libjava/java/io/DataInputStream.java

   1 /* DataInputStream.java -- FilteredInputStream that implements DataInput
   2    Copyright (C) 1998, 1999, 2000, 2001  Free Software Foundation
   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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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.io;
  39
  40 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  41  * "The Java Language Specification", ISBN 0-201-63451-1
  42  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  43  * Status:  Believed complete and correct.
  44  */
  45
  46 /**
  47  * This subclass of <code>FilteredInputStream</code> implements the
  48  * <code>DataInput</code> interface that provides method for reading primitive
  49  * Java data types from a stream.
  50  *
  51  * @see DataInput
  52  *
  53  * @version 0.0
  54  *
  55  * @author Warren Levy <warrenl@cygnus.com>
  56  * @author Aaron M. Renn (arenn@urbanophile.com)
  57  * @date October 20, 1998.
  58  */
  59 public class DataInputStream extends FilterInputStream implements DataInput
  60 {
  61   // readLine() hack to ensure that an '\r' not followed by an '\n' is
  62   // handled correctly. If set, readLine() will ignore the first char it sees
  63   // if that char is a '\n'
  64   boolean ignoreInitialNewline = false;
  65
  66   // Byte buffer, used to make primitive read calls more efficient.
  67   byte[] buf = new byte[8];
  68
  69   /**
  70    * This constructor initializes a new <code>DataInputStream</code>
  71    * to read from the specified subordinate stream.
  72    *
  73    * @param in The subordinate <code>InputStream</code> to read from
  74    */
  75   public DataInputStream(InputStream in)
  76   {
  77     super(in);
  78   }
  79
  80   /**
  81    * This method reads bytes from the underlying stream into the specified
  82    * byte array buffer.  It will attempt to fill the buffer completely, but
  83    * may return a short count if there is insufficient data remaining to be
  84    * read to fill the buffer.
  85    *
  86    * @param b The buffer into which bytes will be read.
  87    *
  88    * @return The actual number of bytes read, or -1 if end of stream reached
  89    * before reading any bytes.
  90    *
  91    * @exception IOException If an error occurs.
  92    */
  93   public final int read(byte[] b) throws IOException
  94   {
  95     return in.read(b, 0, b.length);
  96   }
  97
  98   /**
  99    * This method reads bytes from the underlying stream into the specified
 100    * byte array buffer.  It will attempt to read <code>len</code> bytes and
 101    * will start storing them at position <code>off</code> into the buffer.
 102    * This method can return a short count if there is insufficient data
 103    * remaining to be read to complete the desired read length.
 104    *
 105    * @param b The buffer into which bytes will be read.
 106    * @param off The offset into the buffer to start storing bytes.
 107    * @param len The requested number of bytes to read.
 108    *
 109    * @return The actual number of bytes read, or -1 if end of stream reached
 110    * before reading any bytes.
 111    *
 112    * @exception IOException If an error occurs.
 113    */
 114   public final int read(byte[] b, int off, int len) throws IOException
 115   {
 116     return in.read(b, off, len);
 117   }
 118
 119   /**
 120    * This method reads a Java boolean value from an input stream.  It does
 121    * so by reading a single byte of data.  If that byte is zero, then the
 122    * value returned is <code>false</code>.  If the byte is non-zero, then
 123    * the value returned is <code>true</code>.
 124    * <p>
 125    * This method can read a <code>boolean</code> written by an object
 126    * implementing the <code>writeBoolean()</code> method in the
 127    * <code>DataOutput</code> interface.
 128    *
 129    * @return The <code>boolean</code> value read
 130    *
 131    * @exception EOFException If end of file is reached before reading
 132    * the boolean
 133    * @exception IOException If any other error occurs
 134    */
 135   public final boolean readBoolean() throws IOException
 136   {
 137     return convertToBoolean(in.read());
 138   }
 139
 140   /**
 141    * This method reads a Java byte value from an input stream.  The value
 142    * is in the range of -128 to 127.
 143    * <p>
 144    * This method can read a <code>byte</code> written by an object
 145    * implementing the <code>writeByte()</code> method in the
 146    * <code>DataOutput</code> interface.
