code: /*
   * Copyright (C) 2007 The Guava Authors
   *
   * Licensed 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 com.google.common.io;
  
  import com.google.common.annotations.Beta;
  import com.google.common.base.Preconditions;
  
  import java.io.FilterInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * An InputStream that limits the number of bytes which can be read.
   *
   * @author Charles Fry
   * @since 1.0
   */
  @Beta
  public final class LimitInputStream extends FilterInputStream {
  
    private long left;
    private long mark = -1;
  
    /**
     * Wraps another input stream, limiting the number of bytes which can be read.
     *
     * @param in the input stream to be wrapped
     * @param limit the maximum number of bytes to be read
     */
    public LimitInputStream(InputStream in, long limit) {
      super(in);
      Preconditions.checkNotNull(in);
      Preconditions.checkArgument(limit >= 0, "limit must be non-negative");
      left = limit;
    }
  
    @Override public int available() throws IOException {
      return (int) Math.min(in.available(), left);
    }
  
    @Override public synchronized void mark(int readlimit) {
      in.mark(readlimit);
      mark = left;
      // it's okay to mark even if mark isn't supported, as reset won't work
    }
  
    @Override public int read() throws IOException {
      if (left == 0) {
        return -1;
      }
  
      int result = in.read();
      if (result != -1) {
        --left;
      }
      return result;
    }
  
    @Override public int read(byte[] b, int off, int len) throws IOException {
      if (left == 0) {
        return -1;
      }
  
      len = (int) Math.min(len, left);
      int result = in.read(b, off, len);
      if (result != -1) {
        left -= result;
      }
      return result;
    }
  
    @Override public synchronized void reset() throws IOException {
      if (!in.markSupported()) {
        throw new IOException("Mark not supported");
      }
      if (mark == -1) {
        throw new IOException("Mark not set");
      }
  
      in.reset();
      left = mark;
    }
  
    @Override public long skip(long n) throws IOException {
      n = Math.min(n, left);
      long skipped = in.skip(n);
      left -= skipped;
      return skipped;
    }
  }