Mozilla ctypes, feeding Arraybuffer from c array

Question

I have a JavaScript function with two arguments (buffer, len), where buffer is an array of encoded data of length "len". My function returns two values with no problem. However, I couldn't figure out how to read the actual data to a JavaScript string. readString is not working for me as the data is not UTF-8.

I was wondering if it is possible to feed the data ("buffer" in my case) to an ArrayBuffer of the same length and equal byte-size

Answer 1

Your function returns two values? Do you mean your c function return a pointer to data and an int as length?

suppose your c function is declared as

xxxx.declare('function_name',
             ctypes.default_abi, 
             ctypes.int, //the return value, suppose as length
             ctypes.uint8_t.ptr.ptr);

  var ct_ptr=new ctypes.uint8_t.ptr();
  var ct_len=function_name(ct_ptr.address());

  ct_ptr.contents is the 1st element of the array

How to access the data in javascript from the ctype pointer of type uint8_t suggests ct_ptr[1].contents will access the 2nd element. I tried, and I found that [1] is not acceptable. Then I tried cast

 var ct_array=ctypes.cast(ct_ptr, ctypes.uint8_t.array(4));
 //then ct_array[0 ...  3] is accessible.

It did succeeded when the array size is not more than 4. However, it turns the value of the point into byte array. The right way is:

 var ct_arrayptr=ctypes.cast(ct_ptr, ctypes.uint8_t.array(ct_len.value).ptr);
 var ct_array=ct_arrayptr.contents;
 //now ct_array[0 ...  ct_len.value-1] is accessible.