/*
 * This file Copyright (C) Mnemosyne LLC
 *
 * This file is licensed by the GPL version 2. Works owned by the
 * Transmission project are granted a special exemption to clause 2 (b)
 * so that the bulk of its code can remain under the MIT license.
 * This exemption does not extend to derived works not owned by
 * the Transmission project.
 *
 * $Id$
 */

#define __LIBTRANSMISSION_ANNOUNCER_MODULE___

#include <errno.h> /* errno, EAFNOSUPPORT */
#include <string.h> /* memcpy (), memset () */

#include <event2/buffer.h>
#include <event2/dns.h>
#include <event2/util.h>

#include "transmission.h"
#include "announcer.h"
#include "announcer-common.h"
#include "crypto.h" /* tr_cryptoRandBuf () */
#include "log.h"
#include "peer-io.h"
#include "peer-mgr.h" /* tr_peerMgrCompactToPex () */
#include "ptrarray.h"
#include "tr-udp.h"
#include "utils.h"

#define dbgmsg(name, ...) \
  do \
    { \
      if (tr_logGetDeepEnabled ()) \
        tr_logAddDeep (__FILE__, __LINE__, name, __VA_ARGS__); \
    } \
  while (0)

/****
*****
****/

static void
tau_sockaddr_setport (struct sockaddr * sa, tr_port port)
{
    if (sa->sa_family == AF_INET)
      ((struct sockaddr_in *)sa)->sin_port = htons (port);
    else if (sa->sa_family == AF_INET6)
      ((struct sockaddr_in6 *)sa)->sin6_port = htons (port);
}

static int
tau_sendto (tr_session * session,
            struct evutil_addrinfo * ai, tr_port port,
            const void * buf, size_t buflen)
{
    int sockfd;

    if (ai->ai_addr->sa_family == AF_INET)
        sockfd = session->udp_socket;
    else if (ai->ai_addr->sa_family == AF_INET6)
        sockfd = session->udp6_socket;
    else
        sockfd = -1;

    if (sockfd < 0) {
        errno = EAFNOSUPPORT;
        return -1;
    }

    tau_sockaddr_setport (ai->ai_addr, port);
    return sendto (sockfd, buf, buflen, 0, ai->ai_addr, ai->ai_addrlen);
}

/****
*****
****/

static uint32_t
evbuffer_read_ntoh_32 (struct evbuffer * buf)
{
    uint32_t val;
    evbuffer_remove (buf, &val, sizeof (uint32_t));
    return ntohl (val);
}

static uint64_t
evbuffer_read_ntoh_64 (struct evbuffer * buf)
{
    uint64_t val;
    evbuffer_remove (buf, &val, sizeof (uint64_t));
    return tr_ntohll (val);
}

/****
*****
****/

typedef uint64_t tau_connection_t;

enum
{
    TAU_CONNECTION_TTL_SECS = 60
};

typedef uint32_t tau_transaction_t;

static tau_transaction_t
tau_transaction_new (void)
{
    tau_transaction_t tmp;
    tr_cryptoRandBuf (&tmp, sizeof (tau_transaction_t));
    return tmp;
}

/* used in the "action" field of a request */
typedef enum
{
    TAU_ACTION_CONNECT  = 0,
    TAU_ACTION_ANNOUNCE = 1,
    TAU_ACTION_SCRAPE   = 2,
    TAU_ACTION_ERROR    = 3
}
tau_action_t;

static bool
is_tau_response_message (int action, int msglen)
{
    if (action == TAU_ACTION_CONNECT) return msglen == 16;
    if (action == TAU_ACTION_ANNOUNCE) return msglen >= 20;
    if (action == TAU_ACTION_SCRAPE ) return msglen >= 20;
    if (action == TAU_ACTION_ERROR  ) return msglen >= 8;
    return false;
}

enum
{
    TAU_REQUEST_TTL = 60
};

