restructured zenhttp (#472)

separating the http server implementations into a directory and moved diagsvcs into zenserver since it's somewhat hard-coded for it

1 files changed, 2012 insertions, 0 deletions

diff --git a/src/zenhttp/servers/httpsys.cpp b/src/zenhttp/servers/httpsys.cpp
new file mode 100644
index 000000000..c1b4717cb
--- /dev/null
+++ b/src/zenhttp/servers/httpsys.cpp
@@ -0,0 +1,2012 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "httpsys.h"
+
+#include <zencore/compactbinary.h>
+#include <zencore/compactbinarybuilder.h>
+#include <zencore/compactbinarypackage.h>
+#include <zencore/except.h>
+#include <zencore/filesystem.h>
+#include <zencore/fmtutils.h>
+#include <zencore/logging.h>
+#include <zencore/scopeguard.h>
+#include <zencore/string.h>
+#include <zencore/timer.h>
+#include <zencore/trace.h>
+#include <zenhttp/httpshared.h>
+
+#if ZEN_WITH_HTTPSYS
+#	define _WINSOCKAPI_
+#	include <zencore/windows.h>
+#	include <zencore/workthreadpool.h>
+#	include "iothreadpool.h"
+
+#	include <http.h>
+
+namespace spdlog {
+class logger;
+}
+
+namespace zen {
+
+/**
+ * @brief Windows implementation of HTTP server based on http.sys
+ *
+ * This requires elevation to function by default but system configuration
+ * can soften this requirement.
+ *
+ * See README.md for details.
+ */
+class HttpSysServer : public HttpServer
+{
+	friend class HttpSysTransaction;
+
+public:
+	explicit HttpSysServer(const HttpSysConfig& Config);
+	~HttpSysServer();
+
+	// HttpServer interface implementation
+
+	virtual int	 Initialize(int BasePort) override;
+	virtual void Run(bool TestMode) override;
+	virtual void RequestExit() override;
+	virtual void RegisterService(HttpService& Service) override;
+	virtual void Close() override;
+
+	WorkerThreadPool& WorkPool();
+
+	inline bool IsOk() const { return m_IsOk; }
+	inline bool IsAsyncResponseEnabled() const { return m_IsAsyncResponseEnabled; }
+
+private:
+	int	 InitializeServer(int BasePort);
+	void Cleanup();
+
+	void StartServer();
+	void OnHandlingNewRequest();
+	void IssueNewRequestMaybe();
+
+	void RegisterService(const char* Endpoint, HttpService& Service);
+	void UnregisterService(const char* Endpoint, HttpService& Service);
+
+private:
+	spdlog::logger& m_Log;
+	spdlog::logger& m_RequestLog;
+	spdlog::logger& Log() { return m_Log; }
+
+	bool m_IsOk					   = false;
+	bool m_IsHttpInitialized	   = false;
+	bool m_IsRequestLoggingEnabled = false;
+	bool m_IsAsyncResponseEnabled  = true;
+
+	std::unique_ptr<WinIoThreadPool> m_IoThreadPool;
+
+	RwLock			  m_AsyncWorkPoolInitLock;
+	WorkerThreadPool* m_AsyncWorkPool = nullptr;
+
+	std::vector<std::wstring> m_BaseUris;  // eg: http://*:nnnn/
+	HTTP_SERVER_SESSION_ID	  m_HttpSessionId	   = 0;
+	HTTP_URL_GROUP_ID		  m_HttpUrlGroupId	   = 0;
+	HANDLE					  m_RequestQueueHandle = 0;
+	std::atomic_int32_t		  m_PendingRequests{0};
+	std::atomic_int32_t		  m_IsShuttingDown{0};
+	int32_t					  m_MinPendingRequests = 16;
+	int32_t					  m_MaxPendingRequests = 128;
+	Event					  m_ShutdownEvent;
+	HttpSysConfig			  m_InitialConfig;
+};
+
+}  // namespace zen
+#endif
+
+#if ZEN_WITH_HTTPSYS
+
+#	include <conio.h>
+#	include <mstcpip.h>
+#	pragma comment(lib, "httpapi.lib")
+
+std::wstring
+UTF8_to_UTF16(const char* InPtr)
+{
+	std::wstring OutString;
+	unsigned int Codepoint;
+
+	while (*InPtr != 0)
+	{
+		unsigned char InChar = static_cast<unsigned char>(*InPtr);
+
+		if (InChar <= 0x7f)
+			Codepoint = InChar;
+		else if (InChar <= 0xbf)
+			Codepoint = (Codepoint << 6) | (InChar & 0x3f);
+		else if (InChar <= 0xdf)
+			Codepoint = InChar & 0x1f;
+		else if (InChar <= 0xef)
+			Codepoint = InChar & 0x0f;
+		else
+			Codepoint = InChar & 0x07;
+
+		++InPtr;
+
+		if (((*InPtr & 0xc0) != 0x80) && (Codepoint <= 0x10ffff))
+		{
+			if (Codepoint > 0xffff)
+			{
+				OutString.append(1, static_cast<wchar_t>(0xd800 + (Codepoint >> 10)));
+				OutString.append(1, static_cast<wchar_t>(0xdc00 + (Codepoint & 0x03ff)));
+			}
+			else if (Codepoint < 0xd800 || Codepoint >= 0xe000)
+			{
+				OutString.append(1, static_cast<wchar_t>(Codepoint));
+			}
+		}
+	}
+
+	return OutString;
+}
+
+namespace zen {
+
+using namespace std::literals;
+
+class HttpSysServer;
+class HttpSysTransaction;
+class HttpMessageResponseRequest;
+
+//////////////////////////////////////////////////////////////////////////
+
+HttpVerb
+TranslateHttpVerb(HTTP_VERB ReqVerb)
+{
+	switch (ReqVerb)
+	{
+		case HttpVerbOPTIONS:
+			return HttpVerb::kOptions;
+
+		case HttpVerbGET:
+			return HttpVerb::kGet;
+
+		case HttpVerbHEAD:
+			return HttpVerb::kHead;
+
+		case HttpVerbPOST:
+			return HttpVerb::kPost;
+
+		case HttpVerbPUT:
+			return HttpVerb::kPut;
+
+		case HttpVerbDELETE:
+			return HttpVerb::kDelete;
+
+		case HttpVerbCOPY:
+			return HttpVerb::kCopy;
+
+		default:
+			// TODO: invalid request?
+			return (HttpVerb)0;
+	}
+}
+
+uint64_t
+GetContentLength(const HTTP_REQUEST* HttpRequest)
+{
+	const HTTP_KNOWN_HEADER& clh = HttpRequest->Headers.KnownHeaders[HttpHeaderContentLength];
+	std::string_view		 cl(clh.pRawValue, clh.RawValueLength);
+	uint64_t				 ContentLength = 0;
+	std::from_chars(cl.data(), cl.data() + cl.size(), ContentLength);
+	return ContentLength;
+};
+
+HttpContentType
+GetContentType(const HTTP_REQUEST* HttpRequest)
+{
+	const HTTP_KNOWN_HEADER& CtHdr = HttpRequest->Headers.KnownHeaders[HttpHeaderContentType];
+	return ParseContentType({CtHdr.pRawValue, CtHdr.RawValueLength});
+};
+
+HttpContentType
+GetAcceptType(const HTTP_REQUEST* HttpRequest)
+{
+	const HTTP_KNOWN_HEADER& CtHdr = HttpRequest->Headers.KnownHeaders[HttpHeaderAccept];
+	return ParseContentType({CtHdr.pRawValue, CtHdr.RawValueLength});
+};
+
+/**
+ * @brief Base class for any pending or active HTTP transactions
+ */
+class HttpSysRequestHandler
+{
+public:
+	explicit HttpSysRequestHandler(HttpSysTransaction& Transaction) : m_Transaction(Transaction) {}
+	virtual ~HttpSysRequestHandler() = default;
+
+	virtual void				   IssueRequest(std::error_code& ErrorCode)								= 0;
+	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) = 0;
+	HttpSysTransaction&			   Transaction() { return m_Transaction; }
+
+	HttpSysRequestHandler(const HttpSysRequestHandler&) = delete;
+	HttpSysRequestHandler& operator=(const HttpSysRequestHandler&) = delete;
+
+private:
+	HttpSysTransaction& m_Transaction;
+};
+
+/**
+ * This is the handler for the initial HTTP I/O request which will receive the headers
+ * and however much of the remaining payload might fit in the embedded request buffer.
