recvfd.c

unix环境高级编程的源代码

#include    <sys/types.h>
#include    <sys/socket.h>        /* struct msghdr */
#include    <sys/uio.h>            /* struct iovec */
#include    <stddef.h>
#include    "ourhdr.h"

/* Receive a file descriptor from another process (a server).
 * In addition, any data received from the server is passed
 * to (*userfunc)(STDERR_FILENO, buf, nbytes).  We have a
 * 2-byte protocol for receiving the fd from send_fd(). */

int
recv_fd(int servfd, ssize_t (*userfunc)(int, const void *, size_t))
{
    int                newfd, nread, status;
    char            *ptr, buf[MAXLINE];
    struct iovec    iov[1];
    struct msghdr    msg;
    status = -1;
    for ( ; ; ) {
        iov[0].iov_base = buf;
        iov[0].iov_len  = sizeof(buf);
        msg.msg_iov     = iov;
        msg.msg_iovlen  = 1;
        msg.msg_name    = NULL;
        msg.msg_namelen = 0;
        msg.msg_accrights = (caddr_t) &newfd;/* addr of descriptor */
        msg.msg_accrightslen = sizeof(int);     /* receive 1 descriptor */

        if ( (nread = recvmsg(servfd, &msg, 0)) < 0)
            err_sys("recvmsg error");
        else if (nread == 0) {
            err_ret("connection closed by server");
            return(-1);
        }

            /* See if this is the final data with null & status.
               Null must be next to last byte of buffer, status
               byte is last byte.  Zero status means there must
               be a file descriptor to receive. */
        for (ptr = buf; ptr < &buf[nread]; ) {
            if (*ptr++ == 0) {
                if (ptr != &buf[nread-1])
                    err_dump("message format error");
                 status = *ptr & 255;
                 if (status == 0) {
                    if (msg.msg_accrightslen != sizeof(int))
                        err_dump("status = 0 but no fd");
                    /* newfd = the new descriptor */
                } else
                    newfd = -status;
                nread -= 2;
            }
        }
        if (nread > 0)
            if ((*userfunc)(STDERR_FILENO, buf, nread) != nread)
                return(-1);

        if (status >= 0)    /* final data has arrived */
            return(newfd);    /* descriptor, or -status */
    }
}