Local webserver to provice MAC address

macserv.c

// Compile with -lmicrohttpd

#include <arpa/inet.h>
#include <errno.h>
#include <limits.h>
#include <linux/rtnetlink.h>
#include <linux/types.h>
#include <microhttpd.h>
#include <net/if.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

struct route_info {
  struct in_addr dstAddr;
  struct in_addr srcAddr;
  struct in_addr gateWay;
  char ifName[IF_NAMESIZE];
};

/* Code by gibbon1
 * http://www.linuxquestions.org/questions/linux-networking-3/howto-find-gateway-address-through-code-397078/
*/

#define BUFSIZE 8192
int readNlSock(int sockFd, char *bufPtr, unsigned int seqNum, unsigned int pId) {
  struct nlmsghdr *nlHdr;
  int msgLen = 0;
  do {
    int readLen = 0;
    /* Receive response from the kernel */
    if ((readLen = recv(sockFd, bufPtr, BUFSIZE - msgLen, 0)) < 0) {
      perror("SOCK READ: ");
      return -1;
    }

    nlHdr = (struct nlmsghdr *)bufPtr;

    /* Check if the header is valid */
    if ((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR)) {
      perror("Error in recieved packet");
      return -1;
    }

    /* Check if the its the last message */
    if (nlHdr->nlmsg_type == NLMSG_DONE) {
      break;
    } else {
      /* Else move the pointer to buffer appropriately */
      bufPtr += readLen;
      msgLen += readLen;
    }

    /* Check if its a multi part message */
    if ((nlHdr->nlmsg_flags & NLM_F_MULTI) == 0) {
      /* return if its not */
      break;
    }
  } while ((nlHdr->nlmsg_seq != seqNum) || (nlHdr->nlmsg_pid != pId));

  return msgLen;
}

/* parse the route info returned */
int parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo) {
  struct rtmsg *rtMsg;
  struct rtattr *rtAttr;
  int rtLen;

  rtMsg = (struct rtmsg *)NLMSG_DATA(nlHdr);

  /* If the route is not for AF_INET or does not belong to main routing table then return. */
  if ((rtMsg->rtm_family != AF_INET) || (rtMsg->rtm_table != RT_TABLE_MAIN))
    return 1;

  /* get the rtattr field */
  rtAttr = (struct rtattr *)RTM_RTA(rtMsg);
  rtLen = RTM_PAYLOAD(nlHdr);

  for ( ; RTA_OK(rtAttr, rtLen) ; rtAttr = RTA_NEXT(rtAttr, rtLen)) {
    switch (rtAttr->rta_type) {
      case RTA_OIF:
        if_indextoname(*(int *)RTA_DATA(rtAttr), rtInfo->ifName);
        break;

      case RTA_GATEWAY:
        memcpy(&rtInfo->gateWay, RTA_DATA(rtAttr), sizeof(rtInfo->gateWay));
        break;

      case RTA_PREFSRC:
        memcpy(&rtInfo->srcAddr, RTA_DATA(rtAttr), sizeof(rtInfo->srcAddr));
        break;

      case RTA_DST:
        memcpy(&rtInfo->dstAddr, RTA_DATA(rtAttr), sizeof(rtInfo->dstAddr));
        break;
    }
  }

  return 0;
}

// meat
int get_gatewayif(char *gatewayif, socklen_t size) {
  int found_gatewayip = 0;

  struct nlmsghdr *nlMsg;
  struct rtmsg *rtMsg;
  struct route_info *rtInfo;
  char msgBuf[BUFSIZE]; // pretty large buffer

  int sock, len, msgSeq = 0;

  /* Create Socket */
  if ((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0) {
    perror("Socket Creation: ");
    return(-1);
  }

  /* Initialize the buffer */
  memset(msgBuf, 0, BUFSIZE);

  /* point the header and the msg structure pointers into the buffer */
  nlMsg = (struct nlmsghdr *)msgBuf;
  rtMsg = (struct rtmsg *)NLMSG_DATA(nlMsg);
  rtMsg->rtm_table = RT_TABLE_MAIN;

  /* Fill in the nlmsg header*/
  nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); // Length of message.
  nlMsg->nlmsg_type = RTM_GETROUTE; // Get the routes from kernel routing table .

  nlMsg->nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST; // The message is a request for dump.
  nlMsg->nlmsg_seq = msgSeq++; // Sequence of the message packet.
  nlMsg->nlmsg_pid = getpid(); // PID of process sending the request.