+ *
+ * It is also used to receive any entity body data relating to the request
+ *
+ */
+struct InitialRequestHandler : public HttpSysRequestHandler
+{
+	inline HTTP_REQUEST* HttpRequest() { return (HTTP_REQUEST*)m_RequestBuffer; }
+	inline uint32_t		 RequestBufferSize() const { return sizeof m_RequestBuffer; }
+	inline bool			 IsInitialRequest() const { return m_IsInitialRequest; }
+
+	InitialRequestHandler(HttpSysTransaction& InRequest);
+	~InitialRequestHandler();
+
+	virtual void				   IssueRequest(std::error_code& ErrorCode) override final;
+	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) override;
+
+	bool	 m_IsInitialRequest		= true;
+	uint64_t m_CurrentPayloadOffset = 0;
+	uint64_t m_ContentLength		= ~uint64_t(0);
+	IoBuffer m_PayloadBuffer;
+	UCHAR	 m_RequestBuffer[4096 + sizeof(HTTP_REQUEST)];
+};
+
+/**
+ * This is the class which request handlers use to interact with the server instance
+ */
+
+class HttpSysServerRequest : public HttpServerRequest
+{
+public:
+	HttpSysServerRequest(HttpSysTransaction& Tx, HttpService& Service, IoBuffer PayloadBuffer);
+	~HttpSysServerRequest();
+
+	virtual Oid		 ParseSessionId() const override;
+	virtual uint32_t ParseRequestId() const override;
+
+	virtual IoBuffer ReadPayload() override;
+	virtual void	 WriteResponse(HttpResponseCode ResponseCode) override;
+	virtual void	 WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::span<IoBuffer> Blobs) override;
+	virtual void	 WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::u8string_view ResponseString) override;
+	virtual void	 WriteResponseAsync(std::function<void(HttpServerRequest&)>&& ContinuationHandler) override;
+	virtual bool	 TryGetRanges(HttpRanges& Ranges) override;
+
+	using HttpServerRequest::WriteResponse;
+
+	HttpSysServerRequest(const HttpSysServerRequest&) = delete;
+	HttpSysServerRequest& operator=(const HttpSysServerRequest&) = delete;
+
+	HttpSysTransaction&			 m_HttpTx;
+	HttpSysRequestHandler*		 m_NextCompletionHandler = nullptr;
+	IoBuffer					 m_PayloadBuffer;
+	ExtendableStringBuilder<128> m_UriUtf8;
+	ExtendableStringBuilder<128> m_QueryStringUtf8;
+};
+
+/** HTTP transaction
+
+	There will be an instance of this per pending and in-flight HTTP transaction
+
+  */
+class HttpSysTransaction final
+{
+public:
+	HttpSysTransaction(HttpSysServer& Server);
+	virtual ~HttpSysTransaction();
+
+	enum class Status
+	{
+		kDone,
+		kRequestPending
+	};
+
+	[[nodiscard]] Status HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred);
+
+	static void __stdcall IoCompletionCallback(PTP_CALLBACK_INSTANCE Instance,
+											   PVOID				 pContext /* HttpSysServer */,
+											   PVOID				 pOverlapped,
+											   ULONG				 IoResult,
+											   ULONG_PTR			 NumberOfBytesTransferred,
+											   PTP_IO				 Io);
+
+	void IssueInitialRequest(std::error_code& ErrorCode);
+	bool IssueNextRequest(HttpSysRequestHandler* NewCompletionHandler);
+
+	PTP_IO				  Iocp();
+	HANDLE				  RequestQueueHandle();
+	inline OVERLAPPED*	  Overlapped() { return &m_HttpOverlapped; }
+	inline HttpSysServer& Server() { return m_HttpServer; }
+	inline HTTP_REQUEST*  HttpRequest() { return m_InitialHttpHandler.HttpRequest(); }
+
+	HttpSysServerRequest& InvokeRequestHandler(HttpService& Service, IoBuffer Payload);
+
+	HttpSysServerRequest& ServerRequest() { return m_HandlerRequest.value(); }
+
+	struct CompletionMutexScope
+	{
+		CompletionMutexScope(HttpSysTransaction& Tx) : Lock(Tx.m_CompletionMutex) {}
+		~CompletionMutexScope() = default;
+
+		RwLock::ExclusiveLockScope Lock;
+	};
+
+private:
+	OVERLAPPED	   m_HttpOverlapped{};
+	HttpSysServer& m_HttpServer;
+
+	// Tracks which handler is due to handle the next I/O completion event
+	HttpSysRequestHandler*				m_CompletionHandler = nullptr;
+	RwLock								m_CompletionMutex;
+	InitialRequestHandler				m_InitialHttpHandler{*this};
+	std::optional<HttpSysServerRequest> m_HandlerRequest;
+	Ref<IHttpPackageHandler>			m_PackageHandler;
+};
+
+/**
+ * @brief HTTP request response I/O request handler
+ *
+ * Asynchronously streams out a response to an HTTP request via compound
+ * responses from memory or directly from file
+ */
+
+class HttpMessageResponseRequest : public HttpSysRequestHandler
+{
+public:
+	HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode);
+	HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode, std::string_view Message);
+	HttpMessageResponseRequest(HttpSysTransaction& InRequest,
+							   uint16_t			   ResponseCode,
+							   HttpContentType	   ContentType,
+							   const void*		   Payload,
+							   size_t			   PayloadSize);
+	HttpMessageResponseRequest(HttpSysTransaction& InRequest,
+							   uint16_t			   ResponseCode,
+							   HttpContentType	   ContentType,
+							   std::span<IoBuffer> Blobs);
+	~HttpMessageResponseRequest();
+
+	virtual void				   IssueRequest(std::error_code& ErrorCode) override final;
+	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) override;
+	void						   SuppressResponseBody();	// typically used for HEAD requests
+
+private:
+	std::vector<HTTP_DATA_CHUNK> m_HttpDataChunks;
+	uint64_t					 m_TotalDataSize	   = 0;	 // Sum of all chunk sizes
+	uint16_t					 m_ResponseCode		   = 0;
+	uint32_t					 m_NextDataChunkOffset = 0;	 // Cursor used for very large chunk lists
+	uint32_t					 m_RemainingChunkCount = 0;	 // Backlog for multi-call sends
+	bool						 m_IsInitialResponse   = true;
+	HttpContentType				 m_ContentType		   = HttpContentType::kBinary;
+	std::vector<IoBuffer>		 m_DataBuffers;
+
+	void InitializeForPayload(uint16_t ResponseCode, std::span<IoBuffer> Blobs);
+};
+
+HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode)
+: HttpSysRequestHandler(InRequest)
+{
+	std::array<IoBuffer, 0> EmptyBufferList;
+
+	InitializeForPayload(ResponseCode, EmptyBufferList);
+}
+
+HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode, std::string_view Message)
+: HttpSysRequestHandler(InRequest)
+, m_ContentType(HttpContentType::kText)
+{
+	IoBuffer				MessageBuffer(IoBuffer::Wrap, Message.data(), Message.size());
+	std::array<IoBuffer, 1> SingleBufferList({MessageBuffer});
+
+	InitializeForPayload(ResponseCode, SingleBufferList);
+}
+
+HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest,
+													   uint16_t			   ResponseCode,
+													   HttpContentType	   ContentType,
+													   const void*		   Payload,
+													   size_t			   PayloadSize)
+: HttpSysRequestHandler(InRequest)
+, m_ContentType(ContentType)
+{
+	IoBuffer				MessageBuffer(IoBuffer::Wrap, Payload, PayloadSize);
+	std::array<IoBuffer, 1> SingleBufferList({MessageBuffer});
+
+	InitializeForPayload(ResponseCode, SingleBufferList);
+}
+
+HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest,
+													   uint16_t			   ResponseCode,
+													   HttpContentType	   ContentType,
+													   std::span<IoBuffer> BlobList)
+: HttpSysRequestHandler(InRequest)
+, m_ContentType(ContentType)
+{
+	InitializeForPayload(ResponseCode, BlobList);
+}
+
+HttpMessageResponseRequest::~HttpMessageResponseRequest()
+{
+}
+
+void
+HttpMessageResponseRequest::InitializeForPayload(uint16_t ResponseCode, std::span<IoBuffer> BlobList)
+{
+	ZEN_TRACE_CPU("httpsys::InitializeForPayload");
+
+	const uint32_t ChunkCount = gsl::narrow<uint32_t>(BlobList.size());
+
+	m_HttpDataChunks.reserve(ChunkCount);
+	m_DataBuffers.reserve(ChunkCount);
+
+	for (IoBuffer& Buffer : BlobList)
+	{
+		m_DataBuffers.emplace_back(std::move(Buffer)).MakeOwned();
+	}
+
+	// Initialize the full array up front
+
+	uint64_t LocalDataSize = 0;
+
+	for (IoBuffer& Buffer : m_DataBuffers)
