void dnsDeleteEntry(DnsCacheEntry *entry)
{
//Make sure the specified entry is valid
if(entry != NULL)
{
#if (DNS_CLIENT_SUPPORT == ENABLED)
//DNS resolver?
if(entry->protocol == HOST_NAME_RESOLVER_DNS)
{
//Name resolution in progress?
if(entry->state == DNS_STATE_IN_PROGRESS)
{
//Unregister user callback
udpDetachRxCallback(entry->interface, entry->port);
}
}
#endif
//Delete DNS cache entry
entry->state = DNS_STATE_NONE;
}
}
error_t dnsResolve(NetInterface *interface,
const char_t *name, HostType type, IpAddr *ipAddr)
{
error_t error;
systime_t delay;
DnsCacheEntry *entry;
//Debug message
TRACE_INFO("Resolving host name %s (DNS resolver)...\r\n", name);
//Acquire exclusive access to the DNS cache
osMutexAcquire(dnsCacheMutex);
//Search the DNS cache for the specified host name
entry = dnsFindEntry(interface, name, type, HOST_NAME_RESOLVER_DNS);
//Check whether a matching entry has been found
if(entry)
{
//Host name already resolved?
if(entry->state == DNS_STATE_RESOLVED ||
entry->state == DNS_STATE_PERMANENT)
{
//Return the corresponding IP address
*ipAddr = entry->ipAddr;
//Successful host name resolution
error = NO_ERROR;
}
else
{
//Host name resolution is in progress...
error = ERROR_IN_PROGRESS;
}
}
else
{
//If no entry exists, then create a new one
entry = dnsCreateEntry();
//Record the host name whose IP address is unknown
strcpy(entry->name, name);
//Initialize DNS cache entry
entry->type = type;
entry->protocol = HOST_NAME_RESOLVER_DNS;
entry->interface = interface;
//Select primary DNS server
entry->dnsServerNum = 0;
//Get an ephemeral port number
entry->port = socketGetEphemeralPort();
//An identifier is used by the DNS client to match replies
//with corresponding requests
entry->id = tcpIpStackGetRand();
//Callback function to be called when a DNS response is received
error = udpAttachRxCallback(interface, entry->port, dnsProcessResponse, NULL);
//Check status code
if(!error)
{
//Initialize retransmission counter
entry->retransmitCount = DNS_CLIENT_MAX_RETRIES;
//Send DNS query
error = dnsSendQuery(entry);
//DNS message successfully sent?
if(!error)
{
//Save the time at which the query message was sent
entry->timestamp = osGetTickCount();
//Set timeout value
entry->timeout = DNS_CLIENT_INIT_TIMEOUT;
entry->maxTimeout = DNS_CLIENT_MAX_TIMEOUT;
//Decrement retransmission counter
entry->retransmitCount--;
//Switch state
entry->state = DNS_STATE_IN_PROGRESS;
//Host name resolution is in progress
error = ERROR_IN_PROGRESS;
}
else
{
//Unregister callback function
udpDetachRxCallback(interface, entry->port);
}
}
}
//Release exclusive access to the DNS cache
osMutexRelease(dnsCacheMutex);
//Set default polling interval
delay = DNS_CACHE_INIT_POLLING_INTERVAL;
//Wait the host name resolution to complete
while(error == ERROR_IN_PROGRESS)
{
//Wait until the next polling period
osDelay(delay);
//Acquire exclusive access to the DNS cache
osMutexAcquire(dnsCacheMutex);
//Search the DNS cache for the specified host name
entry = dnsFindEntry(interface, name, type, HOST_NAME_RESOLVER_DNS);
//Check whether a matching entry has been found
if(entry)
{
//Host name successfully resolved?
if(entry->state == DNS_STATE_RESOLVED)
{
//Return the corresponding IP address
*ipAddr = entry->ipAddr;
//Successful host name resolution
error = NO_ERROR;
}
}
else
{
//Host name resolution failed
error = ERROR_FAILURE;
}
//Release exclusive access to the DNS cache
osMutexRelease(dnsCacheMutex);
//Backoff support for less aggressive polling
delay = min(delay * 2, DNS_CACHE_MAX_POLLING_INTERVAL);
}
//Check status code
if(error)
{
//Failed to resolve host name
TRACE_INFO("Host name resolution failed!\r\n");
}
else
{
//Successful host name resolution
TRACE_INFO("Host name resolved to %s...\r\n", ipAddrToString(ipAddr, NULL));
}
//Return status code
return error;
}
void dnsProcessResponse(NetInterface *interface, const IpPseudoHeader *pseudoHeader,
const UdpHeader *udpHeader, const ChunkedBuffer *buffer, size_t offset, void *params)
{
uint_t i;
uint_t j;
size_t n;
size_t pos;
size_t length;
DnsHeader *message;
DnsQuestion *question;
DnsResourceRecord *resourceRecord;
DnsCacheEntry *entry;
//Retrieve the length of the DNS message
length = chunkedBufferGetLength(buffer) - offset;
//Ensure the DNS message is valid
if(length < sizeof(DnsHeader))
return;
if(length > DNS_MESSAGE_MAX_SIZE)
return;
//Point to the DNS message header
message = chunkedBufferAt(buffer, offset);
//Sanity check
if(!message) return;
//Debug message
TRACE_INFO("DNS message received (%" PRIuSIZE " bytes)...\r\n", length);
//Dump message
dnsDumpMessage(message, length);
//Acquire exclusive access to the DNS cache
osMutexAcquire(dnsCacheMutex);
//Loop through DNS cache entries
for(i = 0; i < DNS_CACHE_SIZE; i++)
{
//Point to the current entry
entry = &dnsCache[i];
//DNS name resolution in progress?
