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7f0640b040
lwip/src/core/dns.c
fbernon 7f0640b040 Minor changes on DNS.
2007-11-18 21:04:53 +00:00

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/**
* @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 DNS_QUERY_QUEUED 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/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
/* The maximum number of table entries to maintain locally */
#ifndef DNS_TABLE_SIZE
#define DNS_TABLE_SIZE 4
#endif
/* The maximum length of a host name supported in the name table. */
#ifndef DNS_MAX_NAME_LENGTH
#define DNS_MAX_NAME_LENGTH 256
#endif
/* The maximum number of retries when asking for a name, before "timeout". */
#ifndef DNS_MAX_RETRIES
#define DNS_MAX_RETRIES 4
#endif
/* DNS entry time to live (in DNS_TMR_INTERVAL ticks) */
#ifndef DNS_TTL_ENTRY
#define DNS_TTL_ENTRY 60
#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"
#endif
PACK_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"
#endif
PACK_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"
#endif
PACK_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
#ifdef PACK_STRUCT_USE_INCLUDES
# include "arch/bpstruct.h"
#endif
PACK_STRUCT_BEGIN
/** DNS table entry */
struct dns_table_entry {
u8_t state;
u8_t numdns;
u8_t tmr;
u8_t retries;
u8_t ttl;
u8_t seqno;
u8_t err;
char name[DNS_MAX_NAME_LENGTH];
struct ip_addr ipaddr;
void (* found)(const char *name, struct ip_addr *ipaddr, void *arg); /* pointer to callback on DNS query done */
void *arg;
} PACK_STRUCT_STRUCT;
PACK_STRUCT_END
#ifdef PACK_STRUCT_USE_INCLUDES
# include "arch/epstruct.h"
#endif
/* 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];
static u8_t dns_payload[DNS_MSG_SIZE];
/**
* Initialize the resolver and configure which DNS server to use for queries.
*
* param dnsserver A pointer to a 4-byte representation of the IP
* address of the DNS server to be configured.
*/
err_t
dns_init()
{
u8_t i;
struct ip_addr dnsserver = {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 */
for (i=0; i<DNS_TABLE_SIZE; ++i) {
dns_table[i].state = DNS_STATE_UNUSED;
dns_table[i].found = NULL;
}
/* 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);
}
}
return ERR_OK;
}
/**
* Obtain the currently configured DNS server.
* return unsigned long encoding of the IP address of
* the currently configured DNS server or NULL if no DNS server has
* been configured.
*/
void
dns_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 the currently configured DNS server.
* return unsigned long encoding of the IP address of
* the currently configured DNS server or NULL if no DNS server has
* been configured.
*/
struct ip_addr
dns_getserver(u8_t numdns)
{
return (((numdns<DNS_MAX_SERVERS) && (dns_pcb != NULL))?dns_servers[numdns]:(*IP_ADDR_ANY));
}
/**
* The DNS resolver client timer - handle retries and timeouts
*/
void
dns_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_query() can be used to send a query
* for a hostname.
*
* return A pointer to a 4-byte representation of the hostname's IP
* address, or NULL if the hostname was not found in the array of
* hostnames.
*/
u32_t
dns_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;
}
/**
* dns_parse_name() - walk through a compact encoded DNS name and return the 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;
}
/**
* dns_send
*/
static err_t
dns_send(u8_t numdns, const char* name, u8_t id)
{
struct dns_hdr *hdr;
struct dns_query *qry;
struct pbuf *p;
char *query, *nptr;
const char *pHostname;
u8_t n;
LWIP_DEBUGF(DNS_DEBUG, ("dns_send: dns_servers[%"U16_F"] \"%s\": request\n", (u16_t)(numdns), name));
/* if here, we have either a new query or a retry on a previous query to process */
p = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dns_hdr)+DNS_MAX_NAME_LENGTH+sizeof(struct dns_query), PBUF_RAM);
if (p) {
/* fill dns header */
hdr = (struct dns_hdr *)p->payload;
memset(hdr, 0, sizeof(struct dns_hdr));
hdr->id = htons(id);
hdr->flags1 = DNS_FLAG1_RD;
hdr->numquestions = htons(1);
query = (char *)hdr + sizeof(struct dns_hdr);
pHostname = name;
--pHostname;
/* convert hostname into suitable query format. */
do {
++pHostname;
nptr = query;
++query;
for(n = 0; *pHostname != '.' && *pHostname != 0; ++pHostname) {
*query = *pHostname;
++query;
++n;
}
*nptr = n;
} while(*pHostname != 0);
*query++='\0';
/* fill dns query */
qry = (struct dns_query *)query;
qry->type = htons(DNS_RRTYPE_A);
qry->class = htons(DNS_RRCLASS_IN);
/* resize pbuf to the exact dns query */
pbuf_realloc(p, (query+sizeof(struct dns_query))-((char*)(p->payload)));
/* send dns packet */
udp_sendto(dns_pcb, p, dns_servers+numdns, DNS_SERVER_PORT);
/* free pbuf */
pbuf_free(p);
return ERR_OK;
}
return ERR_BUF;
}
/**
* dns_check_entries() - Runs through the list of names to see if there are any
* that have not yet been queried and, if so, sends out a query.