+	{
+		uint64_t BufferDataSize = Buffer.Size();
+
+		ZEN_ASSERT(BufferDataSize);
+
+		LocalDataSize += BufferDataSize;
+
+		IoBufferFileReference FileRef;
+		if (Buffer.GetFileReference(/* out */ FileRef))
+		{
+			// Use direct file transfer
+
+			auto& Chunk = m_HttpDataChunks.emplace_back();
+
+			Chunk.DataChunkType									   = HttpDataChunkFromFileHandle;
+			Chunk.FromFileHandle.FileHandle						   = FileRef.FileHandle;
+			Chunk.FromFileHandle.ByteRange.StartingOffset.QuadPart = FileRef.FileChunkOffset;
+			Chunk.FromFileHandle.ByteRange.Length.QuadPart		   = BufferDataSize;
+		}
+		else
+		{
+			// Send from memory, need to make sure we chunk the buffer up since
+			// the underlying data structure only accepts 32-bit chunk sizes for
+			// memory chunks. When this happens the vector will be reallocated,
+			// which is fine since this will be a pretty rare case and sending
+			// the data is going to take a lot longer than a memory allocation :)
+
+			const uint8_t* WriteCursor = reinterpret_cast<const uint8_t*>(Buffer.Data());
+
+			while (BufferDataSize)
+			{
+				const ULONG ThisChunkSize = gsl::narrow<ULONG>(zen::Min(1 * 1024 * 1024 * 1024, BufferDataSize));
+
+				auto& Chunk = m_HttpDataChunks.emplace_back();
+
+				Chunk.DataChunkType			  = HttpDataChunkFromMemory;
+				Chunk.FromMemory.pBuffer	  = (void*)WriteCursor;
+				Chunk.FromMemory.BufferLength = ThisChunkSize;
+
+				BufferDataSize -= ThisChunkSize;
+				WriteCursor += ThisChunkSize;
+			}
+		}
+	}
+
+	m_RemainingChunkCount = gsl::narrow<uint32_t>(m_HttpDataChunks.size());
+	m_TotalDataSize		  = LocalDataSize;
+
+	if (m_TotalDataSize == 0 && ResponseCode == 200)
+	{
+		// Some HTTP clients really don't like empty responses unless a 204 response is sent
+		m_ResponseCode = uint16_t(HttpResponseCode::NoContent);
+	}
+	else
+	{
+		m_ResponseCode = ResponseCode;
+	}
+}
+
+void
+HttpMessageResponseRequest::SuppressResponseBody()
+{
+	m_RemainingChunkCount = 0;
+	m_HttpDataChunks.clear();
+	m_DataBuffers.clear();
+}
+
+HttpSysRequestHandler*
+HttpMessageResponseRequest::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
+{
+	ZEN_UNUSED(NumberOfBytesTransferred);
+
+	if (IoResult != NO_ERROR)
+	{
+		ZEN_WARN("response aborted due to error: '{}'", GetSystemErrorAsString(IoResult));
+
+		// if one transmit failed there's really no need to go on
+		return nullptr;
+	}
+
+	if (m_RemainingChunkCount == 0)
+	{
+		return nullptr;	 // All done
+	}
+
+	return this;
+}
+
+void
+HttpMessageResponseRequest::IssueRequest(std::error_code& ErrorCode)
+{
+	ZEN_TRACE_CPU("httpsys::Response::IssueRequest");
+	HttpSysTransaction& Tx		= Transaction();
+	HTTP_REQUEST* const HttpReq = Tx.HttpRequest();
+	PTP_IO const		Iocp	= Tx.Iocp();
+
+	StartThreadpoolIo(Iocp);
+
+	// Split payload into batches to play well with the underlying API
+
+	const int MaxChunksPerCall = 9999;
+
+	const int ThisRequestChunkCount	 = std::min<int>(m_RemainingChunkCount, MaxChunksPerCall);
+	const int ThisRequestChunkOffset = m_NextDataChunkOffset;
+
+	m_RemainingChunkCount -= ThisRequestChunkCount;
+	m_NextDataChunkOffset += ThisRequestChunkCount;
+
+	/* Should this code also use HTTP_SEND_RESPONSE_FLAG_BUFFER_DATA?
+
+		From the docs:
+
+		This flag enables buffering of data in the kernel on a per-response basis. It should
+		be used by an application doing synchronous I/O, or by a an application doing
+		asynchronous I/O with no more than one send outstanding at a time.
+
+		Applications using asynchronous I/O which may have more than one send outstanding at
+		a time should not use this flag.
+
+		When this flag is set, it should be used consistently in calls to the
+		HttpSendHttpResponse function as well.
+	 */
+
+	ULONG SendFlags = HTTP_SEND_RESPONSE_FLAG_BUFFER_DATA;
+
+	if (m_RemainingChunkCount)
+	{
+		// We need to make more calls to send the full amount of data
+		SendFlags |= HTTP_SEND_RESPONSE_FLAG_MORE_DATA;
+	}
+
+	ULONG SendResult = 0;
+
+	if (m_IsInitialResponse)
+	{
+		// Populate response structure
+
+		HTTP_RESPONSE HttpResponse = {};
+
+		HttpResponse.EntityChunkCount = USHORT(ThisRequestChunkCount);
+		HttpResponse.pEntityChunks	  = m_HttpDataChunks.data() + ThisRequestChunkOffset;
+
+		// Server header
+		//
+		// By default this will also add a suffix " Microsoft-HTTPAPI/2.0" to this header
+		//
+		// This is controlled via a registry key 'DisableServerHeader', at:
+		//
+		// Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HTTP\Parameters
+		//
+		// Set DisableServerHeader to 1 to disable suffix, or 2 to disable the header altogether
+		// (only the latter appears to do anything in my testing, on Windows 10).
+		//
+		// (reference https://docs.microsoft.com/en-us/archive/blogs/dsnotes/wswcf-remove-server-header)
+		//
+
+		PHTTP_KNOWN_HEADER ServerHeader = &HttpResponse.Headers.KnownHeaders[HttpHeaderServer];
+		ServerHeader->pRawValue			= "Zen";
+		ServerHeader->RawValueLength	= (USHORT)3;
+
+		// Content-length header
+
+		char ContentLengthString[32];
+		_ui64toa_s(m_TotalDataSize, ContentLengthString, sizeof ContentLengthString, 10);
+
+		PHTTP_KNOWN_HEADER ContentLengthHeader = &HttpResponse.Headers.KnownHeaders[HttpHeaderContentLength];
+		ContentLengthHeader->pRawValue		   = ContentLengthString;
+		ContentLengthHeader->RawValueLength	   = (USHORT)strlen(ContentLengthString);
+
+		// Content-type header
+
+		PHTTP_KNOWN_HEADER ContentTypeHeader = &HttpResponse.Headers.KnownHeaders[HttpHeaderContentType];
+
+		std::string_view ContentTypeString = MapContentTypeToString(m_ContentType);
+
+		ContentTypeHeader->pRawValue	  = ContentTypeString.data();
+		ContentTypeHeader->RawValueLength = (USHORT)ContentTypeString.size();
+
+		std::string_view ReasonString = ReasonStringForHttpResultCode(m_ResponseCode);
+
+		HttpResponse.StatusCode	  = m_ResponseCode;
+		HttpResponse.pReason	  = ReasonString.data();
+		HttpResponse.ReasonLength = (USHORT)ReasonString.size();
+
+		// Cache policy
+
+		HTTP_CACHE_POLICY CachePolicy;
+
+		CachePolicy.Policy		  = HttpCachePolicyNocache;	 //  HttpCachePolicyUserInvalidates;
+		CachePolicy.SecondsToLive = 0;
+
+		// Initial response API call
+
+		SendResult = HttpSendHttpResponse(Tx.RequestQueueHandle(),
+										  HttpReq->RequestId,
+										  SendFlags,
+										  &HttpResponse,
+										  &CachePolicy,
+										  NULL,
+										  NULL,
+										  0,
+										  Tx.Overlapped(),
+										  NULL);
+
+		m_IsInitialResponse = false;
+	}
+	else
+	{
+		// Subsequent response API calls
+
+		SendResult = HttpSendResponseEntityBody(Tx.RequestQueueHandle(),
+												HttpReq->RequestId,
+												SendFlags,
+												(USHORT)ThisRequestChunkCount,				// EntityChunkCount
+												&m_HttpDataChunks[ThisRequestChunkOffset],	// EntityChunks
+												NULL,										// BytesSent
+												NULL,										// Reserved1
+												0,											// Reserved2
+												Tx.Overlapped(),							// Overlapped
+												NULL										// LogData
+		);
+	}
+
+	auto EmitReponseDetails = [&](StringBuilderBase& ResponseDetails) -> void {
+		for (int i = 0; i < ThisRequestChunkCount; ++i)
+		{
+			const HTTP_DATA_CHUNK Chunk = m_HttpDataChunks[ThisRequestChunkOffset + i];
+
+			if (i > 0)
+			{
+				ResponseDetails << " + ";
+			}
+
+			switch (Chunk.DataChunkType)
+			{
+				case HttpDataChunkFromMemory:
+					ResponseDetails << "mem:" << uint64_t(Chunk.FromMemory.BufferLength);
+					break;
+
+				case HttpDataChunkFromFileHandle:
+					ResponseDetails << "file:";
+					{
+						ResponseDetails << uint64_t(Chunk.FromFileHandle.ByteRange.StartingOffset.QuadPart) << ","
