Match web_sessions cache pattern only when synchronized

When high-availability has been instructed not to handle web_sessions
(by setting websession.synchronize=false), it should not trigger
web_sessions cache evictions.

In Gerrit, evicting an entry from the 'web_sessions' is equivalent to
logging out the user associated with that session.

Forwarding web_sessions eviction is the correct behavior when their
handling and storing is responsibility of the high-availability plugin.

It is a bug when this happens unconditionally (even when
websession.synchronize=false), because it triggers a log out of that
user from the peer node.

Remove 'web_sessions' cache from the list of default caches that are
always forwarded and, instead, conditionally add it only when
websession synchronization is enabled.

Bug: Issue 13347
Change-Id: I271dbf8bff31da8c850fc98ff6369dca9a156acc

src/main/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcher.java

diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcher.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcher.java
index cab8f58..9a8adce 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcher.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcher.java
@@ -26,14 +26,18 @@
 @Singleton
 class CachePatternMatcher {
   private static final List<String> DEFAULT_PATTERNS =
-      ImmutableList.of(
-          "^accounts.*", "^groups.*", "ldap_usernames", "projects", "sshkeys", "web_sessions");
+      ImmutableList.of("^accounts.*", "^groups.*", "ldap_usernames", "projects", "sshkeys");
 
   private final Pattern pattern;
 
   @Inject
   CachePatternMatcher(Configuration cfg) {
     List<String> patterns = new ArrayList<>(DEFAULT_PATTERNS);
+
+    if (cfg.websession().synchronize()) {
+      patterns.add("web_sessions");
+    }
+
     patterns.addAll(cfg.cache().patterns());
     this.pattern = Pattern.compile(Joiner.on("|").join(patterns));
   }

src/test/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcherTest.java

diff --git a/src/test/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcherTest.java b/src/test/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcherTest.java
index 9093238..0aac3e4 100644
--- a/src/test/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcherTest.java
+++ b/src/test/java/com/ericsson/gerrit/plugins/highavailability/cache/CachePatternMatcherTest.java
@@ -20,6 +20,7 @@
 
 import com.ericsson.gerrit.plugins.highavailability.Configuration;
 import com.google.common.collect.ImmutableList;
+import java.util.Collections;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
@@ -78,4 +79,28 @@
       assertWithMessage(cache + " should not match").that(matcher.matches(cache)).isFalse();
     }
   }
+
+  @Test
+  public void testShouldNotMatchWebSessionsWhenNotSynchronized() {
+    String cache = "web_sessions";
+    when(configurationMock.cache().patterns()).thenReturn(Collections.emptyList());
+    when(configurationMock.websession().synchronize()).thenReturn(false);
+    CachePatternMatcher matcher = new CachePatternMatcher(configurationMock);
+
+    assertWithMessage(cache + " should NOT match when websession.synchronize is false")
+        .that(matcher.matches(cache))
+        .isFalse();
+  }
+
+  @Test
+  public void testShouldMatchWebSessionsWhenSynchronized() {
+    String cache = "web_sessions";
+    when(configurationMock.cache().patterns()).thenReturn(Collections.emptyList());
+    when(configurationMock.websession().synchronize()).thenReturn(true);
+    CachePatternMatcher matcher = new CachePatternMatcher(configurationMock);
+
+    assertWithMessage(cache + " should match when websession.synchronize is true")
+        .that(matcher.matches(cache))
+        .isTrue();
+  }
 }