From a59a964f9c53aa41b1c3ccb0273c3a1b6886a4ed Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Sat, 9 Jun 2018 15:56:33 +0100
Subject: [PATCH 1/1] noip.c: Support `SO_REUSEADDR', rather sketchily.

If the caller tries to bind, and has previously set the `SO_REUSEADDR'
flag, then unlink any existing socket unless there's an active listener
already.
---
 noip.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/noip.c b/noip.c
index 45ed9a5..f60788e 100644
--- a/noip.c
+++ b/noip.c
@@ -800,6 +800,7 @@ static int encode_unused_inet_addr(struct sockaddr *sa,
  * Returns zero on success; -1 on failure.
  */
 #define ENCF_FRESH 1u
+#define ENCF_REUSEADDR 2u
 static int encode_inet_addr(struct sockaddr_un *sun,
 			    const struct sockaddr *sa,
 			    unsigned f)
@@ -825,6 +826,7 @@ static int encode_inet_addr(struct sockaddr_un *sun,
      * want an existing socket, then we're done.
      */
     rc = encode_single_inet_addr(sa, sun, 0);
+    if ((f&ENCF_REUSEADDR) && !(rc&LISTEN)) unlink(sun->sun_path);
     if ((rc&USED) || (f&ENCF_FRESH)) goto found;
 
     /* We're looking for a socket which already exists.  This is
@@ -1723,6 +1725,9 @@ int bind(int sk, const struct sockaddr *sa, socklen_t len)
 {
   struct sockaddr_un sun;
   int rc;
+  unsigned f;
+  int reusep;
+  socklen_t n;
   Dpid;
 
   D({ char buf[ADDRBUFSZ];
@@ -1738,7 +1743,11 @@ int bind(int sk, const struct sockaddr *sa, socklen_t len)
 	if (fixup_real_ip_socket(sk, sa->sa_family, 0))
 	  return (-1);
       } else {
-	encode_inet_addr(&sun, sa, ENCF_FRESH);
+	f = ENCF_FRESH;
+	n = sizeof(reusep);
+	if (!getsockopt(sk, SOL_SOCKET, SO_REUSEADDR, &reusep, &n) && reusep)
+	  f |= ENCF_REUSEADDR;
+	encode_inet_addr(&sun, sa, f);
 	sa = SA(&sun);
 	len = SUN_LEN(&sun);
       }
-- 
2.11.0