1 files changed, 99 insertions, 0 deletions
diff --git a/src/print_ipv6_addr.c b/src/print_ipv6_addr.c
new file mode 100644
index 0000000..fcb2df8
--- /dev/null
+++ b/src/print_ipv6_addr.c
@@ -0,0 +1,99 @@
+// vim:ts=8:expandtab
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <string.h>
+#include <arpa/inet.h>
+
+/*
+ * 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;
+
+        memset(&hints, 0, sizeof(struct addrinfo));
+        hints.ai_family = AF_INET6;
+
+        /* We resolve the K root server to get a public IPv6 address. You can
+         * replace this with any other host which has an AAAA record, but the
+         * K root server is a pretty safe bet. */
+        if (getaddrinfo("k.root-servers.net", "domain", &hints, &result) != 0) {
+                /* We don’t display the error here because most
+                 * likely, there just is no connectivity.
+                 * Thus, don’t spam the user’s console. */
+                printf("no IPv6");
+                return;
+        }
+
+        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);
+                        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");
+                        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");
+                        return;
+                }
+
+                free(result);
+                printf("%s", buf);
+                return;
+        }
+
+        free(result);
+        printf("no IPv6");
+}
+
+void print_ipv6_info(const char *format) {
+        const char *walk;
+
+        for (walk = format; *walk != '\0'; walk++) {
+                if (*walk != '%') {
+                        putchar(*walk);
+                        continue;
+                }
+
+                if (strncmp(walk+1, "ip", strlen("ip")) == 0) {
+                        print_ipv6_addr();
+                        walk += strlen("ip");
+                }
+        }
+}