DNS support for UDP transport

[captn3m0]

Currently, the code does not resolve domain names for UDP transport:

php-datadogstatsd/src/DogStatsd.php

Lines 295 to 302 in def70c3

	public function flush($udp_message)
	{
	// Non - Blocking UDP I/O - Use IP Addresses!
	$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
	socket_set_nonblock($socket);
	socket_sendto($socket, $udp_message, strlen($udp_message), 0, $this->host, $this->port);
	socket_close($socket);
	}

I understand the need (keep this entirely non-blocking), but was wondering what would be the right approach for this to be added (willing to file a PR, but want to make sure it can be merged before I go ahead).

/cc @jitendra-1217

[timrourke]

Just spitballing, since I'm just a dude, not a DataDog dude, but I wonder if a reasonable strategy here would be to extract the behavior of sending socket messages out into its own object. Sending data over UDP is a different responsibility from serializing UDP message strings so they conform to dogstatsd (which is what most of DogStatsd is about), and if a user could supply their own "sender" object, the specific send implementation could be made entirely flexible.

An interface called \DataDog\DogStatsd\Sender that supported a single public method send would be nice. Then you could extract the curl send logic and the UDP over IP send logic into their own Sender implementations.

I had to stub global socket functions at the namespace level to test that the global socket_* functions were being called correctly, which is boilerplate I could avoid if I could instead pass DogStatsd a mock of a Sender implementation.