/****
*****
*****  SCRAPE
*****
****/

struct tau_scrape_request
{
    void * payload;
    size_t payload_len;

    time_t sent_at;
    time_t created_at;
    tau_transaction_t transaction_id;

    tr_scrape_response response;
    tr_scrape_response_func callback;
    void * user_data;
};

static struct tau_scrape_request *
tau_scrape_request_new (const tr_scrape_request  * in,
                        tr_scrape_response_func    callback,
                        void                     * user_data)
{
    int i;
    struct evbuffer * buf;
    struct tau_scrape_request * req;
    const tau_transaction_t transaction_id = tau_transaction_new ();

    /* build the payload */
    buf = evbuffer_new ();
    evbuffer_add_hton_32 (buf, TAU_ACTION_SCRAPE);
    evbuffer_add_hton_32 (buf, transaction_id);
    for (i=0; i<in->info_hash_count; ++i)
        evbuffer_add (buf, in->info_hash[i], SHA_DIGEST_LENGTH);

    /* build the tau_scrape_request */
    req = tr_new0 (struct tau_scrape_request, 1);
    req->created_at = tr_time ();
    req->transaction_id = transaction_id;
    req->callback = callback;
    req->user_data = user_data;
    req->response.url = tr_strdup (in->url);
    req->response.row_count = in->info_hash_count;
    req->payload_len = evbuffer_get_length (buf);
    req->payload = tr_memdup (evbuffer_pullup (buf, -1), req->payload_len);
    for (i=0; i<req->response.row_count; ++i)
    {
        req->response.rows[i].seeders = -1;
        req->response.rows[i].leechers = -1;
        req->response.rows[i].downloads = -1;
        memcpy (req->response.rows[i].info_hash,
                in->info_hash[i], SHA_DIGEST_LENGTH);
    }

    /* cleanup */
    evbuffer_free (buf);
    return req;
}

static void
tau_scrape_request_free (struct tau_scrape_request * req)
{
    tr_free (req->response.errmsg);
    tr_free (req->response.url);
    tr_free (req->payload);
    tr_free (req);
}

static void
tau_scrape_request_finished (const struct tau_scrape_request  * request)
{
    if (request->callback != NULL)
        request->callback (&request->response, request->user_data);
}

static void
tau_scrape_request_fail (struct tau_scrape_request  * request,
                         bool                         did_connect,
                         bool                         did_timeout,
                         const char                 * errmsg)
{
    request->response.did_connect = did_connect;
    request->response.did_timeout = did_timeout;
    request->response.errmsg = tr_strdup (errmsg);
    tau_scrape_request_finished (request);
}

static void
on_scrape_response (struct tau_scrape_request  * request,
                    tau_action_t                 action,
                    struct evbuffer            * buf)
{
    request->response.did_connect = true;
    request->response.did_timeout = false;

    if (action == TAU_ACTION_SCRAPE)
    {
        int i;
        for (i=0; i<request->response.row_count; ++i)
        {
            struct tr_scrape_response_row * row;

            if (evbuffer_get_length (buf) < (sizeof (uint32_t) * 3))
                break;

            row = &request->response.rows[i];
            row->seeders   = evbuffer_read_ntoh_32 (buf);
            row->downloads = evbuffer_read_ntoh_32 (buf);
            row->leechers  = evbuffer_read_ntoh_32 (buf);
        }

        tau_scrape_request_finished (request);
    }
    else
    {
        char * errmsg;
        const size_t buflen = evbuffer_get_length (buf);

        if ((action == TAU_ACTION_ERROR) && (buflen > 0))
            errmsg = tr_strndup (evbuffer_pullup (buf, -1), buflen);
        else
            errmsg = tr_strdup (_("Unknown error"));

        tau_scrape_request_fail (request, true, false, errmsg);
        tr_free (errmsg);
    }
}

