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/*
* Copyright (c) 1995, 2022, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.io;
/**
* The {@code DataInput} interface provides
* for reading bytes from a binary stream and
* reconstructing from them data in any of
* the Java primitive types. There is also
* a
* facility for reconstructing a {@code String}
* from data in
* <a href="#modified-utf-8">modified UTF-8</a>
* format.
* <p>
* It is generally true of all the reading
* routines in this interface that if end of
* file is reached before the desired number
* of bytes has been read, an {@code EOFException}
* (which is a kind of {@code IOException})
* is thrown. If any byte cannot be read for
* any reason other than end of file, an {@code IOException}
* other than {@code EOFException} is
* thrown. In particular, an {@code IOException}
* may be thrown if the input stream has been
* closed.
*
* <h2><a id="modified-utf-8">Modified UTF-8</a></h2>
* <p>
* Implementations of the DataInput and DataOutput interfaces represent
* Unicode strings in a format that is a slight modification of UTF-8.
* (For information regarding the standard UTF-8 format, see section
* <i>3.9 Unicode Encoding Forms</i> of <i>The Unicode Standard, Version
* 4.0</i>)
*
* <ul>
* <li>Characters in the range {@code '\u005Cu0001'} to
* {@code '\u005Cu007F'} are represented by a single byte.
* <li>The null character {@code '\u005Cu0000'} and characters
* in the range {@code '\u005Cu0080'} to {@code '\u005Cu07FF'} are
* represented by a pair of bytes.
* <li>Characters in the range {@code '\u005Cu0800'}
* to {@code '\u005CuFFFF'} are represented by three bytes.
* </ul>
*
* <table class="plain" style="margin-left:2em;">
* <caption>Encoding of UTF-8 values</caption>
* <thead>
* <tr>
* <th scope="col" rowspan="2">Value</th>
* <th scope="col" rowspan="2">Byte</th>
* <th scope="col" colspan="8" id="bit_a">Bit Values</th>
* </tr>
* <tr>
* <!-- Value -->
* <!-- Byte -->
* <th scope="col" style="width:3em"> 7 </th>
* <th scope="col" style="width:3em"> 6 </th>
* <th scope="col" style="width:3em"> 5 </th>
* <th scope="col" style="width:3em"> 4 </th>
* <th scope="col" style="width:3em"> 3 </th>
* <th scope="col" style="width:3em"> 2 </th>
* <th scope="col" style="width:3em"> 1 </th>
* <th scope="col" style="width:3em"> 0 </th>
* </thead>
* <tbody>
* <tr>
* <th scope="row" style="text-align:left; font-weight:normal">
* {@code \u005Cu0001} to {@code \u005Cu007F} </th>
* <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
* <td style="text-align:center">0
* <td colspan="7" style="text-align:right; padding-right:6em">bits 6-0
* </tr>
* <tr>
* <th scope="row" rowspan="2" style="text-align:left; font-weight:normal">
* {@code \u005Cu0000},<br>
* {@code \u005Cu0080} to {@code \u005Cu07FF} </th>
* <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
* <td style="text-align:center">1
* <td style="text-align:center">1
* <td style="text-align:center">0
* <td colspan="5" style="text-align:right; padding-right:6em">bits 10-6
* </tr>
* <tr>
* <!-- (value) -->
* <th scope="row" style="font-weight:normal; text-align:center"> 2 </th>
* <td style="text-align:center">1
* <td style="text-align:center">0
* <td colspan="6" style="text-align:right; padding-right:6em">bits 5-0
* </tr>
* <tr>
* <th scope="row" rowspan="3" style="text-align:left; font-weight:normal">
* {@code \u005Cu0800} to {@code \u005CuFFFF} </th>
* <th scope="row" style="font-weight:normal; text-align:center"> 1 </th>
* <td style="text-align:center">1
* <td style="text-align:center">1
* <td style="text-align:center">1
* <td style="text-align:center">0
* <td colspan="4" style="text-align:right; padding-right:6em">bits 15-12
* </tr>
* <tr>
* <!-- (value) -->
* <th scope="row" style="font-weight:normal; text-align:center"> 2 </th>
* <td style="text-align:center">1
* <td style="text-align:center">0
* <td colspan="6" style="text-align:right; padding-right:6em">bits 11-6
* </tr>
* <tr>
* <!-- (value) -->
* <th scope="row" style="font-weight:normal; text-align:center"> 3 </th>
* <td style="text-align:center">1
* <td style="text-align:center">0
* <td colspan="6" style="text-align:right; padding-right:6em">bits 5-0
* </tr>
* </tbody>
* </table>
*
* <p>
* The differences between this format and the
* standard UTF-8 format are the following:
* <ul>
* <li>The null byte {@code '\u005Cu0000'} is encoded in 2-byte format
* rather than 1-byte, so that the encoded strings never have
* embedded nulls.
