bind & connect

[Neels Hofmeyr]

Hi osmo_sock experts,

I'm currently looking at making the osmo-hnbgw interface addresses
configurable, an I came across a detail. This is not really pressing, but while
I'm at it I might as well cover all of the addresses.

So far I see in osmo-iuh's hnbgw.c the local address osmo-hnbgw uses to accept
Iuh connections from a 3G cell, and the remote addresses of IuCS and IuPS, each
passed to osmo_sock_init():

   3G cell  -------> 1.2.3.4
                     OSMO-HNBGW
                     IuPS-local? -------> 10.9.8.7 OSMO-SGSN


So we tell one socket to listen on local 1.2.3.4 for Iuh.
We tell another to send IuPS to 10.9.8.7.

But how would I tell the IuPS to use a given local interface 1.2.3.5 to contact
the SGSN's address? Would I bind() to a given local IP address and connect() to
the remote one? I must admit that the details are not 100% clear to me. AFAIK
it can be important to set a local IP address and port to send from. So if
there's something I don't understand yet I would appreciate a hint.

Anyway, in osmo_sock_init, I see:

        if ((flags & (OSMO_SOCK_F_BIND | OSMO_SOCK_F_CONNECT)) ==
                     (OSMO_SOCK_F_BIND | OSMO_SOCK_F_CONNECT)) {
                fprintf(stderr, "invalid: both bind and connect flags set:"
                        " %s:%u\n", host, port);
                return -EINVAL;
        }

Should we have another osmo_sock_init that can set up a socket like this code I
found somewhere at sysmocom to define both ends of a connection?

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if (fd < 0) {
                printf("socket() failed: %s\n", strerror(errno));
                return -1;
        }

        memset(&bindaddr, 0, sizeof(bindaddr));
        bindaddr.sin_family = AF_INET;
        bindaddr.sin_port = htons(lport);
        rc = inet_pton(AF_INET, baddr, &(bindaddr.sin_addr));
        if (rc != 1) {
                printf("inet_pton() failed with %i: %s\n", rc, strerror(errno));
                return -1;
        }

        rc = bind(fd, (struct sockaddr *)&bindaddr, sizeof(bindaddr));
        if (rc < 0) {
                printf("bind() failed: %s\n", strerror(errno));
                return -1;
        }

        memset(&destaddr, 0, sizeof(destaddr));
        destaddr.sin_family = AF_INET;
        destaddr.sin_port = htons(dport);
        rc = inet_pton(AF_INET, dest, &(destaddr.sin_addr));
        if (rc != 1) {
                printf("inet_pton() failed with %i: %s\n", rc, strerror(errno));
                return -1;
        }

        rc = connect(fd, (const struct sockaddr *)&destaddr, sizeof(destaddr));
        if (rc < 0) {
                printf("connect() failed: %s\n", strerror(errno));
                return -1;
        }

        rc = send(fd, buf, len, 0);
        if (rc != len) {
                printf("send() failed\n");
                return -1;
        }


Thanks,

~Neels


-- 
- Neels Hofmeyr <nhofmeyr at sysmocom.de>          http://www.sysmocom.de/
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* sysmocom - systems for mobile communications GmbH
* Alt-Moabit 93
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* Sitz / Registered office: Berlin, HRB 134158 B
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