 147    *
 148    * @return The <code>byte</code> value read
 149    *
 150    * @exception EOFException If end of file is reached before reading the byte
 151    * @exception IOException If any other error occurs
 152    *
 153    * @see DataOutput
 154    */
 155   public final byte readByte() throws IOException
 156   {
 157     return convertToByte(in.read());
 158   }
 159
 160   /**
 161    * This method reads a Java <code>char</code> value from an input stream.
 162    * It operates by reading two bytes from the stream and converting them to
 163    * a single 16-bit Java <code>char</code>.  The two bytes are stored most
 164    * significant byte first (i.e., "big endian") regardless of the native
 165    * host byte ordering.
 166    * <p>
 167    * As an example, if <code>byte1</code> and <code>byte2</code>
 168    * represent the first and second byte read from the stream
 169    * respectively, they will be transformed to a <code>char</code> in
 170    * the following manner:
 171    * <p>
 172    * <code>(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code>
 173    * <p>
 174    * This method can read a <code>char</code> written by an object
 175    * implementing the <code>writeChar()</code> method in the
 176    * <code>DataOutput</code> interface.
 177    *
 178    * @return The <code>char</code> value read
 179    *
 180    * @exception EOFException If end of file is reached before reading the char
 181    * @exception IOException If any other error occurs
 182    *
 183    * @see DataOutput
 184    */
 185   public final char readChar() throws IOException
 186   {
 187     readFully (buf, 0, 2);
 188     return convertToChar(buf);
 189   }
 190
 191   /**
 192    * This method reads a Java double value from an input stream.  It operates
 193    * by first reading a <code>long</code> value from the stream by calling the
 194    * <code>readLong()</code> method in this interface, then converts
 195    * that <code>long</code> to a <code>double</code> using the
 196    * <code>longBitsToDouble</code> method in the class
 197    * <code>java.lang.Double</code>
 198    * <p>
 199    * This method can read a <code>double</code> written by an object
 200    * implementing the <code>writeDouble()</code> method in the
 201    * <code>DataOutput</code> interface.
 202    *
 203    * @return The <code>double</code> value read
 204    *
 205    * @exception EOFException If end of file is reached before reading
 206    * the double
 207    * @exception IOException If any other error occurs
 208    *
 209    * @see java.lang.Double
 210    * @see DataOutput
 211    */
 212   public final double readDouble() throws IOException
 213   {
 214     return Double.longBitsToDouble(readLong());
 215   }
 216
 217   /**
 218    * This method reads a Java float value from an input stream.  It
 219    * operates by first reading an <code>int</code> value from the
 220    * stream by calling the <code>readInt()</code> method in this
 221    * interface, then converts that <code>int</code> to a
 222    * <code>float</code> using the <code>intBitsToFloat</code> method
 223    * in the class <code>java.lang.Float</code>
 224    * <p>
 225    * This method can read a <code>float</code> written by an object
 226    * implementing the * <code>writeFloat()</code> method in the
 227    * <code>DataOutput</code> interface.
 228    *
 229    * @return The <code>float</code> value read
 230    *
 231    * @exception EOFException If end of file is reached before reading the float
 232    * @exception IOException If any other error occurs
 233    *
 234    * @see java.lang.Float
 235    * @see DataOutput */
 236   public final float readFloat() throws IOException
 237   {
 238     return Float.intBitsToFloat(readInt());
 239   }
 240
 241   /**
 242    * This method reads raw bytes into the passed array until the array is
 243    * full.  Note that this method blocks until the data is available and
 244    * throws an exception if there is not enough data left in the stream to
 245    * fill the buffer
 246    *
 247    * @param b The buffer into which to read the data
 248    *
 249    * @exception EOFException If end of file is reached before filling
 250    * the buffer
 251    * @exception IOException If any other error occurs */
 252   public final void readFully(byte[] b) throws IOException
 253   {
 254     readFully(b, 0, b.length);
 255   }
 256
 257   /**
 258    * This method reads raw bytes into the passed array
 259    * <code>buf</code> starting <code>offset</code> bytes into the
 260    * buffer.  The number of bytes read will be exactly
 261    * <code>len</code> Note that this method blocks until the data is
 262    * available and * throws an exception if there is not enough data
 263    * left in the stream to read <code>len</code> bytes.
