Avoid creating HTTP Sessions for Git-over-HTTP

The Change-Id: Iffcd0fbd7 has involuntarily triggered the
creation of a new HTTP Session for every invocation a Git-over-HTTP
request.

All came from the mistake of tracing the HTTP session instead
of the Gerrit session in the audit record.
The HTTP Servlet API specs say that any attempt to access
the current session of an incoming request would result
in the creation of a brand-new session.

The session involuntarily created also had an expiry time
equal to zero, which prevented the session housekeeper
to reclaim them later on, even though they were unused.

The consequence of creating an empty session for every
Git-over-HTTP request isn't immediately tangible, because
the session is empty and doesn't occupy a significant
amount of memory. However, longer-term, the in-memory
hashtable that records all the sessions, each one using
750 bytes on average, will be causing the overload
of the JVM heap and the crash of the process because of
lack of available memory.

Use the correct Gerrit session-id, retrieving
from the Provider<WebSession> the proper session, if active
and logged in, and make sure in tests that no HTTP sessions
are created as a result of a Git-over-http request.

Bug: Issue 13858
Change-Id: I8c086fed54b196c3f46fa88ac78c127784524d30

java/com/google/gerrit/acceptance/GerritServer.java

@@ -602,6 +602,10 @@ public class GerritServer implements AutoCloseable {
     return testInjector;
   }
 
+  public Injector getHttpdInjector() {
+    return daemon.getHttpdInjector();
+  }
+
   Description getDescription() {
     return desc;
   }

java/com/google/gerrit/httpd/GitOverHttpServlet.java

@@ -360,6 +360,7 @@ public class GitOverHttpServlet extends GitServlet {
     private final Metrics metrics;
     private final PluginSetContext<RequestListener> requestListeners;
     private final UsersSelfAdvertiseRefsHook usersSelfAdvertiseRefsHook;
+    private final Provider<WebSession> sessionProvider;
 
     @Inject
     UploadFilter(
@@ -369,7 +370,8 @@ public class GitOverHttpServlet extends GitServlet {
         GroupAuditService groupAuditService,
         Metrics metrics,
         PluginSetContext<RequestListener> requestListeners,
-        UsersSelfAdvertiseRefsHook usersSelfAdvertiseRefsHook) {
+        UsersSelfAdvertiseRefsHook usersSelfAdvertiseRefsHook,
+        Provider<WebSession> sessionProvider) {
       this.uploadValidatorsFactory = uploadValidatorsFactory;
       this.permissionBackend = permissionBackend;
       this.userProvider = userProvider;
@@ -377,6 +379,7 @@ public class GitOverHttpServlet extends GitServlet {
       this.metrics = metrics;
       this.requestListeners = requestListeners;
       this.usersSelfAdvertiseRefsHook = usersSelfAdvertiseRefsHook;
+      this.sessionProvider = sessionProvider;
     }
 
     @Override
@@ -392,7 +395,7 @@ public class GitOverHttpServlet extends GitServlet {
       HttpServletResponseWithStatusWrapper responseWrapper =
           new HttpServletResponseWithStatusWrapper((HttpServletResponse) response);
       HttpServletRequest httpRequest = (HttpServletRequest) request;
-      String sessionId = httpRequest.getSession().getId();
+      String sessionId = getSessionIdOrNull(sessionProvider);
 
       try (TraceContext traceContext = TraceContext.open()) {
         RequestInfo requestInfo =
@@ -495,6 +498,7 @@ public class GitOverHttpServlet extends GitServlet {
     private final Provider<CurrentUser> userProvider;
     private final GroupAuditService groupAuditService;
     private final Metrics metrics;
+    private final Provider<WebSession> sessionProvider;
 
     @Inject
     ReceiveFilter(
@@ -502,12 +506,14 @@ public class GitOverHttpServlet extends GitServlet {
         PermissionBackend permissionBackend,
         Provider<CurrentUser> userProvider,
         GroupAuditService groupAuditService,
-        Metrics metrics) {
+        Metrics metrics,
+        Provider<WebSession> sessionProvider) {
       this.cache = cache;
       this.permissionBackend = permissionBackend;
       this.userProvider = userProvider;
       this.groupAuditService = groupAuditService;
       this.metrics = metrics;
+      this.sessionProvider = sessionProvider;
     }
 
