Issue Passing String from ExtendScript to Custom After Effects Plugin via ExternalObject

[Rewind_]

I'm attempting to pass a string, such as "testCommand," from a JavaScript (ExtendScript) script to a custom After Effects plugin written in C++. Below is my current JavaScript code:

var command = "testCommand";
var pluginPath = "C:/Program Files/Adobe/Common/Plug-ins/7.0/MediaCore/SaveImage/";
var libFilename = "SaveImage.aex";
var consoleLib = new ExternalObject("lib:" + pluginPath + libFilename);
var utf8Command = encodeURIComponent(command);
consoleLib.setCommandString(utf8Command);
consoleLib.unload();

I would appreciate guidance or examples on how to receive this string within the plugin using C++.

[Arie Stavchansky]

How is the `.setCommandString` function implemented on the C++ side?  Its function signature needs to have a parameter as `TaggedData` type.   That data type has members that you set and then return the value.

The examples in the SDK show this function:

    /**
     * Appends a string onto the passed argument.
     *
     * This function only accepts a single argument, a String.  The passed argument
     * is appended with another string and then returned back to the scripting environment.
     * To call from Javascript:
     *
     \code
     myObj.appendString("A String");
     \endcode
     *
     * If the arguments are not correct then a bad argument error code is returned.
     *
     * \param argv - The JavaScript argument
     * \param argc the argument count
     * \param retval The return value to be passed back to JavaScript
     */
    extern "C" BASICEXTERNALOBJECT_API long appendString(TaggedData* argv, long argc, TaggedData * retval)
    {
        // Accept 1 and only 1 argument
        if(argc != 1)
        {
            return kESErrBadArgumentList;
        }
        
        // The argument must be a string
        if(argv[0].type != kTypeString)
        {
            return kESErrBadArgumentList;
        }
        
        // The returned value type
        retval->type = kTypeString;
        
        // argv[0].data.string = the string passed in from the script
        string s (argv[0].data.string);
        
        // add a little bit of data onto the passed in string
        s.append("_appended by BasicExternalObject");
        
        retval->data.string = getNewBuffer(s);
        
        return kESErrOK;
    }

[Rewind_]

I've tried different approaches, but so far I haven't been able to get a working result. I managed to pass a double variable, but I can't pass text. I've tried different text encodings, but it seems that's not the issue. Here are the characters I get instead of the text: �Q? �


here is my code

#include "SaveImage.h"
#include <Windows.h>
#include <string>

static AEGP_PluginID g_plugin_id = 0L;
static SPBasicSuite* g_sp_basic_suite = nullptr;

std::wstring ConvertToWString(const char* str) {

    int len = MultiByteToWideChar(CP_UTF8, 0, str, -1, nullptr, 0);
    std::wstring wide_string(len - 1, L' ');
    MultiByteToWideChar(CP_UTF8, 0, str, -1, &wide_string[0], len);

    return wide_string;
}

extern "C" __declspec(dllexport) const wchar_t* appendString(const char* input_string) {

    std::wstring modified_string = ConvertToWString(input_string);
    MessageBoxW(NULL, modified_string.c_str(), L"Debug", MB_OK);

    return 0;
}

A_Err EntryPointFunc(
    struct SPBasicSuite* pica_basicP,
    A_long major_versionL,
    A_long minor_versionL,
    AEGP_PluginID aegp_plugin_id,
    AEGP_GlobalRefcon* global_refconV
) {
    g_plugin_id = aegp_plugin_id;
    g_sp_basic_suite = pica_basicP;
    AEGP_SuiteHandler suites(pica_basicP);

    return A_Err_NONE;
}

var pluginPath = "C:/Program Files/Adobe/Common/Plug-ins/7.0/MediaCore/SaveImage/";
var pluginLibName = "SaveImage.aex";
var pluginLib = new ExternalObject("lib:" + pluginPath + pluginLibName);
                
var inputString = "My text";
pluginLib.appendString(inputString);

[Rewind_ · Accepted solution]

I managed to pass a string, here is the code that worked
The documentation was especially helpful
https://extendscript.docsforadobe.dev/integrating-external-libraries/defining-entry-points-for-indir... 
https://extendscript.docsforadobe.dev/integrating-external-libraries/defining-entry-points-for-direc... 

Plugin code

#include "SaveImage.h"
#include <Windows.h>

#define kTypeString 4                // Define the type constant for strings
static AEGP_PluginID S_my_id = 0L;
static SPBasicSuite* sP = NULL;

// TaggedData structure (provided by Adobe) https://extendscript.docsforadobe.dev/integrating-external-libraries/defining-entry-points-for-indirect-access.html
typedef struct {
    union {
        long intval;       // Integer value
        double fltval;     // Floating-point value
        char* string;      // String value
    } data;                // Data field
    long type;             // Data type
    long filler;           // Padding for alignment
} TaggedData;

// Exported function for JavaScript to call
extern "C" __declspec(dllexport) long processString(
    TaggedData * argv, 
    long argc, 
    TaggedData * retval)
{
    // Extract the string from the arguments
    const char* receivedString = argv[0].data.string;

    // Debug
    MessageBoxA(NULL, receivedString, "Received String", MB_OK);
    return 0;
}

A_Err EntryPointFunc(
    struct SPBasicSuite* pica_basicP, 
    A_long major_versionL, 
    A_long minor_versionL, 
    AEGP_PluginID aegp_plugin_id, 
    AEGP_GlobalRefcon* global_refconV)
{
    S_my_id = aegp_plugin_id;
    sP = pica_basicP;
    return A_Err_NONE;
}

Extension code

var pluginPath = "C:/Program Files/Adobe/Common/Plug-ins/7.0/MediaCore/SaveImage/";
var libFilename = "SaveImage.aex";
var pluginLib = new ExternalObject("lib:" + pluginPath + libFilename);

var command = "My text";
var result = pluginLib.processString(command);
pluginLib.unload();