Proyecto 1 - Redes de Computadoras

dnsquery.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h> // Linux socket interface
#include <arpa/inet.h> // ?
#include <netinet/in.h> // ?
#include <unistd.h>
#include <sys/types.h>
#include <regex.h>

#define T_A 1 // ipv4 record
#define T_MX 15 // nameserver record
#define T_LOC 29 // location record RFC 1876

// DNS Header
typedef struct dns_header
{
  unsigned short id; // id number
	
  unsigned char qr :1; // query-response
  unsigned char opcode :4; //opcode
	
  unsigned char aa :1; // authoritative answer
  unsigned char tc :1; // truncated message
  unsigned char rd :1; // recursion desired
  unsigned char ra :1; // recursion availability
  unsigned char z :1; // zero

  unsigned char rcode :4; // response code

  unsigned short qdcount; // no question entries
  unsigned short ancount; // no answer entries
  unsigned short nscount; // no name server RRs in the authority section
  unsigned short arcount; // no name server RRs in the additional section
} * headerp;

// Section used to carry the question in queries
typedef struct dns_question
{
  unsigned char * qname;
  unsigned int qtype;
  unsigned int qclass;

} * question;

// Resource data - Shared by Answer, Authority and Additional sections
typedef struct record_data
{
	unsigned int type; // RR type codes
	unsigned int class; // class of the data in RDATA
	unsigned int ttl; // time before the record is discarded
	unsigned int rdlength; // lenght of the RDATA field
} * r_data;

// Pointers to resource records contents
typedef struct resource_record
{
	unsigned char * name; // resource record's domain name
	struct record_data * resource;
	unsigned char * r_data; // describes the resource
} * r_record;

void init_query(unsigned char buffer[], headerp * header);

int main (int argc, char * argv[])
{
  char * nameserver;
  char * programa;
  headerp h;
  unsigned char buffer[65536];

  nameserver = argv[1];
  programa = argv[0];

  printf("Programa: %s\n\n", programa);
  printf("Nameserver: %s\n\n", nameserver);

  init_query(buffer, &h);

  unsigned char * unaURL = "http://google.com";

  printf("Una URL %s\n", unaURL);
 
  int url = checkURL(unaURL);
 
  return 0;

}


int get_dns_servers()
{
	FILE * fp;
	char line[200], * p;

	fp = fopen("/etc/resolv.conf", "r");

	if (fp == NULL)
	{
		printf("Failed opening /etc/resolv.conf file \n");
		return EXIT_FAILURE;
	}

	while (fgets(line, 200, fp))
	{
		if (line[0] == '#')
		{
			continue;
		}

		if (strncmp(line, "nameserver", 10) == 0)
		{
			p = strtok(line, " ");
			
		}
	}
}

void init_query(unsigned char buffer[], headerp * header)
{
  headerp dnsh;
  dnsh = *header;
  dnsh = (struct dns_header *) &buffer;

  dnsh->id = (unsigned short) htons(getpid());

  dnsh->qr = 0;
  dnsh->opcode = 0;

  dnsh->aa = 0;
  dnsh->tc = 0;
  dnsh->rd = 1;
  dnsh->ra = 0;
  dnsh->z = 0;

  dnsh->rcode = 0;

  dnsh->qdcount = htons(1); // 1 question
  dnsh->ancount = 0;
  dnsh->nscount = 0;
  dnsh->arcount = 0;
}

int checkURL (unsigned char * url) {


  unsigned char * reg_exp = "^((https?|ftp)://|(www|ftp)\\.)?[a-z0-9-]+(\\.[a-z0-9-]+)+([/?].*)?$";
  regex_t regex_http;  

  int regc = regcomp(&regex_http, reg_exp , REG_EXTENDED);

  if (regc) {
    printf("Could not compile regex");
    return 1;
  }

  int rege = regexec(&regex_http, url, 0, NULL, 0);

  if (!rege) {
    printf("Match URL!");
  } else if (rege = REG_NOMATCH) {
    printf("No match URL!");
  } else {
    printf("Error!");
    return 1;
  }

  regfree(&regex_http);

  return 0;

}