Extensions

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Revision as of 11:46, 18 March 2024 by Lou Montana (talk | contribs) (Fix example)
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⚠
If you came here because you have been told to install an extension, be warned! Extensions are just like executables. They may contain viruses etc. More on that, in the FAQ section.


Historical


FAQ

How to use Extensions?

Extensions can be accessed using callExtension.

ⓘ
The exact way about how to use an extension is up to the developer of said extension.

Where to put Extensions?

Arma 3 will look at the following places to find your extension files:

  • In all loaded mods root folders (for example: ..\arma3\@ModXYZ\yourextension.dll).
  • In your Arma 3 installation folder (for example: ..\arma3\yourextension.dll).

At best, you place your extensions inside some mod folder and load it.
At worst, you just throw it where the Arma 3 executable is located.

Extensions may require other libraries and runtimes to be installed on the computer it is to run on. Consult the authors installation manual if it exists.

What are Extensions?

Extensions are Dynamic Link Library (DLL) files written in, for example, C.

Linux systems use a different file type: Shared Object (SO).

What do I have to look out for?

Extensions fall under the same rules as executable files. They may require additional runtime libraries or cause the game to crash.

⚠
Extensions can contain malicious code! Be sure to only use extensions from reliable developers, obtained through reliable sources!

How to know which extensions can be trusted?

Theoretically, never trust anything! Including Arma and your OS itself. Technically however, this would make a boring experience, as all you would be left with is an expensive heater.

Thus a better rule is: If the are sources freely available, you probably can trust the extension. Even if you cannot read the source code, chances are that somebody out there can and would find something odd. That will not protect you! Developers might add malicious code that is not exposed in the available source files, they not even need to be aware of this. They may be infected already and the virus is just writing itself into the compiled extension.

When I call the extension method, Arma freezes.

This is most likely caused by the extension taking too much time. Due to the low-level nature of extensions, an extension cannot be suspended like scheduled scripts can be. You should notify the developer of said extension about this freezing issue or use the extension less extensively.

Can I join BattlEye protected servers with my extension?

If the extension is whitelisted by BattlEye, it will be allowed to load - see Getting your extension whitelisted by BattlEye. If it is not, it just will be blocked causing any callExtension attempt to fail.

Generally speaking, joining BattlEye-protected servers should be no problem with or without extensions.

If in doubt, ask the extension's author.

Can I use extensions in my mission?

Yes, you can use extensions in your missions, but you should consider if it is worth it. Using extensions requires that all hosts (servers and clients) which use the extension have it installed. Extensions are not packed into the mission pbo.

ⓘ
If only the server is using the extension, the clients do not need it.

What do i have to look out for when deploying my extension?

Extensions have to be provided for 32bit and 64bit Arma. When you deploy your extension, you thus have to build it twice. Once for the 32bit support and once for the 64bit support.

After you are done, copy both output files to some location and add a _x64.dll suffix to the 64bit file.

Example:

  • Windows:
    • MyExtension.dll (32bit)
    • MyExtension_x64.dll (64bit)
  • Linux:
    • MyExtension.so (32bit)
    • MyExtension_x64.so (64bit)


Creating Extensions

Preamble

Before we start, ask yourself the following questions:

  • is SQF unable to fulfill your needs?
  • Making an extension requires knowledge of a programming language. Are you capable of performing that programming task?
  • Why should a user trust you and use your extension?
  • Is it worth adding an extension for the feature you want to implement?

If the answer to any question was no, you probably should not proceed to create an extension but rather use plain SQF.


Getting Started

At first, we have to choose what language we want to use.

This wiki currently covers the following: C, C++, C#

Preparations

C/C++

Create a new library project in the IDE of your choice.

C#

C# requires you to install additional dependencies to work out of the box. The snippets in here all are using DllExport (sources) which can be installed using NuGet.

Create a new Class Library project in the IDE of your choice.


Available Interfaces

The Extension is required to contain at least the entry point in a form of a method named RVExtension or RVExtensionArgs. Everything else is optional.

The actual exports need to look like this (Windows only):

32-bit requires usage of decorated names following the __stdcall convention

  • _RVExtension@12
  • _RVExtensionArgs@20
  • _RVExtensionVersion@8

64-bit

  • RVExtension
  • RVExtensionArgs
  • RVExtensionVersion

If you use the Visual C++ compiler, this should work out of the box. But other compilers might require some manual work.

