connection.c

Go to the documentation of this file.

/*
 *   This program is 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 St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 91d4f9c837aafcfa73a0187d7913ee5eb7ba2140 $
 *
 * @file src/lib/server/connection.c
 * @brief Simple state machine for managing connection states.
 *
 * @copyright 2017-2019 Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 */
#define LOG_PREFIX conn->pub.name
 
typedef struct connection_s connection_t;
#define _CONNECTION_PRIVATE 1
#include <freeradius-devel/server/connection.h>
 
#include <freeradius-devel/server/log.h>
#include <freeradius-devel/server/trigger.h>
 
#include <freeradius-devel/util/debug.h>
#include <freeradius-devel/util/syserror.h>
 
#ifdef HAVE_STDATOMIC_H
#  include <stdatomic.h>
#  ifndef ATOMIC_VAR_INIT
#    define ATOMIC_VAR_INIT(_x) (_x)
#  endif
#else
#  include <freeradius-devel/util/stdatomic.h>
#endif
 
fr_table_num_ordered_t const connection_states[] = {
        { L("HALTED"),          CONNECTION_STATE_HALTED },
        { L("INIT"),            CONNECTION_STATE_INIT   },
        { L("CONNECTING"),      CONNECTION_STATE_CONNECTING     },
        { L("TIMEOUT"),         CONNECTION_STATE_TIMEOUT        },
        { L("CONNECTED"),       CONNECTION_STATE_CONNECTED      },
        { L("SHUTDOWN"),        CONNECTION_STATE_SHUTDOWN       },
        { L("FAILED"),          CONNECTION_STATE_FAILED },
        { L("CLOSED"),          CONNECTION_STATE_CLOSED },
};
size_t connection_states_len = NUM_ELEMENTS(connection_states);
 
/** Map connection states to trigger names
 *
 */
static fr_table_num_indexed_t const connection_trigger_names[] = {
        [CONNECTION_STATE_HALTED]       =       { L("connection.halted"),       CONNECTION_STATE_HALTED },
        [CONNECTION_STATE_INIT]         =       { L("connection.init"),         CONNECTION_STATE_INIT },
        [CONNECTION_STATE_CONNECTING]   =       { L("connection.connecting"),   CONNECTION_STATE_CONNECTING },
        [CONNECTION_STATE_TIMEOUT]      =       { L("connection.timeout"),      CONNECTION_STATE_TIMEOUT },
        [CONNECTION_STATE_CONNECTED]    =       { L("connection.connected"),    CONNECTION_STATE_CONNECTED },
        [CONNECTION_STATE_SHUTDOWN]     =       { L("connection.shutdown"),     CONNECTION_STATE_SHUTDOWN },
        [CONNECTION_STATE_FAILED]       =       { L("connection.failed"),       CONNECTION_STATE_FAILED },
        [CONNECTION_STATE_CLOSED]       =       { L("connection.closed"),       CONNECTION_STATE_CLOSED }
};
static size_t connection_trigger_names_len = NUM_ELEMENTS(connection_trigger_names);
 
static atomic_uint_fast64_t connection_counter = ATOMIC_VAR_INIT(1);
 
/** An entry in a watch function list
 *
 */
typedef struct connection_watch_entry_s {
        fr_dlist_t              entry;                  //!< List entry.
        connection_watch_t      func;                   //!< Function to call when a connection enters
                                                        ///< the state this list belongs to
        bool                    oneshot;                //!< Remove the function after it's called once.
        bool                    enabled;                //!< Whether the watch entry is enabled.
        void                    *uctx;                  //!< User data to pass to the function.
} connection_watch_entry_t;
 
struct connection_s {
        struct connection_pub_s pub;                    //!< Public fields
 
        void                    *uctx;                  //!< User data.
 
        void                    *in_handler;            //!< Connection is currently in a callback.
        bool                    is_closed;              //!< The close callback has previously been called.
        bool                    processing_signals;     //!< Processing deferred signals, don't let the deferred
                                                        ///< signal processor be called multiple times.
 
        fr_dlist_head_t         watch_pre[CONNECTION_STATE_MAX];        //!< Function called before state callback.
        fr_dlist_head_t         watch_post[CONNECTION_STATE_MAX];       //!< Function called after state callback.
        connection_watch_entry_t *next_watcher; //!< Hack to insulate watcher iterator from deletions.
 
        connection_init_t       init;                   //!< Callback for initialising a connection.
        connection_open_t       open;                   //!< Callback for 'open' notification.
        connection_close_t      close;                  //!< Callback to close a connection.
        connection_shutdown_t shutdown;         //!< Signal the connection handle to start shutting down.
        connection_failed_t     failed;                 //!< Callback for 'failed' notification.
 
        fr_timer_t              *ev;                    //!< State transition timer.
 
        fr_time_delta_t         connection_timeout;     //!< How long to wait in the
                                                        //!< #CONNECTION_STATE_CONNECTING state.
        fr_time_delta_t         reconnection_delay;     //!< How long to wait in the
                                                        //!< #CONNECTION_STATE_FAILED state.
 
        fr_dlist_head_t         deferred_signals;       //!< A list of signals we received whilst we were in
                                                        ///< a handler.
 
 
 
        connection_watch_entry_t *on_halted;            //!< Used by the deferred signal processor to learn
                                                        ///< if a function deeper in the call stack freed
                                                        ///< the connection.
 
        unsigned int            signals_pause;          //!< Temporarily stop processing of signals.
 