*/
static void
dns_check_entries(void)
{
u8_t i;
struct dns_table_entry *pEntry;
for (i = 0; i < DNS_TABLE_SIZE; ++i) {
pEntry = &dns_table[i];
switch(pEntry->state) {
case DNS_STATE_NEW:
case DNS_STATE_ASKING: {
if (pEntry->state == DNS_STATE_ASKING) {
if (--pEntry->tmr == 0) {
if (++pEntry->retries == DNS_MAX_RETRIES) {
if ((pEntry->numdns+1<DNS_MAX_SERVERS) && (dns_servers[pEntry->numdns+1].addr!=0)) {
/* change of server */
pEntry->numdns++;
pEntry->tmr = 1;
pEntry->retries = 0;
continue;
} else {
LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entries: \"%s\": timeout\n", pEntry->name));
/* call specified callback function if provided */
if (pEntry->found)
(*pEntry->found)(pEntry->name, NULL, pEntry->arg);
/* flush this entry */
pEntry->state = DNS_STATE_UNUSED;
pEntry->found = NULL;
continue;
}
}
/* wait longer for the next retry */
pEntry->tmr = pEntry->retries;
} else {
/* Its timer has not run out, so we move on to next entry. */
continue;
}
} else {
pEntry->state = DNS_STATE_ASKING;
pEntry->numdns = 0;
pEntry->tmr = 1;
pEntry->retries = 0;
}
/* send DNS packet for this entry */
dns_send(pEntry->numdns, pEntry->name, i);
break;
}
case DNS_STATE_DONE: {
/* if the time to live is nul */
if (--pEntry->ttl == 0) {
LWIP_DEBUGF(DNS_DEBUG, ("dns_check_entries: \"%s\": flush\n", pEntry->name));
/* flush this entry */
pEntry->state = DNS_STATE_UNUSED;
pEntry->found = NULL;
}
break;
}
}
}
}
/**
* Callback for DNS responses
*/
static void
dns_recv(void *s, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)
{
u8_t i;
char *pHostname;
struct dns_hdr *hdr;
struct dns_answer *ans;
struct dns_table_entry *pEntry;
u8_t nquestions, nanswers;
/* is the dns message too big ? */
if (p->tot_len > DNS_MSG_SIZE) {
LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too big\n"));
pbuf_free(p);
return;
}
/* is the dns message big enought ? */
if (p->tot_len < (sizeof(struct dns_hdr)+sizeof(struct dns_query)+sizeof(struct dns_answer))) {
LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: pbuf too small\n"));
pbuf_free(p);
return;
}
/* copy dns payload inside static buffer for processing */
if (pbuf_copy_partial(p, dns_payload, p->tot_len, 0) == p->tot_len) {
/* The ID in the DNS header should be our entry into the name table. */
hdr = (struct dns_hdr *)dns_payload;
i = htons(hdr->id);
if(i < DNS_TABLE_SIZE) {
pEntry = &dns_table[i];
if(pEntry->state == DNS_STATE_ASKING) {
/* This entry is now completed. */
pEntry->state = DNS_STATE_DONE;
pEntry->ttl = DNS_TTL_ENTRY;
pEntry->err = hdr->flags2 & DNS_FLAG2_ERR_MASK;
/* We only care about the question(s) and the answers. The authrr
and the extrarr are simply discarded. */
nquestions = htons(hdr->numquestions);
nanswers = htons(hdr->numanswers);
/* Check for error. If so, call callback to inform. */
if (((hdr->flags1 & DNS_FLAG1_RESPONSE)==0) ||(pEntry->err != 0) || (nquestions != 1)) {
LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in flags\n", pEntry->name));
/* call specified callback function if provided */
if (pEntry->found)
(*pEntry->found)(pEntry->name, NULL, pEntry->arg);
/* flush this entry */
pEntry->state = DNS_STATE_UNUSED;
pEntry->found = NULL;
/* free pbuf */
pbuf_free(p);
return;
}
/* Skip the name in the "question" part. This should really be checked
agains the name in the question, to be sure that they match. */