 264    *
 265    * @param buf The buffer into which to read the data
 266    * @param offset The offset into the buffer to start storing data
 267    * @param len The number of bytes to read into the buffer
 268    *
 269    * @exception EOFException If end of file is reached before filling
 270    * the buffer
 271    * @exception IOException If any other error occurs
 272    */
 273   public final void readFully(byte[] b, int off, int len) throws IOException
 274   {
 275     while (len > 0)
 276       {
 277         // in.read will block until some data is available.
 278         int numread = in.read(b, off, len);
 279         if (numread < 0)
 280           throw new EOFException();
 281         len -= numread;
 282         off += numread;
 283       }
 284   }
 285
 286   /**
 287    * This method reads a Java <code>int</code> value from an input
 288    * stream It operates by reading four bytes from the stream and
 289    * converting them to a single Java <code>int</code> The bytes are
 290    * stored most significant byte first (i.e., "big endian")
 291    * regardless of the native host byte ordering.
 292    * <p>
 293    * As an example, if <code>byte1</code> through <code>byte4</code>
 294    * represent the first four bytes read from the stream, they will be
 295    * transformed to an <code>int</code> in the following manner:
 296    * <p>
 297    * <code>(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) +
 298    * ((byte3 & 0xFF) << 8) + (byte4 & 0xFF)))</code>
 299    * <p>
 300    * The value returned is in the range of 0 to 65535.
 301    * <p>
 302    * This method can read an <code>int</code> written by an object
 303    * implementing the <code>writeInt()</code> method in the
 304    * <code>DataOutput</code> interface.
 305    *
 306    * @return The <code>int</code> value read
 307    *
 308    * @exception EOFException If end of file is reached before reading the int
 309    * @exception IOException If any other error occurs
 310    *
 311    * @see DataOutput
 312    */
 313   public final int readInt() throws IOException
 314   {
 315     readFully (buf, 0, 4);
 316     return convertToInt(buf);
 317   }
 318
 319   /**
 320    * This method reads the next line of text data from an input
 321    * stream.  It operates by reading bytes and converting those bytes
 322    * to <code>char</code> values by treating the byte read as the low
 323    * eight bits of the <code>char</code> and using 0 as the high eight
 324    * bits.  Because of this, it does not support the full 16-bit
 325    * Unicode character set.
 326    * <p>
 327    * The reading of bytes ends when either the end of file or a line
 328    * terminator is encountered.  The bytes read are then returned as a
 329    * <code>String</code> A line terminator is a byte sequence
 330    * consisting of either <code>\r</code>, <code>\n</code> or
 331    * <code>\r\n</code>.  These termination charaters are discarded and
 332    * are not returned as part of the string.
 333    * <p>
 334    * This method can read data that was written by an object implementing the
 335    * <code>writeLine()</code> method in <code>DataOutput</code>.
 336    *
 337    * @return The line read as a <code>String</code>
 338    *
 339    * @exception IOException If an error occurs
 340    *
 341    * @see DataOutput
 342    *
 343    * @deprecated
 344    */
 345   public final String readLine() throws IOException
 346   {
 347     StringBuffer strb = new StringBuffer();
 348
 349     readloop: while (true)
 350       {
 351         int c = 0;
 352         char ch = ' ';
 353         boolean getnext = true;
 354         while (getnext)
 355           {
 356             getnext = false;
 357             c = in.read();
 358             if (c < 0)  // got an EOF
 359               return strb.length() > 0 ? strb.toString() : null;
 360             ch = (char) c;
 361             if ((ch &= 0xFF) == '\n')
 362               // hack to correctly handle '\r\n' sequences
 363               if (ignoreInitialNewline)
 364                 {
 365                   ignoreInitialNewline = false;
 366                   getnext = true;
 367                 }
 368               else
 369                 break readloop;
 370           }
 371
 372         if (ch == '\r')
 373           {
 374             // FIXME: The following code tries to adjust the stream back one
 375             // character if the next char read is '\n'.  As a last resort,
 376             // it tries to mark the position before reading but the bottom
 377             // line is that it is possible that this method will not properly
 378             // deal with a '\r' '\n' combination thus not fulfilling the
 379             // DataInput contract for readLine.  It's not a particularly
 380             // safe approach threadwise since it is unsynchronized and
 381             // since it might mark an input stream behind the users back.
