Compatible with older version of gRPC.

Signed-off-by: Tao He <sighingnow@gmail.com>

CMakeLists.txt

@@ -10,6 +10,7 @@ set(etcd-cpp-api_VERSION ${etcd-cpp-api_VERSION_MAJOR}.${etcd-cpp-api_VERSION_MI
 set(CMAKE_PROJECT_HOMEPAGE_URL https://github.com/etcd-cpp-apiv3/etcd-cpp-apiv3)
 
 include(CheckCXXCompilerFlag)
+include(CheckCXXSourceCompiles)
 include(CheckLibraryExists)
 include(GNUInstallDirs)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
@@ -86,6 +87,19 @@ if(NOT CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wpedantic -Werror -Wno-string-compare -std=c++11")
 endif()
 
+message("GRPC_INCLUDE_DIR = ${gRPC_FOUND}")
+set(CMAKE_REQUIRED_INCLUDES "${CMAKE_REQUIRED_INCLUDES} ${GRPC_INCLUDE_DIR}")
+set(CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES} ${GRPC_LIBRARIES}")
+set(CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}")
+check_cxx_source_compiles("
+#include <grpc++/grpc++.h>
+namespace grpc { class Channel; }
+int main() {}
+" GRPC_CHANNEL_CLASS_FOUND)
+if(GRPC_CHANNEL_CLASS_FOUND)
+    add_definitions(-DWITH_GRPC_CHANNEL_CLASS)
+endif()
+
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
 
 enable_testing()
@@ -185,5 +199,10 @@ set(CPACK_DEBIAN_PACKAGE_DISTRIBUTION "focal")
 set(DPUT_HOST "ppa:graphscope/etcd-cpp-api")
 set(DPUT_SNAPSHOT_HOST "ppa:graphscope/etcd-cpp-api")
 
+find_program(DEBUILD_EXECUTABLE debuild)
+find_program(DPUT_EXECUTABLE dput)
+
+if(DEBUILD_EXECUTABLE AND DPUT_EXECUTABLE)
     list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
     include(UploadPPA)
+endif()

etcd/Client.hpp

@@ -17,9 +17,15 @@ namespace etcdv3 {
   }
 }
 
+#if defined(WITH_GRPC_CHANNEL_CLASS)
 namespace grpc {
   class Channel;
 }
+#else
+namespace grpc_impl {
+  class Channel;
+}
+#endif
 
 namespace etcd
 {
@@ -383,7 +389,11 @@ namespace etcd
     pplx::task<Response> txn(etcdv3::Transaction const &txn);
 
   private:
+#if defined(WITH_GRPC_CHANNEL_CLASS)
     std::shared_ptr<grpc::Channel> channel;
+#else
+    std::shared_ptr<grpc_impl::Channel> channel;
+#endif
     std::string auth_token;
 
     struct EtcdServerStubs;