001 /* CheckedInputStream.java - Compute checksum of data being read 002 Copyright (C) 1999, 2000, 2004 Free Software Foundation, Inc. 003 004 This file is part of GNU Classpath. 005 006 GNU Classpath is free software; you can redistribute it and/or modify 007 it under the terms of the GNU General Public License as published by 008 the Free Software Foundation; either version 2, or (at your option) 009 any later version. 010 011 GNU Classpath is distributed in the hope that it will be useful, but 012 WITHOUT ANY WARRANTY; without even the implied warranty of 013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014 General Public License for more details. 015 016 You should have received a copy of the GNU General Public License 017 along with GNU Classpath; see the file COPYING. If not, write to the 018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 019 02110-1301 USA. 020 021 Linking this library statically or dynamically with other modules is 022 making a combined work based on this library. Thus, the terms and 023 conditions of the GNU General Public License cover the whole 024 combination. 025 026 As a special exception, the copyright holders of this library give you 027 permission to link this library with independent modules to produce an 028 executable, regardless of the license terms of these independent 029 modules, and to copy and distribute the resulting executable under 030 terms of your choice, provided that you also meet, for each linked 031 independent module, the terms and conditions of the license of that 032 module. An independent module is a module which is not derived from 033 or based on this library. If you modify this library, you may extend 034 this exception to your version of the library, but you are not 035 obligated to do so. If you do not wish to do so, delete this 036 exception statement from your version. */ 037 038 039 package java.util.zip; 040 041 import java.io.FilterInputStream; 042 import java.io.IOException; 043 import 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 */ 059 public 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 }