pHostname = (char *) dns_parse_name((unsigned char *)dns_payload + sizeof(struct dns_hdr)) + sizeof(struct dns_query);
while(nanswers > 0) {
/* skip answer resource record's host name */
pHostname = (char *) dns_parse_name((unsigned char *)pHostname);
/* Check for IP address type and Internet class. Others are discarded. */
ans = (struct dns_answer *)pHostname;
if((ntohs(ans->type) == DNS_RRTYPE_A) && (ntohs(ans->class) == DNS_RRCLASS_IN) && (ntohs(ans->len) == sizeof(struct ip_addr)) ) {
/* read the IP address after answer resource record's header */
pEntry->ipaddr = (*((struct ip_addr*)(ans+1)));
LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": response = ", pEntry->name));
ip_addr_debug_print(DNS_DEBUG, (&(pEntry->ipaddr)));
LWIP_DEBUGF(DNS_DEBUG, ("\n"));
/* call specified callback function if provided */
if (pEntry->found)
(*pEntry->found)(pEntry->name, &pEntry->ipaddr, pEntry->arg);
/* free pbuf */
pbuf_free(p);
return;
} else {
pHostname = pHostname + sizeof(struct dns_answer) + htons(ans->len);
}
--nanswers;
}
LWIP_DEBUGF(DNS_DEBUG, ("dns_recv: \"%s\": error in response\n", pEntry->name));
}
}
}
/* free pbuf */
pbuf_free(p);
}
/**
* Queues a name so that a question for the name will be sent out.
* param name - The hostname that is to be queried.
*/
static void
dns_query(const char *name, void (*found)(const char *name, struct ip_addr *addr, void *arg), void *arg)
{
u8_t i;
u8_t lseq, lseqi;
struct dns_table_entry *pEntry;
/* search an unused entry, or the oldest one */
lseq = lseqi = 0;
for (i = 0; i < DNS_TABLE_SIZE; ++i) {
pEntry = &dns_table[i];
/* is it an unused entry ? */
if (pEntry->state == DNS_STATE_UNUSED)
break;
/* check if this is the oldest entry used */
if (dns_seqno - pEntry->seqno > lseq) {
lseq = dns_seqno - pEntry->seqno;
lseqi = i;
}
}
/* if we don't have found an unused entry, use the oldest one */
if (i == DNS_TABLE_SIZE) {
i = lseqi;
pEntry = &dns_table[i];
/* since we replace the previous entry, we "unblock" the caller */
LWIP_DEBUGF(DNS_DEBUG, ("dns_query: \"%s\": replaced by new entry\n", pEntry->name));
/* call specified callback function if provided */
if (pEntry->found)
(*pEntry->found)(pEntry->name, NULL, pEntry->arg);
}
/* fill the entry */
pEntry->state = DNS_STATE_NEW;
pEntry->seqno = dns_seqno++;
pEntry->found = found;
pEntry->arg = arg;
strcpy( pEntry->name, name);
}
/**
* NON-BLOCKING callback version for use with raw API
*/
DNS_RESULT dns_gethostbyname(const char *hostname, struct ip_addr *addr,
void (*found)(const char *name, struct ip_addr *ipaddr, void *arg),
void *arg
)
{
/* not initialized or no valid server yet, or invalid addr pointer */
if ((dns_pcb == NULL) || (addr == NULL))
return DNS_QUERY_INVALID;
/* invalid hostname */
if ((!hostname) || (!hostname[0]))
return DNS_QUERY_INVALID;
/* invalid hostname length */
if (strlen(hostname) >= DNS_MAX_NAME_LENGTH)
return DNS_QUERY_INVALID;
/* host name already in octet notation? set ip addr and return COMPLETE */
if ((addr->addr = inet_addr(hostname)) != INADDR_NONE)
return DNS_COMPLETE;
/* already have this address cached? */
if ((addr->addr = dns_lookup(hostname)) != 0)
return DNS_COMPLETE;
/* queue query with specified callback */
dns_query(hostname, found, arg);
/* force to send request */
dns_check_entries();
return DNS_QUERY_QUEUED;
}
#endif /* LWIP_DNS */
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