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++ generated 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