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# uvw - libuv wrapper in modern C++

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# Introduction

`uvw` is a header-only, event based, tiny and easy to use *libuv* wrapper in modern C++.<br/>
The basic idea is to hide completely the *C-ish* interface of *libuv* behind a graceful C++ API. Currently, no `uv_*_t` data structure is actually exposed by the library.<br/>
Note that `uvw` stays true to the API of *libuv* and it doesn't add anything to its interface. For the same reasons, users of the library must follow the same rules who are used to follow with *libuv*.<br/>
As an example, a *handle* should be initialized before any other operation and closed once it is no longer in use.

## Code Example

```cpp
#include <uvw.hpp>
#include <memory>

void listen(uvw::Loop &loop) {
    std::shared_ptr<uvw::TcpHandle> tcp = loop.resource<uvw::TcpHandle>();

    tcp->once<uvw::ListenEvent>([](const uvw::ListenEvent &, uvw::TcpHandle &srv) {
        std::shared_ptr<uvw::TcpHandle> client = srv.loop().resource<uvw::TcpHandle>();

        client->on<uvw::CloseEvent>([ptr = srv.shared_from_this()](const uvw::CloseEvent &, uvw::TcpHandle &) { ptr->close(); });
        client->on<uvw::EndEvent>([](const uvw::EndEvent &, uvw::TcpHandle &client) { client.close(); });

        srv.accept(*client);
        client->read();
    });

    tcp->bind("127.0.0.1", 4242);
    tcp->listen();
}

void conn(uvw::Loop &loop) {
    auto tcp = loop.resource<uvw::TcpHandle>();

    tcp->on<uvw::ErrorEvent>([](const uvw::ErrorEvent &, uvw::TcpHandle &) { /* handle errors */ });

    tcp->once<uvw::ConnectEvent>([](const uvw::ConnectEvent &, uvw::TcpHandle &tcp) {
        auto dataWrite = std::unique_ptr<char[]>(new char[2]{ 'b', 'c' });
        tcp.write(std::move(dataWrite), 2);
        tcp.close();
    });

    tcp->connect(std::string{"127.0.0.1"}, 4242);
}

int main() {
    auto loop = uvw::Loop::getDefault();
    listen(*loop);
    conn(*loop);
    loop->run();
}
```

## Motivation

The main reason for which `uvw` has been written is the fact that it does not exist a valid *libuv* wrapper in C++. That's all.

# Build Instructions

## Requirements

To be able to use `uvw`, users must provide the following system-wide tools:

* A full-featured compiler that supports at least C++14.
* `libuv` (which version depends on the tag of `uvw` in use).

The requirements below are mandatory to compile the tests and to extract the documentation:

* CMake version 3.2 or later.
* Doxygen version 1.8 or later.

Note that `libuv` is part of the dependencies of the project and it will be cloned by `cmake` (see below for further details).<br/>
Because of that, users have not to install it to compile and execute the tests.

## Library

`uvw` is a header-only library.<br/>
This means that including the `uvw.hpp` header or one of the other `uvw/*.hpp` headers is enough to use it.<br/>
It's a matter of adding the following line at the top of a file:

```cpp
#include <uvw.hpp>
```

Then pass the proper `-I` argument to the compiler to add the `src` directory to the include paths.<br/>
Note that users are demanded to correctly setup include directories and libraries search paths for *libuv*.

## Versioning

Starting with tag _v1.12.0_ of `libuv`, `uvw` follows the [semantic versioning](http://semver.org/) scheme.<br/>
The problem is that any version of `uvw` also requires to track explicitly the version of `libuv` to which it is bound.<br/>
Because of that, the latter wil be appended to the version of `uvw`. As an example:

    vU.V.W_libuv-vX.Y

In particular, the following applies:

* _U.V.W_ are major, minor and patch versions of `uvw`.
* _X.Y_ is the version of `libuv` to which to refer (where any patch version is valid).

In other terms, tags will look like this from now on:

    v1.0.0_libuv-v1.12

Branch `master` of `uvw` will be a work in progress branch that follows branch _v1.x_ of `libuv` (at least as long as it remains their _master_ branch).<br/>

## Documentation

The documentation is based on [`doxygen`](http://www.stack.nl/~dimitri/doxygen/). To build it:

* `$ cd build`
* `$ cmake ..`
* `$ make docs`

The API reference will be created in HTML format within the directory `build/docs/html`.<br/>
To navigate it with your favorite browser:

* `$ cd build`
* `$ your_favorite_browser docs/html/index.html`

The API reference is also available [online](https://skypjack.github.io/uvw/) for the latest version.