C/C++

Visual C++

	//--- Called by Engine on extension load
	__declspec (dllexport) void __stdcall RVExtensionVersion(char *output, unsigned int outputSize);
	//--- STRING callExtension STRING
	__declspec (dllexport) void __stdcall RVExtension(char *output, unsigned int outputSize, const char *function);
	//--- STRING callExtension ARRAY
	__declspec (dllexport) int __stdcall RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
	//--- Extension Callback
	__declspec (dllexport) void __stdcall RVExtensionRegisterCallback(int(*callbackProc)(char const *name, char const *function, char const *data));
	//--- Engine passed context [steamID, fileSource, missionSourceName, serverName] since Arma 3 v2.12
	__declspec (dllexport) void __stdcall RVExtensionContext(const char **argv, unsigned int argc);

GCC

	//--- Called by Engine on extension load
	__attribute__((dllexport)) void RVExtensionVersion(char *output, unsigned int outputSize);
	//--- STRING callExtension STRING
	__attribute__((dllexport)) void RVExtension(char *output, unsigned int outputSize, const char *function);
	//--- STRING callExtension ARRAY
	__attribute__((dllexport)) int RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
	//--- Extension Callback
	__attribute__((dllexport)) void RVExtensionRegisterCallback(int(*callbackProc)(char const *name, char const *function, char const *data));
	//--- Engine passed context [steamID, fileSource, missionSourceName, serverName] since Arma 3 v2.12
	__attribute__((dllexport)) void RVExtensionContext(const char **argv, unsigned int argc);

See GCC documentation on "How to use the new C++ visibility support"

C#

ⓘ
You might need to install UnmanagedExports. You might also need to additionally set WIN64 and WIN32 in project properties.

Go to: Project->Properties->Build tab->Conditional compilation symbols, add WIN32 for your x86 platform and WIN64 for your x64 platform. Save.

Rename resulting WIN64 dllname.dll to dllname_x64.dll.
		/// <summary>
		/// Gets called when Arma starts up and loads all extension.
		/// It's perfect to load in static objects in a separate thread so that the extension doesn't needs any separate initalization
		/// </summary>
		/// <param name="output">The string builder object that contains the result of the function</param>
		/// <param name="outputSize">The maximum size of bytes that can be returned</param>
#if WIN64
		[DllExport("RVExtensionVersion", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionVersion@8", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtensionVersion(StringBuilder output, unsigned int outputSize) { }

		/// <summary>
		/// The entry point for the default callExtension command.
		/// </summary>
		/// <param name="output">The string builder object that contains the result of the function</param>
		/// <param name="outputSize">The maximum size of bytes that can be returned</param>
		/// <param name="function">The string argument that is used along with callExtension</param>
#if WIN64
		[DllExport("RVExtension", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtension@12", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtension(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function) { }

		/// <summary>
		/// The entry point for the callExtensionArgs command.
		/// </summary>
		/// <param name="output">The string builder object that contains the result of the function</param>
		/// <param name="outputSize">The maximum size of bytes that can be returned</param>
		/// <param name="function">The string argument that is used along with callExtension</param>
		/// <param name="args">The args passed to callExtension as a string array</param>
		/// <param name="argsCount">The size of the string array args</param>
		/// <returns>The result code</returns>
#if WIN64
		[DllExport("RVExtensionArgs", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionArgs@20", CallingConvention = CallingConvention.Winapi)]
#endif
		public static int RvExtensionArgs(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function,
			[MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr, SizeParamIndex = 4)] string[] args, unsigned int argCount) { }


Getting your extension whitelisted by BattlEye

Since Arma 3 logo black.png1.46, client extensions need to be whitelisted in order to get loaded.

The SITREP #00109 said the following on that topic: 

The enhanced BattlEye protection in 1.46 will require extensions to be white-listed, or their access to the game's processes will be blocked.
In order to get your extension white-listed, please contact BattlEye support via its web form or support[at]battleye.com.
Be sure to include the file name, a description and possibly a download link.

This boils down to the following tasks to get your extension whitelisted:

  1. Upload the extension in question somewhere.
  2. Open the BattlEye Contact Page.
  3. Pick the topic Other requests (may change in future, select the most appropriate).
  4. Fill in your Name and E-Mail.
  5. Set the subject to something like Arma extension whitelisting.
  6. Add link to your extension from step 1 (you may include other information too) into the Message.

After a certain time, your extension should be whitelisted.


