From ef586f5930ac761f8e8e18cde2ebd5248efeaa4a Mon Sep 17 00:00:00 2001
From: Stefan Boberg <stefan.boberg@epicgames.com>
Date: Fri, 13 Mar 2026 09:24:59 +0100
Subject: Unix Domain Socket auto discovery (#833)

This PR adds end-to-end Unix domain socket (UDS) support, allowing zen CLI to discover and connect to UDS-only servers automatically.

- **`unix://` URI scheme in zen CLI**: The `-u` / `--hosturl` option now accepts `unix:///path/to/socket` to connect to a zenserver via a Unix domain socket instead of TCP.
- **Per-instance shared memory for extended server info**: Each zenserver instance now publishes a small shared memory section (keyed by SessionId) containing per-instance data that doesn't fit in the fixed-size ZenServerEntry -- starting with the UDS socket path. This is a 4KB pagefile-backed section on Windows (`Global\ZenInstance_{sessionid}`) and a POSIX shared memory object on Linux/Mac (`/UnrealEngineZen_{sessionid}`).
- **Client-side auto-discovery of UDS servers**: `zen info`, `zen status`, etc. now automatically discover and prefer UDS connections when a server publishes a socket path. Servers running with `--no-network` (UDS-only) are no longer invisible to the CLI.
- **`kNoNetwork` flag in ZenServerEntry**: Servers started with `--no-network` advertise this in their shared state entry. Clients skip TCP fallback for these servers, and display commands (`ps`, `status`, `top`) show `-` instead of a port number to indicate TCP is not available.
---
 src/zenutil/include/zenutil/zenserverprocess.h | 56 +++++++++++++++++++++++++-
 1 file changed, 54 insertions(+), 2 deletions(-)

(limited to 'src/zenutil/include')

diff --git a/src/zenutil/include/zenutil/zenserverprocess.h b/src/zenutil/include/zenutil/zenserverprocess.h
index 1b8750628..2f76f0d6c 100644
--- a/src/zenutil/include/zenutil/zenserverprocess.h
+++ b/src/zenutil/include/zenutil/zenserverprocess.h
@@ -224,8 +224,10 @@ public:
 
 		enum class FlagsEnum : uint16_t
 		{
-			kShutdownPlease = 1 << 0,
-			kIsReady		= 1 << 1,
+			kShutdownPlease	 = 1 << 0,
+			kIsReady		 = 1 << 1,
+			kHasInstanceInfo = 1 << 2,
+			kNoNetwork		 = 1 << 3,
 		};
 
 		FRIEND_ENUM_CLASS_FLAGS(FlagsEnum);
@@ -236,6 +238,10 @@ public:
 		bool IsShutdownRequested() const;
 		void SignalReady();
 		bool IsReady() const;
+		void SignalHasInstanceInfo();
+		bool HasInstanceInfo() const;
+		void SignalNoNetwork();
+		bool IsNoNetwork() const;
 		bool AddSponsorProcess(uint32_t Pid, uint64_t Timeout = 0);
 	};
 
@@ -258,6 +264,51 @@ private:
 	bool			m_IsReadOnly	= true;
 };
 
+/** Per-instance extended data published via a small shared memory section keyed by SessionId.
+
+	Servers create a writable section; clients open it read-only during Snapshot()
+	enumeration to discover fields that don't fit in the fixed-size ZenServerEntry
+	(e.g. Unix domain socket path).
+
+	SessionId is preferred over PID for naming because it is unique per server
+	instance lifetime, avoiding issues with PID reuse on crash/restart.
+ */
+
+struct InstanceInfoData
+{
+	std::filesystem::path UnixSocketPath;
+	// Extensible: add more per-instance fields here in the future
+};
+
+class ZenServerInstanceInfo
+{
+public:
+	ZenServerInstanceInfo();
+	~ZenServerInstanceInfo();
+
+	ZenServerInstanceInfo(const ZenServerInstanceInfo&) = delete;
+	ZenServerInstanceInfo& operator=(const ZenServerInstanceInfo&) = delete;
+
+	/// Server-side: create read-write, populate with data
+	void Create(const Oid& SessionId, const InstanceInfoData& Data);
+
+	/// Client-side: open read-only by SessionId, returns false if not found
+	[[nodiscard]] bool OpenReadOnly(const Oid& SessionId);
+
+	/// Read the data (valid after Create or successful OpenReadOnly)
+	[[nodiscard]] InstanceInfoData Read() const;
+
+	bool IsValid() const { return m_Data != nullptr; }
+
+private:
+	static std::string MakeName(const Oid& SessionId);
+
+	void*	 m_hMapFile = nullptr;
+	uint8_t* m_Data		= nullptr;
+	bool	 m_IsOwner	= false;
+	Oid		 m_SessionId;  // for POSIX cleanup (shm_unlink)
+};
+
 struct LockFileInfo
 {
 	int32_t				  Pid;
@@ -266,6 +317,7 @@ struct LockFileInfo
 	bool				  Ready;
 	std::filesystem::path DataDir;
 	std::filesystem::path ExecutablePath;
+	std::filesystem::path UnixSocketPath;
 };
 
 CbObject	 MakeLockFilePayload(const LockFileInfo& Info);
-- 
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