add: reverse dns

src/dns.c

@@ -4,6 +4,8 @@
 #include <arpa/inet.h>
 #include <stddef.h>
 #include <netdb.h>
+#include <stdio.h>
+#include <string.h>
 #include <strings.h>
 
 int dns_lookup(const char *hostname, char *ipstr)
@@ -30,7 +32,32 @@ int dns_lookup(const char *hostname, char *ipstr)
     return 0;
 }
 
-int dns_reverse_lookup(const char *ipstr, char *hostname);
+char *dns_reverse_lookup(const char *ipstr)
 {
+    struct sockaddr_in sa;
+    char host[NI_MAXHOST];
 
+    bzero(&sa, sizeof(sa));
+    sa.sin_family = AF_INET;
+
+    printf("%s\n", ipstr);
+
+    if (inet_pton(AF_INET, ipstr, &sa.sin_addr) <= 0)
+    {
+        print_err("inet_pton failed");
+        return NULL;
+    }
+
+    int ret = getnameinfo(
+        (struct sockaddr *)&sa, sizeof(sa),
+        host, sizeof(host),
+        NULL, 0, NI_NAMEREQD);
+
+    if (ret != 0) 
+    {
+        print_err("reverse dns failed.");
+        return NULL;
+    }
+
+    return strdup(host);
 }

src/dns.h

@@ -1,4 +1,4 @@
 #pragma once
 
 int dns_lookup(const char *hostname, char *ipstr);
-int dns_reverse_lookup(const char *ipstr, char *hostname);
+char *dns_reverse_lookup(const char *ipstr);

src/host.h

@@ -5,4 +5,5 @@
 struct host {
     char ip[INET_ADDRSTRLEN];
     char *hostname;
+    char *reverse_dns;
 };

src/main.c

@@ -2,6 +2,7 @@
 #include "host.h"
 #include "packet.h"
 #include "print.h"
+#include <netinet/ip.h>
 #include <signal.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -21,6 +22,7 @@
 #include <stdbool.h>
 #include <sys/socket.h>
 #include <netdb.h>
+#include <net/ethernet.h>
 
 bool loop = true;
 
@@ -34,21 +36,26 @@ int main(int ac, char **av)
 {
     (void) ac;
     (void) av;
-    struct host hostname;
 
-    size_t payload_size = 48;
+    struct host host;
+
+    host.hostname = "localhost";
+
+    size_t payload_size = 20;
     size_t packet_size = sizeof(struct icmphdr) + payload_size;
 
     signal(SIGINT, signal_handler);
 
-    if (dns_lookup("localhost", hostname.ip))
+    if (dns_lookup(host.hostname, host.ip))
         return 5;
 
+    host.reverse_dns = dns_reverse_lookup(host.ip);
+
     struct sockaddr_in dest;
 
     dest.sin_family = AF_INET;
     dest.sin_port = htons(0);       
-    inet_pton(AF_INET, hostname.ip, &dest.sin_addr);
+    inet_pton(AF_INET, host.ip, &dest.sin_addr);
 
     int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
 
@@ -106,7 +113,7 @@ int main(int ac, char **av)
 
         double time_interval = ((stop.tv_sec - start.tv_sec) * 1000 + ((double)stop.tv_usec - (double) start.tv_usec)  / 1000);
         struct icmphdr *hdr = (struct icmphdr *) packet;
-        printf("%zu bytes from %p (%s): icmp_seq=%d, ttl=%u, time=%fms\n", payload_size, NULL, hostname.ip, htons(hdr->un.echo.sequence), 116, time_interval);
+        printf("%zu bytes from %s (%s): icmp_seq=%d, ttl=%u, time=%fms\n", payload_size + sizeof(struct icmphdr) + sizeof(struct iphdr) + sizeof(struct ether_header), host.reverse_dns, host.ip, htons(hdr->un.echo.sequence), 116, time_interval);
         
         sleep(1);