/****
*****
*****  ANNOUNCE
*****
****/

struct tau_announce_request
{
    void * payload;
    size_t payload_len;

    time_t created_at;
    time_t sent_at;
    tau_transaction_t transaction_id;

    tr_announce_response response;
    tr_announce_response_func callback;
    void * user_data;
};

typedef enum
{
    /* used in the "event" field of an announce request */
    TAU_ANNOUNCE_EVENT_NONE      = 0,
    TAU_ANNOUNCE_EVENT_COMPLETED = 1,
    TAU_ANNOUNCE_EVENT_STARTED   = 2,
    TAU_ANNOUNCE_EVENT_STOPPED   = 3
}
tau_announce_event;

static tau_announce_event
get_tau_announce_event (tr_announce_event e)
{
    switch (e)
    {
        case TR_ANNOUNCE_EVENT_COMPLETED: return TAU_ANNOUNCE_EVENT_COMPLETED;
        case TR_ANNOUNCE_EVENT_STARTED:   return TAU_ANNOUNCE_EVENT_STARTED;
        case TR_ANNOUNCE_EVENT_STOPPED:   return TAU_ANNOUNCE_EVENT_STOPPED;
        default:                          return TAU_ANNOUNCE_EVENT_NONE;
    }
}

static struct tau_announce_request *
tau_announce_request_new (const tr_announce_request  * in,
                          tr_announce_response_func    callback,
                          void                       * user_data)
{
    struct evbuffer * buf;
    struct tau_announce_request * req;
    const tau_transaction_t transaction_id = tau_transaction_new ();

    /* build the payload */
    buf = evbuffer_new ();
    evbuffer_add_hton_32 (buf, TAU_ACTION_ANNOUNCE);
    evbuffer_add_hton_32 (buf, transaction_id);
    evbuffer_add      (buf, in->info_hash, SHA_DIGEST_LENGTH);
    evbuffer_add      (buf, in->peer_id, PEER_ID_LEN);
    evbuffer_add_hton_64 (buf, in->down);
    evbuffer_add_hton_64 (buf, in->leftUntilComplete);
    evbuffer_add_hton_64 (buf, in->up);
    evbuffer_add_hton_32 (buf, get_tau_announce_event (in->event));
    evbuffer_add_hton_32 (buf, 0);
    evbuffer_add_hton_32 (buf, in->key);
    evbuffer_add_hton_32 (buf, in->numwant);
    evbuffer_add_hton_16 (buf, in->port);

    /* build the tau_announce_request */
    req = tr_new0 (struct tau_announce_request, 1);
    req->created_at = tr_time ();
    req->transaction_id = transaction_id;
    req->callback = callback;
    req->user_data = user_data;
    req->payload_len = evbuffer_get_length (buf);
    req->payload = tr_memdup (evbuffer_pullup (buf, -1), req->payload_len);
    req->response.seeders = -1;
    req->response.leechers = -1;
    req->response.downloads = -1;
    memcpy (req->response.info_hash, in->info_hash, SHA_DIGEST_LENGTH);

    evbuffer_free (buf);
    return req;
}

static void
tau_announce_request_free (struct tau_announce_request * req)
{
    tr_free (req->response.tracker_id_str);
    tr_free (req->response.warning);
    tr_free (req->response.errmsg);
    tr_free (req->response.pex6);
    tr_free (req->response.pex);
    tr_free (req->payload);
    tr_free (req);
}

static void
tau_announce_request_finished (const struct tau_announce_request * request)
{
    if (request->callback != NULL)
        request->callback (&request->response, request->user_data);
}

static void
tau_announce_request_fail (struct tau_announce_request  * request,
                           bool                           did_connect,
                           bool                           did_timeout,
                           const char                   * errmsg)
{
    request->response.did_connect = did_connect;
    request->response.did_timeout = did_timeout;
    request->response.errmsg = tr_strdup (errmsg);
    tau_announce_request_finished (request);
}

