Function miracle_get_plugin_userdata 

pub unsafe extern "C" fn miracle_get_plugin_userdata(
    handle: u32,
    buf_ptr: i32,
    buf_len: i32,
) -> i32

Retrieve the JSON-encoded userdata configured for this plugin.

Returns the number of bytes written on success (>0), 0 if no userdata is configured, or -1 if the provided buffer is too small.