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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2686) The skip method for some InputStreams and Readers return invalid values
Date Wed, 23 May 2007 22:25:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12498409
] 

Daniel John Debrunner commented on DERBY-2686:
----------------------------------------------

It might be dangerous to make the assumption that 0 means EOF for internal streams. Future
changes may wrap/push non-internal streams (e.g. buffering) around internal streams. Thus
some code that thought it was reading an internal stream suddenly starts reading a non-internal
stream where as defined by InputStream.skip() 0 is a valid return for any number of reasons:

  "This may result from any of a number of conditions; reaching end of file before n bytes
have been skipped is only one possibility. "

I think it's wise to use InputStreams according to their contract.

What problem is being solved here?

  

> The skip method for some InputStreams and Readers return invalid values
> -----------------------------------------------------------------------
>
>                 Key: DERBY-2686
>                 URL: https://issues.apache.org/jira/browse/DERBY-2686
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC, Store
>    Affects Versions: 10.3.0.0
>            Reporter: Kristian Waagan
>         Assigned To: Kristian Waagan
>         Attachments: derby-2686-1a.diff, derby-2686-1a.stat
>
>
> The Java API docs for InputStream.skip and Reader.skip seem to indicate that returning
a negative value is breaking the contract.
> The contract for Reader.skip is the more clear one, while I have taken the assumption
that all Derby InputStreams will return 0 only when EOF has been reached or 0 is passed in
as the amount of bytes to skip.
> Bad checking in a skip method also caused Derby to enter an infinite loop in a skip method.
> It should also be noted that skipping bytes/characters should be done in a loop, as skip
 is free to skip a smaller amount of bytes than requested. This is true even if EOF is not
reached.

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