* <li>Only the 1-byte, 2-byte, and 3-byte formats are used.
* <li><a href="../lang/Character.html#unicode">Supplementary characters</a>
* are represented in the form of surrogate pairs.
* </ul>
* @author Frank Yellin
* @see java.io.DataInputStream
* @see java.io.DataOutput
* @since 1.0
*/
public interface DataInput {
/**
* Reads some bytes from an input
* stream and stores them into the buffer
* array {@code b}. The number of bytes
* read is equal
* to the length of {@code b}.
* <p>
* This method blocks until one of the
* following conditions occurs:
* <ul>
* <li>{@code b.length}
* bytes of input data are available, in which
* case a normal return is made.
*
* <li>End of
* file is detected, in which case an {@code EOFException}
* is thrown.
*
* <li>An I/O error occurs, in
* which case an {@code IOException} other
* than {@code EOFException} is thrown.
* </ul>
* <p>
* If {@code b} is {@code null},
* a {@code NullPointerException} is thrown.
* If {@code b.length} is zero, then
* no bytes are read. Otherwise, the first
* byte read is stored into element {@code b[0]},
* the next one into {@code b[1]}, and
* so on.
* If an exception is thrown from
* this method, then it may be that some but
* not all bytes of {@code b} have been
* updated with data from the input stream.
*
* @param b the buffer into which the data is read.
* @throws NullPointerException if {@code b} is {@code null}.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
void readFully(byte[] b) throws IOException;
/**
*
* Reads {@code len}
* bytes from
* an input stream.
* <p>
* This method
* blocks until one of the following conditions
* occurs:
* <ul>
* <li>{@code len} bytes
* of input data are available, in which case
* a normal return is made.
*
* <li>End of file
* is detected, in which case an {@code EOFException}
* is thrown.
*
* <li>An I/O error occurs, in
* which case an {@code IOException} other
* than {@code EOFException} is thrown.
* </ul>
* <p>
* If {@code b} is {@code null},
* a {@code NullPointerException} is thrown.
* If {@code off} is negative, or {@code len}
* is negative, or {@code off+len} is
* greater than the length of the array {@code b},
* then an {@code IndexOutOfBoundsException}
* is thrown.
* If {@code len} is zero,
* then no bytes are read. Otherwise, the first
* byte read is stored into element {@code b[off]},
* the next one into {@code b[off+1]},
* and so on. The number of bytes read is,
* at most, equal to {@code len}.
*
* @param b the buffer into which the data is read.
* @param off an int specifying the offset in the data array {@code b}.
* @param len an int specifying the number of bytes to read.
* @throws NullPointerException if {@code b} is {@code null}.
* @throws IndexOutOfBoundsException if {@code off} is negative,
* {@code len} is negative, or {@code len} is greater than
* {@code b.length - off}.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
void readFully(byte[] b, int off, int len) throws IOException;
/**
* Makes an attempt to skip over
* {@code n} bytes
* of data from the input
* stream, discarding the skipped bytes. However,
* it may skip
* over some smaller number of
* bytes, possibly zero. This may result from
* any of a
* number of conditions; reaching
* end of file before {@code n} bytes
* have been skipped is
* only one possibility.
* This method never throws an {@code EOFException}.
* The actual
* number of bytes skipped is returned.
*
* @param n the number of bytes to be skipped.
* @return the number of bytes actually skipped.
* @throws IOException if an I/O error occurs.
*/
int skipBytes(int n) throws IOException;
/**
* Reads one input byte and returns
* {@code true} if that byte is nonzero,
* {@code false} if that byte is zero.
* This method is suitable for reading
* the byte written by the {@code writeBoolean}
* method of interface {@code DataOutput}.
*
* @return the {@code boolean} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
boolean readBoolean() throws IOException;
/**
* Reads and returns one input byte.
