[tor-commits] [tor/master] Comments/explanation for #17873

[nickm at torproject.org]

commit 9f5431c79fbe51af9445f00bb1a4d67d80e5ada5
Author: rl1987 <rl1987 at sdf.lonestar.org>
Date:   Wed May 16 17:16:46 2018 +0200

    Comments/explanation for #17873
---
 src/core/mainloop/connection.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/core/mainloop/connection.c b/src/core/mainloop/connection.c
index 200ea4243..f1716ed8f 100644
--- a/src/core/mainloop/connection.c
+++ b/src/core/mainloop/connection.c
@@ -133,6 +133,22 @@
 #include "feature/nodelist/routerinfo_st.h"
 #include "core/or/socks_request_st.h"
 
+/**
+ * On Windows and Linux we cannot reliably bind() a socket to an
+ * address and port if: 1) There's already a socket bound to wildcard
+ * address (0.0.0.0 or ::) with the same port; 2) We try to bind()
+ * to wildcard address and there's another socket bound to a
+ * specific address and the same port.
+ *
+ * To address this problem on these two platforms we implement a
+ * routine that:
+ * 1) Checks if first attempt to bind() a new socket  failed with
+ * EADDRINUSE.
+ * 2) If so, it will close the appropriate old listener connection and
+ * 3) Attempts bind()'ing the new listener socket again.
+ *
+ * For further information, see ticket #17873.
+ */
 #if defined(__linux__) || defined(_WIN32)
 #define ENABLE_LISTENER_REBIND
 #endif
@@ -1191,6 +1207,9 @@ tor_listen(tor_socket_t fd)
  *
  * <b>address</b> is only used for logging purposes and to add the information
  * to the conn.
+ *
+ * Set <b>addr_in_use</b> to true in case socket binding fails with
+ * EADDRINUSE.
  */
 static connection_t *
 connection_listener_new(const struct sockaddr *listensockaddr,