static void
on_announce_response (struct tau_announce_request  * request,
                      tau_action_t                   action,
                      struct evbuffer              * buf)
{
    const size_t buflen = evbuffer_get_length (buf);

    request->response.did_connect = true;
    request->response.did_timeout = false;

    if ((action == TAU_ACTION_ANNOUNCE) && (buflen >= 3*sizeof (uint32_t)))
    {
        tr_announce_response * resp = &request->response;
        resp->interval = evbuffer_read_ntoh_32 (buf);
        resp->leechers = evbuffer_read_ntoh_32 (buf);
        resp->seeders  = evbuffer_read_ntoh_32 (buf);
        resp->pex = tr_peerMgrCompactToPex (evbuffer_pullup (buf, -1),
                                            evbuffer_get_length (buf),
                                            NULL, 0,
                                            &request->response.pex_count);
        tau_announce_request_finished (request);
    }
    else
    {
        char * errmsg;

        if ((action == TAU_ACTION_ERROR) && (buflen > 0))
            errmsg = tr_strndup (evbuffer_pullup (buf, -1), buflen);
        else
            errmsg = tr_strdup (_("Unknown error"));

        tau_announce_request_fail (request, true, false, errmsg);
        tr_free (errmsg);
    }
}

/****
*****
*****  TRACKERS
*****
****/

struct tau_tracker
{
    tr_session * session;

    char * key;
    char * host;
    int port;

    bool is_asking_dns;
    struct evutil_addrinfo * addr;
    time_t addr_expiration_time;

    time_t connecting_at;
    time_t connection_expiration_time;
    tau_connection_t connection_id;
    tau_transaction_t connection_transaction_id;

    time_t close_at;

    tr_ptrArray announces;
    tr_ptrArray scrapes;
};

static void tau_tracker_upkeep (struct tau_tracker *);

static void
tau_tracker_free (struct tau_tracker * t)
{
    if (t->addr)
        evutil_freeaddrinfo (t->addr);
    tr_ptrArrayDestruct (&t->announces, (PtrArrayForeachFunc)tau_announce_request_free);
    tr_ptrArrayDestruct (&t->scrapes, (PtrArrayForeachFunc)tau_scrape_request_free);
    tr_free (t->host);
    tr_free (t->key);
    tr_free (t);
}

static void
tau_tracker_fail_all (struct tau_tracker  * tracker,
                      bool                  did_connect,
                      bool                  did_timeout,
                      const char          * errmsg)
{
    int i;
    int n;
    tr_ptrArray * reqs;

    /* fail all the scrapes */
    reqs = &tracker->scrapes;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i)
        tau_scrape_request_fail (tr_ptrArrayNth (reqs, i),
                                 did_connect, did_timeout, errmsg);
    tr_ptrArrayDestruct (reqs, (PtrArrayForeachFunc)tau_scrape_request_free);
    *reqs = TR_PTR_ARRAY_INIT;

    /* fail all the announces */
    reqs = &tracker->announces;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i)
        tau_announce_request_fail (tr_ptrArrayNth (reqs, i),
                                   did_connect, did_timeout, errmsg);
    tr_ptrArrayDestruct (reqs, (PtrArrayForeachFunc)tau_announce_request_free);
    *reqs = TR_PTR_ARRAY_INIT;

}

static void
tau_tracker_on_dns (int errcode, struct evutil_addrinfo *addr, void * vtracker)
{
    struct tau_tracker * tracker = vtracker;

    tracker->is_asking_dns = false;

    if (errcode)
    {
        char * errmsg = tr_strdup_printf (_("DNS Lookup failed: %s"),
                                          evdns_err_to_string (errcode));
        dbgmsg (tracker->key, "%s", errmsg);
        tau_tracker_fail_all (tracker, false, false, errmsg);
        tr_free (errmsg);
    }
    else
    {
        dbgmsg (tracker->key, "DNS lookup succeeded");
        tracker->addr = addr;
        tracker->addr_expiration_time = tr_time () + (60*60); /* one hour */
        tau_tracker_upkeep (tracker);
    }
}