Deploying extensions

To correctly deploy your extensions, you have to make sure to have a 32bit and a 64bit variant of your extension. The reason for this is because 64bit Arma cannot load 32bit extensions and vice versa.

You also should create an addon package (even if you only deploy the actual extension binaries) + add the documentation for your extension.

An example might be structured like this:

  • /@MyExtension/
    • /MyExtension.dll
    • /MyExtension_x64.dll
    • /docs/
      • /MyExtension_Documentation.txt

You may also want to provide convenience SQF functions to access your extension.


Minimum Viable Example

The following examples will copy the input into the output. They are provided to show some practical example.

C (Visual C++)
C (GCC)
C++ (Visual C++)
C++ (GCC)
C#
C# (w/ callback)
__declspec(dllexport) void __stdcall RVExtension(char *output, unsigned int outputSize, const char *function);
__declspec(dllexport) int __stdcall RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
__declspec(dllexport) void __stdcall RVExtensionVersion(char *output, unsigned int outputSize);

int strncpy_safe(char *output, const char *src, int size)
{
	int i;
	size--;
	for (i = 0; i < size && src[i] != '\0'; i++)
	{
		output[i] = src[i];
	}
	output[i] = '\0';
	return i;
}

void __stdcall RVExtension(char *output, unsigned int outputSize, const char *function)
{
	strncpy_safe(output, function, outputSize);
}

int __stdcall RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc)
{
	int index = 0;
	for (int i = 0; i < argc && index < outputSize; i++)
	{
		index += strncpy_safe(output + index, argv[i], outputSize - 1 - index);
	}
	return 0;
}

void __stdcall RVExtensionVersion(char *output, unsigned int outputSize)
{
	strncpy_safe(output, "Test-Extension v1.0", outputSize);
}

__attribute__((dllexport)) void RVExtension(char *output, unsigned int outputSize, const char *function);
__attribute__((dllexport)) int RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
__attribute__((dllexport)) void RVExtensionVersion(char *output, unsigned int outputSize);

int strncpy_safe(char *output, const char *src, int size)
{
	int i;
	size--;
	for (i = 0; i < size && src[i] != '\0'; i++)
	{
		output[i] = src[i];
	}
	output[i] = '\0';
	return i;
}

void RVExtension(char *output, unsigned int outputSize, const char *function)
{
	strncpy_safe(output, function, outputSize);
}

int RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc)
{
	int index = 0;
	for (int i = 0; i < argc && index < outputSize; i++)
	{
		index += strncpy_safe(output + index, argv[i], outputSize - 1 - index);
	}
	return 0;
}

void RVExtensionVersion(char *output, unsigned int outputSize)
{
	strncpy_safe(output, "Test-Extension v1.0", outputSize);
}

#include <string>
#include <cstring>
#include <sstream>
extern "C"
{
	__declspec(dllexport) void __stdcall RVExtension(char *output, unsigned int outputSize, const char *function);
	__declspec(dllexport) int __stdcall RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
	__declspec(dllexport) void __stdcall RVExtensionVersion(char *output, unsigned int outputSize);
}
void __stdcall RVExtension(char *output, unsigned int outputSize, const char *function)
{
	std::strncpy(output, function, outputSize - 1);
}

int __stdcall RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc)
{
	std::stringstream sstream;
	for (int i = 0; i < argc; i++)
	{
		sstream << argv[i];
	}
	std::strncpy(output, sstream.str().c_str(), outputSize - 1);
	return 0;
}

void __stdcall RVExtensionVersion(char *output, unsigned int outputSize)
{
	std::strncpy(output, "Test-Extension v1.0", outputSize - 1);
}

#include <string>
#include <cstring>
#include <sstream>
extern "C"
{
	__attribute__((dllexport)) void RVExtension(char *output, unsigned int outputSize, const char *function);
	__attribute__((dllexport)) int RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc);
	__attribute__((dllexport)) void RVExtensionVersion(char *output, unsigned int outputSize);
}
void RVExtension(char *output, unsigned int outputSize, const char *function)
{
	std::strncpy(output, function, outputSize - 1);
}

int RVExtensionArgs(char *output, unsigned int outputSize, const char *function, const char **argv, unsigned int argc)
{
	std::stringstream sstream;
	for (int i = 0; i < argc; i++)
	{
		sstream << argv[i];
	}
	std::strncpy(output, sstream.str().c_str(), outputSize - 1);
	return 0;
}

void RVExtensionVersion(char *output, unsigned int outputSize)
{
	std::strncpy(output, "Test-Extension v1.0", outputSize - 1);
}

using System.Text;
using System.Runtime.InteropServices;
using RGiesecke.DllExport;

class MyExtension {

#if WIN64
		[DllExport("RVExtensionVersion", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionVersion@8", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtensionVersion(StringBuilder output, unsigned int outputSize)
		{
			output.Append("Test-Extension v1.0");
		}

