New draft statuses and magic branches

Adds draft status to Change. DRAFT status in change occurs before NEW
and will be for a change that is not meant for review.
Also adds magic branches refs/draft/ and refs/publish/ that
will handle whether or not a patchset is a draft or goes straight to
review. refs/for/ should be deprecated in favor of explicitly marking
a patchset as a draft or directly to review.
For now, the draft flag and status are unused and refs/draft and
refs/publish just mimic refs/for's functionality.

Change-Id: I95cb336f1944552f842f0b99dc299eb51e586801

gerrit-server/src/main/java/com/google/gerrit/server/util/MagicBranch.java

@@ -0,0 +1,106 @@
+// Copyright (C) 2011 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.util;
+
+import com.google.gerrit.common.data.Capable;
+import com.google.gerrit.reviewdb.Project;
+
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.Map;
+
+public final class MagicBranch {
+  private static final Logger log =
+    LoggerFactory.getLogger(MagicBranch.class);
+
+  public static final String NEW_CHANGE = "refs/for/";
+  public static final String NEW_DRAFT_CHANGE = "refs/draft/";
+  public static final String NEW_PUBLISH_CHANGE = "refs/publish/";
+
+  /** Extracts the destination from a ref name */
+  public static String getDestBranchName(String refName) {
+    String magicBranch = NEW_CHANGE;
+    if (refName.startsWith(NEW_DRAFT_CHANGE)) {
+      magicBranch = NEW_DRAFT_CHANGE;
+    } else if (refName.startsWith(NEW_PUBLISH_CHANGE)) {
+      magicBranch = NEW_PUBLISH_CHANGE;
+    }
+    return refName.substring(magicBranch.length());
+  }
+
+  /** Checks if the supplied ref name is a magic branch */
+  public static boolean isMagicBranch(String refName) {
+    if (refName.startsWith(NEW_DRAFT_CHANGE) ||
+        refName.startsWith(NEW_PUBLISH_CHANGE) ||
+        refName.startsWith(NEW_CHANGE)) {
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Checks if a (magic branch)/branch_name reference exists in the
+   * destination repository and only returns Capable.OK if it does not match any.
+   *
+   * These block the client from being able to even send us a pack file, as it
+   * is very unlikely the user passed the --force flag and the new commit is
+   * probably not going to fast-forward the branch.
+   */
+  public static Capable checkMagicBranchRefs(Repository repo,
+      Project project) {
+    Capable result = checkMagicBranchRef(NEW_CHANGE, repo, project);
+    if (result != Capable.OK) {
+      return result;
+    }
+    result = checkMagicBranchRef(NEW_DRAFT_CHANGE, repo, project);
+    if (result != Capable.OK) {
+      return result;
+    }
+    result = checkMagicBranchRef(NEW_PUBLISH_CHANGE, repo, project);
+    if (result != Capable.OK) {
+      return result;
+    }
+
+    return Capable.OK;
+  }
+
+  private static Capable checkMagicBranchRef(String branchName, Repository repo,
+      Project project) {
+    Map<String, Ref> blockingFors;
+    try {
+      blockingFors = repo.getRefDatabase().getRefs(branchName);
+    } catch (IOException err) {
+      String projName = project.getName();
+      log.warn("Cannot scan refs in '" + projName + "'", err);
+      return new Capable("Server process cannot read '" + projName + "'");
+    }
+    if (!blockingFors.isEmpty()) {
+      String projName = project.getName();
+      log.error("Repository '" + projName
+          + "' needs the following refs removed to receive changes: "
+          + blockingFors.keySet());
+      return new Capable("One or more " + branchName + " names blocks change upload");
+    }
+
+    return Capable.OK;
+  }
+
+  private MagicBranch() {
+  }
+}