001/* CheckedInputStream.java - Compute checksum of data being read 002 Copyright (C) 1999, 2000, 2004 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package java.util.zip; 040 041import java.io.FilterInputStream; 042import java.io.IOException; 043import java.io.InputStream; 044 045/* Written using on-line Java Platform 1.2 API Specification 046 * and JCL book. 047 * Believed complete and correct. 048 */ 049 050/** 051 * InputStream that computes a checksum of the data being read using a 052 * supplied Checksum object. 053 * 054 * @see Checksum 055 * 056 * @author Tom Tromey 057 * @date May 17, 1999 058 */ 059public class CheckedInputStream extends FilterInputStream 060{ 061 /** 062 * Creates a new CheckInputStream on top of the supplied OutputStream 063 * using the supplied Checksum. 064 */ 065 public CheckedInputStream (InputStream in, Checksum sum) 066 { 067 super (in); 068 this.sum = sum; 069 } 070 071 /** 072 * Returns the Checksum object used. To get the data checksum computed so 073 * far call <code>getChecksum.getValue()</code>. 074 */ 075 public Checksum getChecksum () 076 { 077 return sum; 078 } 079 080 /** 081 * Reads one byte, updates the checksum and returns the read byte 082 * (or -1 when the end of file was reached). 083 */ 084 public int read () throws IOException 085 { 086 int x = in.read(); 087 if (x != -1) 088 sum.update(x); 089 return x; 090 } 091 092 /** 093 * Reads at most len bytes in the supplied buffer and updates the checksum 094 * with it. Returns the number of bytes actually read or -1 when the end 095 * of file was reached. 096 */ 097 public int read (byte[] buf, int off, int len) throws IOException 098 { 099 int r = in.read(buf, off, len); 100 if (r != -1) 101 sum.update(buf, off, r); 102 return r; 103 } 104 105 /** 106 * Skips n bytes by reading them in a temporary buffer and updating the 107 * the checksum with that buffer. Returns the actual number of bytes skiped 108 * which can be less then requested when the end of file is reached. 109 */ 110 public long skip (long n) throws IOException 111 { 112 if (n == 0) 113 return 0; 114 115 int min = (int) Math.min(n, 1024); 116 byte[] buf = new byte[min]; 117 118 long s = 0; 119 while (n > 0) 120 { 121 int r = in.read(buf, 0, min); 122 if (r == -1) 123 break; 124 n -= r; 125 s += r; 126 min = (int) Math.min(n, 1024); 127 sum.update(buf, 0, r); 128 } 129 130 return s; 131 } 132 133 /** The checksum object. */ 134 private Checksum sum; 135}