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R9_dns_server.c
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R9_dns_server.c
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#include <event2/dns.h>
#include <event2/dns_struct.h>
#include <event2/util.h>
#include <event2/event.h>
#include <sys/socket.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
/* Let's try binding to 5353. Port 53 is more traditional, but on most
operating systems it requires root privileges. */
#define LISTEN_PORT 5353
#define LOCALHOST_IPV4_ARPA "1.0.0.127.in-addr.arpa"
#define LOCALHOST_IPV6_ARPA ("1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0." \
"0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa")
const ev_uint8_t LOCALHOST_IPV4[] = { 127, 0, 0, 1 };
const ev_uint8_t LOCALHOST_IPV6[] = { 0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,1 };
#define TTL 4242
/* This toy DNS server callback answers requests for localhost (mapping it to
127.0.0.1 or ::1) and for 127.0.0.1 or ::1 (mapping them to localhost).
*/
void server_callback(struct evdns_server_request *request, void *data)
{
int i;
int error=DNS_ERR_NONE;
/* We should try to answer all the questions. Some DNS servers don't do
this reliably, though, so you should think hard before putting two
questions in one request yourself. */
for (i=0; i < request->nquestions; ++i) {
const struct evdns_server_question *q = request->questions[i];
int ok=-1;
/* We don't use regular strcasecmp here, since we want a locale-
independent comparison. */
if (0 == evutil_ascii_strcasecmp(q->name, "localhost")) {
if (q->type == EVDNS_TYPE_A)
ok = evdns_server_request_add_a_reply(
request, q->name, 1, LOCALHOST_IPV4, TTL);
else if (q->type == EVDNS_TYPE_AAAA)
ok = evdns_server_request_add_aaaa_reply(
request, q->name, 1, LOCALHOST_IPV6, TTL);
} else if (0 == evutil_ascii_strcasecmp(q->name, LOCALHOST_IPV4_ARPA)) {
if (q->type == EVDNS_TYPE_PTR)
ok = evdns_server_request_add_ptr_reply(
request, NULL, q->name, "LOCALHOST", TTL);
} else if (0 == evutil_ascii_strcasecmp(q->name, LOCALHOST_IPV6_ARPA)) {
if (q->type == EVDNS_TYPE_PTR)
ok = evdns_server_request_add_ptr_reply(
request, NULL, q->name, "LOCALHOST", TTL);
} else {
error = DNS_ERR_NOTEXIST;
}
if (ok<0 && error==DNS_ERR_NONE)
error = DNS_ERR_SERVERFAILED;
}
/* Now send the reply. */
evdns_server_request_respond(request, error);
}
int main(int argc, char **argv)
{
struct event_base *base;
struct evdns_server_port *server;
evutil_socket_t server_fd;
struct sockaddr_in listenaddr;
base = event_base_new();
if (!base)
return 1;
server_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (server_fd < 0)
return 1;
memset(&listenaddr, 0, sizeof(listenaddr));
listenaddr.sin_family = AF_INET;
listenaddr.sin_port = htons(LISTEN_PORT);
listenaddr.sin_addr.s_addr = INADDR_ANY;
if (bind(server_fd, (struct sockaddr*)&listenaddr, sizeof(listenaddr))<0)
return 1;
server = evdns_add_server_port_with_base(base, server_fd, 0,
server_callback, NULL);
event_base_dispatch(base);
evdns_close_server_port(server);
event_base_free(base);
return 0;
}