Add metrics for http/server/rest_api calls

Break these down by the view implementation class showing what part of
Gerrit handled the request.  Include latency information, aggregate
counts, and errors when HTTP status code is >= 400.

Change-Id: Ifc806e4dbf157b4eea368e9a223d8ad1e551b8e7

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiMetrics.java

@@ -0,0 +1,78 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.httpd.restapi;
+
+import com.google.common.base.Strings;
+import com.google.gerrit.httpd.restapi.RestApiServlet.ViewData;
+import com.google.gerrit.metrics.Counter1;
+import com.google.gerrit.metrics.Counter2;
+import com.google.gerrit.metrics.Description;
+import com.google.gerrit.metrics.Field;
+import com.google.gerrit.metrics.MetricMaker;
+import com.google.gerrit.metrics.Timer1;
+import com.google.gerrit.metrics.Description.Units;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+@Singleton
+public class RestApiMetrics {
+  private static final String[] PKGS = {
+    "com.google.gerrit.server.",
+    "com.google.gerrit.",
+  };
+
+  final Counter1<String> count;
+  final Counter2<String, Integer> errorCount;
+  final Timer1<String> serverLatency;
+
+  @Inject
+  RestApiMetrics(MetricMaker metrics) {
+    Field<String> view = Field.ofString("view", "view implementation class");
+    count = metrics.newCounter(
+        "http/server/rest_api/count",
+        new Description("REST API calls by view")
+          .setRate(),
+        view);
+
+    errorCount = metrics.newCounter(
+        "http/server/rest_api/error_count",
+        new Description("REST API calls by view")
+          .setRate(),
+        view,
+        Field.ofInteger("error_code", "HTTP status code"));
+
+    serverLatency = metrics.newTimer(
+        "http/server/rest_api/server_latency",
+        new Description("REST API call latency by view")
+          .setCumulative()
+          .setUnit(Units.MILLISECONDS),
+        view);
+  }
+
+  String view(ViewData viewData) {
+    String impl = viewData.view.getClass().getName().replace('$', '.');
+    for (String p : PKGS) {
+      if (impl.startsWith(p)) {
+        impl = impl.substring(p.length());
+        break;
+      }
+    }
+    if (!Strings.isNullOrEmpty(viewData.pluginName)
+        && !"gerrit".equals(viewData.pluginName)) {
+      impl = viewData.pluginName + '-' + impl;
+    }
+    return impl;
+  }
+}

gerrit-httpd/src/main/java/com/google/gerrit/httpd/restapi/RestApiServlet.java

@@ -125,6 +125,7 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 import java.util.regex.Pattern;
 import java.util.zip.GZIPOutputStream;
 
@@ -164,16 +165,19 @@ public class RestApiServlet extends HttpServlet {
     final DynamicItem<WebSession> webSession;
     final Provider<ParameterParser> paramParser;
     final AuditService auditService;
+    final RestApiMetrics metrics;
 
     @Inject
     Globals(Provider<CurrentUser> currentUser,
         DynamicItem<WebSession> webSession,
         Provider<ParameterParser> paramParser,
-        AuditService auditService) {
+        AuditService auditService,
+        RestApiMetrics metrics) {
       this.currentUser = currentUser;
       this.webSession = webSession;
       this.paramParser = paramParser;
       this.auditService = auditService;
+      this.metrics = metrics;
     }
   }
 
@@ -197,6 +201,7 @@ public class RestApiServlet extends HttpServlet {
   @Override
   protected final void service(HttpServletRequest req, HttpServletResponse res)
       throws ServletException, IOException {
+    final long startNanos = System.nanoTime();
     long auditStartTs = TimeUtil.nowMs();
     res.setHeader("Content-Disposition", "attachment");
     res.setHeader("X-Content-Type-Options", "nosniff");
@@ -389,6 +394,17 @@ public class RestApiServlet extends HttpServlet {
       status = SC_INTERNAL_SERVER_ERROR;
       handleException(e, req, res);
     } finally {
+      String metric = viewData != null && viewData.view != null
+          ? globals.metrics.view(viewData)
+          : "_unknown";
+      globals.metrics.count.increment(metric);
+      if (status >= SC_BAD_REQUEST) {
+        globals.metrics.errorCount.increment(metric, status);
+      }
+      globals.metrics.serverLatency.record(
+          metric,
+          System.nanoTime() - startNanos,
+          TimeUnit.NANOSECONDS);
       globals.auditService.dispatch(new ExtendedHttpAuditEvent(globals.webSession.get()
           .getSessionId(), globals.currentUser.get(), req,
           auditStartTs, params, inputRequestBody, status,
@@ -1099,7 +1115,7 @@ public class RestApiServlet extends HttpServlet {
     }
   }
 
-  private static class ViewData {
+  static class ViewData {
     String pluginName;
     RestView<RestResource> view;