[
https://issues.apache.org/jira/browse/DERBY-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12698237#action_12698237
]
Knut Anders Hatlen commented on DERBY-3941:
-------------------------------------------
Hi Yun,
My point about DataInput.readByte() was that -1 is not an indication that the
end of the stream has been reached, so it's not correct to throw an
EOFException when readByte() returns -1. I think skipFully() will have to be
implemented along the lines of this untested code:
public static void skipFully(DataInput in, int bytesToSkip)
throws IOException
{
if (in == null) {
throw new NullPointerException();
}
while (bytesToSkip > 0) {
int skipped = in.skipBytes(bytesToSkip);
if (skipped == 0) {
// No bytes skipped, read one byte to see if EOF has been
// reached. DataInput.readByte() will throw an EOFException
// if there's nothing more to read.
in.readByte();
// Still more data to read. Account for the byte we just read.
skipped++;
}
bytesToSkip -= skipped;
}
}
The changes to the javadoc for skipPersistent(InputStream,int) also look wrong,
as that method is not supposed to throw an EOFException if end of stream is
reached before all the bytes have been skipped. If it reaches end of stream
prematurely, it returns the number of bytes actually skipped, just as the old
javadoc said.
As to the compile errors when using the same name for the different variants of
skipFully(), it should be possible to disambiguate the method calls by using a
cast, like this:
InputStreamUtil.skipFully((InputStream) null, x);
or
InputStreamUtil.skipFully((DataInput) null, x);
But perhaps the problem here is that we're trying to overload InputStreamUtil
too much. Since a DataInput is not (necessarily) an InputStream it might be
cleaner to create a new class, DataInputUtil, where we can collect utility
methods for DataInputs without conflicting with the utilities for InputStreams.
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
