/// <summary>
/// Resolve a host IP address to a host name
/// </summary>
/// <param name="hostIp"></param>
/// <param name="HostPort"></param>
/// <returns></returns>
/// <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 = deviceIpEndPointObject as IPEndPoint; // Get the supplied device endpoint as an IPEndPoint
DnsResponse 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
TimeSpan timeOutTime = TimeSpan.FromSeconds(discoveryTime).Subtract(DateTime.Now - discoveryStartTime).Subtract(TimeSpan.FromSeconds(0.2));
if (timeOutTime.TotalSeconds > 0.2)
{
LogMessage("ResolveIpAddressToHostName", $"Resolving IP address: {deviceIpEndPoint.Address.ToString()}, 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 less a small amount
if (dnsWasResolved) // A response was received rather than timing out
{
LogMessage("ResolveIpAddressToHostName", $"{deviceIpEndPoint.ToString()} has host name: {dnsResponse.HostName} IP address count: {dnsResponse.AddressList.Length} Alias count: { dnsResponse.Aliases.Length}");
if (dnsResponse.AddressList.Length > 0)
{
lock (deviceListLockObject)
{
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
{
LogMessage("ResolveIpAddressToHostName", $"***** DNS did not respond within timeout - unable to resolve IP address to host name *****");
}
}
else
{
LogMessage("ResolveIpAddressToHostName", $"***** Insufficient time remains ({timeOutTime.TotalSeconds} seconds) to conduct a DNS query, ignoring request *****");
}
}
/// <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 (Exception ex)
{
LogMessage("GetHostEntryCallback", $"Exception: {ex.ToString()}"); // Log exceptions but don't throw them
}
}