        CONF_SECTION            *trigger_cs;            //!< Where to search locally for triggers.
        fr_pair_list_t          *trigger_args;          //!< Arguments to pass to the trigger functions.
};
 
#define CONN_TRIGGER(_state) do { \
        trigger(unlang_interpret_get_thread_default(), \
                conn->trigger_cs, fr_table_str_by_value(connection_trigger_names, _state, "<INVALID>"), true, conn->trigger_args); \
} while (0)
 
#define STATE_TRANSITION(_new) \
do { \
        DEBUG2("Connection changed state %s -> %s", \
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"), \
               fr_table_str_by_value(connection_states, _new, "<INVALID>")); \
        conn->pub.prev = conn->pub.state; \
        conn->pub.state = _new; \
        CONN_TRIGGER(_new); \
} while (0)
 
#define BAD_STATE_TRANSITION(_new) \
do { \
        if (!fr_cond_assert_msg(0, "Connection %" PRIu64 " invalid transition %s -> %s", \
                                conn->pub.id, \
                                fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"), \
                                fr_table_str_by_value(connection_states, _new, "<INVALID>"))) return; \
} while (0)
 
#define DEFER_SIGNALS(_conn)    ((_conn)->in_handler || (_conn)->signals_pause)
 
/** Deferred signals
 *
 */
typedef enum {
        CONNECTION_DSIGNAL_INIT,                        //!< Restart a halted connection.
        CONNECTION_DSIGNAL_CONNECTED,                   //!< Signal that a connection is connected.
        CONNECTION_DSIGNAL_RECONNECT_FAILED,            //!< Reconnect a failed connection.
        CONNECTION_DSIGNAL_RECONNECT_EXPIRED,           //!< Reconnect an expired connection (gracefully).
        CONNECTION_DSIGNAL_SHUTDOWN,                    //!< Close a connection (gracefully).
        CONNECTION_DSIGNAL_HALT,                        //!< Close a connection (ungracefully).
        CONNECTION_DSIGNAL_FREE                         //!< Free a connection (no further dsignals processed).
} connection_dsignal_t;
 
static fr_table_num_ordered_t const connection_dsignals[] = {
        { L("INIT"),                    CONNECTION_DSIGNAL_INIT                 },
        { L("CONNECTED"),               CONNECTION_DSIGNAL_CONNECTED            },
        { L("RECONNECT-FAILED"),        CONNECTION_DSIGNAL_RECONNECT_FAILED     },
        { L("RECONNECT-EXPIRED"),       CONNECTION_DSIGNAL_RECONNECT_EXPIRED    },
        { L("SHUTDOWN"),                CONNECTION_DSIGNAL_SHUTDOWN             },
        { L("HALT"),                    CONNECTION_DSIGNAL_HALT                 },
        { L("FREE"),                    CONNECTION_DSIGNAL_FREE                 }
};
static size_t connection_dsignals_len = NUM_ELEMENTS(connection_dsignals);
 
/** Holds a signal from a handler until it's safe to process it
 *
 */
typedef struct {
        fr_dlist_t              entry;          //!< Entry in the signals list.
        connection_dsignal_t    signal;         //!< Signal that was deferred.
} connection_dsignal_entry_t;
 
/*
 *      State transition functions
 */
static void connection_state_enter_closed(connection_t *conn);
static void connection_state_enter_failed(connection_t *conn);
static void connection_state_enter_timeout(connection_t *conn);
static void connection_state_enter_connected(connection_t *conn);
static void connection_state_enter_shutdown(connection_t *conn);
static void connection_state_enter_connecting(connection_t *conn);
static void connection_state_enter_halted(connection_t *conn);
static void connection_state_enter_init(connection_t *conn);
 
/** Add a deferred signal to the signal list
 *
 * Processing signals whilst in handlers usually leads to weird
 * inconsistent states within the connection.
 *
 * If a public signal function is called, and detects its being called
 * from within the handler, it instead adds a deferred signal entry
 * and immediately returns.
 *
 * Once the handler is complete, and all pending C stack state changes
 * are complete, the deferred signals are drained and processed.
 */
static inline void connection_deferred_signal_add(connection_t *conn, connection_dsignal_t signal)
{
        connection_dsignal_entry_t *dsignal, *prev;
 
        prev = fr_dlist_tail(&conn->deferred_signals);
        if (prev && (prev->signal == signal)) return;           /* Don't insert duplicates */
 
        MEM(dsignal = talloc_zero(conn, connection_dsignal_entry_t));
        dsignal->signal = signal;
        fr_dlist_insert_tail(&conn->deferred_signals, dsignal);
 
//      DEBUG4("Adding deferred signal - %s", fr_table_str_by_value(connection_dsignals, signal, "<INVALID>"));
}
 
/** Notification function to tell connection_deferred_signal_process that the connection has been freed
 *
 */
static void _deferred_signal_connection_on_halted(UNUSED connection_t *conn,
                                                  UNUSED connection_state_t prev,
                                                  UNUSED connection_state_t state, void *uctx)
{
        bool *freed = uctx;
        *freed = true;
}
 
/** Process any deferred signals
 *
 */
static void connection_deferred_signal_process(connection_t *conn)
{
        connection_dsignal_entry_t      *dsignal;
        bool                            freed = false;
 
        /*
         *      We're inside and an instance of this function
         *      higher in the call stack.  Don't do anything.
         */
        if (conn->processing_signals) return;
 
        /*
         *      Get notified if the connection gets freed
         *      out from under us...
         */
        connection_watch_enable_set_uctx(conn->on_halted, &freed);
        conn->processing_signals = true;
 
        while ((dsignal = fr_dlist_head(&conn->deferred_signals))) {
                connection_dsignal_t signal;
                fr_dlist_remove(&conn->deferred_signals, dsignal);
                signal = dsignal->signal;
                talloc_free(dsignal);
 
                DEBUG4("Processing deferred signal - %s",
                       fr_table_str_by_value(connection_dsignals, signal, "<INVALID>"));
 
                switch (signal) {
                case CONNECTION_DSIGNAL_INIT:
                        connection_signal_init(conn);
                        break;
 
                case CONNECTION_DSIGNAL_CONNECTED:
                        connection_signal_connected(conn);
                        break;
 
                case CONNECTION_DSIGNAL_RECONNECT_FAILED:               /* Reconnect - Failed */
                        connection_signal_reconnect(conn, CONNECTION_FAILED);
                        break;
 
                case CONNECTION_DSIGNAL_RECONNECT_EXPIRED:              /* Reconnect - Expired */
                        connection_signal_reconnect(conn, CONNECTION_EXPIRED);
                        break;
 
                case CONNECTION_DSIGNAL_SHUTDOWN:
                        connection_signal_shutdown(conn);
                        break;
 
                case CONNECTION_DSIGNAL_HALT:
                        connection_signal_halt(conn);
                        break;
 
                case CONNECTION_DSIGNAL_FREE:                           /* Freed */
                        talloc_free(conn);
                        return;
                }
 
                /*
                 *      One of the signal handlers freed the connection
                 *      return immediately.
                 */
                /* coverity[dead_error_line] */
                if (freed) return;
        }
 
        conn->processing_signals = false;
        connection_watch_disable(conn->on_halted);
}
 
