uvpp

uvpp is a Modern C++ wrapper for the wonderful libuv library.

Why uvpp

libuv has been developed with object oriented design. When you use the library into your C project, its class hierarchy is clear. But if you want to use it inside a C++ project, you will actually have to deal with a big amount of reinterpret_cast everywhere. uvw might be an option, but it's more an event library, based on libuv than a simple wrapper, and the overhead isn't so negligible.

uvpp wants to be a simple wrapper over libuv, with limited overhead, proposing a clean Modern C++ interface with exception management.

Usage

uvpp is a header-only C++ library. You will need a C++17 compiler. Just include "uvpp/uv.hpp".

#include <uvpp/uv.hpp>

For everything else, you can stick to libuv engine for the implementation. So you'll mainly need a Loop object, the Reactor, from which the handles will be attached. A default loop is available.

auto loop = uv::Loop::getDefault();

or you can create one, by just instanciate a new Loop object, for example with

uv::Loop loop();

Then create Handles object as needed, and you can directly call the methods from the objects. For example, an Idle is a simple handle that will call its callback on each loop iteration. To instanciate one in a local variable, use

uv::Idle idle(loop);

To allocate a new object instead of using a local variable, use

auto idle = new uv::Idle(loop);

Memory management

uvpp doesn't allocate any object for you. You can allocate them yourself or use local variable, but it's your programmer's duty to correctly manage memory. Don't hesitate to use smart-pointers if you want.

Callbacks

You can use Modern C++ lambda function, but then be careful you can't capture any variable, as the compiler will have to translate it into a simple function pointer.

idle.start([](uv::Idle *idle) {
  static int64_t counter = 0;

  counter++;
  if (counter >= 1000000)
    idle->close();
});

Of course, you can also reference any function.

When you need to pass a callback to a function, you usually have two options. You can pass it as a function parameter, or you can ask uvpp to take care or errors and raise an exception for you if needed. This way, you don't need to manage with libuv status inside your callbacks (but still need to manage exceptions in C++ way)

This safe way require you to use template version of the functions. Even if not every callback will be given a status error code, any callback can be written in a template-style to keep consistency, as a general rule.

To be able to use a lambda as a template parameter, you might have to use a C++20 compiler. As of 2022, g++ still has bug, even compiling with "std=c++20", as it considers the lambda has no linkage. But clang manages very well.

Loop *loop = Loop::getDefault();

Tcp server(loop);

try {
  IPv4 addr("0.0.0.0", 2345);
  server.bind(&addr);

  server.listen<[](Tcp *server) {
    // ... Some useful stuff
    //
    // No need to check status. If there is an error during the
    // listen, an exception should raise during the loop->run()
  }>();

  loop->run();
} catch (uv::Error &e) {
  // ... An error occured
}

Under development

You can notice the sockaddr helper IPv4. The library has some of them. Expect to see more in the future, as well as more C++ oriented types, like std::string for example.

Differences with libuv

The same objects and Handles have been mirrored. But the first noticeable difference, aside of object methods instead of global functions, is that the handles keep their types inside the callbacks. No need to cast anything.

Also, the read method (or start_read) has an additional callback, for EoF event, in its template form:

uv::fs::read<on_read, on_eof>(loop, &req, fd, &iov, 1, -1);

Example

This is a simple TCP echo server using uvpp

#include <fmt/core.h>

#include "uvpp/uv.hpp"

using namespace uv;

int main(int ac, char* av[]) {
  Loop *loop = Loop::getDefault();

  Tcp server(loop);

  try {
    IPv4 addr("0.0.0.0", 2345);
    server.bind(&addr);

    server.listen<[](Tcp *server) {
      fmt::print("New connection\n");

      auto client = new Tcp(server->getLoop());
      server->accept(client);

      client->read_start<[](Tcp *client, size_t suggested_size, Buffer *buf) {
        buf->allocate(suggested_size);
      }, [](Tcp *client, ssize_t nread, const Buffer *buf) {
        auto req = new Tcp::WriteRq;
        auto buf2 = new Buffer(buf->base, nread);
        req->set(buf2);

        client->write<[](Tcp::WriteRq *req) {
          auto buf2 = req->get<Buffer>();
          delete buf2->base;
          delete buf2;
          delete req;
        }>(req, buf2, 1);
      }, [](Tcp *client, const Buffer *buf) {
        fmt::print("Disconnection\n");

        client->close();
        delete buf->base;
      }>();
    }>();

    loop->run();
  } catch (uv::Error &e) {
    fmt::print(stderr, "Error {}\n", e.message());
  }

  return 0;
}

Testing process

Install Clang compiler, Google Test, fmt library and libuv version to test.

On Ubuntu:

sudo apt install clang libgtest-dev libfmt-dev libuv1-dev

And run from working directory:

make