+										<< uint64_t(Chunk.FromFileHandle.ByteRange.Length.QuadPart) << ",";
+
+						std::error_code		  PathEc;
+						HANDLE				  FileHandle = Chunk.FromFileHandle.FileHandle;
+						std::filesystem::path Path		 = PathFromHandle(FileHandle, PathEc);
+
+						if (PathEc)
+						{
+							ResponseDetails << "bad_file(handle=" << reinterpret_cast<uint64_t>(FileHandle) << ",error=" << PathEc.message()
+											<< ")";
+						}
+						else
+						{
+							const uint64_t FileSize = FileSizeFromHandle(FileHandle);
+							ResponseDetails << Path.u8string() << "(" << FileSize << ") handle=" << reinterpret_cast<uint64_t>(FileHandle);
+						}
+					}
+					break;
+
+				case HttpDataChunkFromFragmentCache:
+					ResponseDetails << "frag:???";	// We do not use these
+					break;
+
+				case HttpDataChunkFromFragmentCacheEx:
+					ResponseDetails << "frax:???";	// We do not use these
+					break;
+
+#	if 0  // Not available in older Windows SDKs
+				case HttpDataChunkTrailers:
+					ResponseDetails << "trls:???";	// We do not use these
+					break;
+#	endif
+
+				default:
+					ResponseDetails << "???: " << Chunk.DataChunkType;
+					break;
+			}
+		}
+	};
+
+	if (SendResult == NO_ERROR)
+	{
+		// Synchronous completion, but the completion event will still be posted to IOCP
+
+		ErrorCode.clear();
+	}
+	else if (SendResult == ERROR_IO_PENDING)
+	{
+		// Asynchronous completion, a completion notification will be posted to IOCP
+
+		ErrorCode.clear();
+	}
+	else
+	{
+		ErrorCode = MakeErrorCode(SendResult);
+
+		// An error occurred, no completion will be posted to IOCP
+
+		CancelThreadpoolIo(Iocp);
+
+		// Emit diagnostics
+
+		ExtendableStringBuilder<256> ResponseDetails;
+		EmitReponseDetails(ResponseDetails);
+
+		ZEN_WARN("failed to send HTTP response (error {}: '{}'), request URL: '{}', ({}.{}) response: {}",
+				 SendResult,
+				 ErrorCode.message(),
+				 HttpReq->pRawUrl,
+				 Tx.ServerRequest().SessionId(),
+				 HttpReq->RequestId,
+				 ResponseDetails);
+	}
+}
+
+/** HTTP completion handler for async work
+
+	This is used to allow work to be taken off the request handler threads
+	and to support posting responses asynchronously.
+ */
+
+class HttpAsyncWorkRequest : public HttpSysRequestHandler
+{
+public:
+	HttpAsyncWorkRequest(HttpSysTransaction& Tx, std::function<void(HttpServerRequest&)>&& Response);
+	~HttpAsyncWorkRequest();
+
+	virtual void				   IssueRequest(std::error_code& ErrorCode) override final;
+	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) override;
+
+private:
+	struct AsyncWorkItem : public IWork
+	{
+		virtual void Execute() override;
+
+		AsyncWorkItem(HttpSysTransaction& InTx, std::function<void(HttpServerRequest&)>&& InHandler)
+		: Tx(InTx)
+		, Handler(std::move(InHandler))
+		{
+		}
+
+		HttpSysTransaction&						Tx;
+		std::function<void(HttpServerRequest&)> Handler;
+	};
+
+	Ref<AsyncWorkItem> m_WorkItem;
+};
+
+HttpAsyncWorkRequest::HttpAsyncWorkRequest(HttpSysTransaction& Tx, std::function<void(HttpServerRequest&)>&& Response)
+: HttpSysRequestHandler(Tx)
+{
+	m_WorkItem = new AsyncWorkItem(Tx, std::move(Response));
+}
+
+HttpAsyncWorkRequest::~HttpAsyncWorkRequest()
+{
+}
+
+void
+HttpAsyncWorkRequest::IssueRequest(std::error_code& ErrorCode)
+{
+	ZEN_TRACE_CPU("httpsys::AsyncWork::IssueRequest");
+	ErrorCode.clear();
+
+	Transaction().Server().WorkPool().ScheduleWork(m_WorkItem);
+}
+
+HttpSysRequestHandler*
+HttpAsyncWorkRequest::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
+{
+	// This ought to not be called since there should be no outstanding I/O request
+	// when this completion handler is active
+
+	ZEN_UNUSED(IoResult, NumberOfBytesTransferred);
+
+	ZEN_WARN("Unexpected I/O completion during async work! IoResult: {}, NumberOfBytesTransferred: {}", IoResult, NumberOfBytesTransferred);
+
+	return this;
+}
+
+void
+HttpAsyncWorkRequest::AsyncWorkItem::Execute()
+{
+	ZEN_TRACE_CPU("httpsys::async_execute");
+
+	try
+	{
+		// We need to hold this lock while we're issuing new requests in order to
+		// prevent race conditions between the thread we are running on and any
+		// IOCP service threads. Otherwise the IOCP completion handler can end
+		// up deleting the transaction object before we are done with it!
+		HttpSysTransaction::CompletionMutexScope _(Tx);
+		HttpSysServerRequest&					 ThisRequest = Tx.ServerRequest();
+
+		ThisRequest.m_NextCompletionHandler = nullptr;
+
+		{
+			ZEN_TRACE_CPU("httpsys::HandleRequest");
+			Handler(ThisRequest);
+		}
+
+		// TODO: should Handler be destroyed at this point to ensure there
+		//		 are no outstanding references into state which could be
+		//		 deleted asynchronously as a result of issuing the response?
+
+		if (HttpSysRequestHandler* NextHandler = ThisRequest.m_NextCompletionHandler)
+		{
+			return (void)Tx.IssueNextRequest(NextHandler);
+		}
+		else if (!ThisRequest.IsHandled())
+		{
+			return (void)Tx.IssueNextRequest(new HttpMessageResponseRequest(Tx, 404, "Not found"sv));
+		}
+		else
+		{
+			// "Handled" but no request handler? Shouldn't ever happen
+			return (void)Tx.IssueNextRequest(
+				new HttpMessageResponseRequest(Tx, 500, "Response generated but no request handler scheduled"sv));
+		}
+	}
+	catch (std::exception& Ex)
+	{
+		return (void)Tx.IssueNextRequest(
+			new HttpMessageResponseRequest(Tx, 500, fmt::format("Exception thrown in async work: '{}'", Ex.what())));
+	}
+}
+
+/**
+			  _________
+			 /   _____/ ______________  __ ___________
+			 \_____  \_/ __ \_  __ \  \/ // __ \_  __ \
+			 /        \  ___/|  | \/\   /\  ___/|  | \/
+			/_______  /\___  >__|    \_/  \___  >__|
+					\/     \/                 \/
+*/
+
+HttpSysServer::HttpSysServer(const HttpSysConfig& InConfig)
+: m_Log(logging::Get("http"))
+, m_RequestLog(logging::Get("http_requests"))
+, m_IsRequestLoggingEnabled(InConfig.IsRequestLoggingEnabled)
+, m_IsAsyncResponseEnabled(InConfig.IsAsyncResponseEnabled)
+, m_InitialConfig(InConfig)
+{
+	// Initialize thread pool
+
+	int MinThreadCount;
+	int MaxThreadCount;
+
+	if (m_InitialConfig.ThreadCount == 0)
+	{
+		MinThreadCount = Max(8u, std::thread::hardware_concurrency());
+	}
+	else
+	{
+		MinThreadCount = m_InitialConfig.ThreadCount;
+	}
+
+	MaxThreadCount = MinThreadCount * 2;
+
+	if (m_InitialConfig.IsDedicatedServer)
+	{
+		// In order to limit the potential impact of threads stuck
+		// in locks we allow the thread pool to be oversubscribed
+		// by a fair amount
+
+		MaxThreadCount *= 2;
+	}
+
+	m_IoThreadPool = std::make_unique<WinIoThreadPool>(MinThreadCount, MaxThreadCount);
+
+	if (m_InitialConfig.AsyncWorkThreadCount == 0)
+	{
+		m_InitialConfig.AsyncWorkThreadCount = 16;
+	}
+
+	ULONG Result = HttpInitialize(HTTPAPI_VERSION_2, HTTP_INITIALIZE_SERVER, nullptr);
+
+	if (Result != NO_ERROR)
+	{
+		return;
+	}
+
+	m_IsHttpInitialized = true;
+	m_IsOk				= true;
+
+	ZEN_INFO("http.sys server started in {} mode, using {}-{} I/O threads and {} async worker threads",
+			 m_InitialConfig.IsDedicatedServer ? "DEDICATED" : "NORMAL",
+			 MinThreadCount,
+			 MaxThreadCount,
+			 m_InitialConfig.AsyncWorkThreadCount);
+}
+
+HttpSysServer::~HttpSysServer()
+{
+	if (m_IsHttpInitialized)
+	{
+		ZEN_ERROR("~HttpSysServer() called without calling Close() first");
+	}
+
+	delete m_AsyncWorkPool;
+	m_AsyncWorkPool = nullptr;
+}
+
+void
+HttpSysServer::Close()
+{
+	if (m_IsHttpInitialized)
+	{
+		Cleanup();
+
+		HttpTerminate(HTTP_INITIALIZE_SERVER, nullptr);
+		m_IsHttpInitialized = false;
+	}
+}
+
+int
+HttpSysServer::InitializeServer(int BasePort)
+{
+	using namespace std::literals;
+
+	WideStringBuilder<64> WildcardUrlPath;
