- Added CURLINFO_PRIMARY_IP as a new information retrievable with

curl_easy_getinfo. It returns a pointer to a string with the most recently
  used IP address. Modified test case 500 to also verify this feature. The
  implementing of this feature was sponsored by Lenny Rachitsky at NeuStar.

lib/connect.c

@@ -775,9 +775,12 @@ singleipconnect(struct connectdata *conn,
   /* FIXME: do we have Curl_printable_address-like with struct sockaddr* as
      argument? */
 #if defined(HAVE_SYS_UN_H) && defined(AF_UNIX)
-  if(addr->family==AF_UNIX)
+  if(addr->family==AF_UNIX) {
     infof(data, "  Trying %s... ",
           ((const struct sockaddr_un*)(&addr->addr))->sun_path);
+    snprintf(data->info.ip, MAX_IPADR_LEN, "%s",
+             ((const struct sockaddr_un*)(&addr->addr))->sun_path);
+  }
   else
 #endif
   {
@@ -789,8 +792,10 @@ singleipconnect(struct connectdata *conn,
       iptoprint = &((const struct sockaddr_in*)(&addr->addr))->sin_addr;
 
     if(Curl_inet_ntop(addr->family, iptoprint, addr_buf,
-                      sizeof(addr_buf)) != NULL)
+                      sizeof(addr_buf)) != NULL) {
       infof(data, "  Trying %s... ", addr_buf);
+      snprintf(data->info.ip, MAX_IPADR_LEN, "%s", addr_buf);
+    }
   }
 
   if(data->set.tcp_nodelay)

lib/getinfo.c

@@ -210,6 +210,10 @@ CURLcode Curl_getinfo(struct SessionHandle *data, CURLINFO info, ...)
        option had been enabled! */
     *param_charp = data->info.wouldredirect;
     break;
+  case CURLINFO_PRIMARY_IP:
+    /* Return the ip address of the most recent (primary) connection */
+    *param_charp = data->info.ip;
+    break;
   default:
     return CURLE_BAD_FUNCTION_ARGUMENT;
   }

lib/urldata.h

@@ -48,6 +48,8 @@
 #define CURL_DEFAULT_USER "anonymous"
 #define CURL_DEFAULT_PASSWORD "ftp@example.com"
 
+#define MAX_IPADR_LEN (4*9) /* should be enough to hold the longest ipv6 one */
+
 #include "cookie.h"
 #include "formdata.h"
 
@@ -1036,6 +1038,9 @@ struct PureInfo {
   long numconnects; /* how many new connection did libcurl created */
   char *contenttype; /* the content type of the object */
   char *wouldredirect; /* URL this would've been redirected to if asked to */
+  char ip[MAX_IPADR_LEN]; /* this buffer gets the numerical ip version stored
+                             at the connect *attempt* so it will get the last
+                             tried connect IP even on failures */
 };