1/*
2 * Copyright (C) 2007 The Guava Authors
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 com.google.common.annotations.Beta;
20import com.google.common.base.Preconditions;
21
22import java.io.FilterInputStream;
23import java.io.IOException;
24import java.io.InputStream;
25
26/**
27 * An InputStream that limits the number of bytes which can be read.
28 *
29 * @author Charles Fry
30 * @since 1.0
31 */
32@Beta
33public final class LimitInputStream extends FilterInputStream {
34
35  private long left;
36  private long mark = -1;
37
38  /**
39   * Wraps another input stream, limiting the number of bytes which can be read.
40   *
41   * @param in the input stream to be wrapped
42   * @param limit the maximum number of bytes to be read
43   */
44  public LimitInputStream(InputStream in, long limit) {
45    super(in);
46    Preconditions.checkNotNull(in);
47    Preconditions.checkArgument(limit >= 0, "limit must be non-negative");
48    left = limit;
49  }
50
51  @Override public int available() throws IOException {
52    return (int) Math.min(in.available(), left);
53  }
54
55  @Override public synchronized void mark(int readlimit) {
56    in.mark(readlimit);
57    mark = left;
58    // it's okay to mark even if mark isn't supported, as reset won't work
59  }
60
61  @Override public int read() throws IOException {
62    if (left == 0) {
63      return -1;
64    }
65
66    int result = in.read();
67    if (result != -1) {
68      --left;
69    }
70    return result;
71  }
72
73  @Override public int read(byte[] b, int off, int len) throws IOException {
74    if (left == 0) {
75      return -1;
76    }
77
78    len = (int) Math.min(len, left);
79    int result = in.read(b, off, len);
80    if (result != -1) {
81      left -= result;
82    }
83    return result;
84  }
85
86  @Override public synchronized void reset() throws IOException {
87    if (!in.markSupported()) {
88      throw new IOException("Mark not supported");
89    }
90    if (mark == -1) {
91      throw new IOException("Mark not set");
92    }
93
94    in.reset();
95    left = mark;
96  }
97
98  @Override public long skip(long n) throws IOException {
99    n = Math.min(n, left);
100    long skipped = in.skip(n);
101    left -= skipped;
102    return skipped;
103  }
104}
105