  /* Send the request */
  if (send(sock, nlMsg, nlMsg->nlmsg_len, 0) < 0) {
    fprintf(stderr, "Write To Socket Failed...\n");
    return -1;
  }

  /* Read the response */
  if ((len = readNlSock(sock, msgBuf, msgSeq, getpid())) < 0) {
    fprintf(stderr, "Read From Socket Failed...\n");
    return -1;
  }

  /* Parse and print the response */
  rtInfo = (struct route_info *)malloc(sizeof(struct route_info));

  for ( ; NLMSG_OK(nlMsg, len); nlMsg = NLMSG_NEXT(nlMsg, len)) {
    memset(rtInfo, 0, sizeof(struct route_info));
    if (parseRoutes(nlMsg, rtInfo))
      continue;

    // Check if default gateway
    if (strstr((char *)inet_ntoa(rtInfo->dstAddr), "0.0.0.0")) {
      // copy it over
      //inet_ntop(AF_INET, &rtInfo->gateWay, gatewayip, size);
      strncpy(gatewayif, rtInfo->ifName, size);

      found_gatewayip = 1;
      break;
    }
  }

  free(rtInfo);
  close(sock);

  return found_gatewayip;
}


int getmac(uint8_t mac[]) {
  int sock;
  struct ifreq ifr = {};
  ifr.ifr_addr.sa_family = AF_INET;

  sock = socket(AF_INET, SOCK_DGRAM, 0);
  if (!sock)
    return 1;

  if (!get_gatewayif(ifr.ifr_name, sizeof(ifr.ifr_name))) {
    printf("Cannot get gateway interface, defaulting to eth0 mac\n");
    strncpy(ifr.ifr_name, "eth0", sizeof(ifr.ifr_name));
  }

  ioctl(sock, SIOCGIFHWADDR, &ifr);
  close(sock);

  int i;
  for (i=0; i<6; i++) {
    mac[i] = ifr.ifr_hwaddr.sa_data[i];
  }

  return 0;
}


struct MHD_Daemon *httpd = 0;

void httpd_request_completed(void *cls, struct MHD_Connection *connection, void **con_cls, enum MHD_RequestTerminationCode toe) {
  (void)cls;
  (void)connection;
  (void)toe;

  *con_cls = NULL;
}

int httpd_process_query(void * cls,
        struct MHD_Connection * connection,
        const char * url,
        const char * method,
        const char * version,
        const char * upload_data,
        size_t * upload_data_size,
        void ** ptr) {
  (void)version;
  (void)cls;
  struct MHD_Response * response;
  int ret;
  char * resp=0;
  int returncode = MHD_HTTP_OK;
  size_t resplength = 0;

  if (strcmp(method, "GET")) {
    return MHD_NO;
  }

  if (strcmp(url, "/")==0) {
    resp = strdup("MAC server");
  }
  if (strcmp(url, "/mac")==0) {
    uint8_t mac[6] = {};
    char buf[20];
    if (!getmac(mac)) {
      snprintf(buf, sizeof(buf), "%02x:%02x:%02x:%02x:%02x:%02x",
        mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
      resp = strdup(buf);
    } else {
      resp = strdup("Error");
    }
  }

  if (resp==0) {
    resp = strdup("");
    returncode = MHD_HTTP_NOT_FOUND;
  }

  if (resplength == 0 && resp) {
    resplength = strlen(resp);
  }

  response = MHD_create_response_from_buffer(resplength, (void*)resp, MHD_RESPMEM_MUST_FREE);

  if (returncode == MHD_HTTP_OK) {
    MHD_add_response_header(response, "Content-Type", "text/plain");
  }

  MHD_add_response_header(response, "Access-Control-Allow-Origin", "*");

  ret = MHD_queue_response(connection,
    returncode,
    response);
  MHD_destroy_response(response);

  return ret;
}

int main(int argc, char **argv) {
  httpd = MHD_start_daemon(
    MHD_USE_SELECT_INTERNALLY+MHD_USE_DEBUG+MHD_USE_DUAL_STACK,
    8080,
    NULL,
    NULL,
    &httpd_process_query,
    NULL,
    MHD_OPTION_NOTIFY_COMPLETED, httpd_request_completed, NULL,
    MHD_OPTION_CONNECTION_TIMEOUT, 30,
    MHD_OPTION_END);

  while (1) {
    sleep(1);
  }

  MHD_stop_daemon(httpd);

  return 0;
}