DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org D6BAC3858D33
Date: Tue, 6 Jun 2023 11:01:20 +0000 (UTC)
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Message-ID: <1010129621.187968.1686049280947@mail.yahoo.com>
Subject: On abstract sockets
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References: <1010129621 DOT 187968 DOT 1686049280947 DOT ref AT mail DOT yahoo DOT com>
From: Mike Gran via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Mike Gran <spk121 AT yahoo DOT com>
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Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>
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Hello Cygwin-

I just wanted to double-check my understanding that binding
an abstract socket (a NULL-prefixed filename) is not currently
supported on Cygwin. I think there used to be some sort
of emulation of abstract sockets, but, that's not true anymore,
right?

With the sample program below, bind for AF_UNIX traces into
fhandler_socket_local::bind, since AF_UNIX == AF_LOCAL.

fhandler_socket_local::bind copies the NULL-prefixed abstract
name using 

  strncpy (sun_path, un_addr->sun_path, len);

which truncates sun_path to be an empty string. Searching
for the existence of the empty path causes errno ENOENT.

Also, it seems unclear if winsock2 sockets supports abstract sockets
anyway.

Thanks,
Mike Gran

// tmp.c
#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>
#include <stdio.h>

int main()
{
    int s;
    struct sockaddr_un name;
    int ret;

    s = socket(AF_UNIX, SOCK_STREAM, 0);
    if (s == -1) {
        perror("socket");
        exit(1);
    }

    const char path[5] = { 0, 'f', 'o', 'o', 0};
    memset(&name, 0, sizeof(name));    
    name.sun_family = AF_UNIX;
    memcpy(name.sun_path, path, sizeof(path));
    
    ret = bind(s, (const struct sockaddr *) &name, 2 + sizeof(path));
    if (ret == -1) {
        perror("bind");
        exit(1);
    }
    return 0;
}

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