Go wrapper for SysV Message Queues

sysv_mq is a Go wrapper for [SysV Message Queues](). It's important you
read the manual for SysV Message Queues, msgrcv(2) and
msgsnd(2) before using this library. sysv_mq is a very light
wrapper, and will not hide any errors from you.

Documentation for the public API can be viewed at Godoc.

sysv_mq is tested on Linux and OS X. To run the tests run make test. This
makes sure that any messages queues currently on your system are deleted before
running the tests.

Example

Example which sends a message to the queue with key: 0xDEADBEEF (or creates it
if it doesn't exist).

package main

import (
    "fmt"
    "github.com/Shopify/sysv_mq"
)

func main() {
    mq, err := sysv_mq.NewMessageQueue(&sysv_mq.QueueConfig{
        Key:     0xDEADBEEF,               // SysV IPC key
        MaxSize: 1024,                     // Max size of a message
        Mode:    sysv_mq.IPC_CREAT | 0600, // Creates if it doesn't exist, 0600 permissions
    })
    if err != nil {
        fmt.Println(err)
    }

    // Send a message to the queue, with message type 1, without flags.
    err = mq.SendString("Hello World", 1, 0)
    if err != nil {
        fmt.Println(err)
    }

    // Receive a message from the queue, 0 gives you the top message regardless of
    // message type passed to send().
    response, mtype, err := mq.ReceiveString(0)
    if err != nil {
        fmt.Println(err)
    }
    fmt.Printf("[%d] %s", mtype, response)
    // Output:
    // [1] Hello World
}

Caveats

• The underlying SysV API works with binary data. You can send any kind of byte slice using
  SendBytes() and ReceiveBytes(). SendString() and ReceiveString() are a simple
  wrapper around the byteslice functions for convenience, and will use UTF-8 encoding.
• The send and receive methods are blocking by default. You can pass the sysv_mq.IPC_NOWAIT
  flag to make them return immediately.
• SendBytes(), ReceiveBytes() and NewMessageQueue() all do syscalls, and these could
  be interrupted by a signal (very common if you do a blocking ReceiveBytes()). The
  error will be EAGAIN in that case. It's not wrapped here, because EAGAIN
  is also the error if the call would block or the queue is full. Consult the
  manual for more information.