eve.aio.dns

Asynchronous DNS resolution.

This module provides high-level asynchronous DNS resolution built on top of the EVE event loop and a thread pool. It follows the EVE principles of zero-allocation and non-blocking I/O by offloading blocking libc calls to worker threads.

Thread Pool Requirement

DNS resolution uses getaddrinfo() which is a blocking C library call. EVE offloads it to a ThreadPool so the event loop thread is never blocked. You must create and start a ThreadPool before calling resolve():

auto loop = EventLoop.create();
auto pool = ThreadPool.create(2);
pool.start();              // must call before resolve()
scope (exit) pool.shutdown();

auto resolver = DnsResolver.create(loop, pool);
resolver.resolve("example.com", callback);

If no pool is provided (or null), resolve() fails with ResolveErrorReason.NOT_INITIALIZED.

Timeout

EVE does not impose a built-in DNS timeout. Use CancelSource with a timer to enforce application-level timeouts (see book/dns_with_timeout.d).

Concurrency

The number of simultaneous DNS queries is limited by dnsCapacity in EventLoopConfig (default: 4). Increase it if your application issues many concurrent lookups. Worker threads in the pool execute resolution in parallel.

See Also

DNS Strategy Audit
alias ResolveStatus
enum ResolveErrorReason
struct DnsResolver ResolveError

Types 4

enumResolveErrorReason : ubyte

Reason a DNS resolution request was not queued.

UNSPECIFIED = 0Not a real domain error; the default-constructed payload value.
NOT_INITIALIZEDThe resolver has no loop or no worker pool (`null` at `create()`).
NO_SLOTSThe event loop has no free DNS slots.
structResolveError

Recoverable failure of a DNS resolution request.

Fields
ResolveErrorReason reasonWhy the request was not queued.
int errnoReserved; OS errors do not apply to slot allocation.
aliasResolveStatus = Status!ResolveError
structDnsResolver

Resolver for translating hostnames to IP addresses.

Requires a running ThreadPool to perform resolution. See module documentation for setup instructions.

Example: 

auto resolver = DnsResolver.create(loop, pool);
resolver.resolve("localhost", (ref l, t, addrs, err) @safe nothrow {
    // handle result
});

Fields
private EventLoop * _loop
private ThreadPool _pool
Methods
DnsResolver create(ref EventLoop loop, ThreadPool pool = null) static @trustedCreate a new DNS resolver associated with an event loop.
ResolveStatus resolve(scope const(char)[] hostname, EventLoop.DnsWatcherCallback callback, CancelToken cancel = CancelToken .invalid) @trustedAsynchronously resolve a hostname.
private void performResolution(Token token) @trusted
private DnsError mapDnsError(int err) static pure @safe nothrow @nogc