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use "die"
use "errno"
use "execvp"
use "fmt"
use "result"
use "syswrap"
use "wait"

pkg std =
	const run	: (cmd : byte[:][:]	-> waitstatus)
	const spork	: (cmd : byte[:][:]	-> result((pid, fd, fd), errno))
	const espork	: (cmd : byte[:][:]	-> result((pid, fd, fd, fd), errno))
	const filterfd	: (fd : fd, cmd  : byte[:][:] -> result(pid, errno))
;;

const run = {cmd
	var pid

	pid = fork()
	/* error  */
	if pid < 0
		-> `Waiterror
	elif pid == 0
		execvp(cmd[0], cmd)
		die("failed exec\n")
	else
		-> wait(pid)
	;;
}


const spork = {cmd
	var infds : fd[2], outfds : fd[2]
	var err

	/* open up pipes */
	err = pipe(&infds) 
	if err != Enone
		-> `Err err
	;;
	err = pipe(&outfds)
	if err != Enone
		-> `Err err
	;;

	match sporkfd(cmd, infds, outfds, [-1, 2])
	| `Ok pid:
		/* close unused fd ends */
		close(infds[0]);
		close(outfds[1]);
		-> `Ok (pid, infds[1], outfds[0])
	| `Err m:
		-> `Err m
	;;
}

const espork = {cmd
	var infds : fd[2], outfds : fd[2], errfds : fd[2]
	var err

	/* open up pipes */
	err = pipe(&infds) 
	if err != Enone
		-> `Err err
	;;
	err = pipe(&outfds)
	if err != Enone
		-> `Err err
	;;
	err = pipe(&errfds)
	if err != Enone
		-> `Err err
	;;

	match sporkfd(cmd, infds, outfds, errfds)
	| `Ok pid:
		/* close unused fd ends */
		close(infds[0]);
		close(outfds[1]);
		close(errfds[1]);
		-> `Ok (pid, infds[1], outfds[0], errfds[0])
	| `Err m:
		-> `Err m
	;;
}

const filterfd = {fd, cmd
	var outfds : fd[2]
	var err

	err = pipe(&outfds)
	if err != Enone
		-> `Err err
	;;

	match sporkfd(cmd, [fd, -1], outfds, [-1, 2])
	| `Ok pid:
		dup2(outfds[0], fd)
		close(outfds[0]);
		close(outfds[1]);
		-> `Ok pid
	| `Err e:
		-> `Err e
	;;
}

const sporkfd = {cmd, infds, outfds, errfds
	var pid

	pid = fork()
	/* error  */
	if pid < 0
		/* we don't want to leak the pipe fds on error */
		close(infds[0]);
		close(infds[1]);
		close(outfds[0]);
		close(outfds[1]);
		close(errfds[0]);
		close(errfds[1]);
		-> `Err (pid : errno)
	/* child */
	elif pid == 0
		/* stdin/stdout for our communication. */
		match dup2(infds[0], 0)
		| `Ok _:	/* nothing */
		| `Err e:	-> `Err e
		;;
		match dup2(outfds[1], 1)
		| `Ok _:	/* nothing */
		| `Err e:	-> `Err e
		;;
		match dup2(errfds[1], 2)
		| `Ok _:	/* nothing */
		| `Err e:	-> `Err e
		;;

		/* close the fds we duped */
		if infds[0] != 0
			close(infds[0])
		;;
		if outfds[1] != 1
			close(outfds[1])
		;;
		if errfds[1] != 2
			close(errfds[1])
		;;

		/* close the unused ends */
		close(infds[1])
		close(outfds[0])
		close(errfds[0])

		execvp(cmd[0], cmd)
		/* if fork succeeds, we never return */
		die("exec failed")
	/* parent */
	else
		-> `Ok pid
	;;
}