From a7233f40879a47a30592d682f4570efdb43f179b Mon Sep 17 00:00:00 2001
From: Tomas Mudrunka <tomas@mudrunka.cz>
Date: Wed, 16 Jun 2021 16:16:22 +0200
Subject: [PATCH] ARP library

---
 c/arp/arp.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 c/arp/arp.c

diff --git a/c/arp/arp.c b/c/arp/arp.c
new file mode 100644
index 0000000..aa42fd2
--- /dev/null
+++ b/c/arp/arp.c
@@ -0,0 +1,77 @@
+#define _DEFAULT_SOURCE 1
+#define _POSIX_C_SOURCE 200809L
+#define _XOPEN_SOURCE 700
+
+#include <stdio.h>
+#include <endian.h>
+#include <unistd.h>
+#include <stdint.h>
+#include <arpa/inet.h>
+#include <sys/ioctl.h>
+#include <string.h>
+#include <net/if_arp.h>
+
+uint64_t arp_ip2mac(const char *dev, const char *ip) {
+  int ret;
+  struct arpreq arpreq;
+  int iArpFD;
+
+  struct sockaddr_in *sin = (struct sockaddr_in *) &arpreq.arp_pa;
+  uint64_t mac = 0;
+
+  memset(&arpreq, 0, sizeof(struct arpreq));
+
+  strcpy(arpreq.arp_dev, dev);
+  //sprintf(arpreq.arp_dev, "eth-pub.%d", vlan);
+
+  iArpFD = socket(AF_INET, SOCK_DGRAM, 0);
+  if (iArpFD == -1)
+  {
+    printf("Cannot open packet socket");
+    return 0;
+  }
+
+  struct timeval tv = {
+    .tv_sec = 0,
+    .tv_usec = 200000
+  };
+  setsockopt(iArpFD, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(struct timeval));
+
+  sin->sin_family = AF_INET;
+  sin->sin_addr.s_addr = inet_addr(ip);
+  sin->sin_port = htons(4242);
+
+  sendto(iArpFD, "PING", 4, MSG_NOSIGNAL,
+               (struct sockaddr*) sin, sizeof(struct sockaddr_in));
+
+
+  char blah[5];
+  if(recvfrom(iArpFD, blah, sizeof(blah), 0,
+    (struct sockaddr *) sin, (socklen_t * restrict) sizeof(struct sockaddr)) < 0)
+  {
+    //printf("UDP ping timeout\n");
+  }
+
+  ret = ioctl(iArpFD, SIOCGARP, &arpreq);
+  close(iArpFD);
+
+  if(ret < 0) {
+    printf("RET: %d FAMILY: %d\n", ret, arpreq.arp_ha.sa_family);
+    perror("SIOCGARP");
+    return 0;
+  }
+
+  memcpy(&mac, &arpreq.arp_ha.sa_data[0], 6);
+  mac = be64toh(mac<<16);
+
+  return mac;
+}
+
+int main() {
+  char *dev = "eth0";
+  char *ip = "10.10.161.3";
+  uint64_t mac = arp_ip2mac(dev, ip);
+
+  printf("DEV %s IP %s MAC: %.12lX %s\n", dev, ip, mac, mac?"OK":"FAIL");
+}
+
-- 
2.30.2