[tinc] / src / event.c

/*
    event.c -- I/O, timeout and signal event handling
    Copyright (C) 2012-2021 Guus Sliepen <guus@tinc-vpn.org>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include "system.h"

#include "dropin.h"
#include "event.h"
#include "net.h"
#include "utils.h"
#include "xalloc.h"

struct timeval now;

#ifndef HAVE_MINGW
static fd_set readfds;
static fd_set writefds;
#else
static const long READ_EVENTS = FD_READ | FD_ACCEPT | FD_CLOSE;
static const long WRITE_EVENTS = FD_WRITE | FD_CONNECT;
static DWORD event_count = 0;
#endif
static bool running;

static int io_compare(const io_t *a, const io_t *b) {
#ifndef HAVE_MINGW
        return a->fd - b->fd;
#else

        if(a->event < b->event) {
                return -1;
        }

        if(a->event > b->event) {
                return 1;
        }

        return 0;
#endif
}

static int timeout_compare(const timeout_t *a, const timeout_t *b) {
        struct timeval diff;
        timersub(&a->tv, &b->tv, &diff);

        if(diff.tv_sec < 0) {
                return -1;
        }

        if(diff.tv_sec > 0) {
                return 1;
        }

        if(diff.tv_usec < 0) {
                return -1;
        }

        if(diff.tv_usec > 0) {
                return 1;
        }

        if(a < b) {
                return -1;
        }

        if(a > b) {
                return 1;
        }

        return 0;
}

static splay_tree_t io_tree = {.compare = (splay_compare_t)io_compare};
static splay_tree_t timeout_tree = {.compare = (splay_compare_t)timeout_compare};

void io_add(io_t *io, io_cb_t cb, void *data, int fd, int flags) {
        if(io->cb) {
                return;
        }

        io->fd = fd;
#ifdef HAVE_MINGW

        if(io->fd != -1) {
                io->event = WSACreateEvent();

                if(io->event == WSA_INVALID_EVENT) {
                        abort();
                }
        }

        event_count++;
#endif
        io->cb = cb;
        io->data = data;
        io->node.data = io;

        io_set(io, flags);

        if(!splay_insert_node(&io_tree, &io->node)) {
                abort();
        }
}

#ifdef HAVE_MINGW
void io_add_event(io_t *io, io_cb_t cb, void *data, WSAEVENT event) {
        io->event = event;
        io_add(io, cb, data, -1, 0);
}
#endif

void io_set(io_t *io, int flags) {
        if(flags == io->flags) {
                return;
        }

        io->flags = flags;

        if(io->fd == -1) {
                return;
        }

#ifndef HAVE_MINGW

        if(flags & IO_READ) {
                FD_SET(io->fd, &readfds);
        } else {
                FD_CLR(io->fd, &readfds);
        }

        if(flags & IO_WRITE) {
                FD_SET(io->fd, &writefds);
        } else {
                FD_CLR(io->fd, &writefds);
        }

#else
        long events = 0;

        if(flags & IO_WRITE) {
                events |= WRITE_EVENTS;
        }

        if(flags & IO_READ) {
                events |= READ_EVENTS;
        }

        if(WSAEventSelect(io->fd, io->event, events) != 0) {
                abort();
        }

#endif
}

void io_del(io_t *io) {
        if(!io->cb) {
                return;
        }

        io_set(io, 0);
#ifdef HAVE_MINGW

        if(io->fd != -1 && WSACloseEvent(io->event) == FALSE) {
                abort();
        }

        event_count--;
#endif

        splay_unlink_node(&io_tree, &io->node);
        io->cb = NULL;
}

void timeout_add(timeout_t *timeout, timeout_cb_t cb, void *data, struct timeval *tv) {
        timeout->cb = cb;
        timeout->data = data;
        timeout->node.data = timeout;

        timeout_set(timeout, tv);
}

void timeout_set(timeout_t *timeout, struct timeval *tv) {
        if(timerisset(&timeout->tv)) {
                splay_unlink_node(&timeout_tree, &timeout->node);
        }

