experimental pluggable transport support (#436)

this change adds a `--http=plugin` mode where we support pluggable transports. Currently this defaults to a barebones blocking winsock implementation but there is also support for dynamic loading of transport plugins, which will be further developed in the near future.

2 files changed, 146 insertions, 0 deletions

diff --git a/src/zenhttp/include/zenhttp/httpplugin.h b/src/zenhttp/include/zenhttp/httpplugin.h
new file mode 100644
index 000000000..409eb1b61
--- /dev/null
+++ b/src/zenhttp/include/zenhttp/httpplugin.h
@@ -0,0 +1,49 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#pragma once
+
+#include <zencore/refcount.h>
+#include <zencore/thread.h>
+
+#if !defined(ZEN_WITH_PLUGINS)
+#	if ZEN_PLATFORM_WINDOWS
+#		define ZEN_WITH_PLUGINS 1
+#	else
+#		define ZEN_WITH_PLUGINS 0
+#	endif
+#endif
+
+#if ZEN_WITH_PLUGINS
+#	include "transportplugin.h"
+#	include <zenhttp/httpserver.h>
+
+namespace zen {
+
+struct HttpPluginServerImpl;
+
+class HttpPluginServer : public HttpServer
+{
+public:
+	HttpPluginServer(unsigned int ThreadCount);
+	~HttpPluginServer();
+
+	virtual void RegisterService(HttpService& Service) override;
+	virtual int	 Initialize(int BasePort) override;
+	virtual void Run(bool IsInteractiveSession) override;
+	virtual void RequestExit() override;
+	virtual void Close() override;
+
+	void AddPlugin(Ref<TransportPluginInterface> Plugin);
+	void RemovePlugin(Ref<TransportPluginInterface> Plugin);
+
+private:
+	Event		 m_ShutdownEvent;
+	int			 m_BasePort	   = 0;
+	unsigned int m_ThreadCount = 0;
+
+	HttpPluginServerImpl* m_Impl = nullptr;
+};
+
+}  // namespace zen
+
+#endif
diff --git a/src/zenhttp/include/zenhttp/transportplugin.h b/src/zenhttp/include/zenhttp/transportplugin.h
new file mode 100644
index 000000000..38b07d471
--- /dev/null
+++ b/src/zenhttp/include/zenhttp/transportplugin.h
@@ -0,0 +1,97 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#pragma once
+
+#include <stdint.h>
+
+// Important note: this header is meant to compile standalone
+// and should therefore not depend on anything from the Zen codebase
+
+class TransportConnectionInterface;
+class TransportPluginInterface;
+class TransportServerConnectionHandler;
+class TransportServerInterface;
+
+/*************************************************************************
+
+   The following interfaces are implemented on the server side, and instances
+   are provided to the plugins.
+
+*************************************************************************/
+
+/** Plugin-server interface for connection
+ *
+ *  This is how the transport feeds data to the connection handler
+ *  which will parse the incoming messages and dispatch to
+ *  appropriate request handlers and ultimately call into functions
+ *  which write data back to the client.
+ */
+class TransportServerConnectionHandler
+{
+public:
+	virtual uint32_t AddRef() const									  = 0;
+	virtual uint32_t Release() const								  = 0;
+	virtual void	 OnBytesRead(const void* Buffer, size_t DataSize) = 0;
+};
+
+/** Plugin-server interface
+ *
+ * There will be one instance of this per plugin, and the plugin
+ * should use this to manage lifetimes of connections and any
+ * other resources.
+ */
+class TransportServerInterface
+{
+public:
+	virtual TransportServerConnectionHandler* CreateConnectionHandler(TransportConnectionInterface* Connection) = 0;
+};
+
+/*************************************************************************
+
+   The following interfaces are to be implemented by transport plugins.
+
+*************************************************************************/
+
+/** Interface which needs to be implemented by a transport plugin
+ *
+ *  This is responsible for setting up and running the communication
+ *  for a given transport.
+ */
+class TransportPluginInterface
+{
+public:
+	virtual uint32_t AddRef() const										   = 0;
+	virtual uint32_t Release() const									   = 0;
+	virtual void	 Initialize(TransportServerInterface* ServerInterface) = 0;
+	virtual void	 Shutdown()											   = 0;
+
+	/** Check whether this transport is usable.
+	 */
+	virtual bool IsAvailable() = 0;
+};
+
+/** A transport plugin provider needs to implement this interface
+ *
+ * There will be one instance of this per established connection and
+ * this interface is used to write response data back to the client.
+ */
+class TransportConnectionInterface
+{
+public:
+	virtual int64_t WriteBytes(const void* Buffer, size_t DataSize) = 0;
+	virtual void	Shutdown(bool Receive, bool Transmit)			= 0;
+	virtual void	CloseConnection()								= 0;
+};
+
+#if defined(_MSC_VER)
+#	define DLL_TRANSPORT_API __declspec(dllexport)
+#else
+#	define DLL_TRANSPORT_API
+#endif
+
+extern "C"
+{
+	DLL_TRANSPORT_API TransportPluginInterface* CreateTransportPluginInterface();
+}
+
+typedef TransportPluginInterface* (*PfnCreateTransportPluginInterface)();