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https://issues.apache.org/jira/browse/LUCENE-825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12478733
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Tim Brennan commented on LUCENE-825:
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The reason I suggested changing FSDirectory is that a quick look through the
callers of Directory.list() show that pretty much none of the callsites expect
a null return from this function.
Check out:
1) SegmentInfos.java - boolean hasSeparateNorms():
String[] result = dir.list();
String pattern;
pattern = name + ".s";
int patternLength = pattern.length();
for(int i = 0; i < result.length; i++){
if(result[i].startsWith(pattern) &&
Character.isDigit(result[i].charAt(patternLength)))
(accesses result.length w/o null check on result)
2) IndexFileDeleter.java - void findDeletableFiles():
String[] files = directory.list();
for (int i = 0; i < files.length; i++) {
(access to files.length w/o null check)
3) Directory.java - static void copy(...)
....same thing...
Should probably fix all those callsites as well, if we really expect
Directory.list() to return null...
> NullPointerException from SegmentInfos.FindSegmentsFile.run() if
> FSDirectory.list() returns NULL
> -------------------------------------------------------------------------------------------------
>
> Key: LUCENE-825
> URL: https://issues.apache.org/jira/browse/LUCENE-825
> Project: Lucene - Java
> Issue Type: Bug
> Affects Versions: 2.1
> Reporter: Tim Brennan
> Assigned To: Michael McCandless
> Fix For: 2.2
>
>
> Found this bug while running unit tests to verify an upgrade of our system
> from 1.4.3 to 2.1.0. This bug did *not* occur during 1.4.3, it is new to 2.x
> (I'm pretty sure it's 2.1-only)
> If the index directory gets deleted out from under Lucene after the
> FSDirectory has been created, then attempts to open an IndexWriter or
> IndexReader will result in an NPE. Lucene should be throwing an IOException
> in this case.
> Repro:
> 1) Create an FSDirectory pointing somewhere in the filesystem (e.g.
> /foo/index/1)
> 2) rm -rf the parent dir (rm -rf /foo/index)
> 3) Try to open an IndexReader
> Result: NullPointerException on line "for(int i=0;i<files.length;i++) { " --
> 'files' is NULL.
>
> Expect: IOException
> ....
> This is happening because of a missing NULL check in
> SegmentInfos$FindSegmentsFile.run():
> if (0 == method) {
> if (directory != null) {
> files = directory.list();
> } else {
> files = fileDirectory.list();
> }
> gen = getCurrentSegmentGeneration(files);
> if (gen == -1) {
> String s = "";
> for(int i=0;i<files.length;i++) {
> s += " " + files[i];
> }
> throw new FileNotFoundException("no segments* file found: files:"
> + s);
> }
> }
> The FSDirectory constructor will make sure the index dir exists, but if it is
> for some reason deleted out from underneath Lucene after the FSDirectory is
> instantiated, then java.io.File.list() will return NULL. Probably better to
> fix FSDirectory.list() to just check for null and return a 0-length array:
> (in org/apache/lucene/store/FSDirectory.java)
> 314c314,317
> < return directory.list(IndexFileNameFilter.getFilter());
> ---
> > String[] toRet = directory.list(IndexFileNameFilter.getFilter());
> > if (toRet == null)
> > return new String[]{};
> > return toRet;
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