Store preferred download scheme as arbitrary strings

Although plugins can register download schemes with arbitrary names,
the getter/setter in AccountGeneralPreferences were allowing only a
specific enum type corresponding to the core download schemes. Get rid
of that enum type, and store arbitrary strings in the database. To
avoid a schema upgrade (which would be an annoying multi-step process
for a zero-downtime upgrade), convert to/from the old enum-string
values in AccountGeneralPreferences. Everywhere else, use the key from
the scheme map, e.g. "anonymous http" instead of "ANON_HTTP". This
eliminates the special-case code when sending RPCs from the client,
and avoids weird undocumented behavior in the set preferences REST API
call.

Change-Id: I3e2397d8dfa15d20329cc83e1e3fe069c8e021c4

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/AccountGeneralPreferences.java

@@ -25,11 +25,6 @@ public final class AccountGeneralPreferences {
   /** Valid choices for the page size. */
   public static final short[] PAGESIZE_CHOICES = {10, 25, 50, 100};
 
-  /** Preferred scheme type to download a change. */
-  public static enum DownloadScheme {
-    ANON_GIT, ANON_HTTP, HTTP, SSH, REPO_DOWNLOAD
-  }
-
   /** Preferred method to download a change. */
   public static enum DownloadCommand {
     REPO_DOWNLOAD, PULL, CHECKOUT, CHERRY_PICK, FORMAT_PATCH
@@ -187,19 +182,49 @@ public final class AccountGeneralPreferences {
     useFlashClipboard = b;
   }
 
-  public DownloadScheme getDownloadUrl() {
-    if (downloadUrl == null) {
-      return null;
+  public String getDownloadUrl() {
+    // Translate from legacy enum names to modern display names. (May be removed
+    // if accompanied by a 2-phase schema upgrade.)
+    if (downloadUrl != null) {
+      switch (downloadUrl) {
+        case "ANON_GIT":
+          return CoreDownloadSchemes.ANON_GIT;
+        case "ANON_HTTP":
+          return CoreDownloadSchemes.ANON_HTTP;
+        case "HTTP":
+          return CoreDownloadSchemes.HTTP;
+        case "SSH":
+          return CoreDownloadSchemes.SSH;
+        case "REPO_DOWNLOAD":
+          return CoreDownloadSchemes.REPO_DOWNLOAD;
+      }
     }
-    return DownloadScheme.valueOf(downloadUrl);
+    return downloadUrl;
   }
 
-  public void setDownloadUrl(DownloadScheme url) {
-    if (url != null) {
-      downloadUrl = url.name();
-    } else {
-      downloadUrl = null;
+  public void setDownloadUrl(String url) {
+    // Translate from modern display names to legacy enum names. (May be removed
+    // if accompanied by a 2-phase schema upgrade.)
+    if (downloadUrl != null) {
+      switch (url) {
+        case CoreDownloadSchemes.ANON_GIT:
+          url = "ANON_GIT";
+          break;
+        case CoreDownloadSchemes.ANON_HTTP:
+          url = "ANON_HTTP";
+          break;
+        case CoreDownloadSchemes.HTTP:
+          url = "HTTP";
+          break;
+        case CoreDownloadSchemes.SSH:
+          url = "SSH";
+          break;
+        case CoreDownloadSchemes.REPO_DOWNLOAD:
+          url = "REPO_DOWNLOAD";
+          break;
+      }
     }
+    downloadUrl = url;
   }
 
   public DownloadCommand getDownloadCommand() {

gerrit-reviewdb/src/main/java/com/google/gerrit/reviewdb/client/CoreDownloadSchemes.java

@@ -0,0 +1,30 @@
+// 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.reviewdb.client;
+
+/**
+ * Download scheme string constants supported by the download-commands core
+ * plugin.
+ */
+public class CoreDownloadSchemes {
+  public static final String ANON_GIT = "git";
+  public static final String ANON_HTTP = "anonymous http";
+  public static final String HTTP = "http";
+  public static final String SSH = "ssh";
+  public static final String REPO_DOWNLOAD = "repo";
+
+  private CoreDownloadSchemes() {
+  }
+}