Set SO_REUSEADDR on all sockets, not just listeners

See bug 2850 for rationale: it appears that on some busy exits, the OS
decides that every single port is now unusable because they have been
all used too recently.

changes/bug2850

@@ -0,0 +1,5 @@
+  - Minor features
+    o Set SO_REUSEADDR on all sockets, not just listeners.  This should
+      help busy exit nodes avoid running out of useable ports just because
+      all the ports have been used in the near past.  Resolves issue 2850.
+

src/or/connection.c

@@ -851,6 +851,25 @@ warn_too_many_conns(void)
   }
 }
 
+/** Tell the TCP stack that it shouldn't wait for a long time after
+ * <b>sock</b> has closed before reusing its port. */
+static void
+make_socket_reuseable(int sock)
+{
+#ifdef MS_WINDOWS
+  (void) sock;
+#else
+  int one=1;
+
+  /* REUSEADDR on normal places means you can rebind to the port
+   * right after somebody else has let it go. But REUSEADDR on win32
+   * means you can bind to the port _even when somebody else
+   * already has it bound_. So, don't do that on Win32. */
+  setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void*) &one,
+             (socklen_t)sizeof(one));
+#endif
+}
+
 /** Bind a new non-blocking socket listening to the socket described
  * by <b>listensockaddr</b>.
  *
@@ -873,9 +892,6 @@ connection_create_listener(struct sockaddr *listensockaddr, socklen_t socklen,
 
   if (listensockaddr->sa_family == AF_INET) {
     int is_tcp = (type != CONN_TYPE_AP_DNS_LISTENER);
-#ifndef MS_WINDOWS
-    int one=1;
-#endif
     if (is_tcp)
       start_reading = 1;
 
@@ -893,14 +909,7 @@ connection_create_listener(struct sockaddr *listensockaddr, socklen_t socklen,
       goto err;
     }
 
-#ifndef MS_WINDOWS
-    /* REUSEADDR on normal places means you can rebind to the port
-     * right after somebody else has let it go. But REUSEADDR on win32
-     * means you can bind to the port _even when somebody else
-     * already has it bound_. So, don't do that on Win32. */
-    setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (void*) &one,
-               (socklen_t)sizeof(one));
-#endif
+    make_socket_reuseable(s);
 
     if (bind(s,listensockaddr,socklen) < 0) {
       const char *helpfulhint = "";
@@ -1088,6 +1097,7 @@ connection_handle_listener_read(connection_t *conn, int new_type)
             "Connection accepted on socket %d (child of fd %d).",
             news,conn->s);
 
+  make_socket_reuseable(news);
   set_socket_nonblocking(news);
 
   if (options->ConstrainedSockets)
@@ -1297,6 +1307,8 @@ connection_connect(connection_t *conn, const char *address,
   log_debug(LD_NET, "Connecting to %s:%u.",
             escaped_safe_str_client(address), port);
 
+  make_socket_reuseable(s);
+
   if (connect(s, dest_addr, dest_addr_len) < 0) {
     int e = tor_socket_errno(s);
     if (!ERRNO_IS_CONN_EINPROGRESS(e)) {