Publishing

Publishing advertises a service so other devices can find it. It does not open a socket — you are responsible for having a listener bound to the port you advertise.

// your listener first
var listener = new TcpListener(IPAddress.Any, 8080);
listener.Start();

// then advertise it
await using var publication = await mdns.Publish("Allan's Laptop", "_myapp._tcp", 8080, ct);

With TXT metadata

var registration = new MdnsServiceRegistration("Allan's Laptop", "_myapp._tcp", 8080)
{
    TxtRecords = new Dictionary<string, string>
    {
        ["version"] = "2",
        ["path"] = "/api",
        ["deviceId"] = deviceId
    }
};

await using var publication = await mdns.Publish(registration, ct);

Keep TXT records small. RFC 6763 recommends the whole record stay under 1300 bytes so it fits in a single packet, and a single key=value entry may not exceed 255 bytes — one that does throws MdnsException. A key containing = is also rejected.

Name conflicts and renaming

If another device on the link already advertises your instance name, the responder resolves the conflict by appending a counter — "Allan's Laptop" becomes "Allan's Laptop (2)". This is the same behaviour on all platforms.

Always read the name back

await using var publication = await mdns.Publish(registration, ct);

// this may NOT be the name you asked for
logger.LogInformation("advertising as {Name}", publication.InstanceName);

Never show the requested name in your UI — show publication.InstanceName.

IMdnsPublication exposes InstanceName, ServiceType, Domain, and Port.

Lifetime

The publication stays live until disposed. Disposing sends a goodbye packet — records with a zero TTL — so peers drop it immediately rather than waiting for the TTL to expire.

var publication = await mdns.Publish(registration, ct);
try
{
    await RunServer(ct);
}
finally
{
    await publication.DisposeAsync();   // sends the goodbye
}

await using does the same thing:

await using var publication = await mdns.Publish(registration, ct);

If the process is killed without disposing, peers will drop the service when the records expire instead — 120 seconds for the address and SRV records.

Instance name rules

An instance name is a single DNS-SD label. Spaces, dots, and UTF8 are all fine:

await mdns.Publish("Allan's 2.4Ghz Printer ⚡", "_myapp._tcp", 8080, ct);   // ✔

The only limit is that it must encode to 63 bytes or fewer in UTF8 — a name of 32 accented characters is 64 bytes and throws MdnsException.

Publishing multiple services

Each call returns its own handle; dispose them independently.

await using var api  = await mdns.Publish("My App API", "_myapp._tcp", 8080, ct);
await using var sync = await mdns.Publish("My App Sync", "_myappsync._tcp", 8081, ct);

On Apple platforms, every type you publish must also be listed in NSBonjourServices — see Platform Setup.