神•12mo ago

What should I specify to pass a "char *" in Deno.dlopen?

For example, this is how you would use it in Python:

import ctypes

lib = ctypes.cdll.LoadLibrary('example.dll')
check = lib.check
check.argtypes = [ctypes.c_char_p]
check.restype = ctypes.c_char_p

import ctypes

lib = ctypes.cdll.LoadLibrary('example.dll')
check = lib.check
check.argtypes = [ctypes.c_char_p]
check.restype = ctypes.c_char_p

10 Replies

神•12mo ago

https://deno.land/manual@v1.36.0/runtime/ffi_api#supported-types I looked here but couldn't find the appropriate type Not familiar with native code

Deno

Foreign Function Interface | Manual | Deno

As of Deno 1.13 and later, the FFI (foreign function interface) API allows users to call libraries written in native languages that support the C ABIs (C/C++, Rust, Zig, V, etc.) using Deno.dlopen.

NeTT•12mo ago

buffer should do if it is from the JS side pointer if from Native side check out denonomicon https://denonomicon.deno.dev/types (tho the styles are broken atm)

神•12mo ago

Using buffer gets a funny response. [Object: null prototype] {} So pointer is probably the correct answer. Learn about the pointer. Given pointer, it asks for Deno.PointerValue as its argument, so it tries to find a way to convert the string to Deno.PointerValue. Thank you!

NeTT•12mo ago

are you passing a char * to the native code? or are you sending it from native code to JS?

神•12mo ago

I send it to a Go program compiled from Deno to dll.

func check(ExampleArg *C.char) *C.char {
    // do anything
    return C.CString('a')
}

func check(ExampleArg *C.char) *C.char {
    // do anything
    return C.CString('a')
}

NeTT•12mo ago

ah idk how it is done generally but I can provide an example of how I do it I convert my text into a Uint8Array with a TextEncoder and pass it as a buffer type the native code can parse the byte stream as a string or whatever I also pass an additional Uint8Array to which the native code writes the response and I parse it in the JS side after the FFI call

神•12mo ago

const library = Deno.dlopen('example.dll', {
  check: {
    parameters: ['buffer'],
    result: 'buffer',
    nonblocking: true,
  },
});

const response = await library.symbols.check(new TextEncoder().encode('a'));
console.log(response);

const library = Deno.dlopen('example.dll', {
  check: {
    parameters: ['buffer'],
    result: 'buffer',
    nonblocking: true,
  },
});

const response = await library.symbols.check(new TextEncoder().encode('a'));
console.log(response);

[Object: null prototype] {} The console displays the above results I thought there was a problem with the dll, but I suspect there is a problem with my code because I called it from Python and it successfully asked for a response Sorry [Object: null prototype] {} I looked at it and decided it wasn't the right response, but when I correctly parsed the results, it worked. I mistakenly thought that an empty object was being returned. Thank you 😢

NeTT•12mo ago

<:hooray_deno:1035517542200004688> result: 'buffer' doesn't do anything different from pointer as parameter types, they are different but as return types, they are the same

神•12mo ago

I see, I learn a lot! Thank you so much😭

NeTT•12mo ago

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