From type/IO/Socket/Async

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method write-to(IO::Socket::Async:D: Str() $host, Int() $port, Blob $b --> Promise)

This is the equivalent of write for UDP sockets that have been created with the udp method. It will try send a UDP message comprised of the bytes in the Blob $b to the specified $host and $port returning a Promise that will be kept when the data is successfully sent or broken if it was unable to send the data. In order to send to a broadcast address the :broadcast flag must have been specified when the socket was created.