Fix ineffective cancel() when stuck in perfdata writer handshake

Sometimes, the `stream->lowest_layer().cancel()` in
`PerfdataWriterConnection::Disconnect()` is ineffective when
`EnsureConnected()` is stuck in a handshake. Supposedly there
is a window where the coroutine has already been suspended, but
the handler for the SSL operations has not yet been queued. If
the cancel hits in this window, it is entirely ignored.

This is fixed by issuing a socket close unless the client is fully
connected.

Author: jschmidt-icinga

lib/perfdata/perfdatawriterconnection.cpp

@@ -76,9 +76,14 @@ void PerfdataWriterConnection::Disconnect()
 			 * completion.
 			 */
 			std::visit(
-				[](const auto& stream) {
+				[this](const auto& stream) {
 					if (stream->lowest_layer().is_open()) {
-						stream->lowest_layer().cancel();
+						if (m_Connected) {
+							stream->lowest_layer().cancel();
+						} else {
+							boost::system::error_code ec;
+							stream->lowest_layer().close(ec);
+						}
 					}
 				},
 				m_Stream
@@ -160,7 +165,7 @@ void PerfdataWriterConnection::EnsureConnected(const boost::asio::yield_context&
 
 void PerfdataWriterConnection::Disconnect(boost::asio::yield_context yc)
 {
-	if (!m_Connected.exchange(false, std::memory_order_relaxed)) {
+	if (!m_Connected.exchange(false)) {
 		return;
 	}