evio/README.md

<p align="center">
<img 
    src="logo.png" 
    width="213" height="75" border="0" alt="evio">
<br>
<a href="https://travis-ci.org/tidwall/evio"><img src="https://img.shields.io/travis/tidwall/evio.svg?style=flat-square" alt="Build Status"></a>
<a href="https://godoc.org/github.com/tidwall/evio"><img src="https://img.shields.io/badge/api-reference-blue.svg?style=flat-square" alt="GoDoc"></a>
</p>
<p align="center">Event Networking for Go</a></p>

`evio` is an event driven networking framework that is fast and small. It makes direct [epoll](https://en.wikipedia.org/wiki/Epoll) and [kqueue](https://en.wikipedia.org/wiki/Kqueue) syscalls rather than the standard Go [net](https://golang.org/pkg/net/) package, and works in a similar manner as [libuv](https://github.com/libuv/libuv) and [libevent](https://github.com/libevent/libevent).

The goal of this project is to create a server framework for Go that performs on par with [Redis](http://redis.io) and [Haproxy](http://www.haproxy.org) for packet handling. My hope is to use this as a foundation for [Tile38](https://github.com/tidwall/tile38) and a future L7 proxy for Go... and a bunch of other stuff.

## Features

- [Very fast](#performance) single-threaded event loop
- Simple API
- Low memory usage
- Supports tcp4, tcp6, and unix sockets
- Allows [multiple network binding](#multiple-addresses) on the same event loop
- Flexible [ticker](#ticker) event
- Fallback for non-epoll/kqueue operating systems by simulating events with the [net](https://golang.org/pkg/net/) package.

## Getting Started

### Installing

To start using evio, install Go and run `go get`:

```sh
$ go get -u github.com/tidwall/evio
```

This will retrieve the library.

### Usage

Starting a server is easy with `evio`. Just set up your events and pass them to the `Serve` function along with the binding address(es). Each connections receives an ID that's passed to various events to differentiate the clients. At any point you can close a client or shutdown the server by return a `Close` or `Shutdown` action from an event.

Example echo server that binds to port 5000:

```go
package main

import "github.com/tidwall/evio"

func main() {
	var events evio.Events
	events.Data = func(id int, in []byte) (out []byte, action evio.Action) {
		out = in
		return
	}
	if err := evio.Serve(events, "tcp://localhost:5000"); err != nil {
		panic(err.Error())
	}
}
```

Here the only event being used is `Data`, which fires when the server receives input data from a client.
The exact same input data is then passed through the output return value, which is then sent back to the client. 

Connect to the echo server:

```sh
$ telnet localhost 5000
```

### Events

The event type has a bunch of handy events:

- `Serving` fires when the server is ready to accept new connections.
- `Opened` fires when a connection has opened.
- `Closed` fires when a connection has closed.
- `Detach` fires when a connection has been detached using the `Detach` return action.
- `Data` fires when the server receives new data from a connection.
- `Prewrite` fires prior to all write attempts from the server.
- `Postwrite` fires immediately after every write attempt.
- `Tick` fires immediately after the server starts and will fire again after the amount of time specified by the `delay` return value.

### Multiple addresses

An server can bind to multiple addresses and share the same event loop.

```go
evio.Serve(events, "tcp://192.168.0.10:5000", "unix://socket")
```

### Ticker

The `Tick` event fires ticks at a specified interval. 
The first tick fires immediately after the `Serving` events.

```go
events.Tick = func() (delay time.Duration, action Action){
	log.Printf("tick")
	delay = time.Second
	return
}
```

### Wake up

A connection can be woken up using the `wake` function that is made available through the `Serving` event. This is useful for when you need to offload an operation to a background goroutine and then later notify the event loop that it's time to send some data.

```go
var wake func(id int) bool
var mu sync.Mutex
var done = make(map[int]bool)

events.Serving = func(wakefn func(id int) bool, addrs []net.Addr) (action evio.Action) {
	wake = wakefn // hang on to the wake function
	return
}
events.Data = func(id int, in []byte) (out []byte, action evio.Action) {
	if in == nil {
		// look for `in` param equal to `nil` following a wake call.
		mu.Lock()
		if done[id]{
			out = []byte("done\r\n")
		}
		mu.Unlock()
	} else if string(in) == "exec\r\n" {
		go func(){
			// do some long running operation
			time.Sleep(time.Second*5)
			mu.Lock()
			done[id] = true
			mu.Unlock()
			wake(id)
		}()
	} else {
		out = in
	}
	return
}
```

### Data translations

The `Translate` function is utility that wraps events and provides a `ReadWriter` that's used to translate data off the wire from one format to another. This can be useful for transparently adding compression or encryption.

For example, let's say we need TLS support:

```go
var events Events

// ... fill the events with happy functions

cer, err := tls.LoadX509KeyPair("certs/ssl-cert-snakeoil.pem", "certs/ssl-cert-snakeoil.key")
if err != nil {
	log.Fatal(err)
}
config := &tls.Config{Certificates: []tls.Certificate{cer}}

// wrap the events with a TLS translator

events = evio.Translate(events, nil, 
	func(rw io.ReadWriter) io.ReadWriter {
		return tls.Server(evio.NopConn(rw), config)
	},
)

log.Fatal(Serve(events, "tcp://0.0.0.0:443"))
```

Here we wrapped the event with a TLS translator. The `evio.NopConn` function is used to converts the `ReadWriter` a `net.Conn` so the `tls.Server` will work.

There's a working TLS example at [examples/http-server/main.go](examples/http-server/main.go) that will bind to port 8080 and 4443 using an developer SSL certificate. The 8080 connections will be insecure and the 4443 will be secure.

```sh
$ cd examples/http-server
$ go run main.go --tlscert example.pem
2017/11/02 06:24:33 http server started on port 8080
2017/11/02 06:24:33 https server started on port 4443
```

```sh
$ curl http://localhost:8080
Hello World!
$ curl -k https://localhost:4443
Hello World!
```

## More examples

Please check out the [examples](examples) subdirectory for a simplified [redis](examples/redis-server/main.go) clone, an [echo](examples/echo-server/main.go) server, and a very basic [http](examples/http-server/main.go) server.

To run an example:

```bash
$ go run examples/http-server/main.go
$ go run examples/redis-server/main.go
$ go run examples/echo-server/main.go
```

## Performance

The benchmarks below use pipelining which allows for combining multiple Redis commands into a single packet.

**Real Redis**

```
$ redis-server
```
```
redis-benchmark -p 6379 -t ping,set,get -q -P 32
PING_INLINE: 869565.19 requests per second
PING_BULK: 1694915.25 requests per second
SET: 917431.19 requests per second
GET: 1265822.75 requests per second
```

**Redis clone (evio)**

```
$ go run examples/redis-server/main.go
```
```
redis-benchmark -p 6380 -t ping,set,get -q -P 32
PING_INLINE: 2380952.50 requests per second
PING_BULK: 2380952.50 requests per second
SET: 2325581.25 requests per second
GET: 2222222.25 requests per second
```

*Running on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.7*

## Contact

Josh Baker [@tidwall](http://twitter.com/tidwall)

## License

`evio` source code is available under the MIT [License](/LICENSE).