Add CMake file for C++ SDK (#2523)

src/cc/flwr/.gitignore

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+build/
+*.bak

src/cc/flwr/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.16)
+project(flwr VERSION 1.0
+  DESCRIPTION "Flower Library that packages gRPC and other dependencies"
+  LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(ABSL_PROPAGATE_CXX_STD ON)
+
+# Assume gRPC and other dependencies are necessary
+include(FetchContent)
+FetchContent_Declare(
+  gRPC
+  GIT_REPOSITORY https://github.com/grpc/grpc
+  GIT_TAG        v1.43.2
+)
+FetchContent_MakeAvailable(gRPC)
+
+# Variables for gRPC and Protocol Buffers
+set(_PROTOBUF_LIBPROTOBUF libprotobuf)
+set(_REFLECTION grpc++_reflection)
+set(_PROTOBUF_PROTOC $<TARGET_FILE:protoc>)
+set(_GRPC_GRPCPP grpc++)
+if(CMAKE_CROSSCOMPILING)
+    find_program(_GRPC_CPP_PLUGIN_EXECUTABLE grpc_cpp_plugin)
+else()
+    set(_GRPC_CPP_PLUGIN_EXECUTABLE $<TARGET_FILE:grpc_cpp_plugin>)
+endif()
+
+# FLWR_GRPC_PROTO
+
+get_filename_component(FLWR_PROTO "../../proto/flwr/proto/transport.proto" ABSOLUTE)
+get_filename_component(FLWR_PROTO_PATH "${FLWR_PROTO}" PATH)
+
+set(FLWR_PROTO_SRCS "${CMAKE_CURRENT_BINARY_DIR}/transport.pb.cc")
+set(FLWR_PROTO_HDRS "${CMAKE_CURRENT_BINARY_DIR}/transport.pb.h")
+set(FLWR_GRPC_SRCS "${CMAKE_CURRENT_BINARY_DIR}/transport.grpc.pb.cc")
+set(FLAR_GRPC_HDRS "${CMAKE_CURRENT_BINARY_DIR}/transport.grpc.pb.h")
+
+# External building command to generate gRPC source files.
+add_custom_command(
+  OUTPUT "${FLWR_PROTO_SRCS}" "${FLWR_PROTO_HDRS}" "${FLWR_GRPC_SRCS}" "${FLWR_GRPC_HDRS}"
+  COMMAND ${_PROTOBUF_PROTOC}
+  ARGS  --grpc_out "${CMAKE_CURRENT_BINARY_DIR}"
+        --cpp_out "${CMAKE_CURRENT_BINARY_DIR}"
+	-I "${FLWR_PROTO_PATH}"
+        --plugin=protoc-gen-grpc="${_GRPC_CPP_PLUGIN_EXECUTABLE}"
+        "${FLWR_PROTO}"
+  DEPENDS "${FLWR_PROTO}"
+)
+
+add_library(flwr_grpc_proto STATIC 
+  ${FLWR_GRPC_SRCS}
+  ${FLWR_GRPC_HDRS}
+  ${FLWR_PROTO_SRCS}
+  ${FLWR_PROTO_HDRS}
+)
+
+target_include_directories(flwr_grpc_proto 
+   PUBLIC 
+       $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>
+   PRIVATE
+       ${CMAKE_CURRENT_SOURCE_DIR}
+)
+
+target_link_libraries(flwr_grpc_proto
+  ${_REFLECTION}
+  ${_GRPC_GRPCPP}
+  ${_PROTOBUF_LIBPROTOBUF}
+)
+# For the internal use of flwr
+file(GLOB FLWR_SRCS "src/*.cc")
+
+add_library(flwr ${FLWR_SRCS})
+
+target_include_directories(flwr PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:include>
+)
+
+# Link gRPC and other dependencies
+target_link_libraries(flwr PRIVATE flwr_grpc_proto)
+
+# Merge the two libraries
+add_library(flwr_merged STATIC $<TARGET_OBJECTS:flwr> $<TARGET_OBJECTS:flwr_grpc_proto>)
+
+target_include_directories(flwr_merged PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:include>
+)
+
+# This will create a 'flwrConfig.cmake' for users to find
+install(TARGETS flwr_merged EXPORT flwrTargets
+  LIBRARY DESTINATION lib
+  ARCHIVE DESTINATION lib
+  RUNTIME DESTINATION bin
+  PUBLIC_HEADER DESTINATION include
+)
+install(
+    FILES 
+    ${CMAKE_CURRENT_BINARY_DIR}/transport.grpc.pb.h 
+    ${CMAKE_CURRENT_BINARY_DIR}/transport.pb.h
+    DESTINATION include
+)
+install(DIRECTORY include/ DESTINATION include)
+
+install(EXPORT flwrTargets
+  FILE flwrConfig.cmake
+  NAMESPACE flwr::
+  DESTINATION lib/cmake/flwr
+)
+
+# Optional: Generate and install package version file
+include(CMakePackageConfigHelpers)
+write_basic_package_version_file(
+  "${CMAKE_CURRENT_BINARY_DIR}/flwrConfigVersion.cmake"
+  VERSION ${PROJECT_VERSION}
+  COMPATIBILITY AnyNewerVersion
+)
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/flwrConfigVersion.cmake"
+  DESTINATION lib/cmake/flwr
+)
+

src/cc/flwr/cmake/StartLibConfig.cmake.in

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+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/StartLibTargets.cmake")

src/cc/flwr/cmake/flwrConfig.cmake.in

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+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/flwrTargets.cmake")