#if WIN64
		[DllExport("RVExtension", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtension@12", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtension(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function)
		{
			output.Append(function);
		}

#if WIN64
		[DllExport("RVExtensionArgs", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionArgs@20", CallingConvention = CallingConvention.Winapi)]
#endif
		public static int RvExtensionArgs(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function,
			[MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr, SizeParamIndex = 4)] string[] args, unsigned int argCount)
		{
			foreach(var arg in args)
			{
				output.Append(arg);
			}
			return 0;
		}
}

using System.Text;
using System.Runtime.InteropServices;
using RGiesecke.DllExport;

class MyExtension {

	public static ExtensionCallback callback;
	public delegate int ExtensionCallback([MarshalAs(UnmanagedType.LPStr)] string name, [MarshalAs(UnmanagedType.LPStr)] string function, [MarshalAs(UnmanagedType.LPStr)] string data);

#if WIN64
		[DllExport("RVExtensionRegisterCallback", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionRegisterCallback@4", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RVExtensionRegisterCallback([MarshalAs(UnmanagedType.FunctionPtr)] ExtensionCallback func)
		{
			callback = func;
		}

#if WIN64
		[DllExport("RVExtensionVersion", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionVersion@8", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtensionVersion(StringBuilder output, unsigned int outputSize)
		{
			output.Append("Test-Extension v1.0");
		}

#if WIN64
		[DllExport("RVExtension", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtension@12", CallingConvention = CallingConvention.Winapi)]
#endif
		public static void RvExtension(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function)
		{
			output.Append(function);
		}

#if WIN64
		[DllExport("RVExtensionArgs", CallingConvention = CallingConvention.Winapi)]
#else
		[DllExport("_RVExtensionArgs@20", CallingConvention = CallingConvention.Winapi)]
#endif
		public static int RvExtensionArgs(StringBuilder output, unsigned int outputSize,
			[MarshalAs(UnmanagedType.LPStr)] string function,
			[MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr, SizeParamIndex = 4)] string[] args, unsigned int argCount)
		{
			foreach(var arg in args)
			{
				output.Append(arg);
			}
			return 0;
		}
}


Other Languages

This section contains other languages which may or may not work. Finding out requirements etc. is up to you.

ⓘ
Help Wanted!

If you know any of the following languages, consider editing this page to add the language to the upper list properly.

Delphi/Pascal
D
library dllTest;

uses
  SysUtils;

{Return value is not used.}
procedure RVExtension(toArma: PAnsiChar; outputSize: Integer; fromArma: PAnsiChar); stdcall; export;
begin
  StrCopy(toArma, fromArma);
end;

exports
  { 32-bit }
  RVExtension name '_RVExtension@12';
  { 64-bit }
  RVExtension name 'RVExtension';
begin
end;

import std.c.windows.windows;
import core.sys.windows.dll;

__gshared HINSTANCE g_hInst;

extern (Windows) BOOL DllMain(HINSTANCE hInstance, ULONG ulReason, LPVOID pvReserved) {
	final switch (ulReason) {
		case DLL_PROCESS_ATTACH:
			g_hInst = hInstance;
			dll_process_attach(hInstance, true);
			break;

		case DLL_PROCESS_DETACH:
			dll_process_detach(hInstance, true);
			break;

		case DLL_THREAD_ATTACH:
			dll_thread_attach(true, true);
			break;

		case DLL_THREAD_DETACH:
			dll_thread_detach(true, true);
			break;
	}

	return true;
}

import std.conv;
import std.exception;

export extern (Windows) void RVExtension(char* output, int output_size, const char* cinput) {
	auto dinput = to!string(cinput);
	auto doutput = output[0 .. output_size];
	string result;

	// ...

	enforce(result.length <= output_size, "Output length too long");
	doutput[0 .. result.length] = result[];
	doutput[result.length] = '\0';
}


