/*
* Copyright 2002-2016 Drew Noakes
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* More information about this project is available at:
*
* https://drewnoakes.com/code/exif/
* https://github.com/drewnoakes/metadata-extractor
*/
package com.drew.lang;
import com.drew.lang.annotations.NotNull;
import java.io.EOFException;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
/**
* @author Drew Noakes https://drewnoakes.com
*/
public abstract class SequentialReader
{
// TODO review whether the masks are needed (in both this and RandomAccessReader)
private boolean _isMotorolaByteOrder = true;
/**
* Gets the next byte in the sequence.
*
* @return The read byte value
*/
protected abstract byte getByte() throws IOException;
/**
* Returns the required number of bytes from the sequence.
*
* @param count The number of bytes to be returned
* @return The requested bytes
*/
@NotNull
public abstract byte[] getBytes(int count) throws IOException;
/**
* Skips forward in the sequence. If the sequence ends, an {@link EOFException} is thrown.
*
* @param n the number of byte to skip. Must be zero or greater.
* @throws EOFException the end of the sequence is reached.
* @throws IOException an error occurred reading from the underlying source.
*/
public abstract void skip(long n) throws IOException;
/**
* Skips forward in the sequence, returning a boolean indicating whether the skip succeeded, or whether the sequence ended.
*
* @param n the number of byte to skip. Must be zero or greater.
* @return a boolean indicating whether the skip succeeded, or whether the sequence ended.
* @throws IOException an error occurred reading from the underlying source.
*/
public abstract boolean trySkip(long n) throws IOException;
/**
* Sets the endianness of this reader.
* <ul>
* <li><code>true</code> for Motorola (or big) endianness (also known as network byte order), with MSB before LSB.</li>
* <li><code>false</code> for Intel (or little) endianness, with LSB before MSB.</li>
* </ul>
*
* @param motorolaByteOrder <code>true</code> for Motorola/big endian, <code>false</code> for Intel/little endian
*/
public void setMotorolaByteOrder(boolean motorolaByteOrder)
{
_isMotorolaByteOrder = motorolaByteOrder;
}
/**
* Gets the endianness of this reader.
* <ul>
* <li><code>true</code> for Motorola (or big) endianness (also known as network byte order), with MSB before LSB.</li>
* <li><code>false</code> for Intel (or little) endianness, with LSB before MSB.</li>
* </ul>
*/
public boolean isMotorolaByteOrder()
{
return _isMotorolaByteOrder;
}
/**
* Returns an unsigned 8-bit int calculated from the next byte of the sequence.
*
* @return the 8 bit int value, between 0 and 255
*/
public short getUInt8() throws IOException
{
return (short) (getByte() & 0xFF);
}
/**
* Returns a signed 8-bit int calculated from the next byte the sequence.
*
* @return the 8 bit int value, between 0x00 and 0xFF
*/
public byte getInt8() throws IOException
{
return getByte();
}
/**
* Returns an unsigned 16-bit int calculated from the next two bytes of the sequence.
*
* @return the 16 bit int value, between 0x0000 and 0xFFFF
*/
public int getUInt16() throws IOException
{
if (_isMotorolaByteOrder) {
// Motorola - MSB first
return (getByte() << 8 & 0xFF00) |
(getByte() & 0xFF);
} else {
// Intel ordering - LSB first
return (getByte() & 0xFF) |
(getByte() << 8 & 0xFF00);
}
}
/**
* Returns a signed 16-bit int calculated from two bytes of data (MSB, LSB).
*
* @return the 16 bit int value, between 0x0000 and 0xFFFF
* @throws IOException the buffer does not contain enough bytes to service the request
*/
public short getInt16() throws IOException
{
if (_isMotorolaByteOrder) {
// Motorola - MSB first
return (short) (((short)getByte() << 8 & (short)0xFF00) |
((short)getByte() & (short)0xFF));
} else {
// Intel ordering - LSB first
return (short) (((short)getByte() & (short)0xFF) |
((short)getByte() << 8 & (short)0xFF00));
}
}
/**
* Get a 32-bit unsigned integer from the buffer, returning it as a long.
