fastproto-compiler 0.0.1

Command line compiler for generating fastproto C++ headers

fastproto

fastproto is an early work-in-progress compiler for generating small C++ header files from .fastproto schema files. It is experimenting with a compact, header-only serialization API for C++ projects.

The generated header includes the fastproto runtime, so consumers only need to include the one generated file.

Quick Start

Generate a header from a schema:

uv run fastproto -o generated.hpp example.fastproto

Use it from C++:

#include "generated.hpp"

fastproto::Factory<fastproto::generated::my_namespace::SimpleMessage> factory;
factory.set_simple_int_field(10);

auto serialized = factory.serialize();

fastproto::Parser<fastproto::generated::my_namespace::SimpleMessage> parser;
parser.parse(serialized);
auto value = parser.get_simple_int_field();

Build the example:

c++ -std=c++23 example.cpp -o example

Schema Syntax

Schemas are organized into namespaces and messages:

namespace my_namespace {

message SimpleMessage(1) {
    simple_int_field : int32;
}

message MessageWithArray(3) {
    my_array_field : array<SimpleMessage>;
}

}

Each message has a numeric magic value, which is used when validating parsed buffers. Fields use name : type; syntax.

Currently supported field types include:

• Integers: int8, int16, int32, int64, uint8, uint16, uint32, uint64
• Floating point: float32, float64
• bool
• string
• array<T> for arrays of simple types/messages
• Other simple message types

Nested namespaces are supported with C++-style :: syntax:

namespace my_namespace::my_sub_namespace {
    message Nested(2) {
        value : int32;
    }
}

CLI

Install the command from PyPI:

pip install fastproto-compiler

Then run:

fastproto -o generated.hpp example.fastproto

You can also run it without installing it globally with uv:

uvx --from fastproto-compiler fastproto -o generated.hpp example.fastproto

Run from the repo with uv:

uv run fastproto -o generated.hpp example.fastproto

For local development, install the command from the checkout:

uv tool install --editable .

If -o is omitted, the generated header is written to stdout.

Python Bindings

fastproto can also generate a small Python package containing pybind11 bindings for a schema:

fastproto --python-out fastproto_example example.fastproto

This creates ./fastproto_example with the generated C++ header, pybind11 binding source, pyproject.toml, CMakeLists.txt, and Python package glue. The compiled extension module is named _fastproto_example and is installed inside the fastproto_example package. In this mode, --python-out is the output directory and package name, so -o is not used.

The generated directory looks like:

fastproto_example/
  pyproject.toml
  CMakeLists.txt
  include/generated.hpp
  src/fastproto_example_bindings.cpp
  fastproto_example/__init__.py

Build the package with:

uv build fastproto_example

Or install it into the current environment:

uv pip install ./fastproto_example

Fastproto namespaces become Python submodules. For the top-level example.fastproto, message factories and parsers are available under fastproto_example.my_namespace:

from fastproto_example.my_namespace import SimpleMessageFactory, SimpleMessageParser

factory = SimpleMessageFactory()
factory.simple_int_field = 10

data = factory.serialize()

parser = SimpleMessageParser(data)
print(parser.simple_int_field)

Nested fastproto namespaces map to nested Python modules:

from fastproto_example.my_namespace.my_sub_namespace.my_next_sub_namespace import (
    MessageWithStringFactory,
    MessageWithStringParser,
)

factory = MessageWithStringFactory()
factory.my_int_field = 42
factory.my_string_field = "Hello from Python"

parser = MessageWithStringParser(factory.serialize())
print(parser.my_int_field, parser.my_string_field)

The Python binding generator is also early WIP. It currently emits a pybind11 package scaffold that can be built with scikit-build-core, and it embeds the Python binding runtime into the generated binding source.

Design Notes

fastproto is currently optimized for low-copy serialization and parsing on common GCC/Clang targets. Generated messages use [[gnu::packed]] structs, and parsers view caller-owned byte buffers directly instead of materializing decoded objects.

That keeps the hot path small:

• Simple messages serialize as a span over the factory-owned struct.
• Strings parse as std::string_view into the input buffer.
• Arrays parse as spans or indexed views into the input buffer.
• Builtin scalar values are converted to/from network byte order.

The tradeoff is that this is not trying to be a maximally portable C++ wire format runtime. It assumes GCC/Clang-style packed-struct behavior on common architectures. The parser currently reinterprets bytes as generated structs, which is fast, but leans on compiler and platform behavior around packed layout, alignment, and object lifetime.

Status

This project is still early WIP. The schema language, generated C++ API, binary format, and runtime are all subject to change.