sdks/java/core/src/main/java/org/apache/beam/sdk/io/FileSystemUtils.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.beam.sdk.io;

import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.annotations.VisibleForTesting;

public class FileSystemUtils {

  /**
   * Expands glob expressions to regular expressions.
   *
   * <p>This method is intended for internal usage and does not guarantee backwards compatibility.
   *
   * @param globExp the glob expression to expand
   * @return a string with the regular expression this glob expands to
   */
  @VisibleForTesting
  public static String wildcardToRegexp(String globExp) {
    StringBuilder dst = new StringBuilder();
    char[] src = globExp.replace("**/*", "**").toCharArray();
    int i = 0;
    while (i < src.length) {
      char c = src[i++];
      switch (c) {
        case '*':
          // One char lookahead for **
          if (i < src.length && src[i] == '*') {
            dst.append(".*");
            ++i;
          } else {
            dst.append("[^/]*");
          }
          break;
        case '?':
          dst.append("[^/]");
          break;
        case '.':
        case '+':
        case '{':
        case '}':
        case '(':
        case ')':
        case '|':
        case '^':
        case '$':
          // These need to be escaped in regular expressions
          dst.append('\\').append(c);
          break;
        case '\\':
          i = doubleSlashes(dst, src, i);
          break;
        default:
          dst.append(c);
          break;
      }
    }
    return dst.toString();
  }

  private static int doubleSlashes(StringBuilder dst, char[] src, int i) {
    // Emit the next character without special interpretation
    dst.append('\\');
    if ((i + 1) < src.length) {
      dst.append('\\');
      dst.append(src[i]);
      i++;
    } else {
      // A backslash at the very end is treated like an escaped backslash
      dst.append('\\');
    }
    return i;
  }
}