/** Pause processing of deferred signals
 *
 * @param[in] conn to pause signal processing for.
 */
void connection_signals_pause(connection_t *conn)
{
        conn->signals_pause++;
}
 
/** Resume processing of deferred signals
 *
 * @param[in] conn to resume signal processing for.
 */
void connection_signals_resume(connection_t *conn)
{
        if (conn->signals_pause > 0) conn->signals_pause--;
        if (conn->signals_pause > 0) return;
 
        /*
         *      If we're not in a handler process the
         *      deferred signals now.
         */
        if (!conn->in_handler) {
                connection_deferred_signal_process(conn);
                return;
        }
}
 
/** Called when we enter a handler
 *
 */
#define HANDLER_BEGIN(_conn, _func) \
void *_prev_handler = (_conn)->in_handler; \
do { \
        (_conn)->in_handler = (void *)(_func); \
} while (0)
 
/** Called when we exit a handler
 *
 */
#define HANDLER_END(_conn) \
do { \
        (_conn)->in_handler = _prev_handler; \
        if (!(_conn)->signals_pause && (!(_conn)->in_handler)) connection_deferred_signal_process(_conn); \
} while(0)
 
 
/** Call a list of watch functions associated with a state
 *
 */
CC_NO_UBSAN(function) /* UBSAN: false positive - Public/private version of connection_t trips -fsanitize=function */
static inline void connection_watch_call(connection_t *conn, fr_dlist_head_t *list)
{
        /*
         *      Nested watcher calls are not allowed
         *      and shouldn't be possible because of
         *      deferred signal processing.
         */
        fr_assert(conn->next_watcher == NULL);
 
        while ((conn->next_watcher = fr_dlist_next(list, conn->next_watcher))) {
                connection_watch_entry_t        *entry = conn->next_watcher;
                bool                            oneshot = entry->oneshot;       /* Watcher could be freed, so store now */
 
                if (!entry->enabled) continue;
                if (oneshot) conn->next_watcher = fr_dlist_remove(list, entry);
 
/*
                DEBUG4("Notifying %swatcher - (%p)(conn=%p, prev=%s, state=%s, uctx=%p)",
                       entry->oneshot ? "oneshot " : "",
                       entry->func,
                       conn,
                       fr_table_str_by_value(connection_states, conn->pub.prev, "<INVALID>"),
                       fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"),
                       entry->uctx);
*/
 
                entry->func(conn, conn->pub.prev, conn->pub.state, entry->uctx);
 
                if (oneshot) talloc_free(entry);
        }
        conn->next_watcher = NULL;
}
 
/** Call the pre handler watch functions
 *
 */
#define WATCH_PRE(_conn) \
do { \
        if (fr_dlist_empty(&(_conn)->watch_pre[(_conn)->pub.state])) break; \
        { \
                HANDLER_BEGIN(conn, &(_conn)->watch_pre[(_conn)->pub.state]); \
                connection_watch_call((_conn), &(_conn)->watch_pre[(_conn)->pub.state]); \
                HANDLER_END(conn); \
        } \
} while(0)
 
/** Call the post handler watch functions
 *
 */
#define WATCH_POST(_conn) \
do { \
        if (fr_dlist_empty(&(_conn)->watch_post[(_conn)->pub.state])) break; \
        { \
                HANDLER_BEGIN(conn, &(_conn)->watch_post[(_conn)->pub.state]); \
                connection_watch_call((_conn), &(_conn)->watch_post[(_conn)->pub.state]); \
                HANDLER_END(conn); \
        } \
} while(0)
 
/** Remove a watch function from a pre/post[state] list
 *
 */
static int connection_del_watch(connection_t *conn, fr_dlist_head_t *state_lists,
                                connection_state_t state, connection_watch_t watch)
{
        connection_watch_entry_t        *entry = NULL;
        fr_dlist_head_t                 *list = &state_lists[state];
 
        while ((entry = fr_dlist_next(list, entry))) {
                if (entry->func == watch) {
/*
                        DEBUG4("Removing %s watcher %p",
                               fr_table_str_by_value(connection_states, state, "<INVALID>"),
                               watch);
*/
                        if (conn->next_watcher == entry) {
                                conn->next_watcher = fr_dlist_remove(list, entry);
                        } else {
                                fr_dlist_remove(list, entry);
                        }
                        talloc_free(entry);
                        return 0;
                }
        }
 
        return -1;
}
 
/** Remove a watch function from a pre list
 *
 * @param[in] conn      The connection to remove the watcher from.
 * @param[in] state     to remove the watch from.
 * @param[in] watch     Function to remove.
 * @return
 *      - 0 if the function was removed successfully.
 *      - -1 if the function wasn't present in the watch list.
 *      - -2 an invalid state was passed.
 */
int connection_del_watch_pre(connection_t *conn, connection_state_t state, connection_watch_t watch)
{
        if (state >= CONNECTION_STATE_MAX) return -2;
 
        return connection_del_watch(conn, conn->watch_pre, state, watch);
}
 
/** Remove a watch function from a post list
 *
 * @param[in] conn      The connection to remove the watcher from.
 * @param[in] state     to remove the watch from.
 * @param[in] watch     Function to remove.
 * @return
 *      - 0 if the function was removed successfully.
 *      - -1 if the function wasn't present in the watch list.
 *      - -2 an invalid state was passed.
 */
int connection_del_watch_post(connection_t *conn, connection_state_t state, connection_watch_t watch)
{
        if (state >= CONNECTION_STATE_MAX) return -2;
 
        return connection_del_watch(conn, conn->watch_post, state, watch);
}
 
/** Add a watch entry to the pre/post[state] list
 *
 */
static connection_watch_entry_t *connection_add_watch(connection_t *conn, fr_dlist_head_t *list,
                                                         connection_watch_t watch, bool oneshot, void const *uctx)
{
        connection_watch_entry_t *entry;
 
