GoAutoSocket (GAS)

The GAS library provides auto-reconnecting TCP sockets in a tiny, fully tested, thread-safe API.

The TCPClient struct embeds a net.TCPConn and overrides its Read() and Write() methods, making it entirely compatible with the net.Conn interface and the rest of the net package. This means you should be able to use this library by just replacing net.Dial with gas.Dial in your code.

GAS uses the atomic package to synchronize reconnections between multiple goroutines; it doesn't add any extra locking upon the standard net.TCPConn API, except to protect its configuration from races. Hence, you should always use the TCPClient.Set* methods before you actually start doing any I/O.

Install

go get -u github.com/teh-cmc/goautosocket

Usage

To test the library, you can run a local TCP server with:

$ ncat -l 9999 -k

and run this code:

package main

import (
    "log"
    "time"

    "github.com/teh-cmc/goautosocket"
)

func main() {
    // connect to a TCP server
    conn, err := gas.Dial("tcp", "localhost:9999")
    if err != nil {
        log.Fatal(err)
    }

    // client sends "hello, world!" to the server every second
    for {
        _, err := conn.Write([]byte("hello, world!\n"))
        if err != nil {
            // if the client reached its retry limit, give up
            if err == gas.ErrMaxRetries {
                log.Println("client gave up, reached retry limit")
                return
            }
            // not a GAS error, just panic
            log.Fatal(err)
        }
        log.Println("client says hello!")
        time.Sleep(time.Second)
    }
}

Then try to kill and reboot your server, the client will automatically reconnect and start sending messages again; unless it has reached its retry limit.

Examples

An advanced example of a client writing to a buggy server that's randomly crashing and rebooting:

package main

import (
    "log"
    "math/rand"
    "net"
    "sync"
    "time"

    "github.com/teh-cmc/goautosocket"
)

func main() {
    rand.Seed(time.Now().UnixNano())

    // open a server socket
    s, err := net.Listen("tcp", "localhost:0")
    if err != nil {
        log.Fatal(err)
    }
    // save the original port
    addr := s.Addr()

    // connect a client to the server
    c, err := gas.Dial("tcp", s.Addr().String())
    if err != nil {
        log.Fatal(err)
    }
    defer c.Close()

    // shut down and boot up the server randomly
    var swg sync.WaitGroup
    swg.Add(1)
    go func() {
        defer swg.Done()
        for i := 0; i < 5; i++ {
            log.Println("server up")
            time.Sleep(time.Millisecond * 100 * time.Duration(rand.Intn(20)))
            if err := s.Close(); err != nil {
                log.Fatal(err)
            }
            log.Println("server down")
            time.Sleep(time.Millisecond * 100 * time.Duration(rand.Intn(20)))
            s, err = net.Listen("tcp", addr.String())
            if err != nil {
                log.Fatal(err)
            }
        }
    }()

    // client writes to the server and reconnects when it has to
    // this is the interesting part
    var cwg sync.WaitGroup
    cwg.Add(1)
    go func() {
        defer cwg.Done()
        for {
            if _, err := c.Write([]byte("hello, world!\n")); err != nil {
                switch e := err.(type) {
                case gas.Error:
                    if e == gas.ErrMaxRetries {
                        log.Println("client leaving, reached retry limit")
                        return
                    }
                default:
                    log.Fatal(err)
                }
            }
            log.Println("client says hello!")
        }
    }()

    // terminates the server indefinitely
    swg.Wait()
    if err := s.Close(); err != nil {
        log.Fatal(err)
    }

    // wait for the client to give up
    cwg.Wait()
}

You can also find an example with concurrency here.

Disclaimer

This was built with my needs in mind, no more, no less. That is, I needed a simple, tested and thread-safe API to handle a situation in which I have:

• on one end, a lot of goroutines concurrently writing to a TCP socket
• on the other end, a TCP server that I have no control over (hence the main reason why UDP is out of the question) and which might be rebooted at anytime I also needed the ability to give up on sending a message after an abritrary amount of tries/time (i.e., ERR_MAX_TRIES). Pretty straightforward stuff.

Basically, my use case is this situation.

Surprisingly, I couldn't find such a library (I guess I either didn't look in the right place, or just not hard enough..? oh well); so here it is. Do not hesitate to send a pull request if this doesn't cover all your needs (and it probably won't), they are more than welcome.

If you're looking for some more insight, you might also want to look at this discussion we had on reddit.

License

The MIT License (MIT) - see LICENSE for more details

Copyright (c) 2015 Clement 'cmc' Rey cr.rey.clement@gmail.com