libzmq/tests/test_zmq_ppoll_signals.cpp

/*
    Copyright (c) 2021 Contributors as noted in the AUTHORS file

    This file is part of libzmq, the ZeroMQ core engine in C++.

    libzmq is free software; you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    As a special exception, the Contributors give you permission to link
    this library with independent modules to produce an executable,
    regardless of the license terms of these independent modules, and to
    copy and distribute the resulting executable under terms of your choice,
    provided that you also meet, for each linked independent module, the
    terms and conditions of the license of that module. An independent
    module is a module which is not derived from or based on this library.
    If you modify this library, you must extend this exception to your
    version of the library.

    libzmq is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
    License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

// author: E. G. Patrick Bos, Netherlands eScience Center, 2021

#include "testutil.hpp"
#include "testutil_unity.hpp"

#include <string.h> // memset
// types.h and wait.h for waitpid:
#include <sys/types.h>
#include <sys/wait.h>

static bool sigterm_received = false;

void handle_sigterm (int /*signum*/)
{
    sigterm_received = true;
}

void recv_string_expect_success_or_eagain (void *socket_,
                                           const char *str_,
                                           int flags_)
{
    const size_t len = str_ ? strlen (str_) : 0;
    char buffer[255];
    TEST_ASSERT_LESS_OR_EQUAL_MESSAGE (sizeof (buffer), len,
                                       "recv_string_expect_success cannot be "
                                       "used for strings longer than 255 "
                                       "characters");

    const int rc = zmq_recv (socket_, buffer, sizeof (buffer), flags_);
    if (rc < 0) {
        if (errno == EAGAIN) {
            printf ("got EAGAIN\n");
            return;
        } else {
            TEST_ASSERT_SUCCESS_ERRNO (rc);
        }
    } else {
        TEST_ASSERT_EQUAL_INT ((int) len, rc);
        if (str_)
            TEST_ASSERT_EQUAL_STRING_LEN (str_, buffer, len);
    }
}

void test_ppoll_signals ()
{
#ifdef ZMQ_HAVE_PPOLL
    size_t len = MAX_SOCKET_STRING;
    char my_endpoint[MAX_SOCKET_STRING];
    pid_t child_pid;

    /* Get a random TCP port first */
    setup_test_context ();
    void *sb = test_context_socket (ZMQ_REP);
    bind_loopback (sb, 0, my_endpoint, len);
    test_context_socket_close (sb);
    teardown_test_context ();

    do {
        child_pid = fork ();
    } while (child_pid == -1); // retry if fork fails

    if (child_pid > 0) { // parent
        setup_test_context ();
        void *socket = test_context_socket (ZMQ_REQ);
        // to make sure we don't hang when the child has already exited at the end, we set a receive timeout of five seconds
        int recv_timeout = 5000;
        TEST_ASSERT_SUCCESS_ERRNO (zmq_setsockopt (
          socket, ZMQ_RCVTIMEO, &recv_timeout, sizeof (recv_timeout)));
        TEST_ASSERT_SUCCESS_ERRNO (zmq_bind (socket, my_endpoint));
        // bind is on the master process to avoid zombie children to hold on to binds

        // first send a test message to check whether the signal mask is setup in the child process
        send_string_expect_success (socket, "breaker breaker", 0);
        recv_string_expect_success (socket, "one-niner", 0);

        // then send the signal
        kill (child_pid, SIGTERM);

        // for good measure, and to make sure everything went as expected, close off with another handshake, which will trigger the second poll call on the other side
        send_string_expect_success (socket, "breaker breaker", 0);
        // in case the 1 second sleep was not enough on the child side, we are also fine with an EAGAIN here
        recv_string_expect_success_or_eagain (socket, "one-niner", 0);

        // finish
        test_context_socket_close (socket);

        // wait for child
        int status = 0;
        pid_t pid;
        do {
            pid = waitpid (child_pid, &status, 0);
        } while (-1 == pid
                 && EINTR == errno); // retry on interrupted system call

        if (0 != status) {
            if (WIFEXITED (status)) {
                printf ("exited, status=%d\n", WEXITSTATUS (status));
            } else if (WIFSIGNALED (status)) {
                printf ("killed by signal %d\n", WTERMSIG (status));
            } else if (WIFSTOPPED (status)) {
                printf ("stopped by signal %d\n", WSTOPSIG (status));
            } else if (WIFCONTINUED (status)) {
                printf ("continued\n");
            }
        }

        if (-1 == pid) {
            printf ("waitpid returned -1, with errno %s\n", strerror (errno));
        }
    } else { // child
        setup_test_context ();
        // set up signal mask and install handler for SIGTERM
        sigset_t sigmask, sigmask_without_sigterm;
        sigemptyset (&sigmask);
        sigaddset (&sigmask, SIGTERM);
        sigprocmask (SIG_BLOCK, &sigmask, &sigmask_without_sigterm);
        struct sigaction sa;
        memset (&sa, '\0', sizeof (sa));
        sa.sa_handler = handle_sigterm;
        TEST_ASSERT_SUCCESS_ERRNO (sigaction (SIGTERM, &sa, NULL));

        void *socket = test_context_socket (ZMQ_REP);
        TEST_ASSERT_SUCCESS_ERRNO (zmq_connect (socket, my_endpoint));

        zmq_pollitem_t pollitems[] = {
          {socket, 0, ZMQ_POLLIN, 0},
        };

        // first receive test message and send back handshake
        recv_string_expect_success (socket, "breaker breaker", 0);
        send_string_expect_success (socket, "one-niner", 0);

        // now start ppolling, which should exit with EINTR because of the SIGTERM
        TEST_ASSERT_FAILURE_ERRNO (
          EINTR, zmq_ppoll (pollitems, 1, -1, &sigmask_without_sigterm));
        TEST_ASSERT_TRUE (sigterm_received);

        // poll again for the final handshake
        TEST_ASSERT_SUCCESS_ERRNO (
          zmq_ppoll (pollitems, 1, -1, &sigmask_without_sigterm));
        TEST_ASSERT_BITS_HIGH (ZMQ_POLLIN, pollitems[0].revents);
        // receive and send back handshake
        recv_string_expect_success (socket, "breaker breaker", 0);
        send_string_expect_success (socket, "one-niner", 0);

        // finish
        // wait before closing socket, so that parent has time to receive
        sleep (1);
        test_context_socket_close (socket);
        _Exit (0);
    }
#else
    TEST_IGNORE_MESSAGE ("libzmq without zmq_ppoll, ignoring test");
#endif // ZMQ_HAVE_PPOLL
}

// We note that using zmq_poll instead of zmq_ppoll in the test above, while
// also not using the sigmask, will fail most of the time, because it is
// impossible to predict during which call the signal will be handled. Of
// course, every call could be surrounded with an EINTR check and a subsequent
// check of sigterm_received's value, but even then a race condition can occur,
// see the explanation given here: https://250bpm.com/blog:12/

int main ()
{
    UNITY_BEGIN ();
    RUN_TEST (test_ppoll_signals);
    return UNITY_END ();
}