/// <summary>
/// Wrapper method to perform DNS Query.
/// </summary>
/// <remarks>Makes DnsQuery a little more palatable.</remarks>
/// <param name="domain">The domain.</param>
/// <param name="dnsServerAddress">IPAddress of DNS server (may be null) </param>
/// <param name="recordType">Type of DNS dnsRecord.</param>
/// <param name="ppQueryResults">Pointer to pointer to query results.</param>
/// <returns>Win32 status code.</returns>
internal static int DnsQuery(
string domain,
IPAddress dnsServerAddress,
DnsRecordType recordType,
ref IntPtr ppQueryResults)
{
Debug.Assert(!string.IsNullOrEmpty(domain), "domain cannot be null.");
IntPtr pServerList = IntPtr.Zero;
try
{
pServerList = DnsNativeMethods.AllocDnsServerList(dnsServerAddress);
return(DnsNativeMethods.DnsQuery(
domain,
recordType,
DnsQueryOptions.DNS_QUERY_STANDARD,
pServerList,
ref ppQueryResults,
0));
}
finally
{
// Note: if pServerList is IntPtr.Zero, FreeHGlobal does nothing.
Marshal.FreeHGlobal(pServerList);
}
}
/// <summary>
/// Perform DNS Query.
/// </summary>
/// <typeparam name="T">DnsRecord type.</typeparam>
/// <param name="domain">The domain.</param>
/// <param name="dnsServerAddress">IPAddress of DNS server to use (may be null).</param>
/// <returns>The DNS record list (never null but may be empty).</returns>
internal static List <T> DnsQuery <T>(string domain, IPAddress dnsServerAddress) where T : DnsRecord, new()
{
List <T> dnsRecordList = new List <T>();
// Each strongly-typed DnsRecord type maps to a DnsRecordType enum.
DnsRecordType dnsRecordTypeToQuery = typeToDnsTypeMap.Member[typeof(T)];
// queryResultsPtr will point to unmanaged heap memory if DnsQuery succeeds.
IntPtr queryResultsPtr = IntPtr.Zero;
try
{
// Perform DNS query. If successful, construct a list of results.
int errorCode = DnsNativeMethods.DnsQuery(
domain,
dnsServerAddress,
dnsRecordTypeToQuery,
ref queryResultsPtr);
if (errorCode == Win32Success)
{
DnsRecordHeader dnsRecordHeader;
// Interate through linked list of query result records.
for (IntPtr recordPtr = queryResultsPtr; !recordPtr.Equals(IntPtr.Zero); recordPtr = dnsRecordHeader.NextRecord)
{
dnsRecordHeader = Marshal.PtrToStructure <DnsRecordHeader>(recordPtr);
T dnsRecord = new T();
if (dnsRecordHeader.RecordType == dnsRecord.RecordType)
{
dnsRecord.Load(dnsRecordHeader, recordPtr);
dnsRecordList.Add(dnsRecord);
}
}
}
else
{
throw new DnsException(errorCode);
}
}
finally
{
if (queryResultsPtr != IntPtr.Zero)
{
// DnsQuery allocated unmanaged heap, free it now.
DnsNativeMethods.FreeDnsQueryResults(queryResultsPtr);
}
}
return(dnsRecordList);
}
/// <summary>
/// Free results from DnsQuery call.
/// </summary>
/// <remarks>Makes DnsRecordListFree a little more palatable.</remarks>
/// <param name="ptrRecords">Pointer to records.</param>
internal static void FreeDnsQueryResults(IntPtr ptrRecords)
{
Debug.Assert(!ptrRecords.Equals(IntPtr.Zero), "ptrRecords cannot be null.");
DnsNativeMethods.DnsRecordListFree(ptrRecords, FreeType.RecordList);
}