# μpb - a small protobuf implementation in C

|Platform|Build Status|
|--------|------------|
|macOS|[![Build Status](https://storage.googleapis.com/upb-kokoro-results/status-badge/macos.png)](https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Aupb%2Fmacos%2Fcontinuous)|
|ubuntu|[![Build Status](https://storage.googleapis.com/upb-kokoro-results/status-badge/ubuntu.png)](https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Aupb%2Fubuntu%2Fcontinuous)|

μpb (often written 'upb') is a small protobuf implementation written in C.

upb generates a C API for creating, parsing, and serializing messages
as declared in `.proto` files.  upb is heavily arena-based -- all
messages always live in an arena.  You control where the arena gets
memory from, so the arena can come from stack memory, for example.
Here is a simple example (`ConformanceRequest` and `ConformanceResponse`
are generated message types):

```c
#include "conformance/conformance.upb.h"

void foo(const char* data, size_t size) {
  upb_arena *arena;
  conformance_ConformanceRequest *request;
  conformance_ConformanceResponse *response;

  arena = upb_arena_new();
  request = conformance_ConformanceRequest_parse(data, size, arena);
  response = conformance_ConformanceResponse_new(arena);

  switch (conformance_ConformanceRequest_payload_case(request)) {
    case conformance_ConformanceRequest_payload_protobuf_payload: {
      upb_strview payload = conformance_ConformanceRequest_protobuf_payload(request);
      // ...
      break;
    }

    case conformance_ConformanceRequest_payload_NOT_SET:
      fprintf(stderr, "conformance_upb: Request didn't have payload.\n");
      break;

    default: {
      static const char msg[] = "Unsupported input format.";
      conformance_ConformanceResponse_set_skipped(
          response, upb_strview_make(msg, sizeof(msg)));
      break;
    }
  }

  upb_arena_free(arena);
}
```

Messages are opaque, so you always have to use generated getter/setter
methods to read/write fields.  This is somewhat unfortunate for C
because the function names are long, but this is necessary to provide
correct semantics for oneof fields, proto2 presence, etc.  It is also
necessary for providing a stable ABI, in cases where that is desired.

API and ABI are both subject to change!  Please do not distribute
as a shared library for this reason (for now at least).

## Using upb in your project

Currently only Bazel is supported (CMake support is partial and incomplete
but full CMake support is an eventual goal).

To use upb in your Bazel project, first add upb to your `WORKSPACE` file,
either as a `git_repository()` or as a `new_local_repository()` with a
Git Submodule:

```python
# Add this to your WORKSPACE file.
git_repository(
    name = "upb",
    remote = "https://github.com/protocolbuffers/upb.git",
    # You may want to substitute a more recent commit here.
    commit = "d5af87d06bbe3abad66970ce9c7ae0a7de8bb3c6",
)
```

Then in your BUILD file you can add `upb_proto_library()` rules that
generate code for a corresponding `proto_library()` rule.  For
example:

```python
# Add this to your BUILD file.
load(":upb_proto_library.bzl", "upb_proto_library")

proto_library(
    name = "foo_proto",
    srcs = ["foo.proto"],
)

upb_proto_library(
    name = "foo_upbproto",
    deps = [":foo_proto"],
)

cc_library(
    name = "lib_that_uses_protos",
    srcs = ["lib_that_uses_protos.cc"],
    deps = [":foo_upbproto"],
)
```

Then in your `.c` file you can #include the generated header:

```c
#include "foo.upb.h"

/* Insert code that uses generated types. */
```

## Old "handlers" interfaces

This library contains several semi-deprecated interfaces (see BUILD
file for more info about which interfaces are deprecated).  These
deprecated interfaces are still used in some significant projects,
such as the Ruby and PHP C bindings for protobuf in the [main protobuf
repo](https://github.com/protocolbuffers/protobuf).  The goal is to
migrate the Ruby/PHP bindings to use the newer, simpler interfaces
instead.  Please do not use the old interfaces in new code.

## Lua bindings

This repo has some Lua bindings for the core library.  These are
experimental and very incomplete.  These are currently included in
order to validate that the C API is suitable for wrapping.  As the
project matures these Lua bindings may become publicly available.

## Contact

Author: Josh Haberman ([jhaberman@gmail.com](mailto:jhaberman@gmail.com),
[haberman@google.com](mailto:haberman@google.com))