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protozero

Minimalistic protocol buffer decoder and encoder in C++.

Designed for high performance. Suitable for writing zero copy parsers and encoders with minimal need for run-time allocation of memory.

Low-level: this is designed to be a building block for writing a very customized decoder for a stable protobuf schema. If your protobuf schema is changing frequently or lazy decoding is not critical for your application then this approach offers no value: just use the C++ API that can be generated with the Google Protobufs protoc program.

# Depends

- C++14 compiler
- CMake
- Some tests depend on the Google Protobuf library, but use of Protozero doesn't need it

# How it works

The protozero code does not read .proto files used by the usual Protobuf implementations. The developer using protozero has to manually "translate" the .proto description into code. This means there is no way to access any of the information from the .proto description. This results in a few restrictions:

- The names of the fields are not available.
- Enum names are not available, you'll have to use the values they are defined with.
- Default values are not available.
- Field types have to be hardcoded. The library does not know which types to expect, so the user of the library has to supply the right types. Some checks are made using assert(), but mostly the user has to take care of that.

The library will make sure not to overrun the buffer it was given, but basically all other checks have to be made in user code!

# Documentation

You have to have a working knowledge of how protocol buffer encoding works.

- Read the tutorial for an introduction on how to use Protozero.
- Some advanced topics are described in an extra document.
- There is a table of all types and functions in the cheat sheet.
- Read the upgrading instructions if you are upgrading from an older version of Protozero.

The build process will also build the Doxygen-based reference documentation if you have Doxygen installed. Then open doc/html/index.html in your browser to read it.

# Endianness

Protozero uses a very simplistic test to check the byte order of the system it compiles on. If this check is wrong, you'll get test failures. If this is the case, please open an issue and tell us about your system.

# Building tests

Extensive tests are included. Build them using CMake:

    mkdir build
    cd build
    cmake ..
    make

Call ctest to run the tests.

The unit and reader tests are always build, the writer tests are only build if the Google Protobuf library is found when running CMake.

See test/README.md for more details about the test.

# Coverage report

To get a coverage report set CXXFLAGS and LDFLAGS before calling CMake:

    CXXFLAGS="--coverage" LDFLAGS="--coverage" cmake ..

Then call make as usual and run the tests using ctest.

If you are using g++ use gcov to generate a report (results are in *.gcov files):

    gcov -lp $(find test/ -name '*.o')

If you are using clang++ use llvm-cov instead:

    llvm-cov gcov -lp $(find test/ -name '*.o')

If you are using g++ you can use gcovr to generate nice HTML output:

    mkdir -p coverage
    gcovr . -r SRCDIR --html --html-details -o coverage/index.html

Open coverage/index.html in your browser to see the report.

# Clang-tidy

After the CMake step, run

    make clang-tidy

to check the code with clang-tidy. You might have to set CLANG_TIDY in CMake config.

# Cppcheck

For extra checks with Cppcheck you can, after the CMake step, call

    make cppcheck

# Installation

After the CMake step, call make install to install the include files in /usr/local/include/protozero.

If you are using CMake to build your own software, you can copy the file cmake/FindProtozero.cmake and use it in your build. See the file for details.

# Who is using Protozero?

- Carmen
- Libosmium
- Mapbox GL Native
- Mapbox Vector Tile library
- Mapnik
- OSRM
- Tippecanoe
- Vtzero

Are you using Protozero? Tell us! Send a pull request with changes to this README.