Add support for SO_REUSEADDR

[This introduces some new API functions.]

* Adds new flag to the connection context indicating SO_REUSEADDR
  should be set.
* Adds max number of retries constant for when connect() hits
  EADDRNOTAVAIL.
* Adds new function, redisAsyncConnectBindWithReuse(), letting
  clients enable this functionality.

[Removed trailing whitespace in new header lines.]

Closes #264

async.c

@@ -173,6 +173,14 @@ redisAsyncContext *redisAsyncConnectBind(const char *ip, int port,
     return ac;
 }
 
+redisAsyncContext *redisAsyncConnectBindWithReuse(const char *ip, int port,
+                                                  const char *source_addr) {
+    redisContext *c = redisConnectBindNonBlockWithReuse(ip,port,source_addr);
+    redisAsyncContext *ac = redisAsyncInitialize(c);
+    __redisAsyncCopyError(ac);
+    return ac;
+}
+
 redisAsyncContext *redisAsyncConnectUnix(const char *path) {
     redisContext *c;
     redisAsyncContext *ac;

async.h

@@ -103,6 +103,8 @@ typedef struct redisAsyncContext {
 /* Functions that proxy to hiredis */
 redisAsyncContext *redisAsyncConnect(const char *ip, int port);
 redisAsyncContext *redisAsyncConnectBind(const char *ip, int port, const char *source_addr);
+redisAsyncContext *redisAsyncConnectBindWithReuse(const char *ip, int port,
+                                                  const char *source_addr);
 redisAsyncContext *redisAsyncConnectUnix(const char *path);
 int redisAsyncSetConnectCallback(redisAsyncContext *ac, redisConnectCallback *fn);
 int redisAsyncSetDisconnectCallback(redisAsyncContext *ac, redisDisconnectCallback *fn);

hiredis.c

@@ -1123,6 +1123,15 @@ redisContext *redisConnectBindNonBlock(const char *ip, int port,
     return c;
 }
 
+redisContext *redisConnectBindNonBlockWithReuse(const char *ip, int port,
+                                                const char *source_addr) {
+    redisContext *c = redisContextInit();
+    c->flags &= ~REDIS_BLOCK;
+    c->flags |= REDIS_REUSEADDR;
+    redisContextConnectBindTcp(c,ip,port,NULL,source_addr);
+    return c;
+}
+
 redisContext *redisConnectUnix(const char *path) {
     redisContext *c;
 

hiredis.h

@@ -80,6 +80,9 @@
 /* Flag that is set when monitor mode is active */
 #define REDIS_MONITORING 0x40
 
+/* Flag that is set when we should set SO_REUSEADDR before calling bind() */
+#define REDIS_REUSEADDR 0x80
+
 #define REDIS_REPLY_STRING 1
 #define REDIS_REPLY_ARRAY 2
 #define REDIS_REPLY_INTEGER 3
@@ -91,6 +94,10 @@
 
 #define REDIS_KEEPALIVE_INTERVAL 15 /* seconds */
 
+/* number of times we retry to connect in the case of EADDRNOTAVAIL and
+ * SO_REUSEADDR is being used. */
+#define REDIS_CONNECT_RETRIES  10
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -177,7 +184,10 @@ typedef struct redisContext {
 redisContext *redisConnect(const char *ip, int port);
 redisContext *redisConnectWithTimeout(const char *ip, int port, const struct timeval tv);
 redisContext *redisConnectNonBlock(const char *ip, int port);
-redisContext *redisConnectBindNonBlock(const char *ip, int port, const char *source_addr);
+redisContext *redisConnectBindNonBlock(const char *ip, int port,
+                                       const char *source_addr);
+redisContext *redisConnectBindNonBlockWithReuse(const char *ip, int port,
+                                                const char *source_addr);
 redisContext *redisConnectUnix(const char *path);
 redisContext *redisConnectUnixWithTimeout(const char *path, const struct timeval tv);
 redisContext *redisConnectUnixNonBlock(const char *path);

net.c

@@ -256,10 +256,12 @@ int redisContextSetTimeout(redisContext *c, const struct timeval tv) {
 static int _redisContextConnectTcp(redisContext *c, const char *addr, int port,
                                    const struct timeval *timeout,
                                    const char *source_addr) {
-    int s, rv;
+    int s, rv, n;
     char _port[6];  /* strlen("65535"); */
     struct addrinfo hints, *servinfo, *bservinfo, *p, *b;
     int blocking = (c->flags & REDIS_BLOCK);
+    int reuseaddr = (c->flags & REDIS_REUSEADDR);
+    int reuses = 0;
 
     snprintf(_port, 6, "%d", port);
     memset(&hints,0,sizeof(hints));
@@ -279,6 +281,7 @@ static int _redisContextConnectTcp(redisContext *c, const char *addr, int port,
         }
     }
     for (p = servinfo; p != NULL; p = p->ai_next) {
+addrretry:
         if ((s = socket(p->ai_family,p->ai_socktype,p->ai_protocol)) == -1)
             continue;
 
@@ -294,6 +297,15 @@ static int _redisContextConnectTcp(redisContext *c, const char *addr, int port,
                 __redisSetError(c,REDIS_ERR_OTHER,buf);
                 goto error;
             }
+
+            if (reuseaddr) {
+                n = 1;
+                if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char*) &n,
+                               sizeof(n)) < 0) {
+                    goto error;
+                }
+            }
+
             for (b = bservinfo; b != NULL; b = b->ai_next) {
                 if (bind(s,b->ai_addr,b->ai_addrlen) != -1) {
                     bound = 1;
@@ -314,6 +326,12 @@ static int _redisContextConnectTcp(redisContext *c, const char *addr, int port,
                 continue;
             } else if (errno == EINPROGRESS && !blocking) {
                 /* This is ok. */
+            } else if (errno == EADDRNOTAVAIL && reuseaddr) {
+                if (++reuses >= REDIS_CONNECT_RETRIES) {
+                    goto error;
+                } else {
+                    goto addrretry;
+                }
             } else {
                 if (redisContextWaitReady(c,timeout) != REDIS_OK)
                     goto error;