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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      @Override public int available() throws IOException {
052        return (int) Math.min(in.available(), left);
053      }
054    
055      @Override public synchronized 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 synchronized 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    }