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Date: Sun, 12 Apr 2009 04:33:15 -0700 (PDT)
From: "Yun Lee (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-3941) Unsafe use of DataInput.skipBytes() in
 StoredPage and StoredFieldHeader
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     [ https://issues.apache.org/jira/browse/DERBY-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Yun Lee updated DERBY-3941:
---------------------------

    Attachment: derby-3941-2.stat
                derby-3941-2.diff

Knut, 

>1) skipPersistentDataInput() checks if DataInput.readByte() returns -1 to detect that EOF has been reached, but I think that that method will throw EOFException and not return -1 on EOF 

I have changed both  skipPersistentDataInput() and skipPersistent() to perform like what you need, and changed the document of UTF8Util.internalSkip(final InputStream in, final long charsToSkip) which used the skipPersistent(). I think the new revision can act smartlier. Please check the new patches, thanks!

>2) I think I would have renamed skipPersistentDataInput() and skipFullyDataInput() to skipPersistent() and skipFully().

I have tried this before providing the first patches, however, I found it's not able to use overload here, as it will lead to some compiling-time error on ambiguous use, i.e. InputStreamUtil.skipFully(null, int), and InputStreamUtil.skipFully(dis, int) where dis is an instance of DataInputStream.

Yun


> Unsafe use of DataInput.skipBytes() in StoredPage and StoredFieldHeader
> -----------------------------------------------------------------------
>
>                 Key: DERBY-3941
>                 URL: https://issues.apache.org/jira/browse/DERBY-3941
>             Project: Derby
>          Issue Type: Bug
>          Components: Newcomer, Store
>            Reporter: Knut Anders Hatlen
>            Assignee: Yun Lee
>            Priority: Minor
>         Attachments: derby-3941-1.diff, derby-3941-1.stat, derby-3941-2.diff, derby-3941-2.stat
>
>
> Some methods in StoredFileHeader and StoredPage call java.io.DataInput.skipBytes(int) with the assumption that it always skips the requested number of bytes. According to the javadoc for skipBytes, it may skip fewer bytes than requested, possibly 0, even if the end of the stream hasn't been reached.
> The problem exists in these methods:
>   StoredFieldHeader.readFieldDataLength()
>   StoredPage.readRecordFromStream()
>   StoredPage.skipField()
>   StoredPage.readOneColumnFromPage()
>   StoredPage.readRecordFromArray()
> We should change the code so that it works correctly even if skipBytes() were to skip fewer bytes than requested.

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