TCP port in ZMQ_LAST_ENDPOINT depends on global locale

[carrotIndustries]

Issue description

The TCP port formatting in ZMQ_LAST_ENDPOINT depends on the locale set by std::locale::global. With thousands grouping enabled, the port number contains commas. UDP and other ports are likely affected as well.

Environment

• libzmq version 4.3.1
• OS: Arch Linux

Minimal test code / Steps to reproduce the issue

#include <zmq.h>
#include <assert.h>
#include <iostream>
#include <sstream>

int main(void) {
    struct comma : std::numpunct<char> {
        char do_thousands_sep() const override
        {
            return ',';
        } // comma
        std::string do_grouping() const { return "\3"; } // groups of 3 digits
    };
    std::locale::global(std::locale(std::locale("C"), new comma));
    void *context = zmq_ctx_new ();
    void *sock = zmq_socket (context, ZMQ_REP);
    int rc = zmq_bind (sock, "tcp://127.0.0.1:*");
    assert(rc == 0);
    char ep[1024];
    size_t sz = sizeof(ep);
    zmq_getsockopt(sock, ZMQ_LAST_ENDPOINT, ep, &sz);
    std::cout << "EP " << ep << std::endl;
}

What's the actual result?

EP tcp://127.0.0.1:39,375

What's the expected result?

EP tcp://127.0.0.1:39375

Possible fix

In https://github.com/zeromq/libzmq/blob/master/src/tcp_address.cpp#L134, use s.imbue(std::locale("C"));

[bluca]

In https://github.com/zeromq/libzmq/blob/master/src/tcp_address.cpp#L134, use s.imbue(std::locale("C"));

Sounds about right, could you please send a PR?

[carrotIndustries]

Sounds about right, could you please send a PR?

As far as I can tell MSVC doesn't support the "C" locale: https://stackoverflow.com/a/4497266 I'd rather not have ugly #ifdefs in that code. Any ideas on resetting the locale to something sensible in a portable way?

[bluca]

I'm afraid it's outside of my area - @sigiesec any idea?

[bluca]

but if there isn't any, better an ugly ifdef than an ugly bug

[sigiesec]

I think it would be preferable to change this to use sprintf, e.g., so that this isn't dependent on the locale at all.

[carrotIndustries]

If I read the docs correctly, std::locale::classic() should have the same effect as std::locale("C") while being portable.