* The byte is treated as a signed value in
* the range {@code -128} through {@code 127},
* inclusive.
* This method is suitable for
* reading the byte written by the {@code writeByte}
* method of interface {@code DataOutput}.
*
* @return the 8-bit value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
byte readByte() throws IOException;
/**
* Reads one input byte, zero-extends
* it to type {@code int}, and returns
* the result, which is therefore in the range
* {@code 0}
* through {@code 255}.
* This method is suitable for reading
* the byte written by the {@code writeByte}
* method of interface {@code DataOutput}
* if the argument to {@code writeByte}
* was intended to be a value in the range
* {@code 0} through {@code 255}.
*
* @return the unsigned 8-bit value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
int readUnsignedByte() throws IOException;
/**
* Reads two input bytes and returns
* a {@code short} value. Let {@code a}
* be the first byte read and {@code b}
* be the second byte. The value
* returned
* is:
* <pre>{@code (short)((a << 8) | (b & 0xff))
* }</pre>
* This method
* is suitable for reading the bytes written
* by the {@code writeShort} method of
* interface {@code DataOutput}.
*
* @return the 16-bit value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
short readShort() throws IOException;
/**
* Reads two input bytes and returns
* an {@code int} value in the range {@code 0}
* through {@code 65535}. Let {@code a}
* be the first byte read and
* {@code b}
* be the second byte. The value returned is:
* <pre>{@code (((a & 0xff) << 8) | (b & 0xff))
* }</pre>
* This method is suitable for reading the bytes
* written by the {@code writeShort} method
* of interface {@code DataOutput} if
* the argument to {@code writeShort}
* was intended to be a value in the range
* {@code 0} through {@code 65535}.
*
* @return the unsigned 16-bit value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
int readUnsignedShort() throws IOException;
/**
* Reads two input bytes and returns a {@code char} value.
* Let {@code a}
* be the first byte read and {@code b}
* be the second byte. The value
* returned is:
* <pre>{@code (char)((a << 8) | (b & 0xff))
* }</pre>
* This method
* is suitable for reading bytes written by
* the {@code writeChar} method of interface
* {@code DataOutput}.
*
* @return the {@code char} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
char readChar() throws IOException;
/**
* Reads four input bytes and returns an
* {@code int} value. Let {@code a-d}
* be the first through fourth bytes read. The value returned is:
* <pre>{@code
* (((a & 0xff) << 24) | ((b & 0xff) << 16) |
* ((c & 0xff) << 8) | (d & 0xff))
* }</pre>
* This method is suitable
* for reading bytes written by the {@code writeInt}
* method of interface {@code DataOutput}.
*
* @return the {@code int} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
int readInt() throws IOException;
/**
* Reads eight input bytes and returns
* a {@code long} value. Let {@code a-h}
* be the first through eighth bytes read.
* The value returned is:
* <pre>{@code
* (((long)(a & 0xff) << 56) |
* ((long)(b & 0xff) << 48) |
* ((long)(c & 0xff) << 40) |
* ((long)(d & 0xff) << 32) |
* ((long)(e & 0xff) << 24) |
* ((long)(f & 0xff) << 16) |
* ((long)(g & 0xff) << 8) |
* ((long)(h & 0xff)))
* }</pre>
* <p>
* This method is suitable
* for reading bytes written by the {@code writeLong}
* method of interface {@code DataOutput}.
*
* @return the {@code long} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
long readLong() throws IOException;
/**
* Reads four input bytes and returns
* a {@code float} value. It does this
* by first constructing an {@code int}
* value in exactly the manner
* of the {@code readInt}
* method, then converting this {@code int}
* value to a {@code float} in
* exactly the manner of the method {@code Float.intBitsToFloat}.
* This method is suitable for reading
* bytes written by the {@code writeFloat}
* method of interface {@code DataOutput}.
*
* @return the {@code float} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
float readFloat() throws IOException;
/**
* Reads eight input bytes and returns
* a {@code double} value. It does this
* by first constructing a {@code long}
* value in exactly the manner
* of the {@code readLong}
* method, then converting this {@code long}
* value to a {@code double} in exactly
* the manner of the method {@code Double.longBitsToDouble}.
* This method is suitable for reading
* bytes written by the {@code writeDouble}
* method of interface {@code DataOutput}.
*
* @return the {@code double} value read.
