RemoveDotSegments.java

  private static final boolean DEBUG_RDS = false;
  static void removeDotSegmentsInPlace(StringBuilder path, int left) {
    // The code below has excerpts from the spec interspersed.
    // The "input buffer" and "output buffer" referred to in the spec
    // are both just regions of path.
    // The loop deals with the exclusive cases by continuing instead
    // of proceeding to the bottom.
    boolean isAbsolute = left < path.length() && path.charAt(left) == '/';

    // RFC 3986 Section 5.2.4
    // 1.  The input buffer is initialized with the now-appended path
    //     components and the output buffer is initialized to the empty
    //     string.
    int inputBufferStart = left;
    final int inputBufferEnd = path.length();
    final int outputBufferStart = left;
    int outputBufferEnd = left;

    // 2.  While the input buffer is not empty, loop as follows:
    while (inputBufferStart < inputBufferEnd) {
      if (DEBUG_RDS) {
        System.err.println(
            "\t[" + path.substring(outputBufferStart, outputBufferEnd) + "]" +
                path.substring(outputBufferEnd, inputBufferStart) + "[" +
                path.substring(inputBufferStart, inputBufferEnd) + "]");
      }

      char c0 = path.charAt(inputBufferStart);
      //     A.  If the input buffer begins with a prefix of "../" or "./",
      //         then remove that prefix from the input buffer; otherwise,
      if (c0 == '.') {
        char c1;
        if (inputBufferStart + 1 < inputBufferEnd) {
          if ('/' == (c1 = path.charAt(inputBufferStart + 1))) {
            inputBufferStart += 2;
            continue;
          }
          if ('.' == c1 && inputBufferStart + 2 < inputBufferEnd
              && '/' == path.charAt(inputBufferStart + 2)) {
            inputBufferStart += 3;
            continue;
          }
        }
      }

      //     B.  if the input buffer begins with a prefix of "/./" or "/.",
      //         where "." is a complete path segment, then replace that
      //         prefix with "/" in the input buffer; otherwise,
      if (c0 == '/' && inputBufferStart + 1 < inputBufferEnd
          && '.' == path.charAt(inputBufferStart + 1)) {
        if (inputBufferStart + 2 == inputBufferEnd) {
          inputBufferStart += 1;
          path.setCharAt(inputBufferStart, '/');
          continue;
        } else if ('/' == path.charAt(inputBufferStart + 2)) {
          inputBufferStart += 2;
          continue;
        }
      }

      //     C.  if the input buffer begins with a prefix of "/../" or "/..",
      //         where ".." is a complete path segment, then replace that
      //         prefix with "/" in the input buffer and remove the last
      //         segment and its preceding "/" (if any) from the output
      //         buffer; otherwise,
      if (c0 == '/' && inputBufferStart + 2 < inputBufferEnd
          && '.' == path.charAt(inputBufferStart + 1)
          && '.' == path.charAt(inputBufferStart + 2)) {
        boolean foundDotDot = false;
        if (inputBufferStart + 3 == inputBufferEnd) {
          inputBufferStart += 2;
          path.setCharAt(inputBufferStart, '/');
          foundDotDot = true;
        } else if ('/' == path.charAt(inputBufferStart + 3)) {
          inputBufferStart += 3;
          foundDotDot = true;
        }
        if (foundDotDot) {
          while (outputBufferEnd > outputBufferStart) {
            --outputBufferEnd;
            if (path.charAt(outputBufferEnd) == '/') { break; }
          }
          if (outputBufferEnd == outputBufferStart && !isAbsolute) {
            // !!!This differs from spec!!!
            // Do not convert relative URLs into absolute ones via parent
            // navigation.
            inputBufferStart += 1;
          }
          continue;
        }
      }

      //     D.  if the input buffer consists only of "." or "..", then remove
      //         that from the input buffer; otherwise,
      if (c0 == '.') {
        if (inputBufferStart + 1 == inputBufferEnd) {
          inputBufferStart += 1;
          continue;
        } else if (inputBufferStart + 2 == inputBufferEnd
                   && '.' == path.charAt(inputBufferStart + 1)) {
          inputBufferStart += 2;
          continue;
        }
      }

      //     E.  move the first path segment in the input buffer to the end of
      //         the output buffer, including the initial "/" character (if
      //         any) and any subsequent characters up to, but not including,
      //         the next "/" character or the end of the input buffer.
      do {
        path.setCharAt(outputBufferEnd++, path.charAt(inputBufferStart++));
      } while (inputBufferStart < inputBufferEnd
               && path.charAt(inputBufferStart) != '/');
    }

    // 3.  Finally, the output buffer is returned as the result of
    //     remove_dot_segments.
    path.setLength(outputBufferEnd);
  }