ipv6: cache the result of the DNS query only, the socket needs to be re-created every...

[i3/i3status] / src / print_ipv6_addr.c

diff --git a/src/print_ipv6_addr.c b/src/print_ipv6_addr.c
index fcb2df804f7b3d3672f51bd2d1218f81d7e031cd..b9486bee09f73cc99bac6e8aa7b38f43e9eed69d 100644 (file)
--- a/src/print_ipv6_addr.c
+++ b/src/print_ipv6_addr.c
@@ -1,5 +1,6 @@
 // vim:ts=8:expandtab
 #include <stdio.h>
+#include <stdbool.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <sys/types.h>
@@ -8,15 +9,69 @@
 #include <string.h>
 #include <arpa/inet.h>
 
+static bool print_sockname(struct addrinfo *addr) {
+        static char buf[INET6_ADDRSTRLEN+1];
+        struct sockaddr_storage local;
+        int ret;
+        int fd;
+
+        if ((fd = socket(addr->ai_family, SOCK_DGRAM, 0)) == -1) {
+                perror("socket()");
+                return false;
+        }
+
+        /* Since the socket was created with SOCK_DGRAM, this is
+         * actually not establishing a connection or generating
+         * any other network traffic. Instead, as a side-effect,
+         * it saves the local address with which packets would
+         * be sent to the destination. */
+        if (connect(fd, addr->ai_addr, addr->ai_addrlen) == -1) {
+                /* We don’t display the error here because most
+                 * likely, there just is no IPv6 connectivity.
+                 * Thus, don’t spam the user’s console but just
+                 * try the next address. */
+                (void)close(fd);
+                return false;
+        }
+
+
+        socklen_t local_len = sizeof(struct sockaddr_storage);
+        if (getsockname(fd, (struct sockaddr*)&local, &local_len) == -1) {
+                perror("getsockname()");
+                (void)close(fd);
+                printf("no IPv6");
+                return true;
+        }
+
+        memset(buf, 0, INET6_ADDRSTRLEN + 1);
+        if ((ret = getnameinfo((struct sockaddr*)&local, local_len,
+                               buf, sizeof(buf), NULL, 0,
+                               NI_NUMERICHOST)) != 0) {
+                fprintf(stderr, "getnameinfo(): %s\n", gai_strerror(ret));
+                (void)close(fd);
+                printf("no IPv6");
+                return true;
+        }
+
+        (void)close(fd);
+        printf("%s", buf);
+        return true;
+}
+
 /*
  * Returns the IPv6 address with which you have connectivity at the moment.
  *
  */
 static void print_ipv6_addr() {
-        static char buf[INET6_ADDRSTRLEN+1];
         struct addrinfo hints;
         struct addrinfo *result, *resp;
-        int fd;
+        static struct addrinfo *cached = NULL;
+
+        /* To save dns lookups (if they are not cached locally) and creating
+         * sockets, we save the fd and keep it open. */
+        if (cached != NULL)
+                if (print_sockname(cached))
+                        return;
 
         memset(&hints, 0, sizeof(struct addrinfo));
         hints.ai_family = AF_INET6;
@@ -33,52 +88,22 @@ static void print_ipv6_addr() {
         }
 
         for (resp = result; resp != NULL; resp = resp->ai_next) {
-                if ((fd = socket(resp->ai_family, SOCK_DGRAM, 0)) == -1) {
-                        perror("socket()");
-                        continue;
-                }
-
-                /* Since the socket was created with SOCK_DGRAM, this is
-                 * actually not establishing a connection or generating
-                 * any other network traffic. Instead, as a side-effect,
-                 * it saves the local address with which packets would
-                 * be sent to the destination. */
-                if (connect(fd, resp->ai_addr, resp->ai_addrlen) == -1) {
-                        /* We don’t display the error here because most
-                         * likely, there just is no IPv6 connectivity.
-                         * Thus, don’t spam the user’s console but just
-                         * try the next address. */
-                        (void)close(fd);
+                if (!print_sockname(resp))
                         continue;
-                }
 
-                struct sockaddr_storage local;
-                socklen_t local_len = sizeof(struct sockaddr_storage);
-                if (getsockname(fd, (struct sockaddr*)&local, &local_len) == -1) {
-                        perror("getsockname()");
-                        (void)close(fd);
-                        printf("no IPv6");
+                if ((cached = malloc(sizeof(struct addrinfo))) == NULL)
                         return;
-                }
-
-                (void)close(fd);
-
-                memset(buf, 0, INET6_ADDRSTRLEN + 1);
-                int ret;
-                if ((ret = getnameinfo((struct sockaddr*)&local, local_len,
-                                       buf, sizeof(buf), NULL, 0,
-                                       NI_NUMERICHOST)) != 0) {
-                        fprintf(stderr, "getnameinfo(): %s\n", gai_strerror(ret));
-                        printf("no IPv6");
+                memcpy(cached, resp, sizeof(struct addrinfo));
+                if ((cached->ai_addr = malloc(resp->ai_addrlen)) == NULL) {
+                        cached = NULL;
                         return;
                 }
-
-                free(result);
-                printf("%s", buf);
+                memcpy(cached->ai_addr, resp->ai_addr, resp->ai_addrlen);
+                freeaddrinfo(result);
                 return;
         }
 
-        free(result);
+        freeaddrinfo(result);
         printf("no IPv6");
 }