Introduce Socket.shutdown()

lib/std/net/socket.c3

@@ -155,3 +155,36 @@ fn void! Socket.close(&self) @inline @dynamic
 {
 	self.sock.close()!;
 }
+
+enum SocketShutdownHow
+{
+	RECEIVE,
+	SEND,
+	BOTH,
+}
+
+fn CInt SocketShutdownHow.os_value(self)
+{
+	$switch
+		$case env::WIN32:
+			switch (self) {
+				case RECEIVE: return libc::SD_RECEIVE;
+				case SEND:    return libc::SD_SEND;
+				case BOTH:    return libc::SD_BOTH;
+			}
+		$case env::POSIX:
+			switch (self) {
+				case RECEIVE: return libc::SHUT_RD;
+				case SEND:    return libc::SHUT_WR;
+				case BOTH:    return libc::SHUT_RDWR;
+			}
+		$default: $error("Unsupported environment");
+	$endswitch
+}
+
+fn void! Socket.shutdown(&self, SocketShutdownHow how)
+{
+	if (libc::shutdown(self.sock, how.os_value()) < 0) {
+		return os::socket_error()?;
+	}
+}