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Date: Fri, 22 Aug 2008 09:54:46 -0700 (PDT)
From: "Daniel John Debrunner (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-3770) Create a utility class for skipping
 data in an InputStream
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    [ https://issues.apache.org/jira/browse/DERBY-3770?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624901#action_12624901 ] 

Daniel John Debrunner commented on DERBY-3770:
----------------------------------------------

Some questions/comments about    skipFully(InputStream is) 

What is the purpose of this method, when would it be used? Skipping until EOF seems a useless operation.

SKIP_BUFFER_SIZE is a somewhat confusing name since no buffer is ever allocated.

skipPersistent() states that if a fewer number of bytes is skipped then it is guaranteed that eof has been reached, but skipFully() does not take advantage of this, instead it will always perform an extra call to skipPersistent().

Other input stream utility methods are in org.apache.derby.iapi.services.io, any reason to have this new class in a different package?

> Create a utility class for skipping data in an InputStream
> ----------------------------------------------------------
>
>                 Key: DERBY-3770
>                 URL: https://issues.apache.org/jira/browse/DERBY-3770
>             Project: Derby
>          Issue Type: Improvement
>          Components: Miscellaneous
>    Affects Versions: 10.5.0.0
>            Reporter: Kristian Waagan
>            Assignee: Junjie Peng
>            Priority: Minor
>         Attachments: derby-3770-1.patch, derby-3770-1.stat, derby-3770-2.patch, derby-3770-2.stat, derby-3770-3.patch, derby-3770-3.stat
>
>
> The contract of InputStream.skip is somewhat difficult, some would even say broken.
> See http://java.sun.com/javase/6/docs/api/java/io/InputStream.html#skip(long))
> A utility class should be created to ensure that we use the same skip procedure throughout the Derby code base.
> Suggested functionality:
>  - long skipFully(InputStream) : skips until EOF, returns number of bytes skipped
>  - void skipFully(InputStream,long) : skips requested number of bytes, throws EOFException if there is too few bytes in the stream
> I know of two different approaches, both skipping in a loop:
>  a) Verify EOF with a read call when skip returns zero.
>  b) Throw EOFException if skip returns zero before requested number of bytes have been skipped.
> There's related code in iapi.util.UTF8Util. Maybe this class, say StreamUtil, could be put in the same package?

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