Setting up some response to file descriptor exhaustion

libi2pd/NTCP2.cpp

@@ -1177,7 +1177,8 @@ namespace transport
 
 	NTCP2Server::NTCP2Server ():
 		RunnableServiceWithWork ("NTCP2"), m_TerminationTimer (GetService ()),
-		 m_ProxyType(eNoProxy), m_Resolver(GetService ())
+		 m_ProxyType(eNoProxy), m_Resolver(GetService ()),
+		m_listen_backlog(boost::asio::socket_base::max_listen_connections)
 	{
 	}
 
@@ -1223,6 +1224,7 @@ namespace transport
 							auto ep = m_Address4 ? boost::asio::ip::tcp::endpoint (m_Address4->address(), address->port):
 								boost::asio::ip::tcp::endpoint (boost::asio::ip::tcp::v4(), address->port);
 							m_NTCP2Acceptor.reset (new boost::asio::ip::tcp::acceptor (GetService (), ep));
+							m_NTCP2Acceptor->listen(this->m_listen_backlog);
 						}
 						catch ( std::exception & ex )
 						{
@@ -1261,7 +1263,7 @@ namespace transport
 							else if (m_YggdrasilAddress && !context.SupportsV6 ())
 								ep = boost::asio::ip::tcp::endpoint (m_YggdrasilAddress->address(), address->port);
 							m_NTCP2V6Acceptor->bind (ep);
-							m_NTCP2V6Acceptor->listen ();
+							m_NTCP2V6Acceptor->listen(this->m_listen_backlog);
 
 							LogPrint (eLogInfo, "NTCP2: Start listening v6 TCP port ", address->port);
 							auto conn = std::make_shared<NTCP2Session> (*this);
@@ -1325,6 +1327,7 @@ namespace transport
 	{
 		if (session && session->GetRemoteIdentity ())
 			m_NTCP2Sessions.erase (session->GetRemoteIdentity ()->GetIdentHash ());
+		this->ResumeAcceptingIfOverloaded();
 	}
 
 	std::shared_ptr<NTCP2Session> NTCP2Server::FindNTCP2Session (const i2p::data::IdentHash& ident)
@@ -1422,9 +1425,10 @@ namespace transport
 			}
 			else
 				LogPrint (eLogError, "NTCP2: Connected from error ", ec.message ());
-		}
+		} else  {
-		else
 			LogPrint (eLogError, "NTCP2: Accept error ", error.message ());
+			this->CheckIfOverloaded(conn, error, true);
+		}
 
 		if (error != boost::asio::error::operation_aborted)
 		{
@@ -1455,11 +1459,54 @@ namespace transport
 			}
 			else
 				LogPrint (eLogError, "NTCP2: Connected from error ", ec.message ());
+		} else {
+			LogPrint (eLogError, "NTCP2: Accept error ", error.message ());
+			this->CheckIfOverloaded(conn, error, false);
 		}
 
 		if (error != boost::asio::error::operation_aborted)
 		{
-			conn = std::make_shared<NTCP2Session> (*this);
+			if (!conn) // connection is used, create new one
+				conn = std::make_shared<NTCP2Session> (*this);
+			else // reuse failed
+				conn->Close ();
+			m_NTCP2V6Acceptor->async_accept(conn->GetSocket (), std::bind (&NTCP2Server::HandleAcceptV6, this,
+				conn, std::placeholders::_1));
+		}
+	}
+
+	void NTCP2Server::CheckIfOverloaded (std::shared_ptr<NTCP2Session> conn, const boost::system::error_code& error, bool isv4)
+	{
+		// TODO: high water / low water sophistry
+		if(error == boost::system::errc::too_many_files_open_in_system ||
+		   error == boost::system::errc::too_many_files_open) {
+			// I have to wait until a file closes to accept more.
+			conn->Close();
+			this->m_overloaded = true;
+			this->m_listen_backlog = (this->m_listen_backlog + 128) >> 1;
+			m_NTCP2Acceptor->listen(this->m_listen_backlog);
+			m_NTCP2V6Acceptor->listen(this->m_listen_backlog);
+		}
+		if(this->m_overloaded) {
+			if(isv4) {
+				this->need_resume_v4 = true;
+			} else {
+				this->need_resume_v6 = true;
+			}
+		}
+	}
+
+	void NTCP2Server::ResumeAcceptingIfOverloaded ()
+	{
+		if(!this->m_overloaded) return;
+		std::shared_ptr<NTCP2Session> conn = std::make_shared<NTCP2Session>(*this);
+		if(this->need_resume_v4) {
+			this->need_resume_v4 = false;
+			m_NTCP2Acceptor->async_accept(conn->GetSocket (), std::bind (&NTCP2Server::HandleAccept, this,
+				conn, std::placeholders::_1));
+		}
+		if(this->need_resume_v6) {
+			this->need_resume_v6 = false;
 			m_NTCP2V6Acceptor->async_accept(conn->GetSocket (), std::bind (&NTCP2Server::HandleAcceptV6, this,
 				conn, std::placeholders::_1));
 		}

libi2pd/NTCP2.h

@@ -264,6 +264,9 @@ namespace transport
 			void HandleAccept (std::shared_ptr<NTCP2Session> conn, const boost::system::error_code& error);
 			void HandleAcceptV6 (std::shared_ptr<NTCP2Session> conn, const boost::system::error_code& error);
 
+			void CheckIfOverloaded (std::shared_ptr<NTCP2Session> conn, const boost::system::error_code& error, bool isv4);
+			void ResumeAcceptingIfOverloaded();
+
 			void HandleConnect (const boost::system::error_code& ecode, std::shared_ptr<NTCP2Session> conn, std::shared_ptr<boost::asio::deadline_timer> timer);
 			void HandleProxyConnect(const boost::system::error_code& ecode, std::shared_ptr<NTCP2Session> conn, std::shared_ptr<boost::asio::deadline_timer> timer);
 			void AfterSocksHandshake(std::shared_ptr<NTCP2Session> conn, std::shared_ptr<boost::asio::deadline_timer> timer);
@@ -286,6 +289,11 @@ namespace transport
 			std::unique_ptr<boost::asio::ip::tcp::endpoint> m_ProxyEndpoint;
 			std::shared_ptr<boost::asio::ip::tcp::endpoint> m_Address4, m_Address6, m_YggdrasilAddress;
 
+			bool m_overloaded;
+			bool need_resume_v4;
+			bool need_resume_v6;
+			int m_listen_backlog;
+
 		public:
 
 			// for HTTP/I2PControl