Utility Header

This C++ header file can be used to define most of the Extension interface. It works on Windows and Linux.
It will be used in the following examples to keep them shorter. It also contains useful definitions for Feature Flags and Context - Its name is RVExtensionUtils.hpp 

#pragma once
#include <cstdint>
#ifdef _WIN32
#include <windows.h> // GetModuleHandle, GetProcAddress
#else // Linux
#include <dlfcn.h> // dlopen, dlclose, dlsym
#endif

// bitset
enum DllExtensionFeatureFlags : uint64_t
{
	RVFeature_ContextArgumentsVoidPtr = 1 << 0,
	RVFeature_ContextStackTrace = 1 << 1,
	RVFeature_ContextNoDefaultCall = 1 << 2,
};

struct RVContext_StackTrace
{
	struct StackTraceLine
	{
		// Line number in file (before preprocessing if preprocessed with line numbers)
		uint32_t lineNumber;
		// File offset in bytes from the start of the file (after preprocessing)
		uint32_t fileOffset;
		// Filepath to the source file
		const char* sourceFile;
		// scopeName set on that level
		const char* scopeName;
		// Complete fileContent of the sourceFile (after preprocessing, can be combined with fileOffset to find exact location)
		const char* fileContent;
	};

	StackTraceLine* lines = nullptr;
	uint32_t lineCount = 0;
};

#ifdef _WIN32
#define DLLEXPORT __declspec (dllexport)
#define CALL_CONVENTION __stdcall
#else // Linux
#if __GNUC__ >= 4
#define DLLEXPORT __attribute__ ((visibility ("default")))
#else
#define DLLEXPORT __attribute__((dllexport))
#endif

#define CALL_CONVENTION
#endif

extern "C"
{
	typedef int (CALL_CONVENTION RVExtensionCallbackProc)(char const* name, char const* function, char const* data);
	typedef void CALL_CONVENTION RVExtensionRequestContextProc();

	//--- Called by Engine on extension load
	DLLEXPORT void CALL_CONVENTION RVExtensionVersion(char* output, unsigned int outputSize);
	//--- STRING callExtension STRING
	DLLEXPORT void CALL_CONVENTION RVExtension(char* output, unsigned int outputSize, const char* function);
	//--- STRING callExtension ARRAY
	DLLEXPORT int CALL_CONVENTION RVExtensionArgs(char* output, unsigned int outputSize, const char* function, const char** argv, unsigned int argc);
	//--- Called by Engine on extension load to pass RVExtensionCallbackProc to it
	DLLEXPORT void CALL_CONVENTION RVExtensionRegisterCallback(RVExtensionCallbackProc* callbackProc);
}

//--- Finds a game exported function by its name
inline const void* FindRVFunction(const char* name)
{
#ifdef _WIN32
	return reinterpret_cast<void*>(GetProcAddress(GetModuleHandle(nullptr), name));
#else // Linux
	auto armaHandle = dlopen(nullptr, RTLD_LAZY | RTLD_NOLOAD);
	auto result = dlsym(armaHandle, name);
	dlclose(armaHandle);
	return result;
#endif
}
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Feature Flags

Feature flags can change the behavior of the Extension. Their main purpose is to only enable certain features when they are needed, so that Extensions that don't need them don't have to pay the cost for it. Multiple flags can be combined. To set no flags, either 0 must be specified or the RVExtensionFeatureFlags variable must be omitted.

Flags are checked before every RVExtension/RVExtensionArgs execution. They can be changed at runtime between executions, but make sure that the effects of changed flags are handled correctly.

Existing flags

  • RVFeature_ContextArgumentsVoidPtr - RVExtensionContext takes const void** as argument, instead of the default const char**, and arguments will be passed in their custom types - see Context Arguments.
  • RVFeature_ContextStackTrace - RVExtensionContext will retrieve a full Stacktrace - see Context.
  • RVFeature_ContextNoDefaultCall - RVExtensionContext will not be called automatically. It must be manually requested via RVExtensionRequestContext (This improves performance when context is not needed).

Setting Flags

Example Visual C++ 

#include <cstdint>
#include "RVExtensionUtil.hpp"

extern "C"
{
	__declspec(dllexport) uint64_t RVExtensionFeatureFlags = RVFeature_ContextStackTrace | RVFeature_ContextNoDefaultCall;
}


Game Functions

The Game exports some functions that can be retrieved, in order to call back into Game functionality. The Utility Header defines a function called FindRVFunction that can be used to retrieve their addresses.