### Note

The documentation is mostly inspired by the official [libuv API documentation](http://docs.libuv.org/en/v1.x/) for obvious reasons.<br/>
If you are mainly interested in the way `uvw` imports `libuv` in a `cmake` based project, I suggest you to take a look at [this](https://github.com/skypjack/libuv_cmake) repository instead.

## Tests

To compile and run the tests, `uvw` requires *libuv* and *googletest*.<br/>
`cmake` will download and compile both the libraries before to compile anything else.

To build the tests:

* `$ cd build`
* `$ cmake ..`
* `$ make`
* `$ make test`

# Crash Course

## Vademecum

There is only one rule when using `uvw`: always initialize the resources and terminate them.

Resources belong mainly to two families: _handles_ and _requests_.<br/>
Handles represent long-lived objects capable of performing certain operations while active.<br/>
Requests represent (typically) short-lived operations performed either over a handle or standalone.

The following sections will explain in short what it means to initialize and terminate these kinds of resources.<br/>
For more details, please refer to the [online documentation](https://skypjack.github.io/uvw/).

## Handles

Initialization is usually performed under the hood and can be even passed over, as far as handles are created using the `Loop::resource` member function.<br/>
On the other side, handles keep themselves alive until one explicitly closes them. Because of that, memory usage will grow up if users simply forget about a handle.<br/>
Therefore the rule quickly becomes *always close your handles*. It's as simple as calling the `close` member function on them.

## Requests

Usually initializing a request object is not required. Anyway, the recommended way to create a request is still through the `Loop::resource` member function.<br/>
Requests will keep themselves alive as long as they are bound to unfinished underlying activities. This means that users have not to discard explicitly a request.<br/>
Therefore the rule quickly becomes *feel free to make a request and forget about it*. It's as simple as calling a member function on them.

## The Loop and the Resource

The first thing to do to use `uvw` is to create a loop. In case the default one is enough, it's easy as doing this:

```cpp
auto loop = uvw::Loop::getDefault();
```

Note that loop objects don't require to be closed explicitly, even if they offer the `close` member function in case an user wants to do that.<br/>
Loops can be started using the `run` member function. The two calls below are equivalent:

```cpp
loop->run();
loop->run<uvw::Loop::Mode::DEFAULT>
```

Available modes are: `DEFAULT`, `ONCE`, `NOWAIT`. Please refer to the documentation of *libuv* for further details.

In order to create a resource and to bind it to the given loop, just do the following:

```cpp
auto tcp = loop.resource<uvw::TcpHandle>();
```

The line above will create and initialize a tcp handle, then a shared pointer to that resource will be returned.<br/>
Users should check if pointers have been correctly initialized: in case of errors, they won't be.<br/>
Another way to create a resource is:

```cpp
auto tcp = TcpHandle::create(loop);
tcp->init();
```

Pretty annoying indeed. Using a loop is the recommended approach.

The resources also accept arbitrary user-data that won't be touched in any case.<br/>
Users can set and get them through the `data` member function as it follows:

```cpp
resource->data(std::make_shared<int>(42));
std::shared_ptr<void> data = resource->data();
```

Resources expect a `std::shared_pointer<void>` and return it, therefore any kind of data is welcome.<br/>
Users can explicitly specify a type other than `void` when calling the `data` member function:

```cpp
std::shared_ptr<int> data = resource->data<int>();
```

Remember from the previous section that a handle will keep itself alive until one invokes the `close` member function on it.<br/>
To know what are the handles that are still alive and bound to a given loop, just do the following:

```cpp
loop.walk([](uvw::BaseHandle &){ /* application code here */ });
```

`BaseHandle` exposes a few methods and cannot be promoted to the original type of the handle (even though `type` and `category` member functions fill the gap somehow).<br/>
Anyway, it can be used to close the handle that originated from it. As an example, all the pending handles can be closed easily as it follows:

```cpp
loop.walk([](uvw::BaseHandle &h){ h.close(); });
```

No need to keep track of them.

To know what are the available resources' types, please refer the API reference.

## The event-based approach

For `uvw` offers an event-based approach, resources are small event emitters to which listeners can be attached.<br/>
Attaching a listener to a resource is the recommended way to be notified about changes.<br/>
Listeners must be callable objects of type `void(EventType &, ResourceType &)`, where:

* `EventType` is the type of the event for which they have been designed.
* `ResourceType` is the type of the resource that has originated the event.