static void
tau_tracker_send_request (struct tau_tracker  * tracker,
                          const void          * payload,
                          size_t                payload_len)
{
    struct evbuffer * buf = evbuffer_new ();
    dbgmsg (tracker->key, "sending request w/connection id %"PRIu64"\n",
                          tracker->connection_id);
    evbuffer_add_hton_64 (buf, tracker->connection_id);
    evbuffer_add_reference (buf, payload, payload_len, NULL, NULL);
    tau_sendto (tracker->session, tracker->addr, tracker->port,
                evbuffer_pullup (buf, -1),
                evbuffer_get_length (buf));
    evbuffer_free (buf);
}

static void
tau_tracker_send_reqs (struct tau_tracker * tracker)
{
    int i, n;
    tr_ptrArray * reqs;
    const time_t now = tr_time ();

    assert (tracker->is_asking_dns == false);
    assert (tracker->connecting_at == 0);
    assert (tracker->addr != NULL);
    assert (tracker->connection_expiration_time > now);

    reqs = &tracker->announces;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i) {
        struct tau_announce_request * req = tr_ptrArrayNth (reqs, i);
        if (!req->sent_at) {
            dbgmsg (tracker->key, "sending announce req %p", (void*)req);
            req->sent_at = now;
            tau_tracker_send_request (tracker, req->payload, req->payload_len);
            if (req->callback == NULL) {
                tau_announce_request_free (req);
                tr_ptrArrayRemove (reqs, i);
                --i;
                --n;
            }
        }
    }

    reqs = &tracker->scrapes;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i) {
        struct tau_scrape_request * req = tr_ptrArrayNth (reqs, i);
        if (!req->sent_at) {
            dbgmsg (tracker->key, "sending scrape req %p", (void*)req);
            req->sent_at = now;
            tau_tracker_send_request (tracker, req->payload, req->payload_len);
            if (req->callback == NULL) {
                tau_scrape_request_free (req);
                tr_ptrArrayRemove (reqs, i);
                --i;
                --n;
            }
        }
    }
}

static void
on_tracker_connection_response (struct tau_tracker  * tracker,
                                tau_action_t          action,
                                struct evbuffer     * buf)
{
    const time_t now = tr_time ();

    tracker->connecting_at = 0;
    tracker->connection_transaction_id = 0;

    if (action == TAU_ACTION_CONNECT)
    {
        tracker->connection_id = evbuffer_read_ntoh_64 (buf);
        tracker->connection_expiration_time = now + TAU_CONNECTION_TTL_SECS;
        dbgmsg (tracker->key, "Got a new connection ID from tracker: %"PRIu64,
                tracker->connection_id);
    }
    else
    {
        char * errmsg;
        const size_t buflen = buf ? evbuffer_get_length (buf) : 0;

        if ((action == TAU_ACTION_ERROR) && (buflen > 0))
            errmsg = tr_strndup (evbuffer_pullup (buf, -1), buflen);
        else
            errmsg = tr_strdup (_("Connection failed"));

        dbgmsg (tracker->key, "%s", errmsg);
        tau_tracker_fail_all (tracker, true, false, errmsg);
        tr_free (errmsg);
    }

    tau_tracker_upkeep (tracker);
}

static void
tau_tracker_timeout_reqs (struct tau_tracker * tracker)
{
    int i, n;
    tr_ptrArray * reqs;
    const time_t now = time (NULL);
    const bool cancel_all = tracker->close_at && (tracker->close_at <= now);


    if (tracker->connecting_at && (tracker->connecting_at + TAU_REQUEST_TTL < now)) {
        on_tracker_connection_response (tracker, TAU_ACTION_ERROR, NULL);
    }

