Transparent proxy mode (#823)

Adds a **transparent TCP proxy mode** to zenserver (activated via `zenserver proxy`), allowing it to sit between clients and upstream Zen servers to inspect and monitor HTTP/1.x traffic in real time. Primarily useful during development, to be able to observe multi-server/client interactions in one place.

- **Dedicated proxy port** -- Proxy mode defaults to port 8118 with its own data directory to avoid collisions with a normal zenserver instance.
- **TCP proxy core** (`src/zenserver/proxy/`) -- A new transparent TCP proxy that forwards connections to upstream targets, with support for both TCP/IP and Unix socket listeners. Multi-threaded I/O for connection handling. Supports Unix domain sockets for both upstream/downstream.
- **HTTP traffic inspection** -- Parses HTTP/1.x request/response streams inline to extract method, path, status, content length, and WebSocket upgrades without breaking the proxied data.
- **Proxy dashboard** -- A web UI showing live connection stats, per-target request counts, active connections, bytes transferred, and client IP/session ID rollups.
- **Server mode display** -- Dashboard banner now shows the running server mode (Zen Proxy, Zen Compute, etc.).

Supporting changes included in this branch:

- **Wildcard log level matching** -- Log levels can now be set per-category using wildcard patterns (e.g. `proxy.*=debug`).
- **`zen down --all`** -- New flag to shut down all running zenserver instances; also used by the new `xmake kill` task.
- Minor test stability fixes (flaky hash collisions, per-thread RNG seeds).
- Support ZEN_MALLOC environment variable for default allocator selection and switch default to rpmalloc
- Fixed sentry-native build to allow LTO on Windows

1 files changed, 85 insertions, 0 deletions

diff --git a/src/zenserver/proxy/httptrafficinspector.h b/src/zenserver/proxy/httptrafficinspector.h
new file mode 100644
index 000000000..f4af0e77e
--- /dev/null
+++ b/src/zenserver/proxy/httptrafficinspector.h
@@ -0,0 +1,85 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#pragma once
+
+#include <zencore/logging.h>
+#include <zencore/uid.h>
+
+ZEN_THIRD_PARTY_INCLUDES_START
+#include <http_parser.h>
+ZEN_THIRD_PARTY_INCLUDES_END
+
+#include <atomic>
+#include <cstdint>
+#include <string>
+#include <string_view>
+
+namespace zen {
+
+class HttpTrafficInspector
+{
+public:
+	enum class Direction
+	{
+		Request,
+		Response
+	};
+
+	HttpTrafficInspector(Direction Dir, std::string_view SessionLabel);
+
+	void Inspect(const char* Data, size_t Length);
+
+	uint64_t GetMessageCount() const { return m_MessageCount.load(std::memory_order_relaxed); }
+	bool	 IsUpgraded() const { return m_Upgraded.load(std::memory_order_relaxed); }
+	Oid		 GetSessionId() const;
+	bool	 HasSessionId() const;
+
+	void SetObserver(class IHttpTrafficObserver* Observer) { m_Observer = Observer; }
+
+private:
+	int OnUrl(const char* Data, size_t Length);
+	int OnHeaderField(const char* Data, size_t Length);
+	int OnHeaderValue(const char* Data, size_t Length);
+	int OnHeadersComplete();
+	int OnMessageComplete();
+
+	void ResetMessageState();
+
+	static HttpTrafficInspector* GetThis(http_parser* Parser) { return static_cast<HttpTrafficInspector*>(Parser->data); }
+
+	static http_parser_settings s_RequestSettings;
+	static http_parser_settings s_ResponseSettings;
+
+	LoggerRef Log() { return m_Log; }
+
+	LoggerRef	m_Log;
+	http_parser m_Parser;
+	Direction	m_Direction;
+	std::string m_SessionLabel;
+	bool		m_Disabled = false;
+
+	// Per-message state
+	std::string			  m_Url;
+	std::string			  m_Method;
+	uint16_t			  m_StatusCode	  = 0;
+	int64_t				  m_ContentLength = -1;
+	std::string			  m_CurrentHeaderField;
+	std::atomic<uint64_t> m_MessageCount{0};
+	std::atomic<bool>	  m_Upgraded{false};
+	Oid					  m_SessionId		  = Oid::Zero;
+	bool				  m_SessionIdCaptured = false;
+	IHttpTrafficObserver* m_Observer		  = nullptr;
+};
+
+class IHttpTrafficObserver
+{
+public:
+	virtual ~IHttpTrafficObserver()						  = default;
+	virtual void OnMessageComplete(HttpTrafficInspector::Direction Dir,
+								   std::string_view				   Method,
+								   std::string_view				   Url,
+								   uint16_t						   StatusCode,
+								   int64_t						   ContentLength) = 0;
+};
+
+}  // namespace zen