* @throws EOFException if this stream reaches the end before reading
* all the bytes.
* @throws IOException if an I/O error occurs.
*/
double readDouble() throws IOException;
/**
* Reads the next line of text from the input stream.
* It reads successive bytes, converting
* each byte separately into a character,
* until it encounters a line terminator or
* end of
* file; the characters read are then
* returned as a {@code String}. Note
* that because this
* method processes bytes,
* it does not support input of the full Unicode
* character set.
* <p>
* If end of file is encountered
* before even one byte can be read, then {@code null}
* is returned. Otherwise, each byte that is
* read is converted to type {@code char}
* by zero-extension. If the character {@code '\n'}
* is encountered, it is discarded and reading
* ceases. If the character {@code '\r'}
* is encountered, it is discarded and, if
* the following byte converts to the
* character {@code '\n'}, then that is
* discarded also; reading then ceases. If
* end of file is encountered before either
* of the characters {@code '\n'} and
* {@code '\r'} is encountered, reading
* ceases. Once reading has ceased, a {@code String}
* is returned that contains all the characters
* read and not discarded, taken in order.
* Note that every character in this string
* will have a value less than {@code \u005Cu0100},
* that is, {@code (char)256}.
*
* @return the next line of text from the input stream,
* or {@code null} if the end of file is
* encountered before a byte can be read.
* @throws IOException if an I/O error occurs.
*/
String readLine() throws IOException;
/**
* Reads in a string that has been encoded using a
* <a href="#modified-utf-8">modified UTF-8</a>
* format.
* The general contract of {@code readUTF}
* is that it reads a representation of a Unicode
* character string encoded in modified
* UTF-8 format; this string of characters
* is then returned as a {@code String}.
* <p>
* First, two bytes are read and used to
* construct an unsigned 16-bit integer in
* exactly the manner of the {@code readUnsignedShort}
* method . This integer value is called the
* <i>UTF length</i> and specifies the number
* of additional bytes to be read. These bytes
* are then converted to characters by considering
* them in groups. The length of each group
* is computed from the value of the first
* byte of the group. The byte following a
* group, if any, is the first byte of the
* next group.
* <p>
* If the first byte of a group
* matches the bit pattern {@code 0xxxxxxx}
* (where {@code x} means "may be {@code 0}
* or {@code 1}"), then the group consists
* of just that byte. The byte is zero-extended
* to form a character.
* <p>
* If the first byte
* of a group matches the bit pattern {@code 110xxxxx},
* then the group consists of that byte {@code a}
* and a second byte {@code b}. If there
* is no byte {@code b} (because byte
* {@code a} was the last of the bytes
* to be read), or if byte {@code b} does
* not match the bit pattern {@code 10xxxxxx},
* then a {@code UTFDataFormatException}
* is thrown. Otherwise, the group is converted
* to the character:
* <pre>{@code (char)(((a & 0x1F) << 6) | (b & 0x3F))
* }</pre>
* If the first byte of a group
* matches the bit pattern {@code 1110xxxx},
* then the group consists of that byte {@code a}
* and two more bytes {@code b} and {@code c}.
* If there is no byte {@code c} (because
* byte {@code a} was one of the last
* two of the bytes to be read), or either
* byte {@code b} or byte {@code c}
* does not match the bit pattern {@code 10xxxxxx},
* then a {@code UTFDataFormatException}
* is thrown. Otherwise, the group is converted
* to the character:
* <pre>{@code
* (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
* }</pre>
* If the first byte of a group matches the
* pattern {@code 1111xxxx} or the pattern
* {@code 10xxxxxx}, then a {@code UTFDataFormatException}
* is thrown.
* <p>
* If end of file is encountered
* at any time during this entire process,
* then an {@code EOFException} is thrown.
* <p>
* After every group has been converted to
* a character by this process, the characters
* are gathered, in the same order in which
* their corresponding groups were read from
* the input stream, to form a {@code String},
* which is returned.
* <p>
* The {@code writeUTF}
* method of interface {@code DataOutput}
* may be used to write data that is suitable
* for reading by this method.
* @return a Unicode string.
* @throws EOFException if this stream reaches the end
* before reading all the bytes.
* @throws IOException if an I/O error occurs.
* @throws UTFDataFormatException if the bytes do not represent a
* valid modified UTF-8 encoding of a string.
*/
String readUTF() throws IOException;
}