001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.io;
018
019import com.google.common.annotations.Beta;
020import com.google.common.base.Preconditions;
021
022import java.io.FilterInputStream;
023import java.io.IOException;
024import java.io.InputStream;
025
026/**
027 * An InputStream that limits the number of bytes which can be read.
028 *
029 * @author Charles Fry
030 * @since 1
031 */
032@Beta
033public final class LimitInputStream extends FilterInputStream {
034
035  private long left;
036  private long mark = -1;
037
038  /**
039   * Wraps another input stream, limiting the number of bytes which can be read.
040   *
041   * @param in the input stream to be wrapped
042   * @param limit the maximum number of bytes to be read
043   */
044  public LimitInputStream(InputStream in, long limit) {
045    super(in);
046    Preconditions.checkNotNull(in);
047    Preconditions.checkArgument(limit >= 0, "limit must be non-negative");
048    left = limit;
049  }
050
051  @Override public int available() throws IOException {
052    return (int) Math.min(in.available(), left);
053  }
054
055  @Override public void mark(int readlimit) {
056    in.mark(readlimit);
057    mark = left;
058    // it's okay to mark even if mark isn't supported, as reset won't work
059  }
060
061  @Override public int read() throws IOException {
062    if (left == 0) {
063      return -1;
064    }
065
066    int result = in.read();
067    if (result != -1) {
068      --left;
069    }
070    return result;
071  }
072
073  @Override public int read(byte[] b, int off, int len) throws IOException {
074    if (left == 0) {
075      return -1;
076    }
077
078    len = (int) Math.min(len, left);
079    int result = in.read(b, off, len);
080    if (result != -1) {
081      left -= result;
082    }
083    return result;
084  }
085
086  @Override public void reset() throws IOException {
087    if (!in.markSupported()) {
088      throw new IOException("Mark not supported");
089    }
090    if (mark == -1) {
091      throw new IOException("Mark not set");
092    }
093
094    in.reset();
095    left = mark;
096  }
097
098  @Override public long skip(long n) throws IOException {
099    n = Math.min(n, left);
100    long skipped = in.skip(n);
101    left -= skipped;
102    return skipped;
103  }
104}