package cmsg

//#include "cmsg.c"
import "C"

import (
	"net"
	"os"
	"syscall"
	"unsafe"
)

func BuildScmRights(file *os.File) []byte {
	fd := file.Fd()
	length := unsafe.Sizeof(fd)
	buf := make([]byte, CMSG_SPACE(length))
	cmsg := (*syscall.Cmsghdr)(unsafe.Pointer(&buf[0]))
	cmsg.Level = syscall.SOL_SOCKET
	cmsg.Type = syscall.SCM_RIGHTS
	cmsg.SetLen(CMSG_LEN(length))
	data := CMSG_DATA(cmsg)
	*((*int)(unsafe.Pointer(data))) = fd
	return buf
}

func WriteScmRights(c *net.UnixConn, file *os.File) os.Error {
	buf := BuildScmRights(file)
	_, _, err := c.WriteMsgUnix(nil, buf, nil)
	return err
}

func ReadScmRights(oob []byte) (*os.File, os.Error) {
	cmsg := (*syscall.Cmsghdr)(unsafe.Pointer(&oob[0]))
	if cmsg.Level != syscall.SOL_SOCKET {
		return nil, os.NewError("Level != SOL_SOCKET")
	}
	if cmsg.Type != syscall.SCM_RIGHTS {
		return nil, os.NewError("Type != SCM_RIGHTS")
	}
	fd := *(*int)(unsafe.Pointer(CMSG_DATA(cmsg)))
	file := os.NewFile(fd, "")
	return file, nil
}

func NewShmRightsBuffer() []byte {
	var fd int
	return make([]byte, CMSG_LEN(unsafe.Sizeof(fd)))
}

//#define CMSG_ALIGN(len) (((len) + sizeof (size_t) - 1) & (size_t) ~(sizeof (size_t) - 1))

func CMSG_SPACE(length int) int {
	//#define CMSG_SPACE(len) (CMSG_ALIGN (len) + CMSG_ALIGN (sizeof (struct cmsghdr)))
	return int(C.CMSG_SPACE_(C.size_t(length)))
}

func CMSG_LEN(length int) int {
	//#define CMSG_LEN(len)   (CMSG_ALIGN (sizeof (struct cmsghdr)) + (len))
	return int(C.CMSG_LEN_(C.size_t(length)))
}

func CMSG_DATA(cmsg *syscall.Cmsghdr) *byte {
	//# define CMSG_DATA(cmsg) ((unsigned char *) ((struct cmsghdr *) (cmsg) + 1))
	cCmsg := (*C.cmsghdr_t)(unsafe.Pointer(cmsg))
	return (*byte)(unsafe.Pointer(C.CMSG_DATA_(cCmsg)))
}