 382             // Along the same vein it could try the same thing for
 383             // ByteArrayInputStream and PushbackInputStream, but that is
 384             // probably overkill since this is deprecated & BufferedInputStream
 385             // is the most likely type of input stream.
 386             //
 387             // The alternative is to somehow push back the next byte if it
 388             // isn't a '\n' or to have the reading methods of this class
 389             // keep track of whether the last byte read was '\r' by readLine
 390             // and then skip the very next byte if it is '\n'.  Either way,
 391             // this would increase the complexity of the non-deprecated methods
 392             // and since it is undesirable to make non-deprecated methods
 393             // less efficient, the following seems like the most reasonable
 394             // approach.
 395             int next_c = 0;
 396             char next_ch = ' ';
 397             if (in instanceof BufferedInputStream)
 398               {
 399                 next_c = in.read();
 400                 next_ch = (char) (next_c & 0xFF);
 401                 if ((next_ch != '\n') && (next_c >= 0))
 402                   {
 403                     BufferedInputStream bin = (BufferedInputStream) in;
 404                     if (bin.pos > 0)
 405                       bin.pos--;
 406                   }
 407               }
 408             else if (markSupported())
 409               {
 410                 next_c = in.read();
 411                 next_ch = (char) (next_c & 0xFF);
 412                 if ((next_ch != '\n') && (next_c >= 0))
 413                   {
 414                     mark(1);
 415                     if ((in.read() & 0xFF) != '\n')
 416                       reset();
 417                   }
 418               }
 419             // In order to catch cases where 'in' isn't a BufferedInputStream
 420             // and doesn't support mark() (such as reading from a Socket), set
 421             // a flag that instructs readLine() to ignore the first character
 422             // it sees _if_ that character is a '\n'.
 423             else ignoreInitialNewline = true;
 424             break;
 425           }
 426         strb.append(ch);
 427       }
 428
 429     return strb.length() > 0 ? strb.toString() : "";
 430   }
 431
 432   /**
 433    * This method reads a Java long value from an input stream
 434    * It operates by reading eight bytes from the stream and converting them to
 435    * a single Java <code>long</code>  The bytes are stored most
 436    * significant byte first (i.e., "big endian") regardless of the native
 437    * host byte ordering.
 438    * <p>
 439    * As an example, if <code>byte1</code> through <code>byte8</code>
 440    * represent the first eight bytes read from the stream, they will
 441    * be transformed to an <code>long</code> in the following manner:
 442    * <p>
 443    * <code>(long)((((long)byte1 & 0xFF) << 56) + (((long)byte2 & 0xFF) << 48) +
 444    * (((long)byte3 & 0xFF) << 40) + (((long)byte4 & 0xFF) << 32) +
 445    * (((long)byte5 & 0xFF) << 24) + (((long)byte6 & 0xFF) << 16) +
 446    * (((long)byte7 & 0xFF) << 8) + ((long)byte9 & 0xFF)))</code>
 447    * <p>
 448    * The value returned is in the range of 0 to 65535.
 449    * <p>
 450    * This method can read an <code>long</code> written by an object
 451    * implementing the <code>writeLong()</code> method in the
 452    * <code>DataOutput</code> interface.
 453    *
 454    * @return The <code>long</code> value read
 455    *
 456    * @exception EOFException If end of file is reached before reading the long
 457    * @exception IOException If any other error occurs
 458    *
 459    * @see DataOutput
 460    */
 461   public final long readLong() throws IOException
 462   {
 463     readFully (buf, 0, 8);
 464     return convertToLong(buf);
 465   }
 466
 467   /**
 468    * This method reads a signed 16-bit value into a Java in from the
 469    * stream.  It operates by reading two bytes from the stream and
 470    * converting them to a single 16-bit Java <code>short</code>.  The
 471    * two bytes are stored most significant byte first (i.e., "big
 472    * endian") regardless of the native host byte ordering.
