Date: Sat, 22 Feb 1997 21:37:46 -0500 From: Matt Thomas <matt@lkg.dec.com> To: Terry Lambert <terry@lambert.org> Cc: hackers@FreeBSD.ORG Subject: Re: Alternatives to SYSV IPC? Message-ID: <3.0.32.19970222213738.006a1cb0@netrix.lkg.dec.com>
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>The length field would not be necessary if the framing were enforced
>by the transport: a receive into a buffer larger than the maximum
>allowable message type that could be framed for any given transmitter
>state would be sufficient. You do a recv into the buffer, then you
>dispatch based on a field dereference from the newly acquired data
>(probably a type field), and dispatch the data for processing from
>a big switch statement. No additional recv's necessary.
This can be done today with the BSD4.4 socket framework. With AF_LOCAL
(AF_UNIX) sockets and the use of MSG_EOR with send() and MSG_WAITALL
with recvmsg() it does work. I've attached a small example program
(which works under FreeBSD 2.1.0 and Digital UNIX 4.0).
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/un.h>
#include <sys/fcntl.h>
int
main(
int argc,
void **argv)
{
int fds[2];
struct msghdr msg;
char buf[20];
struct iovec iov[1];
int cc;
if (socketpair(AF_UNIX, SOCK_STREAM, 0, fds) < 0)
perror("socketpair");
if (send(fds[1], "Hi ", 3, MSG_EOR) < 0)
perror("send");
if (send(fds[1], "There", 5, MSG_EOR) < 0)
perror("send");
close(fds[1]);
bzero(&msg, sizeof(msg));
iov[0].iov_base = buf;
iov[0].iov_len = sizeof(buf);
msg.msg_iov = iov;
msg.msg_iovlen = 1;
for (;;) {
cc = recvmsg(fds[0], &msg, 0);
if (cc <= 0)
break;
buf[cc] = '\0';
printf("%d: %s%s", cc, buf, msg.msg_flags & MSG_EOR ? " (EOR)\n" : "");
}
if (cc < 0)
perror("recvmsg");
putchar('\n');
}
--
Matt Thomas Internet: matt@3am-software.com
3am Software Foundry WWW URL:
http://www.3am-software.com/bio/matt.html
Westford, MA Disclaimer: I disavow all knowledge of this message
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