/// <summary>
/// Attempts a lookup from cache.
/// </summary>
/// <param name="uri"></param>
/// <param name="startQuery"></param>
/// <param name="preferIPv6"></param>
/// <returns></returns>
private static SIPEndPoint SIPLookupFromCache(
SIPURI uri,
QueryType startQuery,
bool preferIPv6)
{
SIPEndPoint result = null;
QueryType queryType = startQuery;
string host = uri.MAddrOrHostAddress;
int port = SIPConstants.GetDefaultPort(uri.Protocol);
if (ushort.TryParse(uri.HostPort, out var uriPort))
{
port = uriPort;
}
bool isDone = false;
while (!isDone)
{
switch (queryType)
{
case QueryType.SRV:
var srvProtocol = SIPServices.GetSRVProtocolForSIPURI(uri);
string serviceHost = DnsQueryExtensions.ConcatServiceName(uri.MAddrOrHostAddress, uri.Scheme.ToString(), srvProtocol.ToString());
var srvResult = _lookupClient.QueryCache(serviceHost, QueryType.SRV);
(var srvHost, var srvPort) = GetHostAndPortFromSrvResult(srvResult);
if (srvHost != null)
{
host = srvHost;
port = srvPort != 0 ? srvPort : port;
}
queryType = preferIPv6 ? QueryType.AAAA : QueryType.A;
break;
case QueryType.AAAA:
var aaaaResult = _lookupClient.QueryCache(host, UseANYLookups ? QueryType.ANY : QueryType.AAAA, QueryClass.IN);
if (aaaaResult?.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol, aaaaResult.Answers.OrderByDescending(x => x.RecordType).First(), port);
isDone = true;
}
else
{
queryType = QueryType.A;
}
break;
default:
// A record lookup.
var aResult = _lookupClient.QueryCache(host, QueryType.A, QueryClass.IN);
if (aResult != null)
{
if (aResult.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol, aResult.Answers.First(), port);
}
else
{
// We got a result back but it was empty indicating an unresolvable host or
// some other DNS error condition.
result = SIPEndPoint.Empty;
}
}
isDone = true;
break;
}
}
return(result);
}
/// <summary>
/// Attempts a lookup from DNS.
/// </summary>
/// <param name="uri"></param>
/// <param name="startQuery"></param>
/// <param name="preferIPv6"></param>
/// <param name="ct"></param>
/// <returns></returns>
private static async Task <SIPEndPoint> SIPLookupAsync(
SIPURI uri,
QueryType startQuery,
bool preferIPv6,
CancellationToken ct)
{
SIPEndPoint result = null;
QueryType queryType = startQuery;
string host = uri.MAddrOrHostAddress;
int port = SIPConstants.GetDefaultPort(uri.Protocol);
if (ushort.TryParse(uri.HostPort, out var uriPort))
{
port = uriPort;
}
bool isDone = false;
while (!isDone && !ct.IsCancellationRequested)
{
switch (queryType)
{
case QueryType.SRV:
try
{
var srvProtocol = SIPServices.GetSRVProtocolForSIPURI(uri);
//string serviceHost = DnsQueryExtensions.ConcatResolveServiceName(uri.MAddrOrHostAddress, uri.Scheme.ToString(), srvProtocol.ToString());
//var srvResult = await _lookupClient.QueryAsync(serviceHost, QueryType.SRV, QueryClass.IN, ct).ConfigureAwait(false);
var srvResult = await _lookupClient.ResolveServiceAsync(uri.MAddrOrHostAddress,
uri.Scheme.ToString(), srvProtocol.ToString());
(var srvHost, var srvPort) = GetHostAndPortFromSrvResult(srvResult);
if (srvHost != null)
{
host = srvHost;
port = srvPort != 0 ? srvPort : port;
}
}
catch (Exception srvExcp)
{
logger.LogWarning($"SIPDNS exception on SRV lookup. {srvExcp.Message}.");
}
queryType = preferIPv6 ? QueryType.AAAA : QueryType.A;
break;
case QueryType.AAAA:
try
{
var aaaaResult = await _lookupClient
.QueryAsync(host, UseANYLookups?QueryType.ANY : QueryType.AAAA, QueryClass.IN, ct)
.ConfigureAwait(false);
if (aaaaResult?.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol,
aaaaResult.Answers.AddressRecords().OrderByDescending(x => x.RecordType).First(),
port);
isDone = true;
}
else
{
queryType = QueryType.A;
}
}
catch (Exception srvExcp)
{
logger.LogWarning($"SIPDNS exception on AAAA lookup. {srvExcp.Message}.");
queryType = QueryType.A;
}
break;
default:
// A record lookup.
