Prettify custom parameter and return value marshalling in `ISteam*.cs`

[Akarinnnnn]

@Chicken-Bones pointed out parameter and return value marshalling code in ISteam*.cs from #1 is ugly, but prettify it is hard due to codegen's complexity. This issue is to discuss how to prettify them without introducing complication errors and bugs.

[Chicken-Bones]

I think I was a bit overenthusiastic. Lets make a few case studies:

public static bool GetConnectionInfo(HSteamNetConnection hConn, out SteamNetConnectionInfo_t pInfo) {
	InteropHelp.TestIfAvailableGameServer();
	#if STEAMWORKS_ANYCPU
	bool ret;
	if (!Packsize.IsLargePack) {
		ret = NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
	} else {
		SteamNetConnectionInfo_t_LargePack pInfo_lp;
		ret = NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo_lp);
		pInfo = pInfo_lp;
	}
	#else
	return NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
	#endif
	#if STEAMWORKS_ANYCPU
	return ret;
	#endif
}

At the very least you could do:

public static bool GetConnectionInfo(HSteamNetConnection hConn, out SteamNetConnectionInfo_t pInfo) {
	InteropHelp.TestIfAvailableGameServer();
	#if STEAMWORKS_ANYCPU
	bool ret;
	if (!Packsize.IsLargePack) {
		ret = NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
	} else {
		SteamNetConnectionInfo_t_LargePack pInfo_lp;
		ret = NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo_lp);
		pInfo = pInfo_lp;
	}
	return ret;
	#else
	return NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
	#endif
}

But the best we can do is probably

public static bool GetConnectionInfo(HSteamNetConnection hConn, out SteamNetConnectionInfo_t pInfo) {
	InteropHelp.TestIfAvailableGameServer();
	#if STEAMWORKS_ANYCPU
	if (Packsize.IsLargePack) {
		SteamNetConnectionInfo_t_LargePack pInfo_lp = default;
		try {
			return NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo_lp);
		}
		finally {
			pInfo = pInfo_lp;
		}
	}
	#endif
	return NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
}

For a ref param, we would instead write

SteamNetConnectionInfo_t_LargePack pInfo_lp = pInfo;

[Akarinnnnn]

try-finally looks making confuse to JIT, how about approach 1?

I remember there are some cases like void Method(ParamStruct_t[] param). In such case a intermediate ParamStruct_t_LargePack[] array is needed only in large pack branch. Only case here:

public static bool GetAvailableBeaconLocations(SteamPartyBeaconLocation_t[] pLocationList, uint uMaxNumLocations) {
	InteropHelp.TestIfAvailableClient();
	#if STEAMWORKS_ANYCPU
	bool ret;
	if (!Packsize.IsLargePack) {
		ret = NativeMethods.ISteamParties_GetAvailableBeaconLocations(CSteamAPIContext.GetSteamParties(), pLocationList, uMaxNumLocations);
	} else {
		SteamPartyBeaconLocation_t_LargePack[] pLocationList_lp = new SteamPartyBeaconLocation_t_LargePack[pLocationList.Length];
		for (int i = 0; i < pLocationList.Length; i++)
			pLocationList_lp[i] = pLocationList[i];
		ret = NativeMethods.ISteamParties_GetAvailableBeaconLocations(CSteamAPIContext.GetSteamParties(), pLocationList_lp, uMaxNumLocations);
		for (int i = 0; i < pLocationList.Length; i++)
			pLocationList[i] = pLocationList_lp[i];
	}
	#else
	return NativeMethods.ISteamParties_GetAvailableBeaconLocations(CSteamAPIContext.GetSteamParties(), pLocationList, uMaxNumLocations);
	#endif
	#if STEAMWORKS_ANYCPU
	return ret;
	#endif
}

[Akarinnnnn]

Also there is some edge cases. This case requires marshal IntPtr typed C-style UTF-8 string to managed out string. It also troublesome.

public static bool GetBeaconDetails(PartyBeaconID_t ulBeaconID, out CSteamID pSteamIDBeaconOwner, out SteamPartyBeaconLocation_t pLocation, out string pchMetadata, int cchMetadata) {
	InteropHelp.TestIfAvailableClient();
	IntPtr pchMetadata2 = Marshal.AllocHGlobal(cchMetadata);
	#if STEAMWORKS_ANYCPU
	bool ret;
	if (!Packsize.IsLargePack) {
		ret = NativeMethods.ISteamParties_GetBeaconDetails(CSteamAPIContext.GetSteamParties(), ulBeaconID, out pSteamIDBeaconOwner, out pLocation, pchMetadata2, cchMetadata);
	} else {
		SteamPartyBeaconLocation_t_LargePack pLocation_lp;
		ret = NativeMethods.ISteamParties_GetBeaconDetails(CSteamAPIContext.GetSteamParties(), ulBeaconID, out pSteamIDBeaconOwner, out pLocation_lp, pchMetadata2, cchMetadata);
		pLocation = pLocation_lp;
	}
	#else
	bool ret = NativeMethods.ISteamParties_GetBeaconDetails(CSteamAPIContext.GetSteamParties(), ulBeaconID, out pSteamIDBeaconOwner, out pLocation, pchMetadata2, cchMetadata);
	#endif
	pchMetadata = ret ? InteropHelp.PtrToStringUTF8(pchMetadata2) : null;
	Marshal.FreeHGlobal(pchMetadata2);
	return ret;
}

I tried this form, but it was failed because case above.

	return ret;
	#else
	return NativeMethods.ISteamNetworkingSockets_GetConnectionInfo(CSteamGameServerAPIContext.GetSteamNetworkingSockets(), hConn, out pInfo);
	#endif

[Chicken-Bones]

Is it possible to put the string marshalling in a wrapper func?

public static bool GetBeaconDetails(PartyBeaconID_t ulBeaconID, out CSteamID pSteamIDBeaconOwner, out SteamPartyBeaconLocation_t pLocation, out string pchMetadata, int cchMetadata) {
	IntPtr pchMetadataPtr = Marshal.AllocHGlobal(cchMetadata);
	try {
		bool ret = GetBeaconDetails(ulBeaconID, out pSteamIDBeaconOwner, out pLocation, pchMetadataPtr, cchMetadata);
		pchMetadata = ret ? InteropHelp.PtrToStringUTF8(pchMetadataPtr) : null;
		return ret;
	}
	finally {
		Marshal.FreeHGlobal(pchMetadataPtr);
	}
}


public static bool GetBeaconDetails(PartyBeaconID_t ulBeaconID, out CSteamID pSteamIDBeaconOwner, out SteamPartyBeaconLocation_t pLocation, IntPtr pchMetadata, int cchMetadata) {
	...autogenerated
}

[Akarinnnnn]

Possible, for more exception safety and clearer semantic, I'd convert to using (Utf8StringHandle ...)

[Akarinnnnn]

Convert Utf8StringHandle to use Spans will also take action.