Timothee Maret created SLING-3737:
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Summary: Instance Sling Identifier may be randomly reset on restart
Key: SLING-3737
URL: https://issues.apache.org/jira/browse/SLING-3737
Project: Sling
Issue Type: Bug
Components: Extensions
Affects Versions: Settings 1.3.0
Reporter: Timothee Maret
In our Setup, we experience instances which change their Sling identifier upon
restart.
We experiences only a few occurrences of this issue, but the effect is really
bad, turing the services relying on the Sling Identifier into un expected state
(for instance Sling discovery service).
We have checked that the sling.id.file was present before the issue occurred.
We also checked that the value in this file was valid (36 byte long UUID).
Despite this valid file, the instance reset the Sling ID.
Looking at the latest code in
org.apache.sling.settings.impl.SlingSettingsServiceImpl#readSlingId
it seems there is a bug in the way the sling.id.file file is read.
{code}
private String readSlingId(final File idFile) {
if (idFile.exists() && idFile.length() >= 36) {
FileInputStream fin = null;
try {
fin = new FileInputStream(idFile);
final byte[] rawBytes = new byte[36];
if (fin.read(rawBytes) == 36) {
final String rawString = new String(rawBytes, "ISO-8859-1");
// roundtrip to ensure correct format of UUID value
final String id = UUID.fromString(rawString).toString();
logger.debug("Got Sling ID {} from file {}", id, idFile);
return id;
}
} catch (final Throwable t) {
logger.error("Failed reading UUID from id file " + idFile
+ ", creating new id", t);
} finally {
if (fin != null) {
try {
fin.close();
} catch (IOException ignore) {
}
}
}
}
return null;
}
{code}
In the line
{code}
if (fin.read(rawBytes) == 36) {
{code}
The code miss uses the java.io.FileInputStream#read API.
{code}
/**
* Reads up to <code>b.length</code> bytes of data from this input
* stream into an array of bytes. This method blocks until some input
* is available.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the file has been reached.
* @exception IOException if an I/O error occurs.
*/
{code}
The API stipulates that the method blocks until if finds *some* data.
This is a common pattern with Java IO APIs, and indeed, the method may return
with only one byte read even though the end of the stream was not reached.
If this is the case, the current logic will treat the slingId as invalid and
generate a new one.
A way to fix that is to read the sling id file completely, for instance using
the org.apache.commons.io.FileUtils API
We are running on CentOS 6.2, JDK 1.7.
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