Source for java.util.zip.GZIPInputStream

   1: /* GZIPInputStream.java - Input filter for reading gzip file
   2:    Copyright (C) 1999, 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
   3: 
   4: This file is part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2, or (at your option)
   9: any later version.
  10:  
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; see the file COPYING.  If not, write to the
  18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 USA.
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
  33: or based on this library.  If you modify this library, you may extend
  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version. */
  37: 
  38: package java.util.zip;
  39: 
  40: import java.io.InputStream;
  41: import java.io.IOException;
  42: 
  43: /**
  44:  * This filter stream is used to decompress a "GZIP" format stream. 
  45:  * The "GZIP" format is described in RFC 1952.
  46:  *
  47:  * @author John Leuner
  48:  * @author Tom Tromey
  49:  * @since JDK 1.1
  50:  */
  51: public class GZIPInputStream
  52:   extends InflaterInputStream
  53: {
  54:   /**
  55:    * The magic number found at the start of a GZIP stream.
  56:    */
  57:   public static final int GZIP_MAGIC = 0x8b1f;
  58: 
  59:   static final int Z_DEFLATED = 8;
  60: 
  61:   /**
  62:    * The mask for bit 1 of the flag byte.
  63:    */
  64:   static final int HEAD_CRC = 0x02;
  65: 
  66:   /**
  67:    * The mask for bit 2 of the flag byte.
  68:    */
  69:   static final int EXTRA_FIELD = 0x04;
  70: 
  71:   /**
  72:    * The mask for bit 3 of the flag byte.
  73:    */
  74:   static final int ORIG_NAME = 0x08;
  75: 
  76:   /**
  77:    * The mask for bit 4 of the flag byte.
  78:    */
  79:   static final int COMMENT = 0x10;
  80: 
  81:   /**
  82:    * The mask for all reserved bits of the flag byte.
  83:    */
  84:   static final int RESERVED = 0xe0;
  85:   
  86:   /**
  87:    * The CRC-32 checksum value for uncompressed data.
  88:    */
  89:   protected CRC32 crc; 
  90: 
  91:   /**
  92:    * Indicates whether or not the end of the stream has been reached.
  93:    */  
  94:   protected boolean eos;
  95: 
  96:   /**
  97:    * Creates a GZIPInputStream with the default buffer size.
  98:    *
  99:    * @param in The stream to read compressed data from 
 100:    *           (in GZIP format).
 101:    *
 102:    * @throws IOException if an error occurs during an I/O operation.
 103:    */
 104:   public GZIPInputStream(InputStream in)
 105:     throws IOException
 106:   {
 107:     this(in, 4096);
 108:   }
 109: 
 110:   /**
 111:    * Creates a GZIPInputStream with the specified buffer size.
 112:    *
 113:    * @param in The stream to read compressed data from 
 114:    *           (in GZIP format).
 115:    * @param size The size of the buffer to use.
 116:    *
 117:    * @throws IOException if an error occurs during an I/O operation.
 118:    * @throws IllegalArgumentException if <code>size</code>
 119:    * is less than or equal to 0.
 120:    */
 121:   public GZIPInputStream(InputStream in, int size)
 122:     throws IOException
 123:   {
 124:     super(in, new Inflater(true), size);
 125: 
 126:     // NOTE: header reading code taken from zlib's gzio.c.
 127: 
 128:     // Read the magic number.
 129:     int magic = eof_read() | (eof_read() << 8);
 130:     if (magic != GZIP_MAGIC)
 131:       throw new ZipException("gzip header corrupted");
 132: 
 133:     int method = eof_read();
 134:     int flags = eof_read();
 135:     // Test from zlib.
 136:     if (method != Z_DEFLATED || (flags & RESERVED) != 0)
 137:       throw new ZipException("gzip header corrupted");
 138: 
 139:     // Discard time, xflags, OS code.
 140:     for (int i = 0; i < 6; ++i)
 141:       eof_read();
 142: 
 143:     // Skip the extra field.
 144:     if ((flags & EXTRA_FIELD) != 0)
 145:       {
 146:     int len = eof_read() | (eof_read() << 8);
 147:     while (len-- != 0)
 148:       eof_read();
 149:       }
 150: 
 151:     if ((flags & ORIG_NAME) != 0)
 152:       {
 153:     while (true)
 154:       {
 155:         int c = eof_read();
 156:         if (c == 0)
 157:           break;
 158:       }
 159:       }
 160: 
 161:     if ((flags & COMMENT) != 0)
 162:       {
 163:     while (true)
 164:       {
 165:         int c = eof_read();
 166:         if (c == 0)
 167:           break;
 168:       }
 169:       }
 170: 
 171:     if ((flags & HEAD_CRC) != 0)
 172:       {
 173:     // FIXME: consider checking CRC of the header.
 174:     eof_read();
 175:     eof_read();
 176:       }
 177: 
 178:     crc = new CRC32();
 179:   }
 180: 
 181:   /**
 182:    * Closes the input stream.
 183:    *
 184:    * @throws IOException if an error occurs during an I/O operation.
 185:    */
 186:   public void close()
 187:     throws IOException
 188:   {
 189:     // Nothing to do here.
 190:     super.close();
 191:   }
 192: 
 193:   private final int eof_read() throws IOException
 194:   {
 195:     int r = in.read();
 196:     if (r == -1)
 197:       throw new ZipException("gzip header corrupted");
 198:     return r & 0xff;
 199:   }
 200: 
 201:   /**
 202:    * Reads in GZIP-compressed data and stores it in uncompressed form
 203:    * into an array of bytes.  The method will block until either
 204:    * enough input data becomes available or the compressed stream
 205:    * reaches its end.
 206:    *
 207:    * @param buf the buffer into which the uncompressed data will
 208:    *            be stored.
 209:    * @param offset the offset indicating where in <code>buf</code>
 210:    *               the uncompressed data should be placed.
 211:    * @param len the number of uncompressed bytes to be read.
 212:    */
 213:   public int read(byte[] buf, int offset, int len) throws IOException
 214:   {
 215:     if (eos)
 216:       return -1;
 217:     int r = super.read(buf, offset, len);
 218:     if (r == -1)
 219:       {
 220:     eos = true;
 221: 
 222:     byte[] tmp = new byte[8];
 223:     // First copy remaining bytes from inflater input buffer.
 224:     int avail = inf.getRemaining();
 225:     System.arraycopy(this.buf, this.len - avail, tmp, 0, avail);
 226: 
 227:     // Now read remaining bytes from wrapped input stream.
 228:     for (int i = avail; i < 8; ++i)
 229:       {
 230:         tmp[i] = (byte) eof_read();
 231:       }
 232: 
 233:     // Be careful to avoid sign extension here; CRC32.getValue()
 234:     // returns a long.
 235:     long header_crc = read4(tmp, 0) & 0xffffffffL;
 236:     if (crc.getValue() != header_crc)
 237:       throw new ZipException("corrupted gzip file - crc mismatch");
 238:     int isize = read4(tmp, 4);
 239:     if (inf.getTotalOut() != isize)
 240:       throw new ZipException("corrupted gzip file - size mismatch");
 241:     return -1;
 242:       }
 243:     crc.update(buf, offset, r);
 244:     return r;
 245:   }
 246: 
 247:   private final int read4(byte[] buf, int offset) throws IOException
 248:   {
 249:     return (((buf[offset + 3] & 0xFF) << 24) + ((buf[offset + 2] & 0xFF) << 16)
 250:         + ((buf[offset + 1] & 0xFF) << 8) + (buf[offset] & 0xFF));
 251:   }
 252: }