Protocol buffer v3 claims, that library is json friendly (https://developers.google.com/protocol-buffers/docs/proto3#json), but I cannot find how to achieve get that mapping. Should I add some plugin, or some option into protoc, or call something special instead SerializeTo/ParseFrom?
Is it someone who use that feature?
I'm using Protobuf 3.3.0, which does have a built-in JSON serializer and parser. You can use 2 functions from google/protobuf/util/json_util.h called MessageToJsonString() and JsonStringToMessage() to make your C++ generate Message objects go to and from JSON respectively.
Here's a simple test that uses them: test-protobuf.proto:
syntax = "proto3"; message SearchRequest { string query = 1; int32 page_number = 2; int32 result_per_page = 3; } test-protobuf.cpp:
#include <iostream> #include <google/protobuf/util/json_util.h> #include "test-protobuf.pb.h" int main() { std::string json_string; SearchRequest sr, sr2; // Populate sr. sr.set_query(std::string("Hello!")); sr.set_page_number(1); sr.set_result_per_page(10); // Create a json_string from sr. google::protobuf::util::JsonPrintOptions options; options.add_whitespace = true; options.always_print_primitive_fields = true; options.preserve_proto_field_names = true; MessageToJsonString(sr, &json_string, options); // Print json_string. std::cout << json_string << std::endl; // Parse the json_string into sr2. google::protobuf::util::JsonParseOptions options2; JsonStringToMessage(json_string, &sr2, options2); // Print the values of sr2. std::cout << sr2.query() << ", " << sr2.page_number() << ", " << sr2.result_per_page() << std::endl ; return 0; } You can compile these files (assuming that you have protobuf, a compiler, and CMake installed) by using the following CMakeLists.txt file (tested on Windows).
cmake_minimum_required(VERSION 3.8) project(test-protobuf) find_package(Protobuf REQUIRED) # Use static runtime for MSVC if(MSVC) foreach(flag_var CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO) if(${flag_var} MATCHES "/MD") string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}") endif(${flag_var} MATCHES "/MD") endforeach(flag_var) endif(MSVC) protobuf_generate_cpp(test-protobuf-sources test-protobuf-headers "${CMAKE_CURRENT_LIST_DIR}/test-protobuf.proto" ) list(APPEND test-protobuf-sources "${CMAKE_CURRENT_LIST_DIR}/test-protobuf.cpp" ) add_executable(test-protobuf ${test-protobuf-sources} ${test-protobuf-headers}) target_include_directories(test-protobuf PUBLIC ${PROTOBUF_INCLUDE_DIRS} ${CMAKE_CURRENT_BINARY_DIR} ) target_link_libraries(test-protobuf ${PROTOBUF_LIBRARIES} ) Assuming that CMakeLists.txt, test-protobuf.proto, and test-protobuf.cpp are in the same directory, here are the commands to compile and run them on Windows with Visual Studio 15 2017 and 64-bit protobuf libraries.
mkdir build cd build cmake -G "Visual Studio 15 2017 Win64" .. cmake --build . --config Release Release/test-protobuf You should see the following output:
{ "query": "Hello!", "page_number": 1, "result_per_page": 10 } Hello!, 1, 10 Protobuf has json api for C#. There are some json class for C# in google protobuf reference and You can find some tests in github protobuf repository for java and c++.