 473    * <p>
 474    * As an example, if <code>byte1</code> and <code>byte2</code>
 475    * represent the first and second byte read from the stream
 476    * respectively, they will be transformed to a <code>short</code>. in
 477    * the following manner:
 478    * <p>
 479    * <code>(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)</code>
 480    * <p>
 481    * The value returned is in the range of -32768 to 32767.
 482    * <p>
 483    * This method can read a <code>short</code> written by an object
 484    * implementing the <code>writeShort()</code> method in the
 485    * <code>DataOutput</code> interface.
 486    *
 487    * @return The <code>short</code> value read
 488    *
 489    * @exception EOFException If end of file is reached before reading the value
 490    * @exception IOException If any other error occurs
 491    *
 492    * @see DataOutput
 493    */
 494   public final short readShort() throws IOException
 495   {
 496     readFully (buf, 0, 2);
 497     return convertToShort(buf);
 498   }
 499
 500   /**
 501    * This method reads 8 unsigned bits into a Java <code>int</code>
 502    * value from the stream. The value returned is in the range of 0 to
 503    * 255.
 504    * <p>
 505    * This method can read an unsigned byte written by an object
 506    * implementing the <code>writeUnsignedByte()</code> method in the
 507    * <code>DataOutput</code> interface.
 508    *
 509    * @return The unsigned bytes value read as a Java <code>int</code>.
 510    *
 511    * @exception EOFException If end of file is reached before reading the value
 512    * @exception IOException If any other error occurs
 513    *
 514    * @see DataOutput
 515    */
 516   public final int readUnsignedByte() throws IOException
 517   {
 518     return convertToUnsignedByte(in.read());
 519   }
 520
 521   /**
 522    * This method reads 16 unsigned bits into a Java int value from the stream.
 523    * It operates by reading two bytes from the stream and converting them to
 524    * a single Java <code>int</code>  The two bytes are stored most
 525    * significant byte first (i.e., "big endian") regardless of the native
 526    * host byte ordering.
 527    * <p>
 528    * As an example, if <code>byte1</code> and <code>byte2</code>
 529    * represent the first and second byte read from the stream
 530    * respectively, they will be transformed to an <code>int</code> in
 531    * the following manner:
 532    * <p>
 533    * <code>(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))</code>
 534    * <p>
 535    * The value returned is in the range of 0 to 65535.
 536    * <p>
 537    * This method can read an unsigned short written by an object
 538    * implementing the <code>writeUnsignedShort()</code> method in the
 539    * <code>DataOutput</code> interface.
 540    *
 541    * @return The unsigned short value read as a Java <code>int</code>
 542    *
 543    * @exception EOFException If end of file is reached before reading the value
 544    * @exception IOException If any other error occurs
 545    */
 546   public final int readUnsignedShort() throws IOException
 547   {
 548     readFully (buf, 0, 2);
 549     return convertToUnsignedShort(buf);
 550   }
 551
 552   /**
 553    * This method reads a <code>String</code> from an input stream that
 554    * is encoded in a modified UTF-8 format.  This format has a leading
 555    * two byte sequence that contains the remaining number of bytes to
 556    * read.  This two byte sequence is read using the
 557    * <code>readUnsignedShort()</code> method of this interface.
 558    * <p>
 559    * After the number of remaining bytes have been determined, these
 560    * bytes are read an transformed into <code>char</code> values.
 561    * These <code>char</code> values are encoded in the stream using
 562    * either a one, two, or three byte format.  The particular format
 563    * in use can be determined by examining the first byte read.
