/// <summary>
/// Starts looking up MX records for specified domain.
/// </summary>
/// <param name="dnsClient">DNS client.</param>
/// <param name="domain">Domain name.</param>
/// <param name="domainIsCName">If true domain name is CNAME(alias).</param>
/// <exception cref="ArgumentNullException">Is riased when <b>dnsClient</b> or <b>domain</b> is null reference.</exception>
private void LookupMX(Dns_Client dnsClient,string domain,bool domainIsCName)
{
if(dnsClient == null){
throw new ArgumentNullException("dnsClient");
}
if(domain == null){
throw new ArgumentNullException("domain");
}
// Try to get MX records.
DNS_ClientTransaction transaction_MX = dnsClient.CreateTransaction(DNS_QType.MX,domain,2000);
transaction_MX.StateChanged += delegate(object s1,EventArgs<DNS_ClientTransaction> e1){
try{
if(e1.Value.State == DNS_ClientTransactionState.Completed){
// No errors.
if(e1.Value.Response.ResponseCode == DNS_RCode.NO_ERROR){
List<DNS_rr_MX> mxRecords = new List<DNS_rr_MX>();
foreach(DNS_rr_MX mx in e1.Value.Response.GetMXRecords()){
// Skip invalid MX records.
if(string.IsNullOrEmpty(mx.Host)){
}
else{
mxRecords.Add(mx);
}
}
// Use MX records.
if(mxRecords.Count > 0){
m_pHosts = new HostEntry[mxRecords.Count];
// Create name to index map, so we can map asynchronous A/AAAA lookup results back to MX priority index.
Dictionary<string,int> name_to_index_map = new Dictionary<string,int>();
List<string> lookupQueue = new List<string>();
// Process MX records.
for(int i=0;i<m_pHosts.Length;i++){
DNS_rr_MX mx = mxRecords[i];
IPAddress[] ips = Get_A_or_AAAA_FromResponse(mx.Host,e1.Value.Response);
// No A or AAAA records in addtional answers section for MX, we need todo new query for that.
if(ips.Length == 0){
name_to_index_map[mx.Host] = i;
lookupQueue.Add(mx.Host);
}
else{
m_pHosts[i] = new HostEntry(mx.Host,ips,null);
}
}
// We have MX records which A or AAAA records not provided in DNS response, lookup them.
if(lookupQueue.Count > 0){
GetHostsAddressesAsyncOP op = new GetHostsAddressesAsyncOP(lookupQueue.ToArray(),true);
// This event is raised when lookup completes asynchronously.
op.CompletedAsync += delegate(object s2,EventArgs<GetHostsAddressesAsyncOP> e2){
LookupCompleted(op,name_to_index_map);
};
// Lookup completed synchronously.
if(!dnsClient.GetHostsAddressesAsync(op)){
LookupCompleted(op,name_to_index_map);
}
}
// All MX records resolved.
else{
SetState(AsyncOP_State.Completed);
}
}
// Use CNAME as initial domain name.
else if(e1.Value.Response.GetCNAMERecords().Length > 0){
if(domainIsCName){
m_pException = new Exception("CNAME to CNAME loop dedected.");
SetState(AsyncOP_State.Completed);
}
else{
LookupMX(dnsClient,e1.Value.Response.GetCNAMERecords()[0].Alias,true);
}
}
// Use domain name as MX.
else{
m_pHosts = new HostEntry[1];
// Create name to index map, so we can map asynchronous A/AAAA lookup results back to MX priority index.
Dictionary<string,int> name_to_index_map = new Dictionary<string,int>();
name_to_index_map.Add(domain,0);
GetHostsAddressesAsyncOP op = new GetHostsAddressesAsyncOP(new string[]{domain});
// This event is raised when lookup completes asynchronously.
op.CompletedAsync += delegate(object s2,EventArgs<GetHostsAddressesAsyncOP> e2){
LookupCompleted(op,name_to_index_map);
};
// Lookup completed synchronously.
if(!dnsClient.GetHostsAddressesAsync(op)){
LookupCompleted(op,name_to_index_map);
}
}
}
// DNS server returned error, just return error.
else{
m_pException = new DNS_ClientException(e1.Value.Response.ResponseCode);
SetState(AsyncOP_State.Completed);
}
}
transaction_MX.Timeout += delegate(object s2,EventArgs e2){
m_pException = new IOException("DNS transaction timeout, no response from DNS server.");
SetState(AsyncOP_State.Completed);
};
}
catch(Exception x){
m_pException = x;
SetState(AsyncOP_State.Completed);
}
};
transaction_MX.Start();
}
/// <summary>
/// This method is called when A/AAAA lookup has completed.
/// </summary>
/// <param name="op">Asynchronous operation.</param>
/// <param name="name_to_index">Dns name to index lookup table.</param>
/// <exception cref="ArgumentNullException">Is raised when <b>op</b> or <b>name_to_index</b> is null reference value.</exception>
private void LookupCompleted(GetHostsAddressesAsyncOP op,Dictionary<string,int> name_to_index)
{
if(op == null){
throw new ArgumentNullException("op");
}
if(op.Error != null){
// If we have any resolved DNS, we don't return error if any.
bool anyResolved = false;
foreach(HostEntry host in m_pHosts){
if(host != null){
anyResolved = true;
break;
}
}
if(!anyResolved){
m_pException = op.Error;
}
}
else{
foreach(HostEntry host in op.HostEntries){
m_pHosts[name_to_index[host.HostName]] = host;
}
}
op.Dispose();
// Remove unresolved DNS entries from response.
List<HostEntry> retVal = new List<HostEntry>();
foreach(HostEntry host in m_pHosts){
if(host != null){
retVal.Add(host);
}
}
m_pHosts = retVal.ToArray();
SetState(AsyncOP_State.Completed);
}
/// <summary>
/// Starts resolving multiple host IPv4 and IPv6 addresses.
/// </summary>
/// <param name="op">Asynchronous operation.</param>
/// <returns>Returns true if aynchronous operation is pending (The <see cref="GetHostsAddressesAsyncOP.CompletedAsync"/> event is raised upon completion of the operation).
/// Returns false if operation completed synchronously.</returns>
/// <exception cref="ObjectDisposedException">Is raised when this object is disposed and and this method is accessed.</exception>
/// <exception cref="ArgumentNullException">Is raised when <b>op</b> is null reference.</exception>
public bool GetHostsAddressesAsync(GetHostsAddressesAsyncOP op)
{
if(m_IsDisposed){
throw new ObjectDisposedException(this.GetType().Name);
}
if(op == null){
throw new ArgumentNullException("op");
}
if(op.State != AsyncOP_State.WaitingForStart){
throw new ArgumentException("Invalid argument 'op' state, 'op' must be in 'AsyncOP_State.WaitingForStart' state.","op");
}
return op.Start(this);
}
