error_t dnsResolve(NetInterface *interface, const char_t *name, IpAddr *ipAddr)
{
error_t error;
uint_t i;
size_t length;
uint16_t identifier;
IpAddr serverIpAddr;
Socket *socket;
DnsHeader *dnsMessage;
//Debug message
TRACE_INFO("Trying to resolve %s...\r\n", name);
//Use default network interface?
if(!interface)
interface = tcpIpStackGetDefaultInterface();
//Allocate a memory buffer to hold DNS messages
dnsMessage = memPoolAlloc(DNS_MESSAGE_MAX_SIZE);
//Failed to allocate memory?
if(!dnsMessage)
return ERROR_OUT_OF_MEMORY;
//Open a UDP socket
socket = socketOpen(SOCKET_TYPE_DGRAM, SOCKET_PROTOCOL_UDP);
//Failed to open socket?
if(!socket)
{
//Free previously allocated memory
osMemFree(dnsMessage);
//Return status code
return ERROR_OPEN_FAILED;
}
#if (IPV4_SUPPORT == ENABLED)
//IP address of the DNS server
serverIpAddr.length = sizeof(Ipv4Addr);
serverIpAddr.ipv4Addr = interface->ipv4Config.dnsServer[0];
#elif (IPV6_SUPPORT == ENABLED)
//IP address of the DNS server
serverIpAddr.length = sizeof(Ipv6Addr);
serverIpAddr.ipv6Addr = interface->ipv6Config.dnsServer[0];
#endif
//Associate the socket with the relevant interface
error = socketBindToInterface(socket, interface);
//Any error to report?
if(error)
{
//Free previously allocated memory
osMemFree(dnsMessage);
//Close socket
socketClose(socket);
//Return status code
return error;
}
//Connect the newly created socket to the primary DNS server
error = socketConnect(socket, &serverIpAddr, DNS_PORT);
//Failed to connect?
if(error)
{
//Free previously allocated memory
osMemFree(dnsMessage);
//Close socket
socketClose(socket);
//Return status code
return error;
}
//An identifier is used by the client to match replies
//with corresponding requests
identifier = rand();
//Try to retransmit the DNS message if the previous query timed out
for(i = 0; i < DNS_MAX_RETRIES; i++)
{
//Send DNS query message
error = dnsSendQuery(socket, dnsMessage, identifier, name);
//Failed to send message ?
if(error) break;
//Adjust receive timeout
error = socketSetTimeout(socket, DNS_REQUEST_TIMEOUT);
//Any error to report?
if(error) break;
//Wait for the server response
error = socketReceive(socket, dnsMessage, DNS_MESSAGE_MAX_SIZE, &length, 0);
//Any response from the specified DNS server?
if(!error)
{
//Parse DNS response
error = dnsParseResponse(dnsMessage, length, identifier, ipAddr);
//DNS response successfully decoded?
if(!error) break;
}
}
//The maximum number of retransmissions has been reached?
if(i >= DNS_MAX_RETRIES)
error = ERROR_TIMEOUT;
//Free previously allocated memory
osMemFree(dnsMessage);
//Close socket
socketClose(socket);
//Debug message
if(!error)
{
//Name resolution succeeds
TRACE_INFO("Host name resolved to %s...\r\n", ipAddrToString(ipAddr, NULL));
}
else
{
//Report an error
TRACE_ERROR("DNS resolution failed!\r\n");
}
//Return status code
return error;
}
void dnsTick(void)
{
error_t error;
uint_t i;
systime_t time;
DnsCacheEntry *entry;
//Get current time
time = osGetSystemTime();
//Acquire exclusive access to the DNS cache
osAcquireMutex(&dnsCacheMutex);
//Go through DNS cache
for(i = 0; i < DNS_CACHE_SIZE; i++)
{
//Point to the current entry
entry = &dnsCache[i];
//Name resolution in progress?
if(entry->state == DNS_STATE_IN_PROGRESS)
{
//The request timed out?
if(timeCompare(time, entry->timestamp + entry->timeout) >= 0)
{
//Check whether the maximum number of retransmissions has been exceeded
if(entry->retransmitCount > 0)
{
#if (DNS_CLIENT_SUPPORT == ENABLED)
//DNS resolver?
if(entry->protocol == HOST_NAME_RESOLVER_DNS)
{
//Retransmit DNS query
error = dnsSendQuery(entry);
}
else
#endif
#if (MDNS_CLIENT_SUPPORT == ENABLED)
//mDNS resolver?
if(entry->protocol == HOST_NAME_RESOLVER_MDNS)
{
//Retransmit mDNS query
error = mdnsSendQuery(entry);
}
else
#endif
#if (NBNS_CLIENT_SUPPORT == ENABLED && IPV4_SUPPORT == ENABLED)
//NetBIOS Name Service resolver?
if(entry->protocol == HOST_NAME_RESOLVER_NBNS)
{
//Retransmit NBNS query
error = nbnsSendQuery(entry);
}
else
#endif
//Unknown protocol?
{
error = ERROR_FAILURE;
}
//Query message successfully sent?
if(!error)
{
//Save the time at which the query message was sent
entry->timestamp = time;
//The timeout value is doubled for each subsequent retransmission
entry->timeout = MIN(entry->timeout * 2, entry->maxTimeout);
//Decrement retransmission counter
entry->retransmitCount--;
}
else
{
//The entry should be deleted since name resolution has failed
dnsDeleteEntry(entry);
}
}
#if (DNS_CLIENT_SUPPORT == ENABLED)
//DNS resolver?
else if(entry->protocol == HOST_NAME_RESOLVER_DNS)
{
//Select the next DNS server
entry->dnsServerNum++;
//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 = time;
//Set timeout value
entry->timeout = DNS_CLIENT_INIT_TIMEOUT;
//Decrement retransmission counter
entry->retransmitCount--;
}
else
{
//The entry should be deleted since name resolution has failed
dnsDeleteEntry(entry);
}
}
#endif
else
{
//The maximum number of retransmissions has been exceeded
dnsDeleteEntry(entry);
}
}
}
//Name successfully resolved?
else if(entry->state == DNS_STATE_RESOLVED)
{
//Check the lifetime of the current DNS cache entry
if(timeCompare(time, entry->timestamp + entry->timeout) >= 0)
{
//Periodically time out DNS cache entries
dnsDeleteEntry(entry);
}
}
}
//Release exclusive access to the DNS cache
osReleaseMutex(&dnsCacheMutex);
}
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;
}