 564    * <p>
 565    * If the first byte has a high order bit of 0, then that character
 566    * consists on only one byte.  This character value consists of
 567    * seven bits that are at positions 0 through 6 of the byte.  As an
 568    * example, if <code>byte1</code> is the byte read from the stream,
 569    * it would be converted to a <code>char</code> like so:
 570    * <p>
 571    * <code>(char)byte1</code>
 572    * <p>
 573    * If the first byte has 110 as its high order bits, then the
 574    * character consists of two bytes.  The bits that make up the character
 575    * value are in positions 0 through 4 of the first byte and bit positions
 576    * 0 through 5 of the second byte.  (The second byte should have
 577    * 10 as its high order bits).  These values are in most significant
 578    * byte first (i.e., "big endian") order.
 579    * <p>
 580    * As an example, if <code>byte1</code> and <code>byte2</code> are
 581    * the first two bytes read respectively, and the high order bits of
 582    * them match the patterns which indicate a two byte character
 583    * encoding, then they would be converted to a Java
 584    * <code>char</code> like so:
 585    * <p>
 586    * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code>
 587    * <p>
 588    * If the first byte has a 1110 as its high order bits, then the
 589    * character consists of three bytes.  The bits that make up the character
 590    * value are in positions 0 through 3 of the first byte and bit positions
 591    * 0 through 5 of the other two bytes.  (The second and third bytes should
 592    * have 10 as their high order bits).  These values are in most
 593    * significant byte first (i.e., "big endian") order.
 594    * <p>
 595    * As an example, if <code>byte1</code> <code>byte2</code> and
 596    * <code>byte3</code> are the three bytes read, and the high order
 597    * bits of them match the patterns which indicate a three byte
 598    * character encoding, then they would be converted to a Java
 599    * <code>char</code> like so:
 600    * <p>
 601    * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | (byte3 & 0x3F))</code>
 602    * <p>
 603    * Note that all characters are encoded in the method that requires
 604    * the fewest number of bytes with the exception of the character
 605    * with the value of <code>&#92;u0000</code> which is encoded as two
 606    * bytes.  This is a modification of the UTF standard used to
 607    * prevent C language style <code>NUL</code> values from appearing
 608    * in the byte stream.
 609    * <p>
 610    * This method can read data that was written by an object implementing the
 611    * <code>writeUTF()</code> method in <code>DataOutput</code>
 612    *
 613    * @returns The <code>String</code> read
 614    *
 615    * @exception EOFException If end of file is reached before reading
 616    * the String
 617    * @exception UTFDataFormatException If the data is not in UTF-8 format
 618    * @exception IOException If any other error occurs
 619    *
 620    * @see DataOutput
 621    */
 622   public final String readUTF() throws IOException
 623   {
 624     return readUTF(this);
 625   }
 626
 627   /**
 628    * This method reads a String encoded in UTF-8 format from the
 629    * specified <code>DataInput</code> source.
 630    *
 631    * @param in The <code>DataInput</code> source to read from
 632    *
 633    * @return The String read from the source
 634    *
 635    * @exception IOException If an error occurs
 636    */
 637   public final static String readUTF(DataInput in) throws IOException
 638   {
 639     final int UTFlen = in.readUnsignedShort();
 640     byte[] buf = new byte[UTFlen];
 641
 642     // This blocks until the entire string is available rather than
 643     // doing partial processing on the bytes that are available and then
 644     // blocking.  An advantage of the latter is that Exceptions
 645     // could be thrown earlier.  The former is a bit cleaner.
 646     in.readFully(buf, 0, UTFlen);
 647
 648     return convertFromUTF(buf);
 649   }
 650
 651   /**
 652    * This method attempts to skip and discard the specified number of bytes
 653    * in the input stream.  It may actually skip fewer bytes than requested.
 654    * This method will not skip any bytes if passed a negative number of bytes
 655    * to skip.
 656    *
 657    * @param n The requested number of bytes to skip.
 658    * @return The requested number of bytes to skip.
 659    * @exception IOException If an error occurs.
 660    * @specnote The JDK docs claim that this returns the number of bytes
 661    *  actually skipped. The JCL claims that this method can throw an
 662    *  EOFException. Neither of these appear to be true in the JDK 1.3's
 663    *  implementation. This tries to implement the actual JDK behaviour.
