    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 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    }