Available Game Functions
Name Type Description
RVExtensionCallback 
typedef int (CALL_CONVENTION RVExtensionCallbackProc)(char const* name, char const* function, char const* data);
Adds a callback, see #TODO
RVExtensionRequestContext 
typedef void CALL_CONVENTION RVExtensionRequestContextProc();
Requests execution of RVExtensionContext


Callback

It is possible to call the game directly from the extension via function pointer provided when extension is called for the first time. Since Arma 3 logo black.png2.18 it can also be requested when needed, see Game Functions.
The function pointer passed over to RVExtensionRegisterCallback method is of the following signature: 

int(*callbackProc)(char const *name, char const *function, char const *data)

Calling this function pointer from extension will trigger "ExtensionCallback" mission event handler with three user-supplied params. The params are:

  • name - make it unique name, for example the extension name, so that other modders can quickly filter out calls from own extensions
  • function - make it name of the function the extension sends the result to. (Note: The returned function is just a STRING! So compile is needed, before using call or spawn, to execute it)
  • data - make it the actual result. You can also format it as an array so it could be parsed by parseSimpleArray

Calling function pointer returns an int. This is the number of available slots in the input buffer left for this frame after your call and can range from 99 to -1.
The buffer is processed and cleared every frame and the maximum number of slots that can be filled per frame is 100. If you are planning to call back with more than 100 results per frame, make sure your extension retries if it receives negative int, which means the buffer was full and your call did not succeed. Ideally suited for callbacks from different threads, but if callback is initiated from the calling thread, the EH will fire on the next frame of game simulation.
The "ExtensionCallback" event handler needs to exist before any callbacks, otherwise the data will just stay in the buffer. Removing all "ExtensionCallback" EHs clears the buffer as well as mission restart.

Usage Example:

fncToExecute_1 = { hint format ["Extension Result 1: %1", _this] }; fncToExecute_2 = { hint format ["Extension Result 2: %1", _this] }; fncToExecute_3 = { hint format ["Extension Result 3: %1", _this] }; addMissionEventHandler ["ExtensionCallback", { params ["_name", "_function", "_data"]; if (_name isEqualTo "test_callback") then { parseSimpleArray _data call (missionNamespace getVariable [_function, { hint "Function does not exist!"; }]); }; }]; "test_callback" callExtension str "test data";

Here is a minimal example of an extension using extension callback (do not actually do it like this for a real extension). fncToExecute_X function is called from "ExtensionCallback" event handler when it is triggered after 2 seconds of the extension call. 

#include <thread>
#include <string>
#include <chrono>

#include "RVExtensionUtil.hpp"

RVExtensionCallbackProc* callbackPtr = nullptr;

void CALL_CONVENTION RVExtensionRegisterCallback(RVExtensionCallbackProc* callbackProc)
{
	callbackPtr = callbackProc;
}

void CALL_CONVENTION RVExtension(char *output, unsigned int outputSize, const char *function)
{
	if (!callbackPtr)
		return;

	std::thread ([](std::string fnc)
	{
		using namespace std::chrono_literals;
		fnc = "[1,2,3," + fnc + "]";

		for (int i = 1; i < 4; ++i) // run 3 times
		{
			std::this_thread::sleep_for(2s); // sleep for 2 seconds
			callbackPtr("test_callback", ("fncToExecute_" + std::to_string(i)).c_str(), fnc.c_str());
		}

	}, function).detach();
}
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Context

RVExtensionContext is called before every RVExtension/RVExtensionArgs execution, providing context about where the call came from. Using Feature Flags can change the number of elements passed, but it does not change their order.

Context Arguments

By default (due to backwards compatability) context receives an array of char*. Every value will be converted to a string. However with the RVFeature_ContextArgumentsVoidPtr Feature Flags, it can be switched to an array of void*, where the specific datatype per entry is defined per context element.

