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    
017    package com.google.common.io;
018    
019    import com.google.common.annotations.Beta;
020    import com.google.common.base.Preconditions;
021    
022    import java.io.FilterInputStream;
023    import java.io.IOException;
024    import 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 1.0
031     */
032    @Beta
033    public 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      
052      @Override
053      public int available() throws IOException {
054        return (int) Math.min(in.available(), left);
055      }
056    
057      
058      @Override
059      public synchronized void mark(int readlimit) {
060        in.mark(readlimit);
061        mark = left;
062        // it's okay to mark even if mark isn't supported, as reset won't work
063      }
064    
065      
066      @Override
067      public int read() throws IOException {
068        if (left == 0) {
069          return -1;
070        }
071    
072        int result = in.read();
073        if (result != -1) {
074          --left;
075        }
076        return result;
077      }
078    
079      
080      @Override
081      public int read(byte[] b, int off, int len) throws IOException {
082        if (left == 0) {
083          return -1;
084        }
085    
086        len = (int) Math.min(len, left);
087        int result = in.read(b, off, len);
088        if (result != -1) {
089          left -= result;
090        }
091        return result;
092      }
093    
094      
095      @Override
096      public synchronized void reset() throws IOException {
097        if (!in.markSupported()) {
098          throw new IOException("Mark not supported");
099        }
100        if (mark == -1) {
101          throw new IOException("Mark not set");
102        }
103    
104        in.reset();
105        left = mark;
106      }
107    
108      
109      @Override
110      public long skip(long n) throws IOException {
111        n = Math.min(n, left);
112        long skipped = in.skip(n);
113        left -= skipped;
114        return skipped;
115      }
116    }