     @Override
@@ -547,7 +553,7 @@ public class GitOverHttpServlet extends GitServlet {
       } finally {
         groupAuditService.dispatch(
             new HttpAuditEvent(
-                httpRequest.getSession().getId(),
+                getSessionIdOrNull(sessionProvider),
                 userProvider.get(),
                 extractWhat(httpRequest),
                 TimeUtil.nowMs(),
@@ -603,4 +609,12 @@ public class GitOverHttpServlet extends GitServlet {
     @Override
     public void destroy() {}
   }
+
+  private static String getSessionIdOrNull(Provider<WebSession> sessionProvider) {
+    WebSession session = sessionProvider.get();
+    if (session.isSignedIn()) {
+      return session.getSessionId();
+    }
+    return null;
+  }
 }

java/com/google/gerrit/pgm/Daemon.java

@@ -238,6 +238,11 @@ public class Daemon extends SiteProgram {
     this.replica = replica;
   }
 
+  @VisibleForTesting
+  public Injector getHttpdInjector() {
+    return httpdInjector;
+  }
+
   @Override
   public int run() throws Exception {
     if (stopOnly) {

java/com/google/gerrit/pgm/http/jetty/JettyServer.java

@@ -17,6 +17,7 @@ package com.google.gerrit.pgm.http.jetty;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Strings;
 import com.google.gerrit.extensions.client.AuthType;
 import com.google.gerrit.extensions.events.LifecycleListener;
@@ -42,8 +43,11 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
 import javax.servlet.DispatcherType;
 import javax.servlet.Filter;
+import javax.servlet.http.HttpSessionEvent;
+import javax.servlet.http.HttpSessionListener;
 import org.eclipse.jetty.http.HttpScheme;
 import org.eclipse.jetty.io.ConnectionStatistics;
 import org.eclipse.jetty.jmx.MBeanContainer;
@@ -200,6 +204,8 @@ public class JettyServer {
   private final Metrics metrics;
   private boolean reverseProxy;
   private ConnectionStatistics connStats;
+  private final SessionHandler sessionHandler;
+  private final AtomicLong sessionsCounter;
 
   @Inject
   JettyServer(
@@ -218,8 +224,27 @@ public class JettyServer {
       connector.addBean(connStats);
     }
     metrics = new Metrics(pool, connStats);
+    sessionHandler = new SessionHandler();
+    sessionsCounter = new AtomicLong();
 
-    Handler app = makeContext(env, cfg);
+    /* Code used for testing purposes for making assertions
+     * on the number of active HTTP sessions.
+     */
+    sessionHandler.addEventListener(
+        new HttpSessionListener() {
+
+          @Override
+          public void sessionDestroyed(HttpSessionEvent se) {
+            sessionsCounter.decrementAndGet();
+          }
+
+          @Override
+          public void sessionCreated(HttpSessionEvent se) {
+            sessionsCounter.incrementAndGet();
+          }
+        });
+
+    Handler app = makeContext(env, cfg, sessionHandler);
     if (cfg.getBoolean("httpd", "requestLog", !reverseProxy)) {
       RequestLogHandler handler = new RequestLogHandler();
       handler.setRequestLog(httpLogFactory.get());
@@ -246,6 +271,11 @@ public class JettyServer {
     httpd.setStopAtShutdown(false);
   }
 
+  @VisibleForTesting
+  public long numActiveSessions() {
+    return sessionsCounter.longValue();
+  }
+
   Metrics getMetrics() {
     return metrics;
   }
@@ -445,7 +475,7 @@ public class JettyServer {
     return pool;
   }
 
-  private Handler makeContext(JettyEnv env, Config cfg) {
+  private Handler makeContext(JettyEnv env, Config cfg, SessionHandler sessionHandler) {
     final Set<String> paths = new HashSet<>();
     for (URI u : listenURLs(cfg)) {
       String p = u.getPath();
@@ -460,7 +490,7 @@ public class JettyServer {
 
     final List<ContextHandler> all = new ArrayList<>();
     for (String path : paths) {
-      all.add(makeContext(path, env, cfg));
+      all.add(makeContext(path, env, cfg, sessionHandler));
     }
 
     if (all.size() == 1) {
@@ -478,13 +508,14 @@ public class JettyServer {
     return r;
   }
 
-  private ContextHandler makeContext(final String contextPath, JettyEnv env, Config cfg) {
+  private ContextHandler makeContext(
+      final String contextPath, JettyEnv env, Config cfg, SessionHandler sessionHandler) {
     final ServletContextHandler app = new ServletContextHandler();
 
     // This enables the use of sessions in Jetty, feature available
     // for Gerrit plug-ins to enable user-level sessions.
     //
-    app.setSessionHandler(new SessionHandler());
+    app.setSessionHandler(sessionHandler);
     app.setErrorHandler(new HiddenErrorHandler());
 
     // This is the path we are accessed by clients within our domain.