It will pass the following data in this order:

Caption text
Name Description String content Custom datatype with RVFeature_ContextArgumentsVoidPtr
steamId Steam 64bit userID of the local machine, same as getPlayerUID "0", number as string, no extra quotes const uint64_t* the UID
fileSource file from which the extension was executed or "" if unavailable X const char*
missionName missionNameSource X const char*
serverName serverName X const char*
remoteExecutedOwner remoteExecutedOwner "0", number as string, no extra quotes const int16_t*
stackTrace Stacktrace of the script that executed callExtension. diag_stacktrace In format LineNumber;SourceFile;ScopeName\n for each stack level. const RVContext_StackTrace* 
struct RVContext_StackTrace
{
	struct StackTraceLine
	{
		// Line number in file (before preprocessing if preprocessed with line numbers)
		uint32_t lineNumber;
		// File offset in bytes from the start of the file (after preprocessing)
		uint32_t fileOffset;
		// Filepath to the source file
		const char* sourceFile;
		// scopeName set on that level
		const char* scopeName;
		// Complete fileContent of the sourceFile (after preprocessing, can be combined with fileOffset to find exact location)
		const char* fileContent;
	};

	StackTraceLine* lines = nullptr;
	uint32_t lineCount = 0;
};

Here is a minimal example: 

#include <string>
#include <vector>
#include <iterator>
#include <sstream>
#include <iomanip>
#include "RVExtensionUtil.hpp"

std::vector<std::string> contextInfo;

extern "C"
{
	//--- Engine passed context
	__declspec (dllexport) void __stdcall RVExtensionContext(const char **args, unsigned int argsCnt);
}

//--- name callExtension function
void CALL_CONVENTION RVExtension(char *output, unsigned int outputSize, const char *function)
{
	//--- Not used here
	(void)function;

	if (!contextInfo.empty())
	{
		std::ostringstream oss;
		const char qt = '"';

		for (auto it = contextInfo.begin(); it != contextInfo.end() - 1; ++it)
			oss << std::quoted(*it, qt, qt) << ",";
		oss << std::quoted(contextInfo.back(), qt, qt);

		//--- Send context info back
		strncpy_s(output, outputSize, ("[" + oss.str() + "]").c_str(), _TRUNCATE);
	}
}

//--- Context is executed first, copy it
void CALL_CONVENTION RVExtensionContext(const char **args, unsigned int argsCnt)
{
	contextInfo.assign(args, std::next(args, argsCnt));
}
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Here is a example using RVFeature_ContextArgumentsVoidPtr combined with RVFeature_ContextStackTrace: 

#include <string>
#include <vector>
#include <iterator>
#include <sstream>
#include <iomanip>

#include "RVExtensionUtil.hpp"

struct CallContext
{
	uint64_t steamId;
	std::string fileSource;
	std::string missionName;
	std::string serverName;
	int16_t remoteExecutedOwner;

	struct StackTraceLine
	{
		// Line number in file (before preprocessing if preprocessed with line numbers)
		uint32_t lineNumber;
		// File offset in bytes from the start of the file (after preprocessing)
		uint32_t fileOffset;
		// Filepath to the source file
		std::string sourceFile;
		// scopeName set on that level
		std::string scopeName;
		// Complete fileContent of the sourceFile (after preprocessing, can be combined with fileOffset to find exact location)
		std::string fileContent;
	};

	std::vector<StackTraceLine> stackTrace;
} contextInfo;

extern "C"
{
	//--- Engine passed context
	__declspec (dllexport) void __stdcall RVExtensionContext(const void **args, unsigned int argsCnt);

	__declspec(dllexport) uint64_t RVExtensionFeatureFlags = RVFeature_ContextArgumentsVoidPtr | RVFeature_ContextStackTrace;
}

//--- name callExtension function
void CALL_CONVENTION RVExtension(char *output, unsigned int outputSize, const char *function)
{
	//--- Not used here
	(void)function;

	{
		std::ostringstream oss;
		const char qt = '"';

		oss << qt << contextInfo.steamId << qt << ",";
		oss << std::quoted(contextInfo.fileSource, qt, qt) << ",";
		oss << std::quoted(contextInfo.missionName, qt, qt) << ",";
		oss << std::quoted(contextInfo.serverName, qt, qt) << ",";
		oss << contextInfo.remoteExecutedOwner << ",";

		//--- Send context info back
		strncpy_s(output, outputSize, ("[" + oss.str() + "]").c_str(), _TRUNCATE);
	}
}