+	WildcardUrlPath << u8"http://*:"sv << int64_t(BasePort) << u8"/"sv;
+
+	m_IsOk = false;
+
+	ULONG Result = HttpCreateServerSession(HTTPAPI_VERSION_2, &m_HttpSessionId, 0);
+
+	if (Result != NO_ERROR)
+	{
+		ZEN_ERROR("Failed to create server session for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
+
+		return BasePort;
+	}
+
+	Result = HttpCreateUrlGroup(m_HttpSessionId, &m_HttpUrlGroupId, 0);
+
+	if (Result != NO_ERROR)
+	{
+		ZEN_ERROR("Failed to create URL group for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
+
+		return BasePort;
+	}
+
+	int EffectivePort = BasePort;
+
+	Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, WildcardUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
+
+	// Sharing violation implies the port is being used by another process
+	for (int PortOffset = 1; (Result == ERROR_SHARING_VIOLATION) && (PortOffset < 10); ++PortOffset)
+	{
+		EffectivePort = BasePort + (PortOffset * 100);
+		WildcardUrlPath.Reset();
+		WildcardUrlPath << u8"http://*:"sv << int64_t(EffectivePort) << u8"/"sv;
+
+		Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, WildcardUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
+	}
+
+	m_BaseUris.clear();
+	if (Result == NO_ERROR)
+	{
+		m_BaseUris.push_back(WildcardUrlPath.c_str());
+	}
+	else if (Result == ERROR_ACCESS_DENIED)
+	{
+		// If we can't register the wildcard path, we fall back to local paths
+		// This local paths allow requests originating locally to function, but will not allow
+		// remote origin requests to function.  This can be remedied by using netsh
+		// during an install process to grant permissions to route public access to the appropriate
+		// port for the current user.  eg:
+		// netsh http add urlacl url=http://*:8558/ user=<some_user>
+
+		ZEN_WARN("Unable to register handler using '{}' - falling back to local-only", WideToUtf8(WildcardUrlPath));
+
+		const std::u8string_view Hosts[] = {u8"[::1]"sv, u8"localhost"sv, u8"127.0.0.1"sv};
+
+		ULONG InternalResult = ERROR_SHARING_VIOLATION;
+		for (int PortOffset = 0; (InternalResult == ERROR_SHARING_VIOLATION) && (PortOffset < 10); ++PortOffset)
+		{
+			EffectivePort = BasePort + (PortOffset * 100);
+
+			for (const std::u8string_view Host : Hosts)
+			{
+				WideStringBuilder<64> LocalUrlPath;
+				LocalUrlPath << u8"http://"sv << Host << u8":"sv << int64_t(EffectivePort) << u8"/"sv;
+
+				InternalResult = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, LocalUrlPath.c_str(), HTTP_URL_CONTEXT(0), 0);
+
+				if (InternalResult == NO_ERROR)
+				{
+					ZEN_INFO("Registered local handler '{}'", WideToUtf8(LocalUrlPath));
+
+					m_BaseUris.push_back(LocalUrlPath.c_str());
+				}
+				else
+				{
+					break;
+				}
+			}
+		}
+	}
+
+	if (m_BaseUris.empty())
+	{
+		ZEN_ERROR("Failed to add base URL to URL group for '{}': {:#x}", WideToUtf8(WildcardUrlPath), Result);
+
+		return BasePort;
+	}
+
+	HTTP_BINDING_INFO HttpBindingInfo = {{0}, 0};
+
+	WideStringBuilder<64> QueueName;
+	QueueName << "zenserver_" << EffectivePort;
+
+	Result = HttpCreateRequestQueue(HTTPAPI_VERSION_2,
+									/* Name */ QueueName.c_str(),
+									/* SecurityAttributes */ nullptr,
+									/* Flags */ 0,
+									&m_RequestQueueHandle);
+
+	if (Result != NO_ERROR)
+	{
+		ZEN_ERROR("Failed to create request queue for '{}': {:#x}", WideToUtf8(m_BaseUris.front()), Result);
+
+		return EffectivePort;
+	}
+
+	HttpBindingInfo.Flags.Present	   = 1;
+	HttpBindingInfo.RequestQueueHandle = m_RequestQueueHandle;
+
+	Result = HttpSetUrlGroupProperty(m_HttpUrlGroupId, HttpServerBindingProperty, &HttpBindingInfo, sizeof(HttpBindingInfo));
+
+	if (Result != NO_ERROR)
+	{
+		ZEN_ERROR("Failed to set server binding property for '{}': {:#x}", WideToUtf8(m_BaseUris.front()), Result);
+
+		return EffectivePort;
+	}
+
+	// Configure rejection method. Default is to drop the connection, it's better if we
+	// return an explicit error code when the queue cannot accept more requests
+
+	{
+		HTTP_503_RESPONSE_VERBOSITY VerbosityInformation = Http503ResponseVerbosityLimited;
+
+		Result = HttpSetRequestQueueProperty(m_RequestQueueHandle,
+											 HttpServer503VerbosityProperty,
+											 &VerbosityInformation,
+											 sizeof VerbosityInformation,
+											 0,
+											 0);
+	}
+
+	// Tune the maximum number of pending requests in the http.sys request queue. By default
+	// the value is 1000 which is plenty for single user machines but for dedicated servers
+	// serving many users it makes sense to increase this to a higher number to help smooth
+	// out intermittent stalls like we might experience when GC is triggered
+
+	if (m_InitialConfig.IsDedicatedServer)
+	{
+		ULONG QueueLength = 50000;
+
+		Result = HttpSetRequestQueueProperty(m_RequestQueueHandle, HttpServerQueueLengthProperty, &QueueLength, sizeof QueueLength, 0, 0);
+
+		if (Result != NO_ERROR)
+		{
+			ZEN_WARN("changing request queue length to {} failed: {}", QueueLength, Result);
+		}
+	}
+
+	// Create I/O completion port
+
+	std::error_code ErrorCode;
+	m_IoThreadPool->CreateIocp(m_RequestQueueHandle, HttpSysTransaction::IoCompletionCallback, /* Context */ this, /* out */ ErrorCode);
+
+	if (ErrorCode)
+	{
+		ZEN_ERROR("Failed to create IOCP for '{}': {}", WideToUtf8(m_BaseUris.front()), ErrorCode.message());
+	}
+	else
+	{
+		m_IsOk = true;
+
+		ZEN_INFO("Started http.sys server at '{}'", WideToUtf8(m_BaseUris.front()));
+	}
+
+	// This is not available in all Windows SDK versions so for now we can't use recently
+	// released functionality. We should investigate how to get more recent SDK releases
+	// into the build
+
+#	if 0	
+	if (HttpIsFeatureSupported(/* HttpFeatureHttp3 */ (HTTP_FEATURE_ID) 4))
+	{
+		ZEN_DEBUG("HTTP3 is available");
+	}
+	else
+	{
+		ZEN_DEBUG("HTTP3 is NOT available");
+	}
+#	endif
+
+	return EffectivePort;
+}
+
+void
+HttpSysServer::Cleanup()
+{
+	++m_IsShuttingDown;
+
+	if (m_RequestQueueHandle)
+	{
+		HttpCloseRequestQueue(m_RequestQueueHandle);
+		m_RequestQueueHandle = nullptr;
+	}
+
+	if (m_HttpUrlGroupId)
+	{
+		HttpCloseUrlGroup(m_HttpUrlGroupId);
+		m_HttpUrlGroupId = 0;
+	}
+
+	if (m_HttpSessionId)
+	{
+		HttpCloseServerSession(m_HttpSessionId);
+		m_HttpSessionId = 0;
+	}
+}
+
+WorkerThreadPool&
+HttpSysServer::WorkPool()
+{
+	if (!m_AsyncWorkPool)
+	{
+		RwLock::ExclusiveLockScope _(m_AsyncWorkPoolInitLock);
+
+		if (!m_AsyncWorkPool)
+		{
+			m_AsyncWorkPool = new WorkerThreadPool(m_InitialConfig.AsyncWorkThreadCount, "http_async");
+		}
+	}
+
+	return *m_AsyncWorkPool;
+}
+
+void
+HttpSysServer::StartServer()
+{
+	const int InitialRequestCount = 32;
+
+	for (int i = 0; i < InitialRequestCount; ++i)
+	{
+		IssueNewRequestMaybe();
+	}
+}
+
+void
+HttpSysServer::Run(bool IsInteractive)
+{
+	if (IsInteractive)
+	{
+		zen::logging::ConsoleLog().info("Zen Server running. Press ESC or Q to quit");
+	}
+
+	do
+	{
+		// int WaitTimeout = -1;
+		int WaitTimeout = 100;
+
+		if (IsInteractive)
+		{
+			WaitTimeout = 1000;
+
+			if (_kbhit() != 0)
+			{
+				char c = (char)_getch();
+
+				if (c == 27 || c == 'Q' || c == 'q')
+				{
+					RequestApplicationExit(0);
+				}
+			}
+		}
+
+		m_ShutdownEvent.Wait(WaitTimeout);
+		UpdateLofreqTimerValue();
+	} while (!IsApplicationExitRequested());
+}
+
+void
+HttpSysServer::OnHandlingNewRequest()
+{
+	if (--m_PendingRequests > m_MinPendingRequests)
+	{
+		// We have more than the minimum number of requests pending, just let someone else
+		// enqueue new requests. This should be the common case as we check if we need to
+		// enqueue more requests before exiting the completion handler.
