HttpClient using libcurl, Unix Sockets for HTTP. HTTPS support (#770)

The main goal of this change is to eliminate the cpr back-end altogether and replace it with the curl implementation. I would expect to drop cpr as soon as we feel happy with the libcurl back-end. That would leave us with a direct dependency on libcurl only, and cpr can be eliminated as a dependency.

### HttpClient Backend Overhaul
- Implemented a new **libcurl-based HttpClient** backend (`httpclientcurl.cpp`, ~2000 lines)
  as an alternative to the cpr-based one
- Made HttpClient backend **configurable at runtime** via constructor arguments
  and `-httpclient=...` CLI option (for zen, zenserver, and tests)
- Extended HttpClient test suite to cover multipart/content-range scenarios

### Unix Domain Socket Support
- Added Unix domain socket support to **httpasio** (server side)
- Added Unix domain socket support to **HttpClient**
- Added Unix domain socket support to **HttpWsClient** (WebSocket client)
- Templatized `HttpServerConnectionT<SocketType>` and `WsAsioConnectionT<SocketType>`
  to handle TCP, Unix, and SSL sockets uniformly via `if constexpr` dispatch

### HTTPS Support
- Added **preliminary HTTPS support to httpasio** (for Mac/Linux via OpenSSL)
- Added **basic HTTPS support for http.sys** (Windows)
- Implemented HTTPS test for httpasio
- Split `InitializeServer` into smaller sub-functions for http.sys

### Other Notable Changes
- Improved **zenhttp-test stability** with dynamic port allocation
- Enhanced port retry logic in http.sys (handles ERROR_ACCESS_DENIED)
- Fatal signal/exception handlers for backtrace generation in tests
- Added `zen bench http` subcommand to exercise network + HTTP client/server communication stack

1 files changed, 46 insertions, 18 deletions

diff --git a/src/zenhttp/servers/wsasio.cpp b/src/zenhttp/servers/wsasio.cpp
index b2543277a..5ae48f5b3 100644
--- a/src/zenhttp/servers/wsasio.cpp
+++ b/src/zenhttp/servers/wsasio.cpp
@@ -1,6 +1,7 @@
 // Copyright Epic Games, Inc. All Rights Reserved.
 
 #include "wsasio.h"
+#include "asio_socket_traits.h"
 #include "wsframecodec.h"
 
 #include <zencore/logging.h>
@@ -17,14 +18,16 @@ WsLog()
 
 //////////////////////////////////////////////////////////////////////////
 
-WsAsioConnection::WsAsioConnection(std::unique_ptr<asio::ip::tcp::socket> Socket, IWebSocketHandler& Handler, HttpServer* Server)
+template<typename SocketType>
+WsAsioConnectionT<SocketType>::WsAsioConnectionT(std::unique_ptr<SocketType> Socket, IWebSocketHandler& Handler, HttpServer* Server)
 : m_Socket(std::move(Socket))
 , m_Handler(Handler)
 , m_HttpServer(Server)
 {
 }
 
-WsAsioConnection::~WsAsioConnection()
+template<typename SocketType>
+WsAsioConnectionT<SocketType>::~WsAsioConnectionT()
 {
 	m_IsOpen.store(false);
 	if (m_HttpServer)
@@ -33,14 +36,16 @@ WsAsioConnection::~WsAsioConnection()
 	}
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::Start()
+WsAsioConnectionT<SocketType>::Start()
 {
 	EnqueueRead();
 }
 
+template<typename SocketType>
 bool
-WsAsioConnection::IsOpen() const
+WsAsioConnectionT<SocketType>::IsOpen() const
 {
 	return m_IsOpen.load(std::memory_order_relaxed);
 }
@@ -50,23 +55,25 @@ WsAsioConnection::IsOpen() const
 // Read loop
 //
 
+template<typename SocketType>
 void
-WsAsioConnection::EnqueueRead()
+WsAsioConnectionT<SocketType>::EnqueueRead()
 {
 	if (!m_IsOpen.load(std::memory_order_relaxed))
 	{
 		return;
 	}
 
-	Ref<WsAsioConnection> Self(this);
+	Ref<WsAsioConnectionT> Self(this);
 
 	asio::async_read(*m_Socket, m_ReadBuffer, asio::transfer_at_least(1), [Self](const asio::error_code& Ec, std::size_t ByteCount) {
 		Self->OnDataReceived(Ec, ByteCount);
 	});
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::OnDataReceived(const asio::error_code& Ec, [[maybe_unused]] std::size_t ByteCount)
+WsAsioConnectionT<SocketType>::OnDataReceived(const asio::error_code& Ec, [[maybe_unused]] std::size_t ByteCount)
 {
 	if (Ec)
 	{
@@ -90,8 +97,9 @@ WsAsioConnection::OnDataReceived(const asio::error_code& Ec, [[maybe_unused]] st
 	}
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::ProcessReceivedData()
+WsAsioConnectionT<SocketType>::ProcessReceivedData()
 {
 	while (m_ReadBuffer.size() > 0)
 	{
@@ -162,8 +170,8 @@ WsAsioConnection::ProcessReceivedData()
 