        MEM(entry = talloc_zero(conn, connection_watch_entry_t));
 
        entry->func = watch;
        entry->oneshot = oneshot;
        entry->enabled = true;
        memcpy(&entry->uctx, &uctx, sizeof(entry->uctx));
 
        fr_dlist_insert_tail(list, entry);
 
        return entry;
}
 
/** Add a callback to be executed before a state function has been called
 *
 * @param[in] conn      to add watcher to.
 * @param[in] state     to call watcher on entering.
 * @param[in] watch     function to call.
 * @param[in] oneshot   If true, remove the function after calling.
 * @param[in] uctx      to pass to callbacks.
 * @return
 *      - NULL if state value is invalid.
 *      - A new watch entry handle.
 */
connection_watch_entry_t *connection_add_watch_pre(connection_t *conn, connection_state_t state,
                                                         connection_watch_t watch, bool oneshot, void const *uctx)
{
        if (state >= CONNECTION_STATE_MAX) return NULL;
 
        return connection_add_watch(conn, &conn->watch_pre[state], watch, oneshot, uctx);
}
 
/** Add a callback to be executed after a state function has been called
 *
 * Where a user callback is executed on state change, the post function
 * is only called if the callback succeeds.
 *
 * @param[in] conn      to add watcher to.
 * @param[in] state     to call watcher on entering.
 * @param[in] watch     function to call.
 * @param[in] oneshot   If true, remove the function after calling.
 * @param[in] uctx      to pass to callbacks.
 * @return
 *      - NULL if state value is invalid.
 *      - A new watch entry handle.
 */
connection_watch_entry_t *connection_add_watch_post(connection_t *conn, connection_state_t state,
                                                          connection_watch_t watch, bool oneshot, void const *uctx)
{
        if (state >= CONNECTION_STATE_MAX) return NULL;
 
        return connection_add_watch(conn, &conn->watch_post[state], watch, oneshot, uctx);
}
 
/** Enable a watcher
 *
 * @param[in] entry     to enabled.
 */
void connection_watch_enable(connection_watch_entry_t *entry)
{
        (void)talloc_get_type_abort(entry, connection_watch_entry_t);
        entry->enabled = true;
}
 
/** Disable a watcher
 *
 * @param[in] entry     to disable.
 */
void connection_watch_disable(connection_watch_entry_t *entry)
{
        (void)talloc_get_type_abort(entry, connection_watch_entry_t);
        entry->enabled = false;
}
 
/** Enable a watcher and replace the uctx
 *
 * @param[in] entry     to enabled.
 * @param[in] uctx      Opaque data to pass to the callback.
 */
void connection_watch_enable_set_uctx(connection_watch_entry_t *entry, void const *uctx)
{
        (void)talloc_get_type_abort(entry, connection_watch_entry_t);
        entry->enabled = true;
        memcpy(&entry->uctx, &uctx, sizeof(entry->uctx));
}
 
/** Change the uctx of an entry
 *
 * @param[in] entry     to enabled.
 * @param[in] uctx      Opaque data to pass to the callback.
 */
void connection_watch_set_uctx(connection_watch_entry_t *entry, void const *uctx)
{
        (void)talloc_get_type_abort(entry, connection_watch_entry_t);
        memcpy(&entry->uctx, &uctx, sizeof(entry->uctx));
}
 
/** Return the state of a watch entry
 *
 * @param[in] entry     to return state of.
 * @return
 *      - true if enabled.
 *      - false if disabled.
 */
bool connection_watch_is_enabled(connection_watch_entry_t *entry)
{
        (void)talloc_get_type_abort(entry, connection_watch_entry_t);
        return entry->enabled;
}
 
/** Return the number of times we've attempted to establish or re-establish this connection
 *
 * @param[in] conn      to get count from.
 * @return the number of times the connection has reconnected.
 */
uint64_t connection_get_num_reconnected(connection_t const *conn)
{
        if (conn->pub.reconnected == 0) return 0;       /* Has never been initialised */
 
        return conn->pub.reconnected - 1;               /* We don't count the first connection attempt */
}
 
/** Return the number of times this connection has timed out whilst connecting
 *
 * @param[in] conn      to get count from.
 * @return the number of times the connection has timed out whilst connecting.
 */
uint64_t connection_get_num_timed_out(connection_t const *conn)
{
        return conn->pub.timed_out;
}
 
/** The requisite period of time has passed, try and re-open the connection
 *
 * @param[in] tl        containing the timer event.
 * @param[in] now       The current time.
 * @param[in] uctx      The #connection_t the fd is associated with.
 */
static void _reconnect_delay_done(UNUSED fr_timer_list_t *tl, UNUSED fr_time_t now, void *uctx)
{
        connection_t *conn = talloc_get_type_abort(uctx, connection_t);
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_FAILED:
        case CONNECTION_STATE_CLOSED:
                connection_state_enter_init(conn);
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_INIT);
                break;
        }
}
 
/** Close the connection, then wait for another state change
 *
 */
static void connection_state_enter_closed(connection_t *conn)
{
        switch (conn->pub.state) {
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_CONNECTED:
        case CONNECTION_STATE_FAILED:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_CLOSED);
                return;
        }
 
        STATE_TRANSITION(CONNECTION_STATE_CLOSED);
 
        FR_TIMER_DISARM(conn->ev);
 
        /*
         *      If there's a close callback, call it, so that the
         *      API client can free any resources associated
         *      with the connection handle.
         */
        WATCH_PRE(conn);
 
        /*
         *      is_closed is for pure paranoia.  If everything
         *      is working correctly this state should never
         *      be entered if the connection is closed.
         */
        fr_assert(!conn->is_closed);
        if (conn->close && !conn->is_closed) {
                HANDLER_BEGIN(conn, conn->close);
                DEBUG4("Calling close(el=%p, h=%p, uctx=%p)", conn->pub.el, conn->pub.h, conn->uctx);
                conn->close(conn->pub.el, conn->pub.h, conn->uctx);
                conn->is_closed = true;         /* Ensure close doesn't get called twice if the connection is freed */
                HANDLER_END(conn);
        } else {
                conn->is_closed = true;
        }
        WATCH_POST(conn);
}
 
/** Connection timeout
 *
 * Connection wasn't opened within the configured period of time
 *
 * @param[in] tl        timer list the event belonged to.
 * @param[in] now       The current time.
 * @param[in] uctx      The #connection_t the fd is associated with.
 */
static void _connection_timeout(UNUSED fr_timer_list_t *tl, UNUSED fr_time_t now, void *uctx)
{
        connection_t *conn = talloc_get_type_abort(uctx, connection_t);
 
        connection_state_enter_timeout(conn);
}
 
/** Gracefully shutdown the handle
 *
 */
static void connection_state_enter_shutdown(connection_t *conn)
{
        connection_state_t ret;
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_CONNECTED:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_SHUTDOWN);
                return;
        }
 
