Javascript String to C++ char pointer -LPSTR buffer in JSCTypes

问题

I am accessing the DLL from JavaScript using JSCTypes. I have to receive data by passing a character buffer to the following API,

__declspec(dllexport) WORD WINAPI receive( LPWORD  lpwBufferSize,
                                           LPSTR   lpsBuffer);

My jsctypes looks like this,

let receive = libs.dll.declare("receive",
                               ctypes.stdcall_abi,  
                               ctypes.int32_t,           // Return type - return code
                               ctypes.int32_t.ptr,       // buffer size
                               ctypes.char.ptr,          // Buffer
                               );
var bufferSize = new ctypes.int32_t(3000000).address(); //3000000
var buffer = new ctypes.char().address();
let rvopen = receive(bufferSize, buffer);
return buffer.readString()

With above code, I could receive data for the first time correctly but xulrunner crashes on receive function call in the subsequent times. I tried to reproduce this produce this issue with a common DLL available on windows. This throws an exception, uncaught exception: TypeError: ctypes.char.array(500).address is not a function

var hostName = exports.getString = function() {
    let lib = ctypes.open('Ws2_32.dll');
    let gethostname = lib.declare("gethostname",
                                  ctypes.default_abi,
                                  ctypes.int,
                                  ctypes.char.ptr,
                                  ctypes.int);
    var myArray = ctypes.char.array(500).address();
    gethostname(myArray, 500);
    return myArray.readString();
};

If I drop the address API call and try it as below,

var myArray = ctypes.char.array(64);

I run into this issue, although in C++ arrays are considered as pointers.

'uncaught exception: TypeError: expected type pointer, got ctypes.char.array(640000)' in file '' at line 0, col 0

I don't have access to any of the dll's source code. I just have the include file(.h) for the DLL. I am a Java developer and not sure if I can debug without the source code Any help appreciated!

回答1:

Have finally found a solution,

<code>
 let charArray= ctypes.ArrayType(ctypes.char);
 let myArray = new charArray(500);      
</code>

and the function prototype is the same

回答2:

If I had to guess, I would say that you need to allocate the buffer to the right size. Maybe:

var buffer = new ctypes.char().array(3000000).address();

Try using a debugger with a breakpoint set in the "receive" function to see what data is being passed from JS.

来源：https://stackoverflow.com/questions/6936567/javascript-string-to-c-char-pointer-lpstr-buffer-in-jsctypes

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