 					// Shut down the socket
 					std::error_code ShutdownEc;
-					m_Socket->shutdown(asio::socket_base::shutdown_both, ShutdownEc);
-					m_Socket->close(ShutdownEc);
+					SocketTraits<SocketType>::ShutdownBoth(*m_Socket, ShutdownEc);
+					SocketTraits<SocketType>::Close(*m_Socket, ShutdownEc);
 					return;
 				}
 
@@ -179,8 +187,9 @@ WsAsioConnection::ProcessReceivedData()
 // Write queue
 //
 
+template<typename SocketType>
 void
-WsAsioConnection::SendText(std::string_view Text)
+WsAsioConnectionT<SocketType>::SendText(std::string_view Text)
 {
 	if (!m_IsOpen.load(std::memory_order_relaxed))
 	{
@@ -192,8 +201,9 @@ WsAsioConnection::SendText(std::string_view Text)
 	EnqueueWrite(std::move(Frame));
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::SendBinary(std::span<const uint8_t> Data)
+WsAsioConnectionT<SocketType>::SendBinary(std::span<const uint8_t> Data)
 {
 	if (!m_IsOpen.load(std::memory_order_relaxed))
 	{
@@ -204,14 +214,16 @@ WsAsioConnection::SendBinary(std::span<const uint8_t> Data)
 	EnqueueWrite(std::move(Frame));
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::Close(uint16_t Code, std::string_view Reason)
+WsAsioConnectionT<SocketType>::Close(uint16_t Code, std::string_view Reason)
 {
 	DoClose(Code, Reason);
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::DoClose(uint16_t Code, std::string_view Reason)
+WsAsioConnectionT<SocketType>::DoClose(uint16_t Code, std::string_view Reason)
 {
 	if (!m_IsOpen.exchange(false))
 	{
@@ -227,8 +239,9 @@ WsAsioConnection::DoClose(uint16_t Code, std::string_view Reason)
 	m_Handler.OnWebSocketClose(*this, Code, Reason);
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::EnqueueWrite(std::vector<uint8_t> Frame)
+WsAsioConnectionT<SocketType>::EnqueueWrite(std::vector<uint8_t> Frame)
 {
 	if (m_HttpServer)
 	{
@@ -252,8 +265,9 @@ WsAsioConnection::EnqueueWrite(std::vector<uint8_t> Frame)
 	}
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::FlushWriteQueue()
+WsAsioConnectionT<SocketType>::FlushWriteQueue()
 {
 	std::vector<uint8_t> Frame;
 
@@ -272,7 +286,7 @@ WsAsioConnection::FlushWriteQueue()
 		return;
 	}
 
-	Ref<WsAsioConnection> Self(this);
+	Ref<WsAsioConnectionT> Self(this);
 
 	// Move Frame into a shared_ptr so we can create the buffer and capture ownership
 	// in the same async_write call without evaluation order issues.
@@ -283,8 +297,9 @@ WsAsioConnection::FlushWriteQueue()
 					  [Self, OwnedFrame](const asio::error_code& Ec, std::size_t ByteCount) { Self->OnWriteComplete(Ec, ByteCount); });
 }
 
+template<typename SocketType>
 void
-WsAsioConnection::OnWriteComplete(const asio::error_code& Ec, [[maybe_unused]] std::size_t ByteCount)
+WsAsioConnectionT<SocketType>::OnWriteComplete(const asio::error_code& Ec, [[maybe_unused]] std::size_t ByteCount)
 {
 	if (Ec)
 	{
@@ -308,4 +323,17 @@ WsAsioConnection::OnWriteComplete(const asio::error_code& Ec, [[maybe_unused]] s
 	FlushWriteQueue();
 }
 
+//////////////////////////////////////////////////////////////////////////
+// Explicit template instantiations
+
+template class WsAsioConnectionT<asio::ip::tcp::socket>;
+
+#if defined(ASIO_HAS_LOCAL_SOCKETS)
+template class WsAsioConnectionT<asio::local::stream_protocol::socket>;
+#endif
+
+#if ZEN_USE_OPENSSL
+template class WsAsioConnectionT<asio::ssl::stream<asio::ip::tcp::socket>>;
+#endif
+
 }  // namespace zen::asio_http