        STATE_TRANSITION(CONNECTION_STATE_SHUTDOWN);
 
        WATCH_PRE(conn);
        {
                HANDLER_BEGIN(conn, conn->shutdown);
                DEBUG4("Calling shutdown(el=%p, h=%p, uctx=%p)", conn->pub.el, conn->pub.h, conn->uctx);
                ret = conn->shutdown(conn->pub.el, conn->pub.h, conn->uctx);
                HANDLER_END(conn);
        }
        switch (ret) {
        case CONNECTION_STATE_SHUTDOWN:
                break;
 
        default:
                connection_state_enter_failed(conn);
                return;
        }
        WATCH_POST(conn);
 
        /*
         *      If there's a connection timeout,
         *      set, then add the timer.
         *
         *      The connection may be bad, in which
         *      case we want to automatically fail
         *      if it doesn't shutdown within the
         *      timeout period.
         */
        if (fr_time_delta_ispos(conn->connection_timeout)) {
                if (fr_timer_in(conn, conn->pub.el->tl, &conn->ev,
                                conn->connection_timeout, false, _connection_timeout, conn) < 0) {
                        /*
                         *      Can happen when the event loop is exiting
                         */
                        PERROR("Failed setting connection_timeout timer, closing connection");
                        connection_state_enter_closed(conn);
                }
        }
}
 
/** Connection failed
 *
 * Transition to the CONNECTION_STATE_FAILED state.
 *
 * If the connection was open, or couldn't be opened wait for reconnection_delay before transitioning
 * back to init.
 *
 * If no reconnection_delay was set, transition to halted.
 *
 * @param[in] conn      that failed.
 */
static void connection_state_enter_failed(connection_t *conn)
{
        connection_state_t prev;
        connection_state_t ret = CONNECTION_STATE_INIT;
 
        fr_assert(conn->pub.state != CONNECTION_STATE_FAILED);
 
        /*
         *      Explicit error occurred, delete the connection timer
         */
        FR_TIMER_DISARM(conn->ev);
 
        /*
         *      Record what state the connection is currently in
         *      so we can figure out what to do next.
         */
        prev = conn->pub.state;
 
        /*
         *      Now transition to failed
         */
        STATE_TRANSITION(CONNECTION_STATE_FAILED);
 
        /*
         *      If there's a failed callback, give it the
         *      opportunity to suspend/destroy the
         *      connection.
         */
        WATCH_PRE(conn);
        if (conn->failed) {
                HANDLER_BEGIN(conn, conn->failed);
                DEBUG4("Calling failed(h=%p, state=%s, uctx=%p)", conn->pub.h,
                       fr_table_str_by_value(connection_states, prev, "<INVALID>"), conn->uctx);
                ret = conn->failed(conn->pub.h, prev, conn->uctx);
                HANDLER_END(conn);
        }
        WATCH_POST(conn);
 
        /*
         *      Enter the closed state if we failed during
         *      connecting, or when we were connected.
         */
        switch (prev) {
        case CONNECTION_STATE_CONNECTED:
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_TIMEOUT:          /* Timeout means the connection progress past init */
        case CONNECTION_STATE_SHUTDOWN:         /* Shutdown means the connection failed whilst shutting down */
                connection_state_enter_closed(conn);
                break;
 
        default:
                break;
        }
 
        if (conn->failed) {
                switch (ret) {
                /*
                 *      The callback signalled it wants the
                 *      connection to be reinitialised
                 *      after reconnection_delay, or
                 *      immediately if the failure was due
                 *      to a connection timeout.
                 */
                case CONNECTION_STATE_INIT:
                        break;
 
                /*
                 *      The callback signalled it wants the
                 *      connection to stop.
                 */
                case CONNECTION_STATE_HALTED:
                default:
                        connection_state_enter_halted(conn);
                        return;
                }
        }
 
        /*
         *      What previous state we were in
         *      determines if we need to apply the
         *      reconnect timeout.
         */
        switch (prev) {
        case CONNECTION_STATE_INIT:                             /* Failed during initialisation */
        case CONNECTION_STATE_CONNECTED:                        /* Failed after connecting */
        case CONNECTION_STATE_CONNECTING:                       /* Failed during connecting */
        case CONNECTION_STATE_SHUTDOWN:                 /* Failed during shutdown */
                if (fr_time_delta_ispos(conn->reconnection_delay)) {
                        DEBUG2("Delaying reconnection by %pVs", fr_box_time_delta(conn->reconnection_delay));
                        if (fr_timer_in(conn, conn->pub.el->tl, &conn->ev,
                                        conn->reconnection_delay, false, _reconnect_delay_done, conn) < 0) {
                                /*
                                 *      Can happen when the event loop is exiting
                                 */
                                PERROR("Failed inserting reconnection_delay timer event, halting connection");
                                connection_state_enter_halted(conn);
                        }
                        return;
                }
 
                /*
                 *      If there's no reconnection
                 *      delay, then don't automatically
                 *      reconnect, and wait to be
                 *      signalled.
                 */
                connection_state_enter_halted(conn);
                break;
 
        case CONNECTION_STATE_TIMEOUT:                  /* Failed during connecting due to timeout */
                connection_state_enter_init(conn);
                break;
 
        default:
                fr_assert(0);
        }
}
 
/** Enter the timeout state
 *
 * The connection took took long to open.  Timeout the attempt and transition
 * to the failed state.
 */
static void connection_state_enter_timeout(connection_t *conn)
{
        switch (conn->pub.state) {
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_SHUTDOWN:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_TIMEOUT);
        }
 
        ERROR("Connection failed - timed out after %pVs", fr_box_time_delta(conn->connection_timeout));
 
        STATE_TRANSITION(CONNECTION_STATE_TIMEOUT);
 
        conn->pub.timed_out++;
 
        connection_state_enter_failed(conn);
}
 
/** Enter the halted state
 *
 * Here we wait, until signalled by connection_signal_reconnect.
 */
static void connection_state_enter_halted(connection_t *conn)
{
        fr_assert(conn->is_closed);
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_FAILED:   /* Init failure */
        case CONNECTION_STATE_CLOSED:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_HALTED);
        }
 
        FR_TIMER_DISARM(conn->ev);
 