+		return;
+	}
+
+	IssueNewRequestMaybe();
+}
+
+void
+HttpSysServer::IssueNewRequestMaybe()
+{
+	if (m_IsShuttingDown.load(std::memory_order::acquire))
+	{
+		return;
+	}
+
+	if (m_PendingRequests.load(std::memory_order::relaxed) >= m_MaxPendingRequests)
+	{
+		return;
+	}
+
+	std::unique_ptr<HttpSysTransaction> Request = std::make_unique<HttpSysTransaction>(*this);
+
+	std::error_code ErrorCode;
+	Request->IssueInitialRequest(ErrorCode);
+
+	if (ErrorCode)
+	{
+		// No request was actually issued. What is the appropriate response?
+
+		return;
+	}
+
+	// This may end up exceeding the MaxPendingRequests limit, but it's not
+	// really a problem. I'm doing it this way mostly to avoid dealing with
+	// exceptions here
+	++m_PendingRequests;
+
+	Request.release();
+}
+
+void
+HttpSysServer::RegisterService(const char* UrlPath, HttpService& Service)
+{
+	if (UrlPath[0] == '/')
+	{
+		++UrlPath;
+	}
+
+	const std::wstring PathUtf16 = UTF8_to_UTF16(UrlPath);
+	Service.SetUriPrefixLength(PathUtf16.size() + 1 /* leading slash */);
+
+	// Convert to wide string
+
+	for (const std::wstring& BaseUri : m_BaseUris)
+	{
+		std::wstring Url16 = BaseUri + PathUtf16;
+
+		ULONG Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, Url16.c_str(), HTTP_URL_CONTEXT(&Service), 0 /* Reserved */);
+
+		if (Result != NO_ERROR)
+		{
+			ZEN_ERROR("HttpAddUrlToUrlGroup failed with result: '{}'", GetSystemErrorAsString(Result));
+
+			return;
+		}
+	}
+}
+
+void
+HttpSysServer::UnregisterService(const char* UrlPath, HttpService& Service)
+{
+	ZEN_UNUSED(Service);
+
+	if (UrlPath[0] == '/')
+	{
+		++UrlPath;
+	}
+
+	const std::wstring PathUtf16 = UTF8_to_UTF16(UrlPath);
+
+	// Convert to wide string
+
+	for (const std::wstring& BaseUri : m_BaseUris)
+	{
+		std::wstring Url16 = BaseUri + PathUtf16;
+
+		ULONG Result = HttpRemoveUrlFromUrlGroup(m_HttpUrlGroupId, Url16.c_str(), 0);
+
+		if (Result != NO_ERROR)
+		{
+			ZEN_ERROR("HttpRemoveUrlFromUrlGroup failed with result: '{}'", GetSystemErrorAsString(Result));
+		}
+	}
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+HttpSysTransaction::HttpSysTransaction(HttpSysServer& Server) : m_HttpServer(Server), m_CompletionHandler(&m_InitialHttpHandler)
+{
+}
+
+HttpSysTransaction::~HttpSysTransaction()
+{
+}
+
+PTP_IO
+HttpSysTransaction::Iocp()
+{
+	return m_HttpServer.m_IoThreadPool->Iocp();
+}
+
+HANDLE
+HttpSysTransaction::RequestQueueHandle()
+{
+	return m_HttpServer.m_RequestQueueHandle;
+}
+
+void
+HttpSysTransaction::IssueInitialRequest(std::error_code& ErrorCode)
+{
+	m_InitialHttpHandler.IssueRequest(ErrorCode);
+}
+
+thread_local bool		t_IsHttpSysThreadNamed = false;
+static std::atomic<int> HttpSysThreadIndex	   = 0;
+
+static void
+NameCurrentHttpSysThread()
+{
+	t_IsHttpSysThreadNamed						 = true;
+	const int						 ThreadIndex = ++HttpSysThreadIndex;
+	zen::ExtendableStringBuilder<16> ThreadName;
+	ThreadName << "httpio_" << ThreadIndex;
+	SetCurrentThreadName(ThreadName);
+}
+
+void
+HttpSysTransaction::IoCompletionCallback(PTP_CALLBACK_INSTANCE Instance,
+										 PVOID				   pContext /* HttpSysServer */,
+										 PVOID				   pOverlapped,
+										 ULONG				   IoResult,
+										 ULONG_PTR			   NumberOfBytesTransferred,
+										 PTP_IO				   Io)
+{
+	ZEN_UNUSED(Io, Instance);
+
+	// Assign names to threads for context
+
+	if (!t_IsHttpSysThreadNamed)
+	{
+		NameCurrentHttpSysThread();
+	}
+
+	// Note that for a given transaction we may be in this completion function on more
+	// than one thread at any given moment. This means we need to be careful about what
+	// happens in here
+
+	HttpSysTransaction* Transaction = CONTAINING_RECORD(pOverlapped, HttpSysTransaction, m_HttpOverlapped);
+
+	if (Transaction->HandleCompletion(IoResult, NumberOfBytesTransferred) == HttpSysTransaction::Status::kDone)
+	{
+		delete Transaction;
+	}
+
+	// Ensure new requests are enqueued as necessary. We do this here instead
+	// of inside the transaction completion handler now to avoid spending time
+	// in unrelated API calls while holding the transaction lock
+
+	if (HttpSysServer* HttpServer = reinterpret_cast<HttpSysServer*>(pContext))
+	{
+		HttpServer->IssueNewRequestMaybe();
+	}
+}
+
+bool
+HttpSysTransaction::IssueNextRequest(HttpSysRequestHandler* NewCompletionHandler)
+{
+	ZEN_TRACE_CPU("httpsys::Transaction::IssueNextRequest");
+
+	HttpSysRequestHandler* CurrentHandler = m_CompletionHandler;
+	m_CompletionHandler					  = NewCompletionHandler;
+
+	auto _ = MakeGuard([this, CurrentHandler] {
+		if ((CurrentHandler != &m_InitialHttpHandler) && (CurrentHandler != m_CompletionHandler))
+		{
+			delete CurrentHandler;
+		}
+	});
+
+	if (NewCompletionHandler == nullptr)
+	{
+		return false;
+	}
+
+	try
+	{
+		std::error_code ErrorCode;
+		m_CompletionHandler->IssueRequest(ErrorCode);
+
+		if (!ErrorCode)
+		{
+			return true;
+		}
+
+		ZEN_WARN("IssueRequest() failed: '{}'", ErrorCode.message());
+	}
+	catch (std::exception& Ex)
+	{
+		ZEN_ERROR("exception caught in IssueNextRequest(): '{}'", Ex.what());
+	}
+
+	// something went wrong, no request is pending
+	m_CompletionHandler = nullptr;
+
+	return false;
+}
+
+HttpSysTransaction::Status
+HttpSysTransaction::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
+{
+	// We use this to ensure sequential execution of completion handlers
+	// for any given transaction. It also ensures all member variables are
+	// in a consistent state for the current thread
+
+	RwLock::ExclusiveLockScope _(m_CompletionMutex);
+
+	bool IsRequestPending = false;
+
+	if (HttpSysRequestHandler* CurrentHandler = m_CompletionHandler)
+	{
+		if ((CurrentHandler == &m_InitialHttpHandler) && m_InitialHttpHandler.IsInitialRequest())
+		{
+			// Ensure we have a sufficient number of pending requests outstanding
+			m_HttpServer.OnHandlingNewRequest();
+		}
+
+		auto NewCompletionHandler = CurrentHandler->HandleCompletion(IoResult, NumberOfBytesTransferred);
+
+		IsRequestPending = IssueNextRequest(NewCompletionHandler);
+	}
+
+	if (IsRequestPending)
+	{
+		// There is another request pending on this transaction, so it needs to remain valid
+		return Status::kRequestPending;
+	}
+
+	if (m_HttpServer.m_IsRequestLoggingEnabled)
+	{
+		if (m_HandlerRequest.has_value())
+		{
+			m_HttpServer.m_RequestLog.info("{} {}", ToString(m_HandlerRequest->RequestVerb()), m_HandlerRequest->RelativeUri());
+		}
+	}
+
+	// Transaction done, caller should clean up (delete) this instance
+	return Status::kDone;
+}
+
+HttpSysServerRequest&
+HttpSysTransaction::InvokeRequestHandler(HttpService& Service, IoBuffer Payload)
+{
