpc_channelz_get_servers(request->start_server_id());
  if (json_str == nullptr) {
    return Status(StatusCode::INTERNAL,
                  "grpc_channelz_get_servers returned null");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetServer(ServerContext* unused,
                                  const channelz::v1::GetServerRequest* request,
                                  channelz::v1::GetServerResponse* response) {
  char* json_str = grpc_channelz_get_server(request->server_id());
  if (json_str == nullptr) {
    return Status(StatusCode::INTERNAL,
                  "grpc_channelz_get_server returned null");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetServerSockets(
    ServerContext* unused, const channelz::v1::GetServerSocketsRequest* request,
    channelz::v1::GetServerSocketsResponse* response) {
  char* json_str = grpc_channelz_get_server_sockets(
      request->server_id(), request->start_socket_id(), request->max_results());
  if (json_str == nullptr) {
    return Status(StatusCode::INTERNAL,
                  "grpc_channelz_get_server_sockets returned null");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetChannel(
    ServerContext* unused, const channelz::v1::GetChannelRequest* request,
    channelz::v1::GetChannelResponse* response) {
  char* json_str = grpc_channelz_get_channel(request->channel_id());
  if (json_str == nullptr) {
    return Status(StatusCode::NOT_FOUND, "No object found for that ChannelId");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetSubchannel(
    ServerContext* unused, const channelz::v1::GetSubchannelRequest* request,
    channelz::v1::GetSubchannelResponse* response) {
  char* json_str = grpc_channelz_get_subchannel(request->subchannel_id());
  if (json_str == nullptr) {
    return Status(StatusCode::NOT_FOUND,
                  "No object found for that SubchannelId");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

Status ChannelzService::GetSocket(ServerContext* unused,
                                  const channelz::v1::GetSocketRequest* request,
                                  channelz::v1::GetSocketResponse* response) {
  char* json_str = grpc_channelz_get_socket(request->socket_id());
  if (json_str == nullptr) {
    return Status(StatusCode::NOT_FOUND, "No object found for that SocketId");
  }
  grpc::protobuf::util::Status s =
      grpc::protobuf::json::JsonStringToMessage(json_str, response);
  gpr_free(json_str);
  if (!s.ok()) {
    return Status(StatusCode::INTERNAL, s.ToString());
  }
  return Status::OK;
}

}  // namespace grpc