        if(!now.tv_sec) {
                gettimeofday(&now, NULL);
        }

        timeradd(&now, tv, &timeout->tv);

        if(!splay_insert_node(&timeout_tree, &timeout->node)) {
                abort();
        }
}

void timeout_del(timeout_t *timeout) {
        if(!timeout->cb) {
                return;
        }

        splay_unlink_node(&timeout_tree, &timeout->node);
        timeout->cb = 0;
        timeout->tv = (struct timeval) {
                0, 0
        };
}

#ifndef HAVE_MINGW
static int signal_compare(const signal_t *a, const signal_t *b) {
        return a->signum - b->signum;
}

static io_t signalio;
static int pipefd[2] = {-1, -1};
static splay_tree_t signal_tree = {.compare = (splay_compare_t)signal_compare};

static void signal_handler(int signum) {
        unsigned char num = signum;
        write(pipefd[1], &num, 1);
}

static void signalio_handler(void *data, int flags) {
        (void)data;
        (void)flags;
        unsigned char signum;

        if(read(pipefd[0], &signum, 1) != 1) {
                return;
        }

        signal_t *sig = splay_search(&signal_tree, &((signal_t) {
                .signum = signum
        }));

        if(sig) {
                sig->cb(sig->data);
        }
}

static void pipe_init(void) {
        if(!pipe(pipefd)) {
                io_add(&signalio, signalio_handler, NULL, pipefd[0], IO_READ);
        }
}

void signal_add(signal_t *sig, signal_cb_t cb, void *data, int signum) {
        if(sig->cb) {
                return;
        }

        sig->cb = cb;
        sig->data = data;
        sig->signum = signum;
        sig->node.data = sig;

        if(pipefd[0] == -1) {
                pipe_init();
        }

        signal(sig->signum, signal_handler);

        if(!splay_insert_node(&signal_tree, &sig->node)) {
                abort();
        }
}

void signal_del(signal_t *sig) {
        if(!sig->cb) {
                return;
        }

        signal(sig->signum, SIG_DFL);

        splay_unlink_node(&signal_tree, &sig->node);
        sig->cb = NULL;
}
#endif

static struct timeval *get_time_remaining(struct timeval *diff) {
        gettimeofday(&now, NULL);
        struct timeval *tv = NULL;

        while(timeout_tree.head) {
                timeout_t *timeout = timeout_tree.head->data;
                timersub(&timeout->tv, &now, diff);

                if(diff->tv_sec < 0) {
                        timeout->cb(timeout->data);

                        if(timercmp(&timeout->tv, &now, <)) {
                                timeout_del(timeout);
                        }
                } else {
                        tv = diff;
                        break;
                }
        }

        return tv;
}

bool event_loop(void) {
        running = true;

#ifndef HAVE_MINGW
        fd_set readable;
        fd_set writable;

        while(running) {
                struct timeval diff;
                struct timeval *tv = get_time_remaining(&diff);
                memcpy(&readable, &readfds, sizeof(readable));
                memcpy(&writable, &writefds, sizeof(writable));

                int fds = 0;

                if(io_tree.tail) {
                        io_t *last = io_tree.tail->data;
                        fds = last->fd + 1;
                }

                int n = select(fds, &readable, &writable, NULL, tv);

                if(n < 0) {
                        if(sockwouldblock(sockerrno)) {
                                continue;
                        } else {
                                return false;
                        }
                }

                if(!n) {
                        continue;
                }

                unsigned int curgen = io_tree.generation;

                for splay_each(io_t, io, &io_tree) {
                        if(FD_ISSET(io->fd, &writable)) {
                                io->cb(io->data, IO_WRITE);
                        } else if(FD_ISSET(io->fd, &readable)) {
                                io->cb(io->data, IO_READ);
                        } else {
                                continue;
                        }

