Add support for XEvent logging and bump API version to v3

[miljann995]

This pull request introduces a new optional host callback API (version 3) for SQL language extensions, enabling extensions to log XEvents back to the host infrastructure. The update defines new callback types and structures in the native interface, implements the callback registration and invocation in both native and managed (.NET) layers, and provides the necessary glue to allow the managed extension to log messages through the host's event system.

The most important changes are:

API and Interface Additions:

• Bumped the EXTERNAL_LANGUAGE_EXTENSION_API version from 2 to 3 in sqlexternallanguage.h to indicate the new optional host callback API.
• Added the PFunc_ExtensionLogXEvent callback type, the SQLEXTENSION_HOST_CALLBACKS structure, and the SetHostCallbacks API to sqlexternallanguage.h, allowing the host to provide callback functions to extensions.

Native Extension Integration:

• Added the SetHostCallbacks function and the g_hostCallbacks pointer to nativecsharpextension.h and implemented their logic in nativecsharpextension.cpp, storing the host callbacks and forwarding them to the managed layer. [1] [2]

Managed Extension Support:

• Defined managed representations for the callback delegate and structure in CSharpExtension.cs, and implemented the SetHostCallbacks method to receive and store the callback, enabling managed code to log XEvents through the host.
• Updated the Logging utility in Logging.cs to store the host-provided callback and added the LogXEvent method, allowing managed code to log messages through the host's XEvent infrastructure. [1] [2]

Here's the compatibility matrix for general Extension API in terms of host callbacks.

	Host v2	Host v3
Extension v2	SetHostCallbacks is not defined in Extension and host does not expect it and does not call it.	SetHostCallbacks is not defined in Extension, but host does check it and skips calling it since it's not defined on Extension side.
Extension v3	SetHostCallbacks is defined in Extension but host does not expect it and does not call it.	SetHostCallbacks is defined on both sides and host calls it.

Here's the compatibility matrix for Host Callbacks API. Here, v2 can be interpreted as vNext. v1 is the current version present in this pull request.

	Host v1	Host v2
Extension v1	Host callbacks struct passed from host contains only LogXEvent callback and Extension expects only that one, and saves its address.	Host callbacks struct passed from host contains additional functions apart from LogXEvent, but Extension reads only LogXEvent, ignoring other callbacks.
Extension v2	Host callbacks struct passed from host contains only LogXEvent callback, and Extension expects additional functions apart from LogXEvent, but since they are nullptr in a struct, they will be skipped.	Host callbacks struct passed from host contains additional functions apart from LogXEvent, and Extension expects additional functions apart from LogXEvent, saves their addresses and calls them.

[Copilot]

Pull request overview

This PR introduces a v3 extension interface update to support optional host callbacks, enabling extensions (specifically the .NET C# extension) to log XEvents back through the host infrastructure.

Changes:

• Bumped EXTERNAL_LANGUAGE_EXTENSION_API from 2 to 3 and added a new optional SetHostCallbacks API + callback struct/type in the shared native interface header.
• Implemented native SetHostCallbacks in the .NET C# extension and forwarded the callback struct to the managed layer.
• Added managed callback delegates/structs plus a Logging.LogXEvent(...) helper that invokes the host-provided callback.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
extension-host/include/sqlexternallanguage.h	Bumps API version to v3; adds host callback typedef/struct and SetHostCallbacks API declaration.
language-extensions/dotnet-core-CSharp/include/nativecsharpextension.h	Declares SetHostCallbacks export and stores a host-callbacks pointer.
language-extensions/dotnet-core-CSharp/src/native/nativecsharpextension.cpp	Implements native SetHostCallbacks; resets host callbacks on cleanup.
language-extensions/dotnet-core-CSharp/src/managed/CSharpExtension.cs	Adds managed callback delegate/struct and implements managed SetHostCallbacks.
language-extensions/dotnet-core-CSharp/src/managed/utils/Logging.cs	Stores callback delegate and adds LogXEvent helper for managed code.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

[SicongLiu2000]

Review Summary — XEvent Logging Callback API (v3)

Nice feature — clean API surface and good test coverage. Three items I'd want addressed before merge, plus several medium-severity hardening suggestions:

Must-fix (High)

1. TOCTOU on _logXEventCallback (Logging.cs) — snapshot to local before null-check and invocation to prevent NRE from concurrent SetLogXEventCallback(null).
2. Use-after-free in Cleanup() (nativecsharpextension.cpp) — must clear the managed-side callback delegate before tearing down the .NET runtime, otherwise background threads can invoke a stale host function pointer.
3. char* vs byte* delegate type mismatch (CSharpExtension.cs) — delegate declares char* (2-byte UTF-16) but actually receives byte* (1-byte UTF-8). Should be byte* to match the native SQLCHAR*.

Should-fix (Medium)

4. Dangling pointer — g_hostCallbacks stores borrowed pointer; copy the struct or remove the dead global.
5. fixed on empty array — yields null pointer passed to native code; guard the empty-message case.
6. static globals in header — pre-existing issue, but the new g_hostCallbacks follows the pattern; extern + single definition is correct.

Consider (Low)

7. Version check could use a MAX_SUPPORTED constant for future extensibility.
8. ulong vs nuint for SQLULEN if 32-bit is ever a target.

See inline comments for details and suggested fixes.

[SicongLiu2000]

All 8 findings addressed — TOCTOU snapshot, use-after-free ordering, type mismatch, dangling pointer copy, fixed-null guard, extern globals, version constant, and typo. Good test coverage with the new GTest suite. LGTM 👍

[monamaki]

the struct mismatches with the latest one in the engine

[monamaki]

typedef struct _SQLEXTENSION_HOST_CALLBACKS
{
    SQLUSMALLINT Version;               // 2 bytes
    SQLUSMALLINT Reserved0;             // 2 bytes (explicit padding)
    SQLUINTEGER SizeInBytes;            // 4 bytes
    PFunc_ExtensionLogXEvent LogXEvent; // 8 bytes (pointer)
    void *Reserved1;                    // 8 bytes
    void *Reserved2;                    // 8 bytes
} SQLEXTENSION_HOST_CALLBACKS;          // Total: 32 bytes

[monamaki]

We need to use the latest commit in our internal repo (this is used as git submodule there), generate nugets there, consume it in your DsMainDev private branch, run PVS with it.

[monamaki]

sqlexternallanguage.h to stay similar with what we have in the engine;
right now this enum is not in the same place in the engine code.
can we move ExtensionTraceLevel in there also to sqlexternallanguage.h?

[monamaki]

g_hostCallbacks is a raw pointer to host-owned memory (CExthostExtensionManager::m_hostCallbacks in DsMainDev). Its lifetime is valid from SetHostCallbacks until Cleanup. Please add a comment documenting this ownership contract so future contributors don't cache or use it after Cleanup.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.