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

[David Kirkman]

On Wed, Mar 17, 2010 at 11:51 AM, Alessio Stalla
<alessiostalla at gmail.com> wrote:
> 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?

I think that's a much better solution!  I don't mind ClassCastExceptions, my
code had that structure because it started as something copy/pasted out of
Stream.java.  And I was using _readByte and _writeByte just because I didn't
want to have to make changes to Stream.java and end up with my own version
of abcl.

-david k.