if(entry->state == DNS_STATE_IN_PROGRESS &&
entry->protocol == HOST_NAME_RESOLVER_DNS)
{
//Check destination port number
if(entry->port == ntohs(udpHeader->destPort))
{
//Compare identifier against expected one
if(ntohs(message->id) != entry->id)
break;
//Check message type
if(!message->qr)
break;
//The DNS message shall contain one question
if(ntohs(message->qdcount) != 1)
break;
//Point to the first question
pos = sizeof(DnsHeader);
//Parse domain name
n = dnsParseName(message, length, pos, NULL, 0);
//Invalid name?
if(!n)
break;
//Malformed mDNS message?
if((n + sizeof(DnsQuestion)) > length)
break;
//Compare domain name
if(!dnsCompareName(message, length, pos, entry->name, 0))
break;
//Point to the corresponding entry
question = DNS_GET_QUESTION(message, n);
//Check the class of the query
if(ntohs(question->qclass) != DNS_RR_CLASS_IN)
break;
//Check the type of the query
if(entry->type == HOST_TYPE_IPV4 && ntohs(question->qtype) != DNS_RR_TYPE_A)
break;
if(entry->type == HOST_TYPE_IPV6 && ntohs(question->qtype) != DNS_RR_TYPE_AAAA)
break;
//Make sure recursion is available
if(!message->ra)
{
//The entry should be deleted since name resolution has failed
dnsDeleteEntry(entry);
//Exit immediately
break;
}
//Check return code
if(message->rcode != DNS_RCODE_NO_ERROR)
{
//The entry should be deleted since name resolution has failed
dnsDeleteEntry(entry);
//Exit immediately
break;
}
//Point to the first answer
pos = n + sizeof(DnsQuestion);
//Parse answer resource records
for(j = 0; j < ntohs(message->ancount); j++)
{
//Parse domain name
pos = dnsParseName(message, length, pos, NULL, 0);
//Invalid name?
if(!pos) break;
//Point to the associated resource record
resourceRecord = DNS_GET_RESOURCE_RECORD(message, pos);
//Point to the resource data
pos += sizeof(DnsResourceRecord);
//Make sure the resource record is valid
if(pos >= length)
break;
if((pos + ntohs(resourceRecord->rdlength)) > length)
break;
#if (IPV4_SUPPORT == ENABLED)
//IPv4 address expected?
if(entry->type == HOST_TYPE_IPV4)
{
//A resource record found?
if(ntohs(resourceRecord->rtype) == DNS_RR_TYPE_A)
{
//Verify the length of the data field
if(ntohs(resourceRecord->rdlength) == sizeof(Ipv4Addr))
{
//Copy the IPv4 address
entry->ipAddr.length = sizeof(Ipv4Addr);
ipv4CopyAddr(&entry->ipAddr.ipv4Addr, resourceRecord->rdata);
//Save current time
entry->timestamp = osGetTickCount();
//Save TTL value
entry->timeout = ntohl(resourceRecord->ttl) * 1000;
//Limit the lifetime of the DNS cache entries
entry->timeout = min(entry->timeout, DNS_MAX_LIFETIME);
//Unregister UDP callback function
udpDetachRxCallback(interface, entry->port);
//Host name successfully resolved
entry->state = DNS_STATE_RESOLVED;
//Exit immediately
break;
}
}
}
#endif
#if (IPV6_SUPPORT == ENABLED)
//IPv6 address expected?
if(entry->type == HOST_TYPE_IPV6)
{
//AAAA resource record found?
if(ntohs(resourceRecord->rtype) == DNS_RR_TYPE_AAAA)
{
//Verify the length of the data field
if(ntohs(resourceRecord->rdlength) == sizeof(Ipv6Addr))
{
//Copy the IPv6 address
entry->ipAddr.length = sizeof(Ipv6Addr);
ipv6CopyAddr(&entry->ipAddr.ipv6Addr, resourceRecord->rdata);
//Save current time
entry->timestamp = osGetTickCount();
//Save TTL value
entry->timeout = ntohl(resourceRecord->ttl) * 1000;
//Limit the lifetime of the DNS cache entries
entry->timeout = min(entry->timeout, DNS_MAX_LIFETIME);
//Unregister UDP callback function
udpDetachRxCallback(interface, entry->port);
//Host name successfully resolved
entry->state = DNS_STATE_RESOLVED;
//Exit immediately
break;
}
}
}
#endif
//Point to the next resource record
pos += ntohs(resourceRecord->rdlength);
}
//We are done
break;
}
}
}
//Release exclusive access to the DNS cache
osMutexRelease(dnsCacheMutex);
}