ventgreyV
Deno•2y ago•
13 replies
ventgrey

Help with FFI strings

I've been testing with the deno FFI to see if it's powerful enough to leverage the power of other languages into Deno.

This however has been very unfruitful as FFI documentations seems to be "everywhere" when it comes to types, take for example anything that returns a 
char*
. There are very few hints on how is one supposed to handle such returns.

I was working with a function similar to this:
extern char* searchByDinoSpecies(char* dinosaursString, char* species);


You can assume the 
dinosaurString
 to be a JSON string or a YAML string, idk. Whatever your compiled C-grandson language lets you handle


In my search I found this article: https://medium.com/deno-the-complete-reference/calling-c-functions-from-deno-part-2-pass-buffers-ad168a3b6cc7

However, two problems arise from here:

1. You cannot use the 
pointer
 type in 
parameters: []
 when loading my 
dylib
 because I'll get a 
TypeError: Invalid FFI pointer type, expected null, or External



Reading the official Deno docs, the documentation states:

buffer type accepts TypedArrays as parameter, but it always returns a pointer object or null when used as result type like the pointer type.

- Source: https://docs.deno.com/runtime/manual/runtime/ffi_api/

Okay, so maybe everything as a 
buffer
 should work? Well, both parameters sure work when setting 
buffer
 but another problem arises. The output, either 
pointer
 or 
buffer
 is completely useless.

The previous Medium Post shows something like this:

const ret = dylib.symbols.toAndFroBuffer(buffer);
const dataView = new Deno.UnsafePointerView(ret);


However, when tried to replicate this, another TypeError arises:

Argument of type 'PointerValue<unknown>' is not assignable to parameter of type 'PointerObject<unknown>'.
  Type 'null' is not assignable to type 'PointerObject<unknown>'


Discord has an awfully lame limit, continuing in the comments (?)
Medium
Calling C functions from Deno: Part 2 — Pass buffers
Learn how to call C functions from Deno and pass arbitrary buffers to and fro
Calling C functions from Deno: Part 2 — Pass buffers
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