[armedbear-devel] is there a good method to read/write java byte arrays?

[Alessio Stalla]

On Wed, Mar 17, 2010 at 7:36 PM, David Kirkman <dkirkman at ucsd.edu> wrote:
> On Wed, Mar 17, 2010 at 9:55 AM, Alessio Stalla <alessiostalla at gmail.com> wrote:
>> On Wed, Mar 17, 2010 at 5:32 PM, Alessio Stalla <alessiostalla at gmail.com> wrote:
>>> On Wed, Mar 17, 2010 at 5:22 PM, Mark Evenson <evenson at panix.com> wrote:
>>>> On 3/17/10 5:04 PM, Alessio Stalla wrote:
>>>> […]
>>>>
>>>>> I wrote sys::%make-byte-array-output-stream in order to make the
>>>>> runtime compiler capable of generating bytecode without using
>>>>> temporary files; it wasn't meant to be used by the ABCL user, and as
>>>>> such it's not very polished (for example, the type of a
>>>>> byte-array-output-stream is simply STREAM). In any case, it's defined
>>>>> in the ByteArrayOutputStream Java class, and as you correctly noted,
>>>>> it explicitly sets the element type to (unsigned-byte 8). As a quick
>>>>> and dirty solution, you could more or less copy-paste that class and
>>>>> replace "output" with "input" :) (as well as update Autoload.java to
>>>>> make ABCL know of the new primitives).
>>>>>
>>>>> We should probably polish it a bit and release it as an extension.
>>>>
>>>> Well, at least we should quickly  whip out the inverse version so David
>>>> doesn't have to rely on hacking Stream.java (although I'm not sure when
>>>> telling Stream that initAsBinaryStream() means a format of unsigned 8bit
>>>> bytes will fail).
>>>>
>>>> I think we can commit to the interface you've implemented in
>>>> ByteArrayOutputStream, as those are the basic necessary operations.
>>>>
>>>> Or maybe I am not seeing what potential problems there would be with
>>>> this as a short-term strategy, Alessio?
>>>
>>> No problem at all in the implementation per se; however, when we'll
>>> make it an "official" extension, the interface will change (if
>>> anything, symbols won't probably be in sys anymore and they won't be
>>> prefixed with %). Since this functionality will have approximately 1
>>> user in the near future :), I think it's ok to commit a quick fix for
>>> David. I'm working on it right now.
>>
>> Committed as r12557.
>>
>> A.
>>
>
> Thanks for implementing the inverse function so quickly!
>
> I ended up doing a bit more hacking last night.  When I tried to serialize
> structures that contain raw java objects, I realized that I need a way to
> convert lisp streams into java streams so that I can use the java
> serialization system.   I ended up writing:
>
>  public static OutputStream
>    outputStreamFromABCLStream(final LispObject stream) {
>
>    if (stream instanceof org.armedbear.lisp.Stream) {
>      return new OutputStream() {
>        public void write(int b) {
>          ((org.armedbear.lisp.Stream) stream)._writeByte(b);
>        }
>      };
>    } else {
>      throw new RuntimeException("argument not an abcl stream");
>    }
>  }
>
> and another version for InputStream.  Should something like these
> also go in as primitives?

For binary input/output streams only, I think accessing the Java
streams wrapped by the Lisp stream is a better solution: no extra
objects are allocated and no API mismatch is possible. Unfortunately
those are private fields right now, but a couple of getters are not
hard to add ;)

so, your outputStreamFromABCLStream would become:

public static OutputStream
  outputStreamFromABCLStream(final LispObject stream) {

  if (stream instanceof org.armedbear.lisp.Stream) {
    return ((org.armedbear.lisp.Stream) stream).getOutputStream();
  } else {
    throw new RuntimeException("argument not an abcl stream");
  }
}

or, if you don't mind getting a ClassCastException instead, simply

public static OutputStream
  outputStreamFromABCLStream(final LispObject stream) {
  return ((org.armedbear.lisp.Stream) stream).getOutputStream();
}

what do you think?

Alessio