/// <summary>
/// Record the IPs in the state object for later use.
/// </summary>
private void GetHostEntryCallback(IAsyncResult ar)
{
try
{
DnsResponse dnsResponse = (DnsResponse)ar.AsyncState; // Turn the state object into the DnsResponse type
dnsResponse.IpHostEntry = Dns.EndGetHostEntry(ar); // Save the returned IpHostEntry and populate other fields based on its parameters
dnsResponse.CallComplete.Set(); // Set the wait handle so that the caller knows that the asynchronous call has completed and that the response has been updated
}
catch (SocketException ex)
{
LogMessage("GetHostEntryCallback", $"Socket Exception: {ex.Message}");
}
catch (Exception ex)
{
LogMessage("GetHostEntryCallback", $"Exception: {ex}");
} // Log exceptions but don't throw them
}
/// <summary>
/// Resolve a host IP address to a host name
/// </summary>
/// <remarks>This first makes a DNS query and uses the result if found. If not found it then tries a Microsoft DNS call which also searches the local hosts and makes a netbios query.
/// If this returns an answer it is use. Otherwise the IP address is returned as the host name</remarks>
private void ResolveIpAddressToHostName(object deviceIpEndPointObject)
{
IPEndPoint deviceIpEndPoint = null;
try
{
deviceIpEndPoint = deviceIpEndPointObject as IPEndPoint; // Get the supplied device endpoint as an IPEndPoint
// test whether the cast was successful
if (deviceIpEndPoint is object) // The cast was successful so we can try to search for the host name
{
var dnsResponse = new DnsResponse(); // Create a new DnsResponse to hold and return the
// Calculate the remaining time before this discovery needs to finish and only undertake DNS resolution if sufficient time remains
var timeOutTime = TimeSpan.FromSeconds(discoveryTime).Subtract(DateTime.Now - discoveryStartTime).Subtract(TimeSpan.FromSeconds(0.2d));
if (timeOutTime.TotalSeconds > Constants.MINIMUM_TIME_REMAINING_TO_UNDERTAKE_DNS_RESOLUTION) // We have more than the configured time left so we will attempt a reverse DNS name resolution
{
LogMessage("ResolveIpAddressToHostName", $"Resolving IP address: {deviceIpEndPoint.Address}, Timeout: {timeOutTime}");
Dns.BeginGetHostEntry(deviceIpEndPoint.Address.ToString(), new AsyncCallback(GetHostEntryCallback), dnsResponse);
// Wait here until the resolve completes and the callback calls .Set()
bool dnsWasResolved = dnsResponse.CallComplete.WaitOne(timeOutTime); // Wait for the remaining discovery time
// Execution continues here after either a DNS response is found or the request times out
if (dnsWasResolved) // A response was received rather than timing out
{
LogMessage("ResolveIpAddressToHostName", $"{deviceIpEndPoint} has host name: {dnsResponse.HostName} IP address count: {dnsResponse.AddressList.Length} Alias count: {dnsResponse.Aliases.Length}");
foreach (IPAddress address in dnsResponse.AddressList)
{
LogMessage("ResolveIpAddressToHostName", $" Received {address.AddressFamily} address: {address}");
}
foreach (string hostAlias in dnsResponse.Aliases)
{
LogMessage("ResolveIpAddressToHostName", $" Received alias: {hostAlias}");
}
if (dnsResponse.AddressList.Length > 0) // We got a reply that contains host addresses so there may be a valid host name
{
lock (deviceListLockObject)
{
if (!string.IsNullOrEmpty(dnsResponse.HostName))
{
alpacaDeviceList[deviceIpEndPoint].HostName = dnsResponse.HostName;
}
}
RaiseAnAlpacaDevicesChangedEvent(); // Device list was changed so set the changed flag
}
else
{
LogMessage("ResolveIpAddressToHostName", $"***** DNS responded with a name ({dnsResponse.HostName}) but this has no associated IP addresses and is probably a NETBIOS name *****");
}
foreach (IPAddress address in dnsResponse.AddressList)
{
LogMessage("ResolveIpAddressToHostName", $"Address: {address}");
}
foreach (string alias in dnsResponse.Aliases)
{
LogMessage("ResolveIpAddressToHostName", $"Alias: {alias}");
}
}
else // DNS did not respond in time
{
LogMessage("ResolveIpAddressToHostName", $"***** DNS did not respond within timeout - unable to resolve IP address to host name *****");
}
}
else // There was insufficient time to query DNS
{
LogMessage("ResolveIpAddressToHostName", $"***** Insufficient time remains ({timeOutTime.TotalSeconds} seconds) to conduct a DNS query, ignoring request *****");
}
}
else // The IPEndPoint cast was not successful so we cannot carry out a DNS name search because we don't have the device's IP address
{
LogMessage("ResolveIpAddressToHostName", $"DNS resolution could not be undertaken - It was not possible to cast the supplied IPEndPoint object to an IPEndPoint type: {deviceIpEndPoint}.");
}
}
catch (TimeoutException)
{
LogMessage("ResolveIpAddressToHostName", $"Timed out trying to resolve the DNS name for {(deviceIpEndPoint is null ? "Unknown IP address" : deviceIpEndPoint.ToString()) }");
}
catch (Exception ex)
{
// Something went wrong, so log the issue and sent a message to the user
LogMessage("ResolveIpAddressToHostName", $"Exception: {ex}");
}
}
