Iterating keys of proxy object

[alandefreitas]

I'm virtualizing an object as a duktape Proxy object but can't iterate or get all the keys in this object. When I try to get the object keys, I always get an empty array. Is there a solution or even a workaround to this?

I created a minimal example just in case:

duk_context* ctx = duk_create_heap_default();
duk_push_object(ctx); // [target]
duk_push_object(ctx); // [target] [handler]
duk_push_c_function(ctx, ownKeysFn, 1); // [target] [handler] [function]
duk_put_prop_string(ctx, -2, "ownKeys"); // [target] [handler]
duk_push_c_function(ctx, getKeyFn, 1); // [target] [handler] [function]
duk_put_prop_string(ctx, -2, "get"); // [target] [handler]
duk_push_proxy(ctx, 0); // [proxy]

where

duk_ret_t
ownKeysFn(duk_context* ctx)
{
    // return ["k1", "k2", "k3"]
    duk_idx_t arr_idx = duk_push_array(ctx); // [target] [array]
    duk_push_string(ctx, "k1"); // [target] [array] [string]
    duk_put_prop_index(ctx, arr_idx, 0); // [target] [array]
    duk_push_string(ctx, "k2"); // [target] [array] [string]
    duk_put_prop_index(ctx, arr_idx, 1); // [target] [array]
    duk_push_string(ctx, "k3"); // [target] [array] [string]
    duk_put_prop_index(ctx, arr_idx, 2); // [target] [array]
    return 1;
}

and

duk_ret_t
getKeyFn(duk_context* ctx)
{
    // Any key returns 1 just for the sake of the test.
    duk_idx_t arr_idx = duk_push_array(ctx); // [target] [key] [recv]
    duk_push_int(ctx, 1); // [target] [key] [recv] [int]
    return 1;
}

When I try to get or iterate the keys, I get an empty array. I tried many ways of iterating these values (scripts, from C, etc), including the following:

duk_enum(ctx, -1, DUK_ENUM_OWN_PROPERTIES_ONLY); // this triggers ownKeysFn
while (duk_next(ctx, -1, 1))
{
    // This never executes:
    const char * key = duk_get_string(ctx, -2); // [proxy] [key] [value]
    do_something_with_key(key);
    duk_pop_2(ctx); // [proxy]
}
duk_pop(ctx);

I guess this issue could be related to #2153 but I'm not sure if the use cases are the same because I honestly don't completely understand that discussion since I'm not as fluent in JavaScript. If I understand that discussion correctly, do I need either to define getOwnPropertyDescriptor (which duktape doesn't support) or somehow define the keys explicitly (which breaks virtualization)? Is there a workaround to achieve virtualization somehow with duktape? #2153 issue is from 2019 so maybe some things have changed?

[alandefreitas]

Update: I tried another version where the target stores a "keys" property containing an array with the keys and ownKeysFn returns that array instead of creating it. Unfortunately, this doesn't work either.

It's an unreasonable solution anyway, but I thought ownKeysFn could update the keys in target whenever it's called. It would be a last-resort workaround.