1 /* 2 * Copyright (C) 2007 Google Inc. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.io; 18 19 import com.google.common.base.Preconditions; 20 21 import java.io.FilterInputStream; 22 import java.io.InputStream; 23 import java.io.IOException; 24 25 /** 26 * An InputStream that limits the number of bytes which can be read. 27 * 28 * @author Charles Fry 29 * @since 2009.09.15 <b>tentative</b> 30 */ 31 public class LimitInputStream extends FilterInputStream { 32 33 private long left; 34 private long mark = -1; 35 36 /** 37 * Wraps another input stream, limiting the number of bytes which can be read. 38 * 39 * @param in the input stream to be wrapped 40 * @param limit the maximum number of bytes to be read 41 */ LimitInputStream(InputStream in, long limit)42 public LimitInputStream(InputStream in, long limit) { 43 super(in); 44 Preconditions.checkNotNull(in); 45 Preconditions.checkArgument(limit >= 0, "limit must be non-negative"); 46 left = limit; 47 } 48 available()49 @Override public int available() throws IOException { 50 return (int) Math.min(in.available(), left); 51 } 52 mark(int readlimit)53 @Override public void mark(int readlimit) { 54 in.mark(readlimit); 55 mark = left; 56 // it's okay to mark even if mark isn't supported, as reset won't work 57 } 58 read()59 @Override public int read() throws IOException { 60 if (left == 0) { 61 return -1; 62 } 63 64 int result = in.read(); 65 if (result != -1) { 66 --left; 67 } 68 return result; 69 } 70 read(byte[] b, int off, int len)71 @Override public int read(byte[] b, int off, int len) throws IOException { 72 if (left == 0) { 73 return -1; 74 } 75 76 len = (int) Math.min(len, left); 77 int result = in.read(b, off, len); 78 if (result != -1) { 79 left -= result; 80 } 81 return result; 82 } 83 reset()84 @Override public void reset() throws IOException { 85 if (!in.markSupported()) { 86 throw new IOException("Mark not supported"); 87 } 88 if (mark == -1) { 89 throw new IOException("Mark not set"); 90 } 91 92 in.reset(); 93 left = mark; 94 } 95 skip(long n)96 @Override public long skip(long n) throws IOException { 97 n = Math.min(n, left); 98 long skipped = in.skip(n); 99 left -= skipped; 100 return skipped; 101 } 102 103 } 104