        STATE_TRANSITION(CONNECTION_STATE_HALTED);
        WATCH_PRE(conn);
        WATCH_POST(conn);
}
 
/** Enter the connected state
 *
 * The connection is now fully connected.  At this point we call the open callback
 * so that the API client can install its normal set of I/O callbacks to deal with
 * sending/receiving actual data.
 *
 * After this, the connection will only transition states if an API client
 * explicitly calls connection_signal_reconnect.
 *
 * The connection API cannot monitor the connection for failure conditions.
 *
 * @param[in] conn      Entering the connecting state.
 */
static void connection_state_enter_connected(connection_t *conn)
{
        int     ret;
 
        fr_assert(conn->pub.state == CONNECTION_STATE_CONNECTING || conn->pub.state == CONNECTION_STATE_INIT);
 
        STATE_TRANSITION(CONNECTION_STATE_CONNECTED);
 
        FR_TIMER_DISARM(conn->ev);
        WATCH_PRE(conn);
        if (conn->open) {
                HANDLER_BEGIN(conn, conn->open);
                DEBUG4("Calling open(el=%p, h=%p, uctx=%p)", conn->pub.el, conn->pub.h, conn->uctx);
                ret = conn->open(conn->pub.el, conn->pub.h, conn->uctx);
                HANDLER_END(conn);
        } else {
                ret = CONNECTION_STATE_CONNECTED;
        }
 
        switch (ret) {
        /*
         *      Callback agrees everything is connected
         */
        case CONNECTION_STATE_CONNECTED:
                DEBUG2("Connection established");
                WATCH_POST(conn);       /* Only call if we successfully connected */
                return;
 
        /*
         *      Open callback failed
         */
        case CONNECTION_STATE_FAILED:
        default:
                PERROR("Connection failed");
                connection_state_enter_failed(conn);
                return;
        }
}
 
/** Enter the connecting state
 *
 * After this function returns we wait to be signalled with connection_singal_connected
 * or for the connection timer to expire.
 *
 * @param[in] conn      Entering the connecting state.
 */
static void connection_state_enter_connecting(connection_t *conn)
{
        switch (conn->pub.state) {
        case CONNECTION_STATE_INIT:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_CONNECTING);
                return;
        }
 
        STATE_TRANSITION(CONNECTION_STATE_CONNECTING);
 
        WATCH_PRE(conn);
        WATCH_POST(conn);
 
        /*
         *      If there's a connection timeout,
         *      set, then add the timer.
         */
        if (fr_time_delta_ispos(conn->connection_timeout)) {
                if (fr_timer_in(conn, conn->pub.el->tl, &conn->ev,
                                conn->connection_timeout, false, _connection_timeout, conn) < 0) {
                        PERROR("Failed setting connection_timeout event, failing connection");
 
                        /*
                         *      This can happen when the event loop
                         *      is exiting.
                         *
                         *      Entering fail will close partially
                         *      open connection and then, if we still
                         *      can't insert a timer, then the connection
                         *      will be halted and sit idle until its
                         *      freed.
                         */
                        connection_state_enter_failed(conn);
                }
        }
}
 
/** Initial state of the connection
 *
 * Calls the init function we were passed to allocate a library specific handle or
 * file descriptor.
 *
 * @param[in] conn      To initialise.
 */
static void connection_state_enter_init(connection_t *conn)
{
        connection_state_t      ret;
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_HALTED:
        case CONNECTION_STATE_CLOSED:
        case CONNECTION_STATE_FAILED:
                break;
 
        default:
                BAD_STATE_TRANSITION(CONNECTION_STATE_INIT);
                return;
        }
 
        /*
         *      Increment every time we enter
         *      We have to do this, as we don't know
         *      whether the connection was halted by
         *      the failed callback, and is now being
         *      reconnected, or was automatically
         *      reconnected.
         */
        conn->pub.reconnected++;
 
        STATE_TRANSITION(CONNECTION_STATE_INIT);
 
        /*
         *      If we have an init callback, call it.
         */
        WATCH_PRE(conn);
        if (conn->init) {
                HANDLER_BEGIN(conn, conn->init);
                DEBUG4("Calling init(h_out=%p, conn=%p, uctx=%p)", &conn->pub.h, conn, conn->uctx);
                ret = conn->init(&conn->pub.h, conn, conn->uctx);
                HANDLER_END(conn);
        } else {
                ret = CONNECTION_STATE_CONNECTING;
        }
 
        switch (ret) {
        case CONNECTION_STATE_CONNECTING:
                conn->is_closed = false;        /* We now have a handle */
                WATCH_POST(conn);               /* Only call if we successfully initialised the handle */
                connection_state_enter_connecting(conn);
                return;
 
        case CONNECTION_STATE_CONNECTED:
                conn->is_closed = false;        /* We now have a handle */
                WATCH_POST(conn);               /* Only call if we successfully initialised the handle */
                connection_state_enter_connected(conn);
                return;
 
        /*
         *      Initialisation callback failed
         */
        case CONNECTION_STATE_FAILED:
        default:
                PERROR("Connection initialisation failed");
                connection_state_enter_failed(conn);
                break;
        }
}
 
/** Asynchronously signal a halted connection to start
 *
 */
void connection_signal_init(connection_t *conn)
{
        DEBUG2("Signalled to start from %s state",
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"));
 
        if (DEFER_SIGNALS(conn)) {
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_INIT);
                return;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_HALTED:
                connection_state_enter_init(conn);
                break;
 
        default:
                break;
        }
}
 
/** Asynchronously signal that the connection is open
 *
 * Some libraries like libldap are extremely annoying and only return control
 * to the caller after a connection is open.
 *
 * For these libraries, we can't use an I/O handler to determine when the
 * connection is open so we rely on callbacks built into the library to
 * signal that the transition has occurred.
 *
 */
void connection_signal_connected(connection_t *conn)
{
        fr_assert(!conn->open); /* Use one or the other not both! */
 
        DEBUG2("Signalled connected from %s state",
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"));
 
        if (DEFER_SIGNALS(conn)) {
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_CONNECTED);
                return;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_CONNECTING:
                connection_state_enter_connected(conn);
                break;
 
        default:
                break;
        }
}
 
/** Asynchronously signal the connection should be reconnected
 *
 * Should be called if the caller has knowledge that the connection is bad
 * and should be reconnected.
 *
 * @param[in] conn              to reconnect.
 * @param[in] reason            Why the connection was signalled to reconnect.
 */
void connection_signal_reconnect(connection_t *conn, connection_reason_t reason)
{
        DEBUG2("Signalled to reconnect from %s state",
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"));
 
        if (DEFER_SIGNALS(conn)) {
                if ((reason == CONNECTION_EXPIRED) && conn->shutdown) {
                        connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_RECONNECT_EXPIRED);
                        return;
                }
 
