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package org.dcache.resilience.util;
import com.google.common.annotations.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.Serializable;
import java.util.UUID;
import dmg.cells.nucleus.CDC;
/**
* <p>Used to check whether the incoming message carries the replication
* handler session id. This is necessary to distinguish messages
* which require handling from those which do not.</p>
*
* <p>Also stores messages which arrive during the DISABLED state, and
* provides them on a one-time-basis to the caller,
* when re-enabled.</p>
*
* <p>Class is not marked final for stubbing/mocking purposes.</p>
*/
public class MessageGuard {
private static final String RESILIENCE_KEY = "RESILIENCE-";
@VisibleForTesting
static final String RESILIENCE_ID = RESILIENCE_KEY + UUID.randomUUID();
private static final Logger LOGGER = LoggerFactory.getLogger(MessageGuard.class);
static void setResilienceSession() {
CDC.setSession(RESILIENCE_ID);
}
public enum Status {
DISABLED, // replication handler is not accepting messages
REPLICA, // message contains the replication session id
EXTERNAL // message does not contain replication session id
}
private BackloggedMessageHandler backlogHandler;
private boolean enabled = false;
private boolean dropMessages = false;
/**
* @param message informative statement for logging purposes.
* @param messageObject received by the handler.
* @return status of the message (EXCLUDED, REPLICA, EXTERNAL).
*/
public Status getStatus(String message, Object messageObject) {
LOGGER.trace("**** acceptMessage **** {}: {} -- {}.", message,
messageObject, enabled);
String session = CDC.getSession();
LOGGER.trace("{} – session {}", message, session);
synchronized (backlogHandler) {
if (!enabled) {
if (!dropMessages && !isResilientSession(session)
&& messageObject instanceof Serializable) {
backlogHandler.saveToBacklog((Serializable) messageObject);
}
LOGGER.trace("{}: {}.", message, Status.DISABLED);
return Status.DISABLED;
}
}
if (isResilientSession(session)) {
LOGGER.trace("{} originated within the replication system ({}).",
message, RESILIENCE_ID);
return Status.REPLICA;
}
LOGGER.trace("{}: {}.", message, Status.EXTERNAL);
return Status.EXTERNAL;
}
public boolean isEnabled() {
synchronized (backlogHandler) {
return enabled;
}
}
public void setBacklogHandler(BackloggedMessageHandler backlogHandler) {
this.backlogHandler = backlogHandler;
}
public void disable(boolean drop) {
synchronized (backlogHandler) {
enabled = false;
dropMessages = drop;
if (!drop) {
backlogHandler.initialize();
} else {
backlogHandler.shutdown();
}
}
}
public void enable() {
synchronized (backlogHandler) {
enabled = true;
backlogHandler.handleBacklog();
}
}
private boolean isResilientSession(String session) {
return session != null && session.startsWith(RESILIENCE_KEY);
}
}