+	HttpSysServerRequest& ThisRequest = m_HandlerRequest.emplace(*this, Service, Payload);
+
+	// Default request handling
+
+	if (!HandlePackageOffers(Service, ThisRequest, m_PackageHandler))
+	{
+		Service.HandleRequest(ThisRequest);
+	}
+
+	return ThisRequest;
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+HttpSysServerRequest::HttpSysServerRequest(HttpSysTransaction& Tx, HttpService& Service, IoBuffer PayloadBuffer)
+: m_HttpTx(Tx)
+, m_PayloadBuffer(std::move(PayloadBuffer))
+{
+	const HTTP_REQUEST* HttpRequestPtr = Tx.HttpRequest();
+
+	const int PrefixLength	= Service.UriPrefixLength();
+	const int AbsPathLength = HttpRequestPtr->CookedUrl.AbsPathLength / sizeof(wchar_t);
+
+	HttpContentType AcceptContentType = HttpContentType::kUnknownContentType;
+
+	if (AbsPathLength >= PrefixLength)
+	{
+		// We convert the URI immediately because most of the code involved prefers to deal
+		// with utf8. This is overhead which I'd prefer to avoid but for now we just have
+		// to live with it
+
+		WideToUtf8({(wchar_t*)HttpRequestPtr->CookedUrl.pAbsPath + PrefixLength, gsl::narrow<size_t>(AbsPathLength - PrefixLength)},
+				   m_UriUtf8);
+
+		std::string_view UriSuffix8{m_UriUtf8};
+
+		m_UriWithExtension = UriSuffix8;  // Retain URI with extension for user access
+		m_Uri			   = UriSuffix8;
+
+		const size_t LastComponentIndex = UriSuffix8.find_last_of('/');
+
+		if (LastComponentIndex != std::string_view::npos)
+		{
+			UriSuffix8.remove_prefix(LastComponentIndex);
+		}
+
+		const size_t LastDotIndex = UriSuffix8.find_last_of('.');
+
+		if (LastDotIndex != std::string_view::npos)
+		{
+			UriSuffix8.remove_prefix(LastDotIndex + 1);
+
+			AcceptContentType = ParseContentType(UriSuffix8);
+			if (AcceptContentType != HttpContentType::kUnknownContentType)
+			{
+				m_Uri.remove_suffix(UriSuffix8.size() + 1);
+			}
+		}
+	}
+	else
+	{
+		m_UriUtf8.Reset();
+		m_Uri			   = {};
+		m_UriWithExtension = {};
+	}
+
+	if (uint16_t QueryStringLength = HttpRequestPtr->CookedUrl.QueryStringLength)
+	{
+		--QueryStringLength;  // We skip the leading question mark
+
+		WideToUtf8({(wchar_t*)(HttpRequestPtr->CookedUrl.pQueryString) + 1, QueryStringLength / sizeof(wchar_t)}, m_QueryStringUtf8);
+	}
+	else
+	{
+		m_QueryStringUtf8.Reset();
+	}
+
+	m_QueryString	= std::string_view(m_QueryStringUtf8);
+	m_Verb			= TranslateHttpVerb(HttpRequestPtr->Verb);
+	m_ContentLength = GetContentLength(HttpRequestPtr);
+	m_ContentType	= GetContentType(HttpRequestPtr);
+
+	// It an explicit content type extension was specified then we'll use that over any
+	// Accept: header value that may be present
+
+	if (AcceptContentType != HttpContentType::kUnknownContentType)
+	{
+		m_AcceptType = AcceptContentType;
+	}
+	else
+	{
+		m_AcceptType = GetAcceptType(HttpRequestPtr);
+	}
+
+	if (m_Verb == HttpVerb::kHead)
+	{
+		SetSuppressResponseBody();
+	}
+}
+
+HttpSysServerRequest::~HttpSysServerRequest()
+{
+}
+
+Oid
+HttpSysServerRequest::ParseSessionId() const
+{
+	const HTTP_REQUEST* HttpRequestPtr = m_HttpTx.HttpRequest();
+
+	for (int i = 0; i < HttpRequestPtr->Headers.UnknownHeaderCount; ++i)
+	{
+		HTTP_UNKNOWN_HEADER& Header = HttpRequestPtr->Headers.pUnknownHeaders[i];
+		std::string_view	 HeaderName{Header.pName, Header.NameLength};
+
+		if (HeaderName == "UE-Session"sv)
+		{
+			if (Header.RawValueLength == Oid::StringLength)
+			{
+				return Oid::FromHexString({Header.pRawValue, Header.RawValueLength});
+			}
+		}
+	}
+
+	return {};
+}
+
+uint32_t
+HttpSysServerRequest::ParseRequestId() const
+{
+	const HTTP_REQUEST* HttpRequestPtr = m_HttpTx.HttpRequest();
+
+	for (int i = 0; i < HttpRequestPtr->Headers.UnknownHeaderCount; ++i)
+	{
+		HTTP_UNKNOWN_HEADER& Header = HttpRequestPtr->Headers.pUnknownHeaders[i];
+		std::string_view	 HeaderName{Header.pName, Header.NameLength};
+
+		if (HeaderName == "UE-Request"sv)
+		{
+			std::string_view RequestValue{Header.pRawValue, Header.RawValueLength};
+			uint32_t		 RequestId = 0;
+			std::from_chars(RequestValue.data(), RequestValue.data() + RequestValue.size(), RequestId);
+			return RequestId;
+		}
+	}
+
+	return 0;
+}
+
+IoBuffer
+HttpSysServerRequest::ReadPayload()
+{
+	return m_PayloadBuffer;
+}
+
+void
+HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode)
+{
+	ZEN_ASSERT(IsHandled() == false);
+
+	auto Response = new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode);
+
+	if (SuppressBody())
+	{
+		Response->SuppressResponseBody();
+	}
+
+	m_NextCompletionHandler = Response;
+
+	SetIsHandled();
+}
+
+void
+HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::span<IoBuffer> Blobs)
+{
+	ZEN_ASSERT(IsHandled() == false);
+
+	auto Response = new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode, ContentType, Blobs);
+
+	if (SuppressBody())
+	{
+		Response->SuppressResponseBody();
+	}
+
+	m_NextCompletionHandler = Response;
+
+	SetIsHandled();
+}
+
+void
+HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::u8string_view ResponseString)
+{
+	ZEN_ASSERT(IsHandled() == false);
+
+	auto Response =
+		new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode, ContentType, ResponseString.data(), ResponseString.size());
+
+	if (SuppressBody())
+	{
+		Response->SuppressResponseBody();
+	}
+
+	m_NextCompletionHandler = Response;
+
+	SetIsHandled();
+}
+
+void
+HttpSysServerRequest::WriteResponseAsync(std::function<void(HttpServerRequest&)>&& ContinuationHandler)
+{
+	if (m_HttpTx.Server().IsAsyncResponseEnabled())
+	{
+		m_NextCompletionHandler = new HttpAsyncWorkRequest(m_HttpTx, std::move(ContinuationHandler));
+	}
+	else
+	{
+		ContinuationHandler(m_HttpTx.ServerRequest());
+	}
+}
+
+bool
+HttpSysServerRequest::TryGetRanges(HttpRanges& Ranges)
+{
+	HTTP_REQUEST*			 Req		 = m_HttpTx.HttpRequest();
+	const HTTP_KNOWN_HEADER& RangeHeader = Req->Headers.KnownHeaders[HttpHeaderRange];
+
+	return TryParseHttpRangeHeader({RangeHeader.pRawValue, RangeHeader.RawValueLength}, Ranges);
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+InitialRequestHandler::InitialRequestHandler(HttpSysTransaction& InRequest) : HttpSysRequestHandler(InRequest)
+{
+}
+
+InitialRequestHandler::~InitialRequestHandler()
+{
+}
+
+void
+InitialRequestHandler::IssueRequest(std::error_code& ErrorCode)
+{
+	ZEN_TRACE_CPU("httpsys::Request::IssueRequest");
+
+	HttpSysTransaction& Tx		= Transaction();
+	PTP_IO				Iocp	= Tx.Iocp();
+	HTTP_REQUEST*		HttpReq = Tx.HttpRequest();
+
+	StartThreadpoolIo(Iocp);
+
+	ULONG HttpApiResult;
+
+	if (IsInitialRequest())
+	{
+		HttpApiResult = HttpReceiveHttpRequest(Tx.RequestQueueHandle(),
+											   HTTP_NULL_ID,
