Move all static ref pattern related methods into a RefPattern class

The goal of this refactoring is to have a single place where a ref
pattern is validated as regular expression. So far this was done in 2
places (in RefControl and in ProjectConfig). For validating a ref
pattern as regular expression we must remove placeholder variables
such as '${username}' because it would be an invalid regular
expression otherwise. We don't want to do this in several places
especially because we want to support further placeholder variables in
future.

Change-Id: I11c76e37f22233d89b631375ac6f2ef60f97801f
Signed-off-by: Edwin Kempin <ekempin@google.com>

gerrit-server/src/main/java/com/google/gerrit/server/project/RefPattern.java

@@ -0,0 +1,85 @@
+// Copyright (C) 2016 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.project;
+
+import com.google.gerrit.common.data.AccessSection;
+import com.google.gerrit.common.data.RefConfigSection;
+import com.google.gerrit.common.errors.InvalidNameException;
+
+import dk.brics.automaton.RegExp;
+
+import org.eclipse.jgit.lib.Repository;
+
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
+
+public class RefPattern {
+  public static final String USERNAME = "username";
+
+  public static String shortestExample(String refPattern) {
+    if (isRE(refPattern)) {
+      // Since Brics will substitute dot [.] with \0 when generating
+      // shortest example, any usage of dot will fail in
+      // Repository.isValidRefName() if not combined with star [*].
+      // To get around this, we substitute the \0 with an arbitrary
+      // accepted character.
+      return toRegExp(refPattern).toAutomaton().getShortestExample(true)
+          .replace('\0', '-');
+    } else if (refPattern.endsWith("/*")) {
+      return refPattern.substring(0, refPattern.length() - 1) + '1';
+    } else {
+      return refPattern;
+    }
+  }
+
+  public static boolean isRE(String refPattern) {
+    return refPattern.startsWith(AccessSection.REGEX_PREFIX);
+  }
+
+  public static RegExp toRegExp(String refPattern) {
+    if (isRE(refPattern)) {
+      refPattern = refPattern.substring(1);
+    }
+    return new RegExp(refPattern, RegExp.NONE);
+  }
+
+  public static void validate(String refPattern)
+      throws InvalidNameException {
+    if (refPattern.startsWith(RefConfigSection.REGEX_PREFIX)) {
+      if (!Repository.isValidRefName(shortestExample(refPattern))) {
+        throw new InvalidNameException(refPattern);
+      }
+    } else if (refPattern.equals(RefConfigSection.ALL)) {
+      // This is a special case we have to allow, it fails below.
+    } else if (refPattern.endsWith("/*")) {
+      String prefix = refPattern.substring(0, refPattern.length() - 2);
+      if (!Repository.isValidRefName(prefix)) {
+        throw new InvalidNameException(refPattern);
+      }
+    } else if (!Repository.isValidRefName(refPattern)) {
+      throw new InvalidNameException(refPattern);
+    }
+    validateRegExp(refPattern);
+  }
+
+  public static void validateRegExp(String refPattern)
+      throws InvalidNameException {
+    try {
+      Pattern.compile(refPattern.replace("${" + USERNAME + "}/", ""));
+    } catch (PatternSyntaxException e) {
+      throw new InvalidNameException(refPattern + " " + e.getMessage());
+    }
+  }
+}