    reqs = &tracker->announces;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i) {
        struct tau_announce_request * req = tr_ptrArrayNth (reqs, i);
        if (cancel_all || (req->created_at + TAU_REQUEST_TTL < now)) {
            dbgmsg (tracker->key, "timeout announce req %p", (void*)req);
            tau_announce_request_fail (req, false, true, NULL);
            tau_announce_request_free (req);
            tr_ptrArrayRemove (reqs, i);
            --i;
            --n;
        }
    }

    reqs = &tracker->scrapes;
    for (i=0, n=tr_ptrArraySize (reqs); i<n; ++i) {
        struct tau_scrape_request * req = tr_ptrArrayNth (reqs, i);
        if (cancel_all || (req->created_at + TAU_REQUEST_TTL < now)) {
            dbgmsg (tracker->key, "timeout scrape req %p", (void*)req);
            tau_scrape_request_fail (req, false, true, NULL);
            tau_scrape_request_free (req);
            tr_ptrArrayRemove (reqs, i);
            --i;
            --n;
        }
    }
}

static bool
tau_tracker_is_idle (const struct tau_tracker * tracker)
{
    return tr_ptrArrayEmpty (&tracker->announces)
        && tr_ptrArrayEmpty (&tracker->scrapes);
}

static void
tau_tracker_upkeep (struct tau_tracker * tracker)
{
    const time_t now = tr_time ();

    /* if the address info is too old, expire it */
    if (tracker->addr && (tracker->addr_expiration_time <= now)) {
        dbgmsg (tracker->host, "Expiring old DNS result");
        evutil_freeaddrinfo (tracker->addr);
        tracker->addr = NULL;
    }

    /* are there any requests pending? */
    if (tau_tracker_is_idle (tracker))
        return;

    /* if we don't have an address yet, try & get one now. */
    if (!tracker->addr && !tracker->is_asking_dns)
    {
        struct evutil_addrinfo hints;
        memset (&hints, 0, sizeof (hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_DGRAM;
        hints.ai_protocol = IPPROTO_UDP;
        tracker->is_asking_dns = true;
        dbgmsg (tracker->host, "Trying a new DNS lookup");
        evdns_getaddrinfo (tracker->session->evdns_base,
                           tracker->host, NULL, &hints,
                           tau_tracker_on_dns, tracker);
        return;
    }

    dbgmsg (tracker->key, "addr %p -- connected %d (%"TR_PRIuSIZE" %"TR_PRIuSIZE") -- connecting_at %"TR_PRIuSIZE,
            (void*)tracker->addr,
            (int)(tracker->connection_expiration_time > now),
            (size_t)tracker->connection_expiration_time,
            (size_t)now,
            (size_t)tracker->connecting_at);

    /* also need a valid connection ID... */
    if (tracker->addr
        && (tracker->connection_expiration_time <= now)
        && (!tracker->connecting_at))
    {
        struct evbuffer * buf = evbuffer_new ();
        tracker->connecting_at = now;
        tracker->connection_transaction_id = tau_transaction_new ();
        dbgmsg (tracker->key, "Trying to connect. Transaction ID is %u",
                tracker->connection_transaction_id);
        evbuffer_add_hton_64 (buf, 0x41727101980LL);
        evbuffer_add_hton_32 (buf, TAU_ACTION_CONNECT);
        evbuffer_add_hton_32 (buf, tracker->connection_transaction_id);
        tau_sendto (tracker->session, tracker->addr, tracker->port,
                    evbuffer_pullup (buf, -1),
                    evbuffer_get_length (buf));
        evbuffer_free (buf);
        return;
    }

    tau_tracker_timeout_reqs (tracker);

    if ((tracker->addr != NULL) && (tracker->connection_expiration_time > now))
        tau_tracker_send_reqs (tracker);
}

