ModuleReader does not have a method for getting size hint for a named resource

[Alan Bateman]

On 08/08/2018 06:16, Luke Hutchison wrote:
> The current ModuleReader API has methods list(), open(String name), and
> read(String name). However, there is no way to get the length (file size)
> of a resource short of opening or reading the whole resource, then
> examining the number of bytes read or mapped. This can lead to unnecessary
> resizing of arrays, and therefore unnecessary array copying.
>
> Internally, the resource size is available in
> ImageLocation#getUncompressedSize(). Can this be exposed as a size hint in
> the ModuleReader API, e.g. in a method ModuleReader#getSizeHint(String
> name) ?
The issue of exposing the resource size, in the context of the Module 
API, was issue #ResourceExistenceAndSize in JSR 376. It was decided to 
defer it as it wasn't critical for a first version.

If you are using the ModuleReader API then I assume you are doing 
something that is scanning the module path (although your other mail 
seems to be about resources in run-time image with compression so you 
might be doing something else). If you need the size then one way to do 
this is with:

     int size = reader.read(name)
                     .map(bb -> {
                         int rem = bb.remaining();
                         reader.release(bb);
                         return rem;
                     }).orElseThrow(() -> new RuntimeException("not 
found"));

When not using compression then this should be backed by a region from 
the underlying file mapping. Yes, the compressed case is more expensive 
but it's not the default.

-Alan