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diff --git a/java/com/google/gerrit/server/config/UrlFormatter.java b/java/com/google/gerrit/server/config/UrlFormatter.java
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+// Copyright (C) 2018 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.server.config;
+
+import com.google.common.base.Strings;
+import com.google.gerrit.common.Nullable;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.reviewdb.client.Project;
+import java.util.Optional;
+
+/**
+ * Formats URLs to different parts of the Gerrit API and UI.
+ *
+ * <p>By default, these gerrit URLs are formed by adding suffixes to the web URL. The interface
+ * centralizes these conventions, and also allows introducing different, custom URL schemes.
+ *
+ * <p>Unfortunately, Gerrit operates in modes for which there is no canonical URL. This can be in
+ * standalone utilities that have no HTTP server (eg. index upgrade commands), in servers that run
+ * SSH only, or in a HTTP/SSH server that is accessed over SSH without canonical web URL configured.
+ */
+public interface UrlFormatter {
+
+  /**
+   * The canonical base URL where this Gerrit installation can be reached.
+   *
+   * <p>For the default implementations below to work, it must end in "/".
+   */
+  Optional<String> getWebUrl();
+
+  /** Returns the URL for viewing a change. */
+  default Optional<String> getChangeViewUrl(@Nullable Project.NameKey project, Change.Id id) {
+
+    // In the PolyGerrit URL (contrary to REST URLs) there is no need to URL-escape strings, since
+    // the /+/ separator unambiguously defines how to parse the path.
+    return getWebUrl()
+        .map(url -> url + "c/" + (project != null ? project.get() + "/+/" : "") + id.get());
+  }
+
+  /** Returns a URL pointing to a section of the settings page. */
+  default Optional<String> getSettingsUrl(String section) {
+    return getWebUrl()
+        .map(url -> url + "settings" + (Strings.isNullOrEmpty(section) ? "" : "#" + section));
+  }
+
+  /** Returns a URL pointing to a documentation page, at a given named anchor. */
+  default Optional<String> getDocUrl(String page, String anchor) {
+    return getWebUrl().map(url -> url + "Documentation/" + page + "#" + anchor);
+  }
+
+  /** Returns a REST API URL for a given suffix (eg. "accounts/self/details") */
+  default Optional<String> getRestUrl(String suffix) {
+    return getWebUrl().map(url -> url + suffix);
+  }
+}