/****
*****
*****  SESSION
*****
****/

struct tr_announcer_udp
{
    /* tau_tracker */
    tr_ptrArray trackers;

    tr_session * session;
};

static struct tr_announcer_udp*
announcer_udp_get (tr_session * session)
{
    struct tr_announcer_udp * tau;

    if (session->announcer_udp != NULL)
        return session->announcer_udp;

    tau = tr_new0 (struct tr_announcer_udp, 1);
    tau->trackers = TR_PTR_ARRAY_INIT;
    tau->session = session;
    session->announcer_udp = tau;
    return tau;
}

/* Finds the tau_tracker struct that corresponds to this url.
   If it doesn't exist yet, create one. */
static struct tau_tracker *
tau_session_get_tracker (struct tr_announcer_udp * tau, const char * url)
{
    int i;
    int n;
    int port;
    char * host;
    char * key;
    struct tau_tracker * tracker = NULL;

    /* see if we've already got a tracker that matches this host + port */
    tr_urlParse (url, -1, NULL, &host, &port, NULL);
    key = tr_strdup_printf ("%s:%d", host, port);
    for (i=0, n=tr_ptrArraySize (&tau->trackers); !tracker && i<n; ++i) {
        struct tau_tracker * tmp = tr_ptrArrayNth (&tau->trackers, i);
        if (!tr_strcmp0 (tmp->key, key))
            tracker = tmp;
    }

    /* if we don't have a match, build a new tracker */
    if (tracker == NULL)
    {
        tracker = tr_new0 (struct tau_tracker, 1);
        tracker->session = tau->session;
        tracker->key = key;
        tracker->host = host;
        tracker->port = port;
        tracker->scrapes = TR_PTR_ARRAY_INIT;
        tracker->announces = TR_PTR_ARRAY_INIT;
        tr_ptrArrayAppend (&tau->trackers, tracker);
        dbgmsg (tracker->key, "New tau_tracker created");
    }
    else
    {
        tr_free (key);
        tr_free (host);
    }

    return tracker;
}

/****
*****
*****  PUBLIC API
*****
****/

void
tr_tracker_udp_upkeep (tr_session * session)
{
    struct tr_announcer_udp * tau = session->announcer_udp;

    if (tau != NULL)
        tr_ptrArrayForeach (&tau->trackers,
                          (PtrArrayForeachFunc)tau_tracker_upkeep);
}

bool
tr_tracker_udp_is_idle (const tr_session * session)
{
    int i;
    int n;
    struct tr_announcer_udp * tau = session->announcer_udp;

    if (tau != NULL)
        for (i=0, n=tr_ptrArraySize (&tau->trackers); i<n; ++i)
            if (!tau_tracker_is_idle (tr_ptrArrayNth (&tau->trackers, i)))
                return false;

    return true;
}

/* drop dead now. */
void
tr_tracker_udp_close (tr_session * session)
{
    struct tr_announcer_udp * tau = session->announcer_udp;

    if (tau != NULL)
    {
        session->announcer_udp = NULL;
        tr_ptrArrayDestruct (&tau->trackers, (PtrArrayForeachFunc)tau_tracker_free);
        tr_free (tau);
    }
}

/* start shutting down.
   This doesn't destroy everything if there are requests,
   but sets a deadline on how much longer to wait for the remaining ones */
void
tr_tracker_udp_start_shutdown (tr_session * session)
{
    const time_t now = time (NULL);
    struct tr_announcer_udp * tau = session->announcer_udp;

    if (tau != NULL)
    {
        int i, n;
        for (i=0, n=tr_ptrArraySize (&tau->trackers); i<n; ++i)
        {
            struct tau_tracker * tracker = tr_ptrArrayNth (&tau->trackers, i);
            tracker->close_at = now + 3;
            tau_tracker_upkeep (tracker);
        }
    }
}

/* @brief process an incoming udp message if it's a tracker response.
 * @return true if msg was a tracker response; false otherwise */
bool
tau_handle_message (tr_session * session, const uint8_t * msg, size_t msglen)
{
    int i;
    int n;
    struct tr_announcer_udp * tau;
    tau_action_t action_id;
    tau_transaction_t transaction_id;
    struct evbuffer * buf;

