Add asIpUnsafe to GenSocketAddress

Author: mpilquist

shared/src/main/scala/com/comcast/ip4s/GenSocketAddress.scala

@@ -25,4 +25,14 @@ package com.comcast.ip4s
   * This trait is left open for extension, allowing other address types to be defined.
   * When using this trait, pattern match on the supported subtypes.
   */
-abstract class GenSocketAddress private[ip4s] ()
+abstract class GenSocketAddress private[ip4s] () {
+
+  /** Downcasts this address to a `SocketAddress[IpAddress]`.
+   *
+   * @throws UnsupportedOperationException if this address is not a `SocketAddress[IpAddress]`
+   */
+  def asIpUnsafe: SocketAddress[IpAddress] = this match {
+    case addr @ SocketAddress(_: IpAddress, _) => addr.asInstanceOf[SocketAddress[IpAddress]]
+    case other => throw new UnsupportedOperationException(s"asIpUnsafe only supported on SocketAddress[IpAddress]: $other")
+  }
+}