Add a delay for contacting the same announce url. This way we don't spam

a tracker with connections even if we add a lot of torrents with the same
tracker at the same time.

btpd/http.c

@@ -19,6 +19,7 @@ enum http_state {
 };
 
 struct http {
+    long t_created;
     enum http_state state;
     char *url;
     CURL *curlh;
@@ -62,6 +63,7 @@ http_get(struct http **ret,
     h->state = HS_ADD;
     h->cb = cb;
     h->cb_arg = arg;
+    h->t_created = btpd_seconds;
     if ((h->curlh = curl_easy_init()) == NULL)
         btpd_err("Fatal error in curl.\n");
 
@@ -88,6 +90,26 @@ http_get(struct http **ret,
     return 0;
 }
 
+long
+http_server_busy_time(const char *url, long s)
+{
+    struct http *h;
+    size_t len = strlen(url);
+
+    pthread_mutex_lock(&m_httpq_lock);
+    h = BTPDQ_LAST(&m_httpq, http_tq);
+    while (h != NULL &&
+            !((h->state == HS_ACTIVE || h->state == HS_ADD) &&
+                strncmp(url, h->url, len) == 0))
+        h = BTPDQ_PREV(h, http_tq, entry);
+    pthread_mutex_unlock(&m_httpq_lock);
+
+    if (h == NULL || btpd_seconds - h->t_created >= s)
+        return 0;
+    else
+        return s - (btpd_seconds - h->t_created);
+}
+
 void
 http_cancel(struct http *http)
 {

btpd/http.h

@@ -24,6 +24,8 @@ int http_get(struct http **ret,
 void http_cancel(struct http *http);
 int http_succeeded(struct http_res *res);
 
+long http_server_busy_time(const char *url, long s);
+
 void http_init(void);
 
 #endif

btpd/tracker_req.c

@@ -180,6 +180,7 @@ timer_cb(int fd, short type, void *arg)
 static void
 tr_send(struct torrent *tp, enum tr_event event)
 {
+    long busy_secs;
     char e_hash[61], e_id[61], qc;;
     const uint8_t *peer_id = btpd_get_peer_id();
 
@@ -187,6 +188,13 @@ tr_send(struct torrent *tp, enum tr_event event)
     tr->event = event;
     if (tr->ttype == TIMER_TIMEOUT)
         http_cancel(tr->req);
+
+    if ((busy_secs = http_server_busy_time(tp->meta.announce, 3)) > 0) {
+        tr->ttype = TIMER_RETRY;
+        btpd_ev_add(&tr->timer, (& (struct timeval) { busy_secs, 0 }));
+        return;
+    }
+
     tr->ttype = TIMER_TIMEOUT;
     btpd_ev_add(&tr->timer, REQ_TIMEOUT);