                        /*
                           There are scenarios in which the callback will remove another io_t from the tree
                           (e.g. closing a double connection). Since splay_each does not support that, we
                           need to exit the loop if that happens. That's okay, since any remaining events will
                           get picked up by the next select() call.
                         */
                        if(curgen != io_tree.generation) {
                                break;
                        }
                }
        }

#else

        while(running) {
                struct timeval diff;
                struct timeval *tv = get_time_remaining(&diff);
                DWORD timeout_ms = tv ? (DWORD)(tv->tv_sec * 1000 + tv->tv_usec / 1000 + 1) : WSA_INFINITE;

                if(!event_count) {
                        Sleep(timeout_ms);
                        continue;
                }

                /*
                   For some reason, Microsoft decided to make the FD_WRITE event edge-triggered instead of level-triggered,
                   which is the opposite of what select() does. In practice, that means that if a FD_WRITE event triggers,
                   it will never trigger again until a send() returns EWOULDBLOCK. Since the semantics of this event loop
                   is that write events are level-triggered (i.e. they continue firing until the socket is full), we need
                   to emulate these semantics by making sure we fire each IO_WRITE that is still writeable.

                   Note that technically FD_CLOSE has the same problem, but it's okay because user code does not rely on
                   this event being fired again if ignored.
                */
                unsigned int curgen = io_tree.generation;

                for splay_each(io_t, io, &io_tree) {
                        if(io->flags & IO_WRITE && send(io->fd, NULL, 0, 0) == 0) {
                                io->cb(io->data, IO_WRITE);

                                if(curgen != io_tree.generation) {
                                        break;
                                }
                        }
                }

                if(event_count > WSA_MAXIMUM_WAIT_EVENTS) {
                        WSASetLastError(WSA_INVALID_PARAMETER);
                        return(false);
                }

                WSAEVENT events[WSA_MAXIMUM_WAIT_EVENTS];
                io_t *io_map[WSA_MAXIMUM_WAIT_EVENTS];
                DWORD event_index = 0;

                for splay_each(io_t, io, &io_tree) {
                        events[event_index] = io->event;
                        io_map[event_index] = io;
                        event_index++;
                }

                /*
                 * If the generation number changes due to event addition
                 * or removal by a callback we restart the loop.
                 */
                curgen = io_tree.generation;

                for(DWORD event_offset = 0; event_offset < event_count;) {
                        DWORD result = WSAWaitForMultipleEvents(event_count - event_offset, &events[event_offset], FALSE, timeout_ms, FALSE);

                        if(result == WSA_WAIT_TIMEOUT) {
                                break;
                        }

                        if(result < WSA_WAIT_EVENT_0 || result >= WSA_WAIT_EVENT_0 + event_count - event_offset) {
                                return false;
                        }

                        /* Look up io in the map by index. */
                        event_index = result - WSA_WAIT_EVENT_0 + event_offset;
                        io_t *io = io_map[event_index];

                        if(io->fd == -1) {
                                io->cb(io->data, 0);

                                if(curgen != io_tree.generation) {
                                        break;
                                }
                        } else {
                                WSANETWORKEVENTS network_events;

                                if(WSAEnumNetworkEvents(io->fd, io->event, &network_events) != 0) {
                                        return(false);
                                }

                                if(network_events.lNetworkEvents & READ_EVENTS) {
                                        io->cb(io->data, IO_READ);

                                        if(curgen != io_tree.generation) {
                                                break;
                                        }
                                }

                                /*
                                    The fd might be available for write too. However, if we already fired the read callback, that
                                    callback might have deleted the io (e.g. through terminate_connection()), so we can't fire the
                                    write callback here. Instead, we loop back and let the writable io loop above handle it.
                                 */
                        }

                        /* Continue checking the rest of the events. */
                        event_offset = event_index + 1;

                        /* Just poll the next time through. */
                        timeout_ms = 0;
                }
        }

#endif

        return true;
}

void event_exit(void) {
        running = false;
}