option for zenserver - `--http-forceloopback` (#516)

* New option for zenserver - `--http-forceloopback` which forces opening of the server http server using loopback (local) connection (UE-199776)
* add fallback to local connection for asio if we get access denied on public port

1 files changed, 30 insertions, 17 deletions

diff --git a/src/zenhttp/servers/httpasio.cpp b/src/zenhttp/servers/httpasio.cpp
index 75852fe89..c62aca001 100644
--- a/src/zenhttp/servers/httpasio.cpp
+++ b/src/zenhttp/servers/httpasio.cpp
@@ -62,7 +62,7 @@ public:
 	HttpAsioServerImpl();
 	~HttpAsioServerImpl();
 
-	int			 Start(uint16_t Port, int ThreadCount);
+	int			 Start(uint16_t Port, bool ForceLooopback, int ThreadCount);
 	void		 Stop();
 	void		 RegisterService(const char* UrlPath, HttpService& Service);
 	HttpService* RouteRequest(std::string_view Url);
@@ -569,7 +569,7 @@ HttpServerConnection::HandleRequest()
 
 struct HttpAcceptor
 {
-	HttpAcceptor(HttpAsioServerImpl& Server, asio::io_service& IoService, uint16_t BasePort)
+	HttpAcceptor(HttpAsioServerImpl& Server, asio::io_service& IoService, uint16_t BasePort, bool ForceLoopback)
 	: m_Server(Server)
 	, m_IoService(IoService)
 	, m_Acceptor(m_IoService, asio::ip::tcp::v6())
@@ -587,25 +587,36 @@ struct HttpAcceptor
 		m_Acceptor.set_option(asio::socket_base::receive_buffer_size(128 * 1024));
 		m_Acceptor.set_option(asio::socket_base::send_buffer_size(256 * 1024));
 
-		uint16_t EffectivePort = BasePort;
+		asio::ip::address_v6 BindAddress   = ForceLoopback ? asio::ip::address_v6::loopback() : asio::ip::address_v6::any();
+		uint16_t			 EffectivePort = BasePort;
 
 		asio::error_code BindErrorCode;
-		m_Acceptor.bind(asio::ip::tcp::endpoint(asio::ip::address_v6::any(), EffectivePort), BindErrorCode);
+		m_Acceptor.bind(asio::ip::tcp::endpoint(BindAddress, EffectivePort), BindErrorCode);
+		if (BindErrorCode == asio::error::access_denied && !BindAddress.is_loopback())
+		{
+			// Access denied for a public port - lets try fall back to local port only
+			BindAddress = asio::ip::address_v6::loopback();
+			m_Acceptor.bind(asio::ip::tcp::endpoint(BindAddress, EffectivePort), BindErrorCode);
+		}
 		// Sharing violation implies the port is being used by another process
 		for (uint16_t PortOffset = 1; (BindErrorCode == asio::error::address_in_use) && (PortOffset < 10); ++PortOffset)
 		{
 			EffectivePort = BasePort + (PortOffset * 100);
-			m_Acceptor.bind(asio::ip::tcp::endpoint(asio::ip::address_v6::any(), EffectivePort), BindErrorCode);
+			m_Acceptor.bind(asio::ip::tcp::endpoint(BindAddress, EffectivePort), BindErrorCode);
 		}
 		if (BindErrorCode == asio::error::access_denied)
 		{
 			EffectivePort = 0;
-			m_Acceptor.bind(asio::ip::tcp::endpoint(asio::ip::address_v6::any(), EffectivePort), BindErrorCode);
+			m_Acceptor.bind(asio::ip::tcp::endpoint(BindAddress, EffectivePort), BindErrorCode);
 		}
 		if (BindErrorCode)
 		{
 			ZEN_ERROR("Unable open asio service, error '{}'", BindErrorCode.message());
 		}
+		else if (BindAddress.is_loopback())
+		{
+			ZEN_INFO("Registered local-only handler 'http://{}:{}/' - this is not accessible from remote hosts", "[::1]", EffectivePort);
+		}
 
