HttpServerConnection: Don't spawn useless coroutines

Currently, for each `Disconnect()` call, we spawn a coroutine, but every
one of them is just usesless, except the first one. Thus, we should not
spawn a coroutine if someone has already triggered a disconnect.

lib/remote/httpserverconnection.cpp

@@ -72,12 +72,10 @@ void HttpServerConnection::Disconnect()
 {
 	namespace asio = boost::asio;
 
-	HttpServerConnection::Ptr keepAlive (this);
-
-	IoEngine::SpawnCoroutine(m_IoStrand, [this, keepAlive](asio::yield_context yc) {
-		if (!m_ShuttingDown) {
-			m_ShuttingDown = true;
+	if (!m_ShuttingDown.exchange(true)) {
+		HttpServerConnection::Ptr keepAlive (this);
 
+		IoEngine::SpawnCoroutine(m_IoStrand, [this, keepAlive](asio::yield_context yc) {
 			Log(LogInformation, "HttpServerConnection")
 				<< "HTTP client disconnected (from " << m_PeerAddress << ")";
 
@@ -104,8 +102,8 @@ void HttpServerConnection::Disconnect()
 			if (listener) {
 				listener->RemoveHttpClient(this);
 			}
-		}
-	});
+		});
+	}
 }
 
 void HttpServerConnection::StartStreaming()
@@ -131,7 +129,7 @@ void HttpServerConnection::StartStreaming()
 	});
 }
 
-bool HttpServerConnection::Disconnected()
+bool HttpServerConnection::Disconnected() const
 {
 	return m_ShuttingDown;
 }

lib/remote/httpserverconnection.hpp

@@ -31,17 +31,17 @@ class HttpServerConnection final : public Object
 	void Disconnect();
 	void StartStreaming();
 
-	bool Disconnected();
+	bool Disconnected() const;
 
 private:
 	ApiUser::Ptr m_ApiUser;
 	Shared<AsioTlsStream>::Ptr m_Stream;
 	double m_Seen;
 	String m_PeerAddress;
 	boost::asio::io_context::strand m_IoStrand;
-	bool m_ShuttingDown;
-	bool m_HasStartedStreaming;
 	boost::asio::deadline_timer m_CheckLivenessTimer;
+	std::atomic<bool> m_ShuttingDown;
+	bool m_HasStartedStreaming;
 
 	HttpServerConnection(const String& identity, bool authenticated, const Shared<AsioTlsStream>::Ptr& stream, boost::asio::io_context& io);