/** * @file * DNS - host name to IP address resolver. * *//** * This file implements a DNS host name to IP address resolver. * Port to lwIP from uIP * by Jim Pettinato April 2007 * uIP version Copyright (c) 2002-2003, Adam Dunkels. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright *    notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright *    notice, this list of conditions and the following disclaimer in the *    documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote *    products derived from this software without specific prior *    written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * * * DNS.C * * The lwIP DNS resolver functions are used to lookup a host name and * map it to a numerical IP address. It maintains a list of resolved * hostnames that can be queried with the dns_lookup() function. * New hostnames can be resolved using the dns_query() function. * * The lwIP version of the resolver also adds a non-blocking version of * gethostbyname() that will work with a raw API application. This function * checks for an IP address string first and converts it if it is valid. * gethostbyname() then does a dns_lookup() to see if the name is  * already in the table. If so, the IP is returned. If not, a query is  * issued and the function returns with a ERR_INPROGRESS status. The app * using the dns client must then go into a waiting state. * * Once a hostname has been resolved (or found to be non-existent), * the resolver code calls a specified callback function (which  * must be implemented by the module that uses the resolver). *//*----------------------------------------------------------------------------- * RFC 1035 - Domain names - implementation and specification * RFC 2181 - Clarifications to the DNS Specification *----------------------------------------------------------------------------*//** @todo: define good default values (rfc compliance) *//** @todo: improve answer parsing, more checkings... *//** @todo: check RFC1035 - 7.3. Processing responses *//*----------------------------------------------------------------------------- * Includes *----------------------------------------------------------------------------*/#include "lwip/opt.h"#if LWIP_DNS /* don't build if not configured for use in lwipopts.h */#include "lwip/udp.h"#include "lwip/mem.h"#include "lwip/dns.h"#include <string.h>/** DNS server IP address */#ifndef DNS_SERVER_ADDRESS#define DNS_SERVER_ADDRESS        inet_addr("208.67.222.222") /* resolver1.opendns.com */#endif/** DNS server port address */#ifndef DNS_SERVER_PORT#define DNS_SERVER_PORT           53#endif/** DNS maximum number of retries when asking for a name, before "timeout". */#ifndef DNS_MAX_RETRIES#define DNS_MAX_RETRIES           4#endif/** DNS resource record max. TTL (one week as default) */#ifndef DNS_MAX_TTL#define DNS_MAX_TTL               604800#endif/* DNS protocol flags */#define DNS_FLAG1_RESPONSE        0x80#define DNS_FLAG1_OPCODE_STATUS   0x10#define DNS_FLAG1_OPCODE_INVERSE  0x08#define DNS_FLAG1_OPCODE_STANDARD 0x00#define DNS_FLAG1_AUTHORATIVE     0x04#define DNS_FLAG1_TRUNC           0x02#define DNS_FLAG1_RD              0x01#define DNS_FLAG2_RA              0x80#define DNS_FLAG2_ERR_MASK        0x0f#define DNS_FLAG2_ERR_NONE        0x00#define DNS_FLAG2_ERR_NAME        0x03/* DNS protocol states */#define DNS_STATE_UNUSED          0#define DNS_STATE_NEW             1#define DNS_STATE_ASKING          2#define DNS_STATE_DONE            3#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/bpstruct.h"#endifPACK_STRUCT_BEGIN/** DNS message header */struct dns_hdr {  u16_t id;  u8_t flags1;  u8_t flags2;  u16_t numquestions;  u16_t numanswers;  u16_t numauthrr;  u16_t numextrarr;} PACK_STRUCT_STRUCT;PACK_STRUCT_END#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/epstruct.h"#endif#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/bpstruct.h"#endifPACK_STRUCT_BEGIN/** DNS query message structure */struct dns_query {  /* DNS query record starts with either a domain name or a pointer     to a name already present somewhere in the packet. */  u16_t type;  u16_t class;} PACK_STRUCT_STRUCT;PACK_STRUCT_END#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/epstruct.h"#endif#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/bpstruct.h"#endifPACK_STRUCT_BEGIN/** DNS answer message structure */struct dns_answer {  /* DNS answer record starts with either a domain name or a pointer     to a name already present somewhere in the packet. */  u16_t type;  u16_t class;  u32_t ttl;  u16_t len;} PACK_STRUCT_STRUCT;PACK_STRUCT_END#ifdef PACK_STRUCT_USE_INCLUDES#  include "arch/epstruct.h"#endif/** DNS table entry */struct dns_table_entry {  u8_t  state;  u8_t  numdns;  u8_t  tmr;  u8_t  retries;  u8_t  seqno;  u8_t  err;  u32_t ttl;  char name[DNS_MAX_NAME_LENGTH];  struct ip_addr ipaddr;  /* pointer to callback on DNS query done */  dns_found_callback found;  void *arg;};/* forward declarations */static void dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);static void dns_check_entries(void);/*----------------------------------------------------------------------------- * Globales *----------------------------------------------------------------------------*//* DNS variables */static struct udp_pcb        *dns_pcb;static u8_t                   dns_seqno;static struct dns_table_entry dns_table[DNS_TABLE_SIZE];static struct ip_addr         dns_servers[DNS_MAX_SERVERS];#if (DNS_USES_STATIC_BUF == 1)static u8_t                   dns_payload[DNS_MSG_SIZE];#endif /* (DNS_USES_STATIC_BUF == 1) *//** * Initialize the resolver: set up the UDP pcb and configure the default server * (DNS_SERVER_ADDRESS). */voiddns_init(){  struct ip_addr dnsserver;    /* initialize default DNS server address */  dnsserver.addr = DNS_SERVER_ADDRESS;  LWIP_DEBUGF(DNS_DEBUG, ("dns_init: initializing\n"));  /* if dns client not yet initialized... */  if (dns_pcb == NULL) {    dns_pcb = udp_new();    if (dns_pcb != NULL) {      /* initialize DNS table not needed (initialized to zero since it is a       * global variable) */      LWIP_ASSERT("For implicit initialization to work, DNS_STATE_UNUSED needs to be 0",        DNS_STATE_UNUSED == 0);      /* initialize DNS client */      udp_bind(dns_pcb, IP_ADDR_ANY, 0);      udp_recv(dns_pcb, dns_recv, NULL);      /* initialize default DNS primary server */      dns_setserver(0, &dnsserver);    }  }}/** * Initialize one of the DNS servers. * * @param numdns the index of the DNS server to set must be < DNS_MAX_SERVERS * @param dnsserver IP address of the DNS server to set */voiddns_setserver(u8_t numdns, struct ip_addr *dnsserver){  if ((numdns < DNS_MAX_SERVERS) && (dns_pcb != NULL) &&      (dnsserver != NULL) && (dnsserver->addr !=0 )) {    dns_servers[numdns] = (*dnsserver);  }}/** * Obtain one of the currently configured DNS server. * * @param numdns the index of the DNS server * @return IP address of the indexed DNS server or "ip_addr_any" if the DNS *         server has not been configured. */struct ip_addrdns_getserver(u8_t numdns){  if (numdns < DNS_MAX_SERVERS) {    return dns_servers[numdns];  } else {    return *IP_ADDR_ANY;  }}/** * The DNS resolver client timer - handle retries and timeouts and should * be called every DNS_TMR_INTERVAL milliseconds (every second by default). */voiddns_tmr(void){  if (dns_pcb != NULL) {    LWIP_DEBUGF(DNS_DEBUG, ("dns_tmr: dns_check_entries\n"));    dns_check_entries();  }}/** * Look up a hostname in the array of known hostnames. * * @note This function only looks in the internal array of known * hostnames, it does not send out a query for the hostname if none * was found. The function dns_enqueue() can be used to send a query * for a hostname. * * @param name the hostname to look up * @return the hostname's IP address, as u32_t (instead of struct ip_addr to *         better check for failure: != 0) or 0 if the hostname was not found *         in the cached dns_table. */static u32_tdns_lookup(const char *name){  u8_t i;  /* Walk through name list, return entry if found. If not, return NULL. */  for (i = 0; i < DNS_TABLE_SIZE; ++i) {    if ((dns_table[i].state == DNS_STATE_DONE) &&        (strcmp(name, dns_table[i].name) == 0)) {      LWIP_DEBUGF(DNS_DEBUG, ("dns_lookup: \"%s\": found = ", name));      ip_addr_debug_print(DNS_DEBUG, &(dns_table[i].ipaddr));      LWIP_DEBUGF(DNS_DEBUG, ("\n"));      return dns_table[i].ipaddr.addr;    }  }  return 0;}#if DNS_DOES_NAME_CHECK/** * Compare the "dotted" name "query" with the encoded name "response" * to make sure an answer from the DNS server matches the current dns_table * entry (otherwise, answers might arrive late for hostname not on the list * any more). * * @param query hostname (not encoded) from the dns_table * @param response encoded hostname in the DNS response * @return 0: names equal; 1: names differ */static u8_tdns_compare_name(unsigned char *query, unsigned char *response){  unsigned char n;  do {    n = *response++;    /** @see RFC 1035 - 4.1.4. Message compression */    if ((n & 0xc0) == 0xc0) {      /* Compressed name */      break;    } else {      /* Not compressed name */      while (n > 0) {        if ((*query) != (*response)) {          return 1;        }        ++response;        ++query;        --n;      };      ++query;    }  } while (*response != 0);  return 0;}#endif /* DNS_DOES_NAME_CHECK *//** * Walk through a compact encoded DNS name and return the end of the name. * * @param query encoded DNS name in the DNS server response * @return end of the name */static unsigned char *dns_parse_name(unsigned char *query){  unsigned char n;  do {    n = *query++;    /** @see RFC 1035 - 4.1.4. Message compression */    if ((n & 0xc0) == 0xc0) {      /* Compressed name */      break;    } else {      /* Not compressed name */      while (n > 0) {        ++query;        --n;      };    }  } while (*query != 0);  return query + 1;}/** * Send a DNS query packet. * * @param numdns index of the DNS server in the dns_servers table * @param name hostname to query * @param id index of the hostname in dns_table, used as transaction ID in the *        DNS query packet * @return ERR_OK if packet is sent; an err_t indicating the problem otherwise */static err_tdns_send(u8_t numdns, const char* name, u8_t id){  err_t err;  struct dns_hdr *hdr;  struct dns_query qry;  struct pbuf *p;  char *query, *nptr;