 #if ZEN_PLATFORM_WINDOWS
 		// On Windows, loopback connections can take advantage of a faster code path optionally with this flag.
@@ -627,7 +638,7 @@ struct HttpAcceptor
 #endif
 		m_Acceptor.listen();
 
-		ZEN_INFO("Started asio server at port '{}'", EffectivePort);
+		ZEN_INFO("Started asio server at 'http://{}:{}'", BindAddress.is_loopback() ? "[::1]" : "*", EffectivePort);
 	}
 
 	void Start()
@@ -831,13 +842,13 @@ HttpAsioServerImpl::~HttpAsioServerImpl()
 }
 
 int
-HttpAsioServerImpl::Start(uint16_t Port, int ThreadCount)
+HttpAsioServerImpl::Start(uint16_t Port, bool ForceLooopback, int ThreadCount)
 {
 	ZEN_ASSERT(ThreadCount > 0);
 
 	ZEN_INFO("starting asio http with {} service threads", ThreadCount);
 
-	m_Acceptor.reset(new asio_http::HttpAcceptor(*this, m_IoService, Port));
+	m_Acceptor.reset(new asio_http::HttpAcceptor(*this, m_IoService, Port, ForceLooopback));
 	m_Acceptor->Start();
 
 	// This should consist of a set of minimum threads and grow on demand to
@@ -926,7 +937,7 @@ namespace zen {
 class HttpAsioServer : public HttpServer
 {
 public:
-	HttpAsioServer(unsigned int ThreadCount);
+	HttpAsioServer(bool ForceLoopback, unsigned int ThreadCount);
 	~HttpAsioServer();
 
 	virtual void RegisterService(HttpService& Service) override;
@@ -937,14 +948,16 @@ public:
 
 private:
 	Event		 m_ShutdownEvent;
-	int			 m_BasePort	   = 0;
-	unsigned int m_ThreadCount = 0;
+	int			 m_BasePort		 = 0;
+	bool		 m_ForceLoopback = false;
+	unsigned int m_ThreadCount	 = 0;
 
 	std::unique_ptr<asio_http::HttpAsioServerImpl> m_Impl;
 };
 
-HttpAsioServer::HttpAsioServer(unsigned int ThreadCount)
-: m_ThreadCount(ThreadCount != 0 ? ThreadCount : Max(std::thread::hardware_concurrency(), 8u))
+HttpAsioServer::HttpAsioServer(bool ForceLoopback, unsigned int ThreadCount)
+: m_ForceLoopback(ForceLoopback)
+, m_ThreadCount(ThreadCount != 0 ? ThreadCount : Max(std::thread::hardware_concurrency(), 8u))
 , m_Impl(std::make_unique<asio_http::HttpAsioServerImpl>())
 {
 	ZEN_DEBUG("Request object size: {} ({:#x})", sizeof(HttpRequestParser), sizeof(HttpRequestParser));
@@ -981,7 +994,7 @@ HttpAsioServer::RegisterService(HttpService& Service)
 int
 HttpAsioServer::Initialize(int BasePort)
 {
-	m_BasePort = m_Impl->Start(gsl::narrow<uint16_t>(BasePort), m_ThreadCount);
+	m_BasePort = m_Impl->Start(gsl::narrow<uint16_t>(BasePort), m_ForceLoopback, m_ThreadCount);
 	return m_BasePort;
 }
 
@@ -1036,9 +1049,9 @@ HttpAsioServer::RequestExit()
 }
 
 Ref<HttpServer>
-CreateHttpAsioServer(unsigned int ThreadCount)
+CreateHttpAsioServer(bool ForceLoopback, unsigned int ThreadCount)
 {
-	return Ref<HttpServer>{new HttpAsioServer(ThreadCount)};
+	return Ref<HttpServer>{new HttpAsioServer(ForceLoopback, ThreadCount)};
 }
 
 }  // namespace zen