CURLOPT_INTERFACE: avoid resolving interfaces names

Do not try to resolve interfaces names via DNS by recognizing interface
names in a few ways.  If the interface option argument has a prefix of
"if!" then treat the argument as only an interface.  Similarly, if the
interface argument is the name of an interface (even if it does not have
an IP address assigned), treat it as an interface name.  Finally, if the
interface argument is prefixed by "host!" treat it as a hostname that
must be resolved by /etc/hosts or DNS.

These changes allow a client using the multi interfaces to avoid
blocking on name resolution if the interface loses its IP address or
disappears.

3 files changed, 48 insertions, 1 deletions

diff --git a/lib/connect.c b/lib/connect.c
index af225ab83..906fd9d18 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -240,6 +240,10 @@ static CURLcode bindlocal(struct connectdata *conn,
   int error;
   char myhost[256] = "";
   int done = 0; /* -1 for error, 1 for address found */
+  int is_interface = FALSE;
+  int is_host = FALSE;
+  static const char *if_prefix = "if!";
+  static const char *host_prefix = "host!";
 
   /*************************************************************
    * Select device to bind socket to
@@ -251,9 +255,20 @@ static CURLcode bindlocal(struct connectdata *conn,
   memset(&sa, 0, sizeof(struct Curl_sockaddr_storage));
 
   if(dev && (strlen(dev)<255) ) {
+    if(strncmp(if_prefix, dev, strlen(if_prefix)) == 0) {
+      dev += strlen(if_prefix);
+      is_interface = TRUE;
+    }
+    else if(strncmp(host_prefix, dev, strlen(host_prefix)) == 0) {
+      dev += strlen(host_prefix);
+      is_host = TRUE;
+    }
 
     /* interface */
-    if(Curl_if2ip(af, dev, myhost, sizeof(myhost))) {
+    if(!is_host && (is_interface || Curl_if_is_interface_name(dev))) {
+      if(Curl_if2ip(af, dev, myhost, sizeof(myhost)) == NULL)
+        return CURLE_INTERFACE_FAILED;
+
       /*
        * We now have the numerical IP address in the 'myhost' buffer
        */
diff --git a/lib/if2ip.c b/lib/if2ip.c
index 4924f7301..0ae375b15 100644
--- a/lib/if2ip.c
+++ b/lib/if2ip.c
@@ -71,6 +71,24 @@
 
 #if defined(HAVE_GETIFADDRS)
 
+bool Curl_if_is_interface_name(const char *interface)
+{
+  bool result = FALSE;
+
+  struct ifaddrs *iface, *head;
+
+  if(getifaddrs(&head) >= 0) {
+    for(iface=head; iface != NULL; iface=iface->ifa_next) {
+      if(curl_strequal(iface->ifa_name, interface)) {
+        result = TRUE;
+        break;
+      }
+    }
+    freeifaddrs(head);
+  }
+  return result;
+}
+
 char *Curl_if2ip(int af, const char *interface, char *buf, int buf_size)
 {
   struct ifaddrs *iface, *head;
@@ -109,6 +127,14 @@ char *Curl_if2ip(int af, const char *interface, char *buf, int buf_size)
 
 #elif defined(HAVE_IOCTL_SIOCGIFADDR)
 
+bool Curl_if_is_interface_name(const char *interface)
+{
+  /* This is here just to support the old interfaces */
+  char buf[256];
+
+  return (Curl_if2ip(AF_INET, interface, buf, sizeof(buf)) != NULL);
+}
+
 char *Curl_if2ip(int af, const char *interface, char *buf, int buf_size)
 {
   struct ifreq req;
@@ -148,6 +174,11 @@ char *Curl_if2ip(int af, const char *interface, char *buf, int buf_size)
 
 #else
 
+bool Curl_if_is_interface_name(const char *interface)
+{
+  return FALSE;
+}
+
 char *Curl_if2ip(int af, const char *interf, char *buf, int buf_size)
 {
     (void) af;
diff --git a/lib/if2ip.h b/lib/if2ip.h
index cdf2638ae..678e3a556 100644
--- a/lib/if2ip.h
+++ b/lib/if2ip.h
@@ -23,6 +23,7 @@
  ***************************************************************************/
 #include "setup.h"
 
+extern bool Curl_if_is_interface_name(const char *interface);
 extern char *Curl_if2ip(int af, const char *interf, char *buf, int buf_size);
 
 #ifdef __INTERIX