Function pio_arrow_catalog_json 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_arrow_catalog_json(
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut c_char

Return the Arrow table catalog as owned compact JSON.

The catalog is feature based rather than handle based: it describes what this library build can export, not what a particular network contains. Top level fields are powerio_version, producer, and tables. Each table entry includes id, name, format, feature_requirements, available, row_axis, col_axis, units, and columns. Each column entry includes name, type, and nullable. Through v4 both levels carried a schema_version; one release version now covers every document powerio authors, so the top level names it and the per-table copy is gone.

Free the returned string with pio_string_free. On error this returns NULL and writes the message into errbuf. Only built with the arrow cargo feature.