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_RECONNECT_FAILED);
                return;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_CLOSED:                   /* Don't circumvent reconnection_delay */
        case CONNECTION_STATE_INIT:                             /* Already initialising */
                break;
 
        case CONNECTION_STATE_HALTED:
                connection_signal_init(conn);
                break;
 
        case CONNECTION_STATE_SHUTDOWN:
                if (reason == CONNECTION_EXPIRED) break;        /* Already shutting down */
                connection_state_enter_failed(conn);
                break;
 
        case CONNECTION_STATE_CONNECTED:
                if (reason == CONNECTION_EXPIRED) {
                        if (conn->shutdown) {
                                connection_state_enter_shutdown(conn);
                                break;
                        }
                        connection_state_enter_closed(conn);
                        break;
                }
                FALL_THROUGH;
 
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_TIMEOUT:
        case CONNECTION_STATE_FAILED:
                connection_state_enter_failed(conn);
                break;
 
        case CONNECTION_STATE_MAX:
                fr_assert(0);
                return;
        }
}
 
/** Shuts down a connection gracefully
 *
 * If a shutdown function has been provided, it is called.
 * It's then up to the shutdown function to install I/O handlers to signal
 * when the connection has finished shutting down and should be closed
 * via #connection_signal_halt.
 *
 * @param[in] conn      to shutdown.
 */
void connection_signal_shutdown(connection_t *conn)
{
        DEBUG2("Signalled to shutdown from %s state",
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"));
 
        if (DEFER_SIGNALS(conn)) {
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_SHUTDOWN);
                return;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_HALTED:
        case CONNECTION_STATE_SHUTDOWN:
                break;
 
        case CONNECTION_STATE_INIT:
                connection_state_enter_halted(conn);
                break;
 
        /*
         *      If the connection is connected it needs to be
         *      shutdown first.
         *
         *      The shutdown callback or an FD event it inserts then
         *      to signal that the connection should be closed.
         */
        case CONNECTION_STATE_CONNECTED:
                if (conn->shutdown) {
                        connection_state_enter_shutdown(conn);
                        break;
                }
        FALL_THROUGH;
 
        /*
         *      If the connection is any of these states it
         *      must have completed INIT which means it has
         *      an active handle which needs to be closed before
         *      the connection is halted.
         */
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_TIMEOUT:
        case CONNECTION_STATE_FAILED:
                connection_state_enter_closed(conn);
                fr_assert(conn->is_closed);
 
        FALL_THROUGH;
        case CONNECTION_STATE_CLOSED:
                connection_state_enter_halted(conn);
                break;
 
        case CONNECTION_STATE_MAX:
                fr_assert(0);
                return;
        }
}
 
/** Shuts down a connection ungracefully
 *
 * If a connection is in an open or connection state it will be closed immediately.
 * Otherwise the connection will transition directly to the halted state.
 *
 * @param[in] conn      to halt.
 */
void connection_signal_halt(connection_t *conn)
{
        DEBUG2("Signalled to halt from %s state",
               fr_table_str_by_value(connection_states, conn->pub.state, "<INVALID>"));
 
        if (DEFER_SIGNALS(conn)) {
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_HALT);
                return;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_HALTED:
                break;
 
        case CONNECTION_STATE_INIT:
        case CONNECTION_STATE_CLOSED:
                connection_state_enter_halted(conn);
                break;
 
        /*
         *      If the connection is any of these states it
         *      must have completed INIT which means it has
         *      an active handle which needs to be closed before
         *      the connection is halted.
         *
         *      The exception is when a connection fails to open
         *      so goes from INIT -> FAILED, means is_closed
         *      is true, as the connection has never opened.
         */
        case CONNECTION_STATE_CONNECTED:
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_SHUTDOWN:
        case CONNECTION_STATE_TIMEOUT:
        case CONNECTION_STATE_FAILED:
                if (!conn->is_closed) connection_state_enter_closed(conn);
                fr_assert(conn->is_closed);
                connection_state_enter_halted(conn);
                break;
 
        case CONNECTION_STATE_MAX:
                fr_assert(0);
                return;
        }
}
/** Receive an error notification when we're connecting a socket
 *
 * @param[in] el        event list the I/O event occurred on.
 * @param[in] fd        the I/O even occurred for.
 * @param[in] flags     from_kevent.
 * @param[in] fd_errno  from kevent.
 * @param[in] uctx      The #connection_t this fd is associated with.
 */
static void _connection_error(UNUSED fr_event_list_t *el, int fd, UNUSED int flags, int fd_errno, void *uctx)
{
        connection_t *conn = talloc_get_type_abort(uctx, connection_t);
 
        ERROR("Connection failed for fd (%d): %s", fd, fr_syserror(fd_errno));
        connection_state_enter_failed(conn);
}
 
/** Receive a write notification after a socket is connected
 *
 * @param[in] el        event list the I/O event occurred on.
 * @param[in] fd        the I/O even occurred for.
 * @param[in] flags     from kevent.
 * @param[in] uctx      The #connection_t this fd is associated with.
 */
static void _connection_writable(fr_event_list_t *el, int fd, UNUSED int flags, void *uctx)
{
        connection_t            *conn = talloc_get_type_abort(uctx, connection_t);
 
        fr_event_fd_delete(el, fd, FR_EVENT_FILTER_IO);
        connection_state_enter_connected(conn);
}
 
/** Remove the FD we were watching for connection open/fail from the event loop
 *
 */
static void _connection_signal_on_fd_cleanup(connection_t *conn,
                                             UNUSED connection_state_t prev, connection_state_t state, void *uctx)
{
        int fd = *(talloc_get_type_abort(uctx, int));
 
