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https://issues.apache.org/jira/browse/KNOX-2777?focusedWorklogId=793657&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-793657
 ]

ASF GitHub Bot logged work on KNOX-2777:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 21/Jul/22 10:09
            Start Date: 21/Jul/22 10:09
    Worklog Time Spent: 10m 
      Work Description: smolnar82 commented on code in PR #608:
URL: https://github.com/apache/knox/pull/608#discussion_r926499605


##########
gateway-spi-common/src/main/java/org/apache/knox/gateway/session/control/ConcurrentSessionVerifier.java:
##########
@@ -0,0 +1,102 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.knox.gateway.session.control;
+
+
+import org.apache.knox.gateway.config.GatewayConfig;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class ConcurrentSessionVerifier {
+  public static final ConcurrentSessionVerifier INSTANCE = new 
ConcurrentSessionVerifier();
+  private Set<String> privilegedUsers;
+  private Set<String> nonPrivilegedUsers;
+  private int privilegedUserConcurrentSessionLimit;
+  private int nonPrivilegedUserConcurrentSessionLimit;
+  private Map<String, Integer> concurrentSessionCounter;
+  private final Lock sessionCountModifyLock = new ReentrantLock();
+
+  private ConcurrentSessionVerifier() {
+  }
+
+  public static ConcurrentSessionVerifier getInstance() {
+    return INSTANCE;
+  }
+
+  public void init(GatewayConfig config) {
+    this.privilegedUsers = config.getPrivilegedUsers();
+    this.nonPrivilegedUsers = config.getNonPrivilegedUsers();
+    this.privilegedUserConcurrentSessionLimit = 
config.getPrivilegedUsersConcurrentSessionLimit();
+    this.nonPrivilegedUserConcurrentSessionLimit = 
config.getNonPrivilegedUsersConcurrentSessionLimit();
+    this.concurrentSessionCounter = new ConcurrentHashMap<>();
+  }
+
+  public boolean verifySessionForUser(String username) {
+    if (!privilegedUsers.contains(username) && 
!nonPrivilegedUsers.contains(username)) {
+      return true;
+    }
+
+    sessionCountModifyLock.lock();
+    try {
+      concurrentSessionCounter.putIfAbsent(username, 0);
+      if (privilegedUserCheckLimitReached(username) || 
nonPrivilegedUserCheckLimitReached(username)) {
+        return false;
+      }
+      concurrentSessionCounter.compute(username, (key, value) -> value + 1);
+    } finally {
+      sessionCountModifyLock.unlock();
+    }
+    return true;
+  }
+
+  private boolean privilegedUserCheckLimitReached(String username) {
+    if (privilegedUserConcurrentSessionLimit < 0) {
+      return false;
+    }
+    return privilegedUsers.contains(username) && 
(concurrentSessionCounter.get(username) >= 
privilegedUserConcurrentSessionLimit);
+  }
+
+  private boolean nonPrivilegedUserCheckLimitReached(String username) {
+    if (nonPrivilegedUserConcurrentSessionLimit < 0) {
+      return false;
+    }
+    return nonPrivilegedUsers.contains(username) && 
(concurrentSessionCounter.get(username) >= 
nonPrivilegedUserConcurrentSessionLimit);
+  }
+
+  public void sessionEndedForUser(String username) {
+    if (concurrentSessionCounter.containsKey(username)) {
+      sessionCountModifyLock.lock();
+      try {
+        int count = concurrentSessionCounter.get(username);

Review Comment:
   I agree; this is a better approach. Nice catch, Attila! :) 





Issue Time Tracking
-------------------

    Worklog Id:     (was: 793657)
    Time Spent: 3h  (was: 2h 50m)

> Implement concurrent session verifier
> -------------------------------------
>
>                 Key: KNOX-2777
>                 URL: https://issues.apache.org/jira/browse/KNOX-2777
>             Project: Apache Knox
>          Issue Type: Sub-task
>          Components: Server
>    Affects Versions: 2.0.0
>            Reporter: Sandor Molnar
>            Assignee: Balazs Marton
>            Priority: Major
>             Fix For: 2.0.0
>
>          Time Spent: 3h
>  Remaining Estimate: 0h
>
> The following needs to be implemented in the scope of this JIRA:
>  * we need 4 new Gateway-level configurations:
>  ** privileged user list (defaults to an empty collection)
>  ** non-privileged user list (defaults to an empty collection)
>  ** session limit for privileged users (defaults to 3)
>  ** session limit for non-privileged users (defaults to 2)
>  * if a session limit for any of the groups is set to a negative number, that 
> means the users in that group are allowed to have an unlimited number of 
> sessions
>  * In addition to the new configs, a verifier has to be implemented that 
> enforces the following business logic: if a user is listed in the 
> above-introduced privileged/non-privileged collection AND is about to pass a 
> configured session limit the verification should fail. The verification 
> should succeed if the given user is declared neither a privileged nor a 
> non-privileged user.
> The new verifier implementation may be placed in the {{gateway-spi-common}} 
> project for now.



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