anetResolveIP() added to anet.c.

The new function is used when we want to normalize an IP address without
performing a DNS lookup if the string to resolve is not a valid IP.

This is useful every time only IPs are valid inputs or when we want to
skip DNS resolution that is slow during runtime operations if we are
required to block.

src/anet.c

@@ -163,12 +163,21 @@ int anetTcpKeepAlive(char *err, int fd)
     return ANET_OK;
 }
 
-int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len)
+/* anetGenericResolve() is called by anetResolve() and anetResolveIP() to
+ * do the actual work. It resolves the hostname "host" and set the string
+ * representation of the IP address into the buffer pointed by "ipbuf".
+ *
+ * If flags is set to ANET_IP_ONLY the function only resolves hostnames
+ * that are actually already IPv4 or IPv6 addresses. This turns the function
+ * into a validating / normalizing function. */
+int anetGenericResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len,
+                       int flags)
 {
     struct addrinfo hints, *info;
     int rv;
 
     memset(&hints,0,sizeof(hints));
+    if (flags & ANET_IP_ONLY) hints.ai_flags = AI_NUMERICHOST;
     hints.ai_family = AF_UNSPEC;
     hints.ai_socktype = SOCK_STREAM;  /* specify socktype to avoid dups */
 
@@ -188,6 +197,14 @@ int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len)
     return ANET_OK;
 }
 
+int anetResolve(char *err, char *host, char *ipbuf, size_t ipbuf_len) {
+    return anetGenericResolve(err,host,ipbuf,ipbuf_len,ANET_NONE);
+}
+
+int anetResolveIP(char *err, char *host, char *ipbuf, size_t ipbuf_len) {
+    return anetGenericResolve(err,host,ipbuf,ipbuf_len,ANET_IP_ONLY);
+}
+
 static int anetSetReuseAddr(char *err, int fd) {
     int yes = 1;
     /* Make sure connection-intensive things like the redis benckmark

src/anet.h

@@ -35,6 +35,10 @@
 #define ANET_ERR -1
 #define ANET_ERR_LEN 256
 
+/* Flags used with certain functions. */
+#define ANET_NONE 0
+#define ANET_IP_ONLY (1<<0)
+
 #if defined(__sun)
 #define AF_LOCAL AF_UNIX
 #endif