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// vim:ts=8:expandtab
#include <stdio.h>
#include <stdbool.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>
static char * get_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 NULL;
}
/* 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 NULL;
}
socklen_t local_len = sizeof(struct sockaddr_storage);
if (getsockname(fd, (struct sockaddr*)&local, &local_len) == -1) {
perror("getsockname()");
(void)close(fd);
return NULL;
}
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);
return NULL;
}
(void)close(fd);
return buf;
}
/*
* Returns the IPv6 address with which you have connectivity at the moment.
* The char * is statically allocated and mustn't be freed
*/
static char *get_ipv6_addr() {
struct addrinfo hints;
struct addrinfo *result, *resp;
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)
return get_sockname(cached);
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. */
return NULL;
}
for (resp = result; resp != NULL; resp = resp->ai_next) {
char *addr_string = get_sockname(resp);
if (!addr_string)
continue;
if ((cached = malloc(sizeof(struct addrinfo))) == NULL)
return NULL;
memcpy(cached, resp, sizeof(struct addrinfo));
if ((cached->ai_addr = malloc(resp->ai_addrlen)) == NULL) {
cached = NULL;
return NULL;
}
memcpy(cached->ai_addr, resp->ai_addr, resp->ai_addrlen);
freeaddrinfo(result);
return addr_string;
}
freeaddrinfo(result);
return NULL;
}
void print_ipv6_info(const char *format_up, const char *format_down) {
const char *walk;
char * addr_string = get_ipv6_addr();
if (addr_string == NULL) {
printf("%s", format_down);
} else {
for (walk = format_up; *walk != '\0'; walk++) {
if (*walk != '%') {
putchar(*walk);
continue;
}
if (strncmp(walk+1, "ip", strlen("ip")) == 0) {
printf("%s", addr_string);
walk += strlen("ip");
}
}
}
}
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