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Date: Wed, 26 Apr 2006 19:04:50 +0700
From: "Mikhail Loenko" <mloenko@gmail.com>
To: harmony-dev@incubator.apache.org
Subject: Re: [classlib] charset decoding
In-Reply-To: <444F5FEA.1020203@gmail.com>
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References: <e3b630230604260320k40acebfub02a235af52f8285@mail.gmail.com>
	 <444F5FEA.1020203@gmail.com>

2006/4/26, Andrew Zhang <zhanghuangzhu@gmail.com>:
> Vladimir Strigun wrote:
> > On 4/26/06, Andrew Zhang <zhanghuangzhu@gmail.com> wrote:
>
> >
> > I try to find best solution for Harmony-166 and during fix preparation
> > I've found current issue.
> >
> > Method test_read from tests.api.java.io.InputStreamReaderTest failed
> > and first fix I've created was with in.available() but I agree with
> > Mikhail that it's possible not the best solution.
> why?
>
> Yes, the spec says "The available method for class InputStream always
> returns 0.". But it also says "This method should be overridden by
> subclasses.". :)
>
> Here's the available description:
> "Returns the number of bytes that can be read (or skipped over) from
> this input stream without blocking by the next caller of a method for
> this input stream."
>
> If someone writes a subclass of InputStream that available returns 0
> even if there are some data available, then he should take the result of
> cheating or contradicting with spec.

What if someone just unable to say if the bytes are available?
For example, he reads something from a hardware module and
the only way to know whether there are bytes is try reading?

Thanks,
Mikhail

> >
> > In current implementation of InputStreamReader endOfInput variable
> > sets to true if reader can't read less that 8192 bytes. When
> > InputStreamReader try to read one character from
> > LimitedByteArrayInputStream (A ByteArrayInputStream that only returns
> > a single byte per read) true as a parameter passed to charset decoder,
> > nevertheless we still have further input from
> > LimitedByteArrayInputStream.
> >
> > 2 methods from tests.api.java.io.OutputStreamWriterTest also failed
> > because of read() method implementation of InputStreamReader.
> >
> > IMO, we have 2 ways to fix Harmony-166 :
> >
> > 1. Don't change the behavior of CharsetDecoder, and use in.available()
> > method for endOfInput variable. If in.available() > 0 pass false to
> > decoder, read additional one byte from input stream and try to decode
> > again. If decoding operation can decode remaining portion + one
> > additional byte to character, stop here, else try to read addition
> > byte again. Function fillBuf will invoke with the next invocation of
> > read() method and next portion of 8192 bytes will be read from input
> > stream.
> >
> It's reasonable.
> After all, streaming decode is useful and helpful to users.
> IMO, streaming decode is a highlight compared with some RI :)
>
> > 2. Change the behavior of CharsetDecoder and operate with
> > bytes.remaining() for calculating endOfInput. In this case, we always
> > pass false with first invocation of decode method. Algorithm further
> > is almost the same as above, but we stop the cycle if all bytes
> > decoded successfully (i.e if bytes.hasRemaining() is false).
> >
> > What do you think about it?
> >
> >
> > Thanks.
> > Vladimir.
>
> Thanks!
>
> --
> Andrew Zhang
> China Software Development Lab, IBM
>
> >
> >> Any comment?
> >>
> >> Thanks !
> >>
> >>
> >> Vladimir Strigun commented on HARMONY-410:
> >> ------------------------------------------
> >>
> >> Hi Richard,
> >>
> >> Thanks for the clarification, I agree that streaming decode is good th=
ing,
> >> but I'd like to explain my understanding of specification :)
> >> According to specification of CharsetDecoder decoding operation should
> >> process by the following steps:
> >> "
> >> 2. Invoke the decode method zero or more times, as long as additional =
input
> >> may be available, passing false for the endOfInput argument and fillin=
g the
> >> input buffer and flushing the output buffer between invocations;
> >>
> >> 3. Invoke the decode method one final time, passing true for the endOf=
Input
> >> argument; and then
> >> "
> >> spec also says:
> >> "The buffers' positions will be advanced to reflect the bytes read and=
 the
> >> characters written, but their marks and limits will not be modified"
> >>
> >> I understand these sentences in the next way:
> >> invoke decode with endOfInput =3D false if you have additional input, =
then
> >> fill the buffer (i.e. add to buffer some additional input), invoke dec=
ode
> >> again and pass correct endOfInput parameter dependent of availability =
of
> >> input.
> >>
> >> Example you provided is very useful and, of course, 1st option looks b=
etter,
> >> but what I'm suggest here is to reflect actual processed bytes in inpu=
t.
> >> After first invocation of decode, not all bytes processed actually, i.=
e.
> >> almost all bytes processed, but some stored in decoder to further oper=
ation.
> >> Is it possible to store bytes in decoder, support streaming decoding, =
and,
> >> at the same time sets correct position in input buffer after each oper=
ation?
> >>
> >> Thanks.
> >> Vladimir.
> >>
> >>> method decode(ByteBuffer, CharBuffer, boolean) should set correct pos=
ition
> >> in ByteBuffer
> >> ----------------------------------------------------------------------=
------------------
> >>>          Key: HARMONY-410
> >>>          URL: http://issues.apache.org/jira/browse/HARMONY-410
> >>>      Project: Harmony
> >>>         Type: Bug
> >>>   Components: Classlib
> >>>     Reporter: Vladimir Strigun
> >>>     Assignee: Mikhail Loenko
> >>>     Priority: Minor
> >>>  Attachments: Harmony-410_patch.txt, harmony-410_test.txt
> >>>
> >>> When ByteBuffer contain incomplete sequence of bytes for successful
> >> decoding, position in ByteBuffer should be set to latest successful by=
te. I
> >> will attach testcase and patch soon.
> >>
> >> --
> >> This message is automatically generated by JIRA.
> >> -
> >> If you think it was sent incorrectly contact one of the administrators=
:
> >>  http://issues.apache.org/jira/secure/Administrators.jspa
> >> -
> >> For more information on JIRA, see:
> >>  http://www.atlassian.com/software/jira
> >>
> >>
> >>
> >>
> >>
> >> --
> >> Andrew Zhang
> >> China Software Development Lab, IBM
> >>
> >>
> >
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> >
> >
>
>
>
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