ipcmsg example

test.go

package main

import (
	"log"
	"os"
	"os/exec"
	"syscall"
	"time"

	"github.com/poolpOrg/ipcmsg"
)

// fork a child and build an ipcmsg channel over the child fd
//
func parent() {
	log.Println("starting parent")
	pid, fd := fork_child()

	_, child_w := ipcmsg.Channel(pid, fd)

	for {
		time.Sleep(1 * time.Second)
		pfd, _ := syscall.Open("/private/etc/passwd", 0700, 0)
		child_w <- ipcmsg.MessageWithFd(42, []byte("foobar"), pfd)

		child_w <- ipcmsg.Message(42, []byte("barbaz"))
		child_w <- ipcmsg.Message(42, []byte("barbaz"))
		child_w <- ipcmsg.Message(42, []byte("barbaz"))
		child_w <- ipcmsg.Message(42, []byte("barbaz"))

	}
}

// build an ipcmsg channel over fd 3
//
func child() {
	log.Println("hellow, i'm child of", os.Getppid())

	parent_r, _ := ipcmsg.Channel(os.Getppid(), 3)

	for {
		msg := <-parent_r
		if msg.Fd != -1 {
			log.Println(string(msg.Data), "fd=", msg.Fd)
			syscall.Close(msg.Fd)
		} else {
			log.Println(string(msg.Data), "nofd")
		}
	}
}

// fork a child and reexec the process with env REEXEC=CHILD so executable can assign a
// different task to child in main()
//
func fork_child() (int, int) {
	binary, err := exec.LookPath(os.Args[0])
	if err != nil {
		log.Fatal(err)
	}

	sp, err := syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM, syscall.AF_UNSPEC)
	if err != nil {
		log.Fatal(err)
	}

	procAttr := syscall.ProcAttr{}
	procAttr.Files = []uintptr{
		uintptr(syscall.Stdin),
		uintptr(syscall.Stdout),
		uintptr(syscall.Stderr),
		uintptr(sp[0]),
	}
	procAttr.Env = []string{
		"REEXEC=CHILD",
	}

	var pid int

	pid, err = syscall.ForkExec(binary, []string{os.Args[0]}, &procAttr)
	if err != nil {
		log.Fatal(err)
	}

	if syscall.Close(sp[0]) != nil {
		log.Fatal(err)
	}

	return pid, sp[1]
}

// execute parent() or child() depending on the process REEXEC name
//
func main() {
	reexec := os.Getenv("REEXEC")
	switch reexec {
	case "":
		parent()
	case "CHILD":
		child()
	}
}