1 files changed, 118 insertions, 0 deletions
diff --git a/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/server/CacheHeaders.java b/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/server/CacheHeaders.java
new file mode 100644
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+++ b/gerrit-gwtexpui/src/main/java/com/google/gwtexpui/server/CacheHeaders.java
@@ -0,0 +1,118 @@
+// Copyright (C) 2013 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.gwtexpui.server;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static java.util.concurrent.TimeUnit.SECONDS;
+
+import java.util.concurrent.TimeUnit;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+/** Utilities to manage HTTP caching directives in responses. */
+public class CacheHeaders {
+  private static final long MAX_CACHE_DURATION = DAYS.toSeconds(365);
+
+  /**
+   * Do not cache the response, anywhere.
+   *
+   * @param res response being returned.
+   */
+  public static void setNotCacheable(HttpServletResponse res) {
+    String cc = "no-cache, no-store, max-age=0, must-revalidate";
+    res.setHeader("Cache-Control", cc);
+    res.setHeader("Pragma", "no-cache");
+    res.setHeader("Expires", "Fri, 01 Jan 1990 00:00:00 GMT");
+    res.setDateHeader("Date", System.currentTimeMillis());
+  }
+
+  /**
+   * Permit caching the response for up to the age specified.
+   * <p>
+   * If the request is on a secure connection (e.g. SSL) private caching is
+   * used. This allows the user-agent to cache the response, but requests
+   * intermediate proxies to not cache. This may offer better protection for
+   * Set-Cookie headers.
+   * <p>
+   * If the request is on plaintext (insecure), public caching is used. This may
+   * allow an intermediate proxy to cache the response, including any Set-Cookie
+   * header that may have also been included.
+   *
+   * @param req current request.
+   * @param res response being returned.
+   * @param age how long the response can be cached.
+   * @param unit time unit for age, usually {@link TimeUnit#SECONDS}.
+   */
+  public static void setCacheable(
+      HttpServletRequest req, HttpServletResponse res,
+      long age, TimeUnit unit) {
+    if (req.isSecure()) {
+      setCacheablePrivate(res, age, unit);
+    } else {
+      setCacheablePublic(res, age, unit);
+    }
+  }
+
+  /**
+   * Allow the response to be cached by proxies and user-agents.
+   * <p>
+   * If the response includes a Set-Cookie header the cookie may be cached by a
+   * proxy and returned to multiple browsers behind the same proxy. This is
+   * insecure for authenticated connections.
+   *
+   * @param res response being returned.
+   * @param age how long the response can be cached.
+   * @param unit time unit for age, usually {@link TimeUnit#SECONDS}.
+   */
+  public static void setCacheablePublic(HttpServletResponse res,
+      long age, TimeUnit unit) {
+    long now = System.currentTimeMillis();
+    long sec = maxAgeSeconds(age, unit);
+
+    res.setDateHeader("Expires", now + SECONDS.toMillis(sec));
+    res.setDateHeader("Date", now);
+    cache(res, "public", age, unit);
+  }
+
+  /**
+   * Allow the response to be cached only by the user-agent.
+   *
+   * @param res response being returned.
+   * @param age how long the response can be cached.
+   * @param unit time unit for age, usually {@link TimeUnit#SECONDS}.
+   */
+  public static void setCacheablePrivate(HttpServletResponse res,
+      long age, TimeUnit unit) {
+    long now = System.currentTimeMillis();
+    res.setDateHeader("Expires", now);
+    res.setDateHeader("Date", now);
+    cache(res, "private", age, unit);
+  }
+
+  private static void cache(HttpServletResponse res,
+      String type, long age, TimeUnit unit) {
+    res.setHeader("Cache-Control", String.format(
+        "%s, max-age=%d",
+        type, maxAgeSeconds(age, unit)));
+  }
+
+  private static long maxAgeSeconds(long age, TimeUnit unit) {
+    return Math.min(unit.toSeconds(age), MAX_CACHE_DURATION);
+  }
+
+  private CacheHeaders() {
+  }
+}