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# μpb: small, fast C protos
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μpb (often written 'upb') is a small
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[protobuf](https://github.com/protocolbuffers/protobuf) implementation written
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in C.
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upb is the core runtime for protobuf languages extensions in
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[Ruby](https://github.com/protocolbuffers/protobuf/tree/main/ruby),
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[PHP](https://github.com/protocolbuffers/protobuf/tree/main/php), and
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[Python](https://github.com/protocolbuffers/protobuf/tree/main/python).
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While upb offers a C API, the C API & ABI **are not stable**. For this reason,
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upb is not generally offered as a C library for direct consumption, and there
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are no releases.
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## Features
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upb has comparable speed to protobuf C++, but is an order of magnitude smaller
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in code size.
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Like the main protobuf implementation in C++, it supports:
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- a generated API (in C)
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- reflection
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- binary & JSON wire formats
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- text format serialization
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- all standard features of protobufs (oneofs, maps, unknown fields, extensions,
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etc.)
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- full conformance with the protobuf conformance tests
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upb also supports some features that C++ does not:
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- **optional reflection:** generated messages are agnostic to whether
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reflection will be linked in or not.
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- **no global state:** no pre-main registration or other global state.
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- **fast reflection-based parsing:** messages loaded at runtime parse
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just as fast as compiled-in messages.
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However there are a few features it does not support:
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- text format parsing
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- deep descriptor verification: upb's descriptor validation is not as exhaustive
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as `protoc`.
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## Install
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For Ruby, use [RubyGems](https://rubygems.org/gems/google-protobuf):
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```
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$ gem install google-protobuf
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```
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For PHP, use [PECL](https://pecl.php.net/package/protobuf):
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```
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$ sudo pecl install protobuf
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```
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For Python, use [PyPI](https://pypi.org/project/protobuf/):
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```
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$ sudo pip install protobuf
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```
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Alternatively, you can build and install upb using
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[vcpkg](https://github.com/microsoft/vcpkg/) dependency manager:
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git clone https://github.com/Microsoft/vcpkg.git
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cd vcpkg
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./bootstrap-vcpkg.sh
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./vcpkg integrate install
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./vcpkg install upb
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The upb port in vcpkg is kept up to date by microsoft team members and community
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contributors.
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If the version is out of date, please
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[create an issue or pull request](https://github.com/Microsoft/vcpkg) on the
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vcpkg repository.
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## Contributing
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Please see [CONTRIBUTING.md](CONTRIBUTING.md).
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