try
{
var aResult = await _lookupClient.QueryAsync(host, QueryType.A, QueryClass.IN, ct)
.ConfigureAwait(false);
if (aResult != null)
{
if (aResult.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol, aResult.Answers.AddressRecords().First(),
port);
}
else
{
// We got a result back but it was empty indicating an unresolvable host or
// some other DNS error condition.
result = SIPEndPoint.Empty;
}
}
}
catch (Exception srvExcp)
{
logger.LogWarning($"SIPDNS exception on A lookup. {srvExcp.Message}.");
result = SIPEndPoint.Empty;
}
isDone = true;
break;
}
}
return(result);
}
/// <summary>
/// Resolve method that performs either an A or AAAA record lookup. If required
/// a SRV record lookup will be performed prior to the A or AAAA lookup.
/// </summary>
/// <param name="uri">The SIP URI to lookup.</param>
/// <param name="queryType">Whether the address lookup should be A or AAAA.</param>
/// <returns>A SIPEndPoint or null.</returns>
private static async Task <SIPEndPoint> Resolve(SIPURI uri, QueryType queryType)
{
if (uri == null || String.IsNullOrWhiteSpace(uri.MAddrOrHostAddress))
{
throw new ArgumentNullException("uri", "SIP DNS resolve was supplied an empty input.");
}
if (!ushort.TryParse(uri.HostPort, out var uriPort))
{
uriPort = SIPConstants.DEFAULT_SIP_PORT;
}
if (IPAddress.TryParse(uri.MAddrOrHostAddress, out var ipAddress))
{
// Target is already an IP address, no DNS lookup required.
return(new SIPEndPoint(uri.Protocol, ipAddress, uriPort));
}
else
{
if (!uri.MAddrOrHostAddress.Contains(".") || uri.MAddrOrHostAddress.EndsWith(MDNS_TLD))
{
AddressFamily family = (queryType == QueryType.AAAA) ? AddressFamily.InterNetworkV6 :
AddressFamily.InterNetwork;
// The lookup is for a local network host. Use the OS DNS logic as the
// main DNS client can be configured to use external DNS servers that won't
// be able to lookup this hostname.
IPHostEntry hostEntry = null;
try
{
hostEntry = Dns.GetHostEntry(uri.MAddrOrHostAddress);
}
catch (SocketException)
{
// Socket exception gets thrown for failed lookups,
}
if (hostEntry != null)
{
var addressList = hostEntry.AddressList;
if (addressList?.Length == 0)
{
logger.LogWarning($"Operating System DNS lookup failed for {uri.MAddrOrHostAddress}.");
return(null);
}
else
{
if (addressList.Any(x => x.AddressFamily == family))
{
var addressResult = addressList.First(x => x.AddressFamily == family);
return(new SIPEndPoint(uri.Protocol, addressResult, uriPort));
}
else
{
// Didn't get a result for the preferred address family so just use the
// first available result.
var addressResult = addressList.First();
return(new SIPEndPoint(uri.Protocol, addressResult, uriPort));
}
}
}
else
{
return(null);
}
}
else
{
if (uri.HostPort != null)
{
// Explicit port means no SRV lookup.
return(HostQuery(uri.Protocol, uri.MAddrOrHostAddress, uriPort, queryType));
}
else
{
// No explicit port so use a SRV -> (A | AAAA -> A | ANY) record lookup.
var srvProtocol = SIPServices.GetSRVProtocolForSIPURI(uri);
try
{
ServiceHostEntry srvResult = null;
var srvResults = await _lookupClient.ResolveServiceAsync(uri.MAddrOrHostAddress, uri.Scheme.ToString(), srvProtocol.ToString()).ConfigureAwait(false);
if (srvResults == null || srvResults.Count() == 0)
{
logger.LogWarning($"SIP DNS SRV lookup returned no results for {uri}.");
}
else
{
srvResult = srvResults.OrderBy(y => y.Priority).ThenByDescending(w => w.Weight).FirstOrDefault();
}
string host = uri.MAddrOrHostAddress; // If no SRV results then fallback is to lookup the hostname directly.
int port = SIPConstants.DEFAULT_SIP_PORT; // If no SRV results then fallback is to use the default port.
if (srvResult != null)
{
host = srvResult.HostName;
port = srvResult.Port;
}
return(HostQuery(uri.Protocol, host, port, queryType));
}
catch (Exception e)
{
logger.LogWarning($"SIP DNS SRV lookup failure for {uri}. {e?.InnerException?.Message}");
}
}
}
return(null);
}
}