    /*fprintf (stderr, "got an incoming udp message w/len %"TR_PRIuSIZE"\n", msglen);*/

    if (!session || !session->announcer_udp)
        return false;
    if (msglen < (sizeof (uint32_t)*2))
        return false;

    /* extract the action_id and see if it makes sense */
    buf = evbuffer_new ();
    evbuffer_add_reference (buf, msg, msglen, NULL, NULL);
    action_id = evbuffer_read_ntoh_32 (buf);
    if (!is_tau_response_message (action_id, msglen)) {
        evbuffer_free (buf);
        return false;
    }

    /* extract the transaction_id and look for a match */
    tau = session->announcer_udp;
    transaction_id = evbuffer_read_ntoh_32 (buf);
    /*fprintf (stderr, "UDP got a transaction_id %u...\n", transaction_id);*/
    for (i=0, n=tr_ptrArraySize (&tau->trackers); i<n; ++i)
    {
        int j, jn;
        tr_ptrArray * reqs;
        struct tau_tracker * tracker = tr_ptrArrayNth (&tau->trackers, i);

        /* is it a connection response? */
        if (tracker->connecting_at
            && (transaction_id == tracker->connection_transaction_id))
        {
            dbgmsg (tracker->key, "%"PRIu32" is my connection request!", transaction_id);
            on_tracker_connection_response (tracker, action_id, buf);
            evbuffer_free (buf);
            return true;
        }

        /* is it a response to one of this tracker's announces? */
        reqs = &tracker->announces;
        for (j=0, jn=tr_ptrArraySize (reqs); j<jn; ++j) {
            struct tau_announce_request * req = tr_ptrArrayNth (reqs, j);
            if (req->sent_at && (transaction_id == req->transaction_id)) {
                dbgmsg (tracker->key, "%"PRIu32" is an announce request!", transaction_id);
                tr_ptrArrayRemove (reqs, j);
                on_announce_response (req, action_id, buf);
                tau_announce_request_free (req);
                evbuffer_free (buf);
                return true;
            }
        }

        /* is it a response to one of this tracker's scrapes? */
        reqs = &tracker->scrapes;
        for (j=0, jn=tr_ptrArraySize (reqs); j<jn; ++j) {
            struct tau_scrape_request * req = tr_ptrArrayNth (reqs, j);
            if (req->sent_at && (transaction_id == req->transaction_id)) {
                dbgmsg (tracker->key, "%"PRIu32" is a scrape request!", transaction_id);
                tr_ptrArrayRemove (reqs, j);
                on_scrape_response (req, action_id, buf);
                tau_scrape_request_free (req);
                evbuffer_free (buf);
                return true;
            }
        }
    }

    /* no match... */
    evbuffer_free (buf);
    return false;
}

void
tr_tracker_udp_announce (tr_session                 * session,
                         const tr_announce_request  * request,
                         tr_announce_response_func    response_func,
                         void                       * user_data)
{
    struct tr_announcer_udp * tau = announcer_udp_get (session);
    struct tau_tracker * tracker = tau_session_get_tracker (tau, request->url);
    struct tau_announce_request * r = tau_announce_request_new (request,
                                                                response_func,
                                                                user_data);
    tr_ptrArrayAppend (&tracker->announces, r);
    tau_tracker_upkeep (tracker);
}

void
tr_tracker_udp_scrape (tr_session               * session,
                       const tr_scrape_request  * request,
                       tr_scrape_response_func    response_func,
                       void                     * user_data)
{
    struct tr_announcer_udp * tau = announcer_udp_get (session);
    struct tau_tracker * tracker = tau_session_get_tracker (tau, request->url);
    struct tau_scrape_request * r = tau_scrape_request_new (request,
                                                            response_func,
                                                            user_data);
    tr_ptrArrayAppend (&tracker->scrapes, r);
    tau_tracker_upkeep (tracker);
}