1/*
2 * Copyright (C) 2007 Google Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.io;
18
19import java.io.IOException;
20
21/**
22 * Package-protected abstract class that implements the line reading
23 * algorithm used by {@link LineReader}. Line separators are per {@link
24 * java.io.BufferedReader}: line feed, carriage return, or carriage
25 * return followed immediately by a linefeed.
26 *
27 * <p>Subclasses must implement {@link #handleLine}, call {@link #add}
28 * to pass character data, and call {@link #finish} at the end of stream.
29 *
30 * @author Chris Nokleberg
31 * @since 2009.09.15 <b>tentative</b>
32 */
33abstract class LineBuffer {
34  /** Holds partial line contents. */
35  private StringBuilder line = new StringBuilder();
36  /** Whether a line ending with a CR is pending processing. */
37  private boolean sawReturn;
38
39  /**
40   * Process additional characters from the stream. When a line separator
41   * is found the contents of the line and the line separator itself
42   * are passed to the abstract {@link #handleLine} method.
43   *
44   * @param cbuf the character buffer to process
45   * @param off the offset into the buffer
46   * @param len the number of characters to process
47   * @throws IOException if an I/O error occurs
48   * @see #finish
49   */
50  @SuppressWarnings("fallthrough")
51  protected void add(char[] cbuf, int off, int len) throws IOException {
52    int pos = off;
53    if (sawReturn && len > 0) {
54      // Last call to add ended with a CR; we can handle the line now.
55      if (finishLine(cbuf[pos] == '\n')) {
56        pos++;
57      }
58    }
59
60    int start = pos;
61    for (int end = off + len; pos < end; pos++) {
62      switch (cbuf[pos]) {
63        case '\r':
64          line.append(cbuf, start, pos - start);
65          sawReturn = true;
66          if (pos + 1 < end) {
67            if (finishLine(cbuf[pos + 1] == '\n')) {
68              pos++;
69            }
70          }
71          start = pos + 1;
72          break;
73
74        case '\n':
75          line.append(cbuf, start, pos - start);
76          finishLine(true);
77          start = pos + 1;
78          break;
79      }
80    }
81    line.append(cbuf, start, off + len - start);
82  }
83
84  /** Called when a line is complete. */
85  private boolean finishLine(boolean sawNewline) throws IOException {
86    handleLine(line.toString(), sawReturn
87        ? (sawNewline ? "\r\n" : "\r")
88        : (sawNewline ? "\n" : ""));
89    line = new StringBuilder();
90    sawReturn = false;
91    return sawNewline;
92  }
93
94  /**
95   * Subclasses must call this method after finishing character processing,
96   * in order to ensure that any unterminated line in the buffer is
97   * passed to {@link #handleLine}.
98   *
99   * @throws IOException if an I/O error occurs
100   */
101  protected void finish() throws IOException {
102    if (sawReturn || line.length() > 0) {
103      finishLine(false);
104    }
105  }
106
107  /**
108   * Called for each line found in the character data passed to
109   * {@link #add}.
110   *
111   * @param line a line of text (possibly empty), without any line separators
112   * @param end the line separator; one of {@code "\r"}, {@code "\n"},
113   *     {@code "\r\n"}, or {@code ""}
114   * @throws IOException if an I/O error occurs
115   */
116  protected abstract void handleLine(String line, String end)
117      throws IOException;
118}
119