 664    */
 665   public final int skipBytes(int n) throws IOException
 666   {
 667     if (n <= 0)
 668       return 0;
 669     try
 670       {
 671         return (int) in.skip(n);
 672       }
 673     catch (EOFException x)
 674       {
 675         // do nothing.
 676       }
 677     return n;
 678   }
 679
 680   static boolean convertToBoolean(int b) throws EOFException
 681   {
 682     if (b < 0)
 683       throw new EOFException();
 684     return (b != 0);
 685   }
 686
 687   static byte convertToByte(int i) throws EOFException
 688   {
 689     if (i < 0)
 690       throw new EOFException();
 691     return (byte) i;
 692   }
 693
 694   static int convertToUnsignedByte(int i) throws EOFException
 695   {
 696     if (i < 0)
 697       throw new EOFException();
 698     return (i & 0xFF);
 699   }
 700
 701   static char convertToChar(byte[] buf)
 702   {
 703     return (char) ((buf[0] << 8) | (buf[1] & 0xff));
 704   }
 705
 706   static short convertToShort(byte[] buf)
 707   {
 708     return (short) ((buf[0] << 8) | (buf[1] & 0xff));
 709   }
 710
 711   static int convertToUnsignedShort(byte[] buf)
 712   {
 713     return (((buf[0] & 0xff) << 8) | (buf[1] & 0xff));
 714   }
 715
 716   static int convertToInt(byte[] buf)
 717   {
 718     return (((buf[0] & 0xff) << 24) | ((buf[1] & 0xff) << 16) |
 719             ((buf[2] & 0xff) << 8) | (buf[3] & 0xff));
 720   }
 721
 722   static long convertToLong(byte[] buf)
 723   {
 724     return (((long)(buf[0] & 0xff) << 56) |
 725             ((long)(buf[1] & 0xff) << 48) |
 726             ((long)(buf[2] & 0xff) << 40) |
 727             ((long)(buf[3] & 0xff) << 32) |
 728             ((long)(buf[4] & 0xff) << 24) |
 729             ((long)(buf[5] & 0xff) << 16) |
 730             ((long)(buf[6] & 0xff) <<  8) |
 731             ((long)(buf[7] & 0xff)));
 732   }
 733
 734   static String convertFromUTF(byte[] buf)
 735     throws EOFException, UTFDataFormatException
 736   {
 737     // Give StringBuffer an initial estimated size to avoid
 738     // enlarge buffer frequently
 739     StringBuffer strbuf = new StringBuffer(buf.length/2 + 2);
 740
 741     for (int i = 0; i < buf.length; )
 742       {
 743         if ((buf[i] & 0x80) == 0)               // bit pattern 0xxxxxxx
 744           strbuf.append((char) (buf[i++] & 0xFF));
 745         else if ((buf[i] & 0xE0) == 0xC0)       // bit pattern 110xxxxx
 746           {
 747             if (i + 1 >= buf.length || (buf[i+1] & 0xC0) != 0x80)
 748               throw new UTFDataFormatException();
 749
 750             strbuf.append((char) (((buf[i++] & 0x1F) << 6) |
 751                                   (buf[i++] & 0x3F)));
 752           }
 753         else if ((buf[i] & 0xF0) == 0xE0)       // bit pattern 1110xxxx
 754           {
 755             if (i + 2 >= buf.length ||
 756                 (buf[i+1] & 0xC0) != 0x80 || (buf[i+2] & 0xC0) != 0x80)
 757               throw new UTFDataFormatException();
 758
 759             strbuf.append((char) (((buf[i++] & 0x0F) << 12) |
 760                                   ((buf[i++] & 0x3F) << 6) |
 761                                   (buf[i++] & 0x3F)));
 762           }
 763         else // must be ((buf[i] & 0xF0) == 0xF0 || (buf[i] & 0xC0) == 0x80)
 764           throw new UTFDataFormatException();   // bit patterns 1111xxxx or
 765                                                 //              10xxxxxx
 766       }
 767
 768     return strbuf.toString();
 769   }
 770 }