        /*
         *      Two states can trigger a cleanup
         *      Remove the watch on the one that didn't
         */
        switch (state) {
        case CONNECTION_STATE_CLOSED:
                connection_del_watch_pre(conn, CONNECTION_STATE_CONNECTED, _connection_signal_on_fd_cleanup);
                break;
 
        case CONNECTION_STATE_CONNECTED:
                connection_del_watch_pre(conn, CONNECTION_STATE_CLOSED, _connection_signal_on_fd_cleanup);
                break;
 
        default:
                fr_assert(0);
                break;
        }
 
        fr_event_fd_delete(conn->pub.el, fd, FR_EVENT_FILTER_IO);
        talloc_free(uctx);
}
 
/** Setup the connection to change states to connected or failed based on I/O events
 *
 * Will automatically cleanup after itself, in preparation for
 * new I/O handlers to be installed in the open() callback.
 *
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int connection_signal_on_fd(connection_t *conn, int fd)
{
        int             *fd_s;
 
        /*
         *      If connection becomes writable we
         *      assume it's open.
         */
        if (fr_event_fd_insert(conn, NULL, conn->pub.el, fd,
                               NULL,
                               _connection_writable,
                               _connection_error,
                               conn) < 0) {
                PERROR("Failed inserting fd (%d) into event loop %p",
                       fd, conn->pub.el);
                connection_state_enter_failed(conn);
                return -1;
        }
 
        /*
         *      Stop the static analysis tools
         *      complaining about assigning ints
         *      to pointers.
         */
        MEM(fd_s = talloc_zero(conn, int));
        *fd_s = fd;
 
        /*
         *      Add a oneshot watcher to remove
         *      the I/O handlers if the connection
         *      fails, or is connected.
         */
        connection_add_watch_pre(conn, CONNECTION_STATE_CLOSED,
                                    _connection_signal_on_fd_cleanup, true, fd_s);
        connection_add_watch_pre(conn, CONNECTION_STATE_CONNECTED,
                                    _connection_signal_on_fd_cleanup, true, fd_s);
        return 0;
}
 
/** Tell a failed connection to move to CONNECTION_STATE_INIT
 *
 */
connection_state_t connection_failed_reinit(UNUSED void *handle, UNUSED connection_state_t state, UNUSED void *uctx)
{
        return CONNECTION_STATE_INIT;
}
 
/** Close a connection if it's freed
 *
 * @param[in] conn to free.
 * @return
 *      - 0 connection was freed immediately.
 *      - 1 connection free was deferred.
 */
static int _connection_free(connection_t *conn)
{
        /*
         *      Explicitly cancel any pending events
         */
        FR_TIMER_DELETE_RETURN(&conn->ev);
        /*
         *      Don't allow the connection to be
         *      arbitrarily freed by a callback.
         *
         *      Add a deferred signal to free the
         *      connection later.
         */
        if (DEFER_SIGNALS(conn)) {
                connection_deferred_signal_add(conn, CONNECTION_DSIGNAL_FREE);
                return -1;
        }
 
        switch (conn->pub.state) {
        case CONNECTION_STATE_HALTED:
                break;
 
        /*
         *      Need to close the connection first
         */
        case CONNECTION_STATE_CONNECTING:
        case CONNECTION_STATE_CONNECTED:
                connection_state_enter_closed(conn);
                FALL_THROUGH;
 
        default:
                connection_state_enter_halted(conn);
                break;
        }
        return 0;
}
 
/** Allocate a new connection
 *
 * After the connection has been allocated, it should be started with a call to #connection_signal_init.
 *
 * The connection state machine can detect when the connection is open in one of two ways.
 * - You can install a generic socket open/fail callback, using connection_signal_on_fd.
 * - You can call either #connection_signal_connected or connection_signal_recommend.
 *   This allows the connection state machine to work with more difficult library APIs,
 *   which may not return control to the caller as connections are opened.
 *
 * @param[in] ctx               to allocate connection handle in.  If the connection
 *                              handle is freed, and the #connection_state_t is
 *                              #CONNECTION_STATE_CONNECTING or #CONNECTION_STATE_CONNECTED the
 *                              close callback will be called.
 * @param[in] el                to use for timer events, and to pass to the #connection_open_t callback.
 * @param[in] funcs             callback functions.
 * @param[in] conf              our configuration.
 * @param[in] log_prefix        To prepend to log messages.
 * @param[in] uctx              User context to pass to callbacks.
 * @return
 *      - A new #connection_t on success.
 *      - NULL on failure.
 */
connection_t *connection_alloc(TALLOC_CTX *ctx, fr_event_list_t *el,
                               connection_funcs_t const *funcs,
                               connection_conf_t const *conf,
                               char const *log_prefix,
                               void const *uctx)
{
        size_t i;
        connection_t *conn;
        uint64_t id;
 
        fr_assert(el);
 
        MEM(conn = talloc(ctx, connection_t));
        talloc_set_destructor(conn, _connection_free);
 
        id = atomic_fetch_add_explicit(&connection_counter, 1, memory_order_relaxed);
 
        *conn = (connection_t){
                .pub = {
                        .id = id,
                        .state = CONNECTION_STATE_HALTED,
                        .el = el
                },
                .reconnection_delay = conf->reconnection_delay,
                .connection_timeout = conf->connection_timeout,
                .init = funcs->init,
                .open = funcs->open,
                .close = funcs->close,
                .failed = funcs->failed,
                .shutdown = funcs->shutdown,
                .is_closed = true,              /* Starts closed */
                .trigger_args = conf->trigger_args,
                .trigger_cs = conf->trigger_cs,
                .pub.name = talloc_asprintf(conn, "%s - [%" PRIu64 "]", log_prefix, id)
        };
        memcpy(&conn->uctx, &uctx, sizeof(conn->uctx));
 
        for (i = 0; i < NUM_ELEMENTS(conn->watch_pre); i++) {
                fr_dlist_talloc_init(&conn->watch_pre[i], connection_watch_entry_t, entry);
        }
        for (i = 0; i < NUM_ELEMENTS(conn->watch_post); i++) {
                fr_dlist_talloc_init(&conn->watch_post[i], connection_watch_entry_t, entry);
        }
        fr_dlist_talloc_init(&conn->deferred_signals, connection_dsignal_entry_t, entry);
 
        /*
         *      Pre-allocate a on_halt watcher for deferred signal processing
         */
        conn->on_halted = connection_add_watch_post(conn, CONNECTION_STATE_HALTED,
                                                    _deferred_signal_connection_on_halted, true, NULL);
        connection_watch_disable(conn->on_halted);      /* Start disabled */
 
        return conn;
}