Resolver configuration

Everything is set through ResolverBuilder, which returns itself from each call so it chains.

var resolver = ResolverBuilder.Begin()
    .AddDnsServer("1.1.1.1")
    .AddDnsServer(IPAddress.Parse("8.8.8.8"))
    .SetTimeout(5000)
    .SetRetries(2)
    .UseRecursion()
    .EnableCache()
    .EnableLogging(logManager)
    .Build();

Servers

Overload	Notes
`AddDnsServer(IPEndPoint)`	Full control over address and port.
`AddDnsServer(IPAddress)`	Port 53.
`AddDnsServer(IPAddress, int)`	Explicit port.
`AddDnsServer(string)`	Parsed; port 53.
`AddDnsServer(string, int)`	Parsed; explicit port.
`AddDnsServers(IEnumerable<IPEndPoint>)`	Several at once.

Servers are tried in the order added. Passing null throws ArgumentNullException. A string that is not a valid address is a different case: it is dropped and the builder returned unchanged, on the grounds that such a value may have come from configuration rather than from a mistake in code.

If no server is added, Build falls back to the addresses configured on the machine's network interfaces.

Transport

Queries go over TCP by default. Switch after building:

resolver.TransportType = TransportType.Udp;

TCP is the more capable choice: UDP replies are size limited, and a zone transfer only works over TCP. UDP avoids a connection handshake and is usually quicker for ordinary lookups.

Timeout and retries

SetTimeout is milliseconds and applies to both transports; it defaults to 1000. SetRetries defaults to 1 and counts full passes over the server list, so two servers with three retries is up to six attempts before the resolver gives up and returns a timed out response.

A timeout is not an error you catch. It fails over to the next server, and only if every attempt fails do you get a response with TimedOut set.

Caching

EnableCache keeps successful, error-free responses keyed by question. A cached answer is returned without touching the network, including from QueryAsync, which returns without awaiting anything.

Entries are dropped once any record in the response outlives its TTL. ClearCache empties it.

Caching is off by default.

Logging

EnableLogging takes an IUbietyLogManager from Ubiety.Logging.Core. Without one the library logs nothing.

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