+											   HTTP_RECEIVE_REQUEST_FLAG_COPY_BODY,
+											   HttpReq,
+											   RequestBufferSize(),
+											   NULL,
+											   Tx.Overlapped());
+	}
+	else
+	{
+		// The http.sys team recommends limiting the size to 128KB
+		static const uint64_t kMaxBytesPerApiCall = 128 * 1024;
+
+		uint64_t	   BytesToRead		   = m_ContentLength - m_CurrentPayloadOffset;
+		const uint64_t BytesToReadThisCall = zen::Min(BytesToRead, kMaxBytesPerApiCall);
+		void*		   BufferWriteCursor   = reinterpret_cast<uint8_t*>(m_PayloadBuffer.MutableData()) + m_CurrentPayloadOffset;
+
+		HttpApiResult = HttpReceiveRequestEntityBody(Tx.RequestQueueHandle(),
+													 HttpReq->RequestId,
+													 0, /* Flags */
+													 BufferWriteCursor,
+													 gsl::narrow<ULONG>(BytesToReadThisCall),
+													 nullptr,  // BytesReturned
+													 Tx.Overlapped());
+	}
+
+	if (HttpApiResult != ERROR_IO_PENDING && HttpApiResult != NO_ERROR)
+	{
+		CancelThreadpoolIo(Iocp);
+
+		ErrorCode = MakeErrorCode(HttpApiResult);
+
+		ZEN_WARN("HttpReceiveHttpRequest failed, error: '{}'", ErrorCode.message());
+
+		return;
+	}
+
+	ErrorCode.clear();
+}
+
+HttpSysRequestHandler*
+InitialRequestHandler::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
+{
+	auto _ = MakeGuard([&] { m_IsInitialRequest = false; });
+
+	switch (IoResult)
+	{
+		default:
+		case ERROR_OPERATION_ABORTED:
+			return nullptr;
+
+		case ERROR_MORE_DATA:  // Insufficient buffer space
+		case NO_ERROR:
+			break;
+	}
+
+	ZEN_TRACE_CPU("httpsys::HandleCompletion");
+
+	// Route request
+
+	try
+	{
+		HTTP_REQUEST* HttpReq = HttpRequest();
+
+#	if 0
+		for (int i = 0; i < HttpReq->RequestInfoCount; ++i)
+		{
+			auto& ReqInfo = HttpReq->pRequestInfo[i];
+
+			switch (ReqInfo.InfoType)
+			{
+				case HttpRequestInfoTypeRequestTiming:
+					{
+						const HTTP_REQUEST_TIMING_INFO* TimingInfo = reinterpret_cast<HTTP_REQUEST_TIMING_INFO*>(ReqInfo.pInfo);
+
+						ZEN_INFO("");
+					}
+					break;
+				case HttpRequestInfoTypeAuth:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeChannelBind:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeSslProtocol:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeSslTokenBindingDraft:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeSslTokenBinding:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeTcpInfoV0:
+					{
+						const TCP_INFO_v0* TcpInfo = reinterpret_cast<const TCP_INFO_v0*>(ReqInfo.pInfo);
+
+						ZEN_INFO("");
+					}
+					break;
+				case HttpRequestInfoTypeRequestSizing:
+					{
+						const HTTP_REQUEST_SIZING_INFO* SizingInfo = reinterpret_cast<const HTTP_REQUEST_SIZING_INFO*>(ReqInfo.pInfo);
+						ZEN_INFO("");
+					}
+					break;
+				case HttpRequestInfoTypeQuicStats:
+					ZEN_INFO("");
+					break;
+				case HttpRequestInfoTypeTcpInfoV1:
+					{
+						const TCP_INFO_v1* TcpInfo = reinterpret_cast<const TCP_INFO_v1*>(ReqInfo.pInfo);
+
+						ZEN_INFO("");
+					}
+					break;
+			}
+		}
+#	endif
+
+		if (HttpService* Service = reinterpret_cast<HttpService*>(HttpReq->UrlContext))
+		{
+			if (m_IsInitialRequest)
+			{
+				m_ContentLength					  = GetContentLength(HttpReq);
+				const HttpContentType ContentType = GetContentType(HttpReq);
+
+				if (m_ContentLength)
+				{
+					// Handle initial chunk read by copying any payload which has already been copied
+					// into our embedded request buffer
+
+					m_PayloadBuffer = IoBuffer(m_ContentLength);
+					m_PayloadBuffer.SetContentType(ContentType);
+
+					uint64_t	   BytesToRead		 = m_ContentLength;
+					uint8_t* const BufferBase		 = reinterpret_cast<uint8_t*>(m_PayloadBuffer.MutableData());
+					uint8_t*	   BufferWriteCursor = BufferBase;
+
+					const int EntityChunkCount = HttpReq->EntityChunkCount;
+
+					for (int i = 0; i < EntityChunkCount; ++i)
+					{
+						HTTP_DATA_CHUNK& EntityChunk = HttpReq->pEntityChunks[i];
+
+						ZEN_ASSERT(EntityChunk.DataChunkType == HttpDataChunkFromMemory);
+
+						const uint64_t BufferLength = EntityChunk.FromMemory.BufferLength;
+
+						ZEN_ASSERT(BufferLength <= BytesToRead);
+
+						memcpy(BufferWriteCursor, EntityChunk.FromMemory.pBuffer, BufferLength);
+
+						BufferWriteCursor += BufferLength;
+						BytesToRead -= BufferLength;
+					}
+
+					m_CurrentPayloadOffset = BufferWriteCursor - BufferBase;
+				}
+			}
+			else
+			{
+				m_CurrentPayloadOffset += NumberOfBytesTransferred;
+			}
+
+			if (m_CurrentPayloadOffset != m_ContentLength)
+			{
+				// Body not complete, issue another read request to receive more body data
+				return this;
+			}
+
+			// Request body received completely
+
+			m_PayloadBuffer.MakeImmutable();
+
+			HttpSysServerRequest& ThisRequest = Transaction().InvokeRequestHandler(*Service, m_PayloadBuffer);
+
+			if (HttpSysRequestHandler* Response = ThisRequest.m_NextCompletionHandler)
+			{
+				return Response;
+			}
+
+			if (!ThisRequest.IsHandled())
+			{
+				return new HttpMessageResponseRequest(Transaction(), 404, "Not found"sv);
+			}
+		}
+
+		// Unable to route
+		return new HttpMessageResponseRequest(Transaction(), 404, "No suitable route found"sv);
+	}
+	catch (std::system_error& SystemError)
+	{
+		if (IsOOM(SystemError.code()) || IsOOD(SystemError.code()))
+		{
+			return new HttpMessageResponseRequest(Transaction(), (uint16_t)HttpResponseCode::InsufficientStorage, SystemError.what());
+		}
+
+		ZEN_ERROR("Caught system error exception while handling request: {}", SystemError.what());
+		return new HttpMessageResponseRequest(Transaction(), (uint16_t)HttpResponseCode::InternalServerError, SystemError.what());
+	}
+	catch (std::bad_alloc& BadAlloc)
+	{
+		return new HttpMessageResponseRequest(Transaction(), (uint16_t)HttpResponseCode::InsufficientStorage, BadAlloc.what());
+	}
+	catch (std::exception& ex)
+	{
+		ZEN_ERROR("Caught exception while handling request: '{}'", ex.what());
+		return new HttpMessageResponseRequest(Transaction(), (uint16_t)HttpResponseCode::InternalServerError, ex.what());
+	}
+}
+
+//////////////////////////////////////////////////////////////////////////
+//
+// HttpServer interface implementation
+//
+
+int
+HttpSysServer::Initialize(int BasePort)
+{
+	int EffectivePort = InitializeServer(BasePort);
+	StartServer();
+	return EffectivePort;
+}
+
+void
+HttpSysServer::RequestExit()
+{
+	m_ShutdownEvent.Set();
+}
+void
+HttpSysServer::RegisterService(HttpService& Service)
+{
+	RegisterService(Service.BaseUri(), Service);
+}
+
+Ref<HttpServer>
+CreateHttpSysServer(HttpSysConfig Config)
+{
+	return Ref<HttpServer>(new HttpSysServer(Config));
+}
+
+}  // namespace zen
+#endif