//--- Context is executed before RVExtension is called, and its values are only valid while inside RVExtensionContext function, so we need to copy them to use them later
void CALL_CONVENTION RVExtensionContext(const void **args, unsigned int argsCnt)
{
	size_t index = 0;
	contextInfo.steamId = *static_cast<const uint64_t*>(args[index++]);
	contextInfo.fileSource = static_cast<const char*>(args[index++]);
	contextInfo.missionName = static_cast<const char*>(args[index++]);
	contextInfo.serverName = static_cast<const char*>(args[index++]);
	contextInfo.remoteExecutedOwner = *static_cast<const int16_t*>(args[index++]);

	if (RVExtensionFeatureFlags & RVFeature_ContextStackTrace) {
		auto stackTrace = static_cast<const RVContext_StackTrace*>(argv[index++]);

		std::transform(stackTrace->lines, stackTrace->lines + stackTrace->lineCount, std::back_inserter(contextInfo.stackTrace),
			[](const RVContext_StackTrace::StackTraceLine& line)
			{
					return CallContext::StackTraceLine
					{
						line.lineNumber,
						line.fileOffset,
						line.sourceFile,
						line.scopeName,
						line.fileContent // File content is large and expensive to copy
					};
			});
	}
}
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Manually Context Request

Having RVExtensionContext be called every time before every extension execution can be a waste of performance if the context is not required every time. This automatic call can be disabled with the RVFeature_ContextNoDefaultCall Feature Flag. When the flag is set, the context must be requested.

The Game is exporting a function called RVExtensionRequestContext that can be used to request it, it will then call RVExtensionContext. The RVExtensionContext execution will be completed when RVExtensionRequestContext returns. If the RVExtensionContext exported function is not defined, requesting context will have no effect. The RVExtensionContext call will respect the currently set RVExtensionFeatureFlags, RVExtensionContext can also be called multiple times, with different feature flags.

Here is a example on how to fetch the RequestContext function, and how to use it: 

#include <string>
#include <vector>
#include <iterator>
#include <sstream>
#include <iomanip>

#include "RVExtensionUtil.hpp"

struct CallContext
{
	uint64_t steamId;
	std::string fileSource;
	std::string missionName;
	std::string serverName;
	int16_t remoteExecutedOwner;
} contextInfo;

extern "C"
{
	//--- Engine passed context
	__declspec (dllexport) void __stdcall RVExtensionContext(const void **args, unsigned int argsCnt);

	__declspec(dllexport) uint64_t RVExtensionFeatureFlags = RVFeature_ContextArgumentsVoidPtr | RVFeature_ContextStackTrace | RVFeature_ContextNoDefaultCall;
}

RVExtensionRequestContextProc* requestContext;

void CALL_CONVENTION RVExtensionVersion(char *output, unsigned int outputSize)
{
	requestContext = reinterpret_cast<RVExtensionRequestContextProc*>(FindRVFunction("RVExtensionRequestContext"));
	std::strncpy(output, "Test-Extension v1.0", outputSize - 1);
}

//--- name callExtension function
void CALL_CONVENTION RVExtension(char *output, unsigned int outputSize, const char *function)
{
	//--- Not used here
	(void)function;

	requestContext(); // Request the context dynamically when we need it

	{
		std::ostringstream oss;
		const char qt = '"';

		oss << qt << contextInfo.steamId << qt << ",";
		oss << std::quoted(contextInfo.fileSource, qt, qt) << ",";
		oss << std::quoted(contextInfo.missionName, qt, qt) << ",";
		oss << std::quoted(contextInfo.serverName, qt, qt) << ",";
		oss << contextInfo.remoteExecutedOwner << ",";

		//--- Send context info back
		strncpy_s(output, outputSize, ("[" + oss.str() + "]").c_str(), _TRUNCATE);
	}
}

//--- Its values are only valid while inside RVExtensionContext function, so we need to copy them to use them later
void CALL_CONVENTION RVExtensionContext(const void **args, unsigned int argsCnt)
{
	size_t index = 0;
	contextInfo.steamId = *static_cast<const uint64_t*>(args[index++]);
	contextInfo.fileSource = static_cast<const char*>(args[index++]);
	contextInfo.missionName = static_cast<const char*>(args[index++]);
	contextInfo.serverName = static_cast<const char*>(args[index++]);
	contextInfo.remoteExecutedOwner = *static_cast<const int16_t*>(args[index++]);
}
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External References

The Community-Lead Examples Repository can be used for further examples which go more into detail. To get your example on there, just fork the repository and create a Pull-Request afterwards.

C/C++

Killzone_Kid's "How To Make an Arma Extension" tutorials:

Part 1 Part 2 Part 3 Part 4

C#

Rust

Golang

  • a3go, an Arma Go library by IndigoFox - for Go 1.20
  • Armago, an Arma template extension - for Go 1.16

External Applications

Retrieved from "https://community.bistudio.com/wiki?title=Extensions&oldid=353416"