It means that the following function types are all valid:

* `void(EventType &, ResourceType &)`
* `void(const EventType &, ResourceType &)`
* `void(EventType &, const ResourceType &)`
* `void(const EventType &, const ResourceType &)`

Once more, please note that there is no need to keep around references to the resources: they will pass themselves as an argument whenever an event is published.

There exist two methods to attach an event to a resource:

* `resource.once<EventType>(listener)`: the listener will be automatically removed after the first event of the given type.
* `resource.on<EventType>(listener)`: to be used for long-running listeners.

Both of them return an object of type `ResourceType::Connection` (as an example, `TcpHandle::Connection`).<br/>
A connection object can be used later as an argument to the `erase` member function of the resource to remove the listener.<br/>
There exists also the `clear` member function to drop all the listeners at once.

Almost all the resources use to emit `ErrorEvent` events in case of errors.<br/>
All the other events are specific for the given resource and documented in the API reference.

The code below shows how to create a simple tcp server using `uvw`:

```cpp
auto loop = uvw::Loop::getDefault();
auto tcp = loop.resource<uvw::TcpHandle>();

tcp->on<uvw::ErrorEvent>([](const uvw::ErrorEvent &, uvw::TcpHandle &) { /* something went wrong */ });

tcp->on<uvw::ListenEvent>([](const uvw::ListenEvent &, uvw::TcpHandle &srv) {
    std::shared_ptr<uvw::TcpHandle> client = srv.loop().resource<uvw::TcpHandle>();
    client->once<uvw::EndEvent>([](const uvw::EndEvent &, uvw::TcpHandle &client) { client.close(); });
    client->on<uvw::DataEvent>([](const uvw::DataEvent &, uvw::TcpHandle &) { /* data received */ });
    srv.accept(*client);
    client->read();
});

tcp->bind("127.0.0.1", 4242);
tcp->listen();
```

Note also that `uvw::TcpHandle` already supports _IPv6_ out-of-the-box. The statement above is equivalent to `tcp->bind<uvw::IPv4>("127.0.0.1", 4242)`.<br/>
It's suffice to explicitly specify `uvw::IPv6` as the underlying protocol to use it.

The API reference is the recommended documentation for further details about resources and their methods.

# Contributors

If you want to contribute, please send patches as pull requests against the branch master.<br/>
Check the [contributors list](https://github.com/skypjack/uvw/blob/master/AUTHORS) to see who has partecipated so far.

# Projects that use `uvw`

Below an incomplete list of projects that use `uvw`:

* Internal tools (not publicly available) at **[Cynny SpA](https://www.morphcast.com/)** and **[Cynny Space](http://www.cynnyspace.com/)**.
* **[Calaos.fr](https://www.calaos.fr/en/)** (Open source home automation) on [GitHub](https://github.com/calaos).
* **[Iroha](http://iroha.tech/en/) - A simple, decentralized ledger** on [Github](https://github.com/hyperledger/iroha).
* **Iroha blockchain core** on [Github](https://github.com/finshield/iroha-core).
* **Ecwid Console Downloader** on [GitHub](https://github.com/dvetutnev/Ecwid-Console-downloader).
* **Simple network ping pong for lazy students** on [GitHub](https://github.com/dvetutnev/ping_pong).

If you know of other projects that use `libuv` through `uvw`, feel free to open a PR and I'll be glad to add them to the list.

# License

Code and documentation Copyright (c) 2017 Michele Caini.<br/>
Code released under [the MIT license](https://github.com/skypjack/uvw/blob/master/LICENSE).<br/>
Docs released under [Creative Commons](https://github.com/skypjack/uvw/blob/master/docs/LICENSE).

# Donation

Developing and maintaining `uvw` takes some time and lots of coffee. It still lacks a proper test suite, documentation is partially incomplete and not all functionalities have been fully implemented yet.<br/>
If you want to support this project, you can offer me an espresso. I'm from Italy, we're used to turning the best coffee ever in code. If you find that it's not enough, feel free to support me the way you prefer.<br/>
Take a look at the donation button at the top of the page for more details or just click [here](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=W2HF9FESD5LJY&lc=IT&item_name=Michele%20Caini&currency_code=EUR&bn=PP%2dDonationsBF%3abtn_donateCC_LG%2egif%3aNonHosted).