*
* @return the unsigned 32-bit int value as a long, between 0x00000000 and 0xFFFFFFFF
* @throws IOException the buffer does not contain enough bytes to service the request
*/
public long getUInt32() throws IOException
{
if (_isMotorolaByteOrder) {
// Motorola - MSB first (big endian)
return (((long)getByte()) << 24 & 0xFF000000L) |
(((long)getByte()) << 16 & 0xFF0000L) |
(((long)getByte()) << 8 & 0xFF00L) |
(((long)getByte()) & 0xFFL);
} else {
// Intel ordering - LSB first (little endian)
return (((long)getByte()) & 0xFFL) |
(((long)getByte()) << 8 & 0xFF00L) |
(((long)getByte()) << 16 & 0xFF0000L) |
(((long)getByte()) << 24 & 0xFF000000L);
}
}
/**
* Returns a signed 32-bit integer from four bytes of data.
*
* @return the signed 32 bit int value, between 0x00000000 and 0xFFFFFFFF
* @throws IOException the buffer does not contain enough bytes to service the request
*/
public int getInt32() throws IOException
{
if (_isMotorolaByteOrder) {
// Motorola - MSB first (big endian)
return (getByte() << 24 & 0xFF000000) |
(getByte() << 16 & 0xFF0000) |
(getByte() << 8 & 0xFF00) |
(getByte() & 0xFF);
} else {
// Intel ordering - LSB first (little endian)
return (getByte() & 0xFF) |
(getByte() << 8 & 0xFF00) |
(getByte() << 16 & 0xFF0000) |
(getByte() << 24 & 0xFF000000);
}
}
/**
* Get a signed 64-bit integer from the buffer.
*
* @return the 64 bit int value, between 0x0000000000000000 and 0xFFFFFFFFFFFFFFFF
* @throws IOException the buffer does not contain enough bytes to service the request
*/
public long getInt64() throws IOException
{
if (_isMotorolaByteOrder) {
// Motorola - MSB first
return ((long)getByte() << 56 & 0xFF00000000000000L) |
((long)getByte() << 48 & 0xFF000000000000L) |
((long)getByte() << 40 & 0xFF0000000000L) |
((long)getByte() << 32 & 0xFF00000000L) |
((long)getByte() << 24 & 0xFF000000L) |
((long)getByte() << 16 & 0xFF0000L) |
((long)getByte() << 8 & 0xFF00L) |
((long)getByte() & 0xFFL);
} else {
// Intel ordering - LSB first
return ((long)getByte() & 0xFFL) |
((long)getByte() << 8 & 0xFF00L) |
((long)getByte() << 16 & 0xFF0000L) |
((long)getByte() << 24 & 0xFF000000L) |
((long)getByte() << 32 & 0xFF00000000L) |
((long)getByte() << 40 & 0xFF0000000000L) |
((long)getByte() << 48 & 0xFF000000000000L) |
((long)getByte() << 56 & 0xFF00000000000000L);
}
}
/**
* Gets a s15.16 fixed point float from the buffer.
* <p>
* This particular fixed point encoding has one sign bit, 15 numerator bits and 16 denominator bits.
*
* @return the floating point value
* @throws IOException the buffer does not contain enough bytes to service the request
*/
public float getS15Fixed16() throws IOException
{
if (_isMotorolaByteOrder) {
float res = (getByte() & 0xFF) << 8 |
(getByte() & 0xFF);
int d = (getByte() & 0xFF) << 8 |
(getByte() & 0xFF);
return (float)(res + d/65536.0);
} else {
// this particular branch is untested
int d = (getByte() & 0xFF) |
(getByte() & 0xFF) << 8;
float res = (getByte() & 0xFF) |
(getByte() & 0xFF) << 8;
return (float)(res + d/65536.0);
}
}
public float getFloat32() throws IOException
{
return Float.intBitsToFloat(getInt32());
}
public double getDouble64() throws IOException
{
return Double.longBitsToDouble(getInt64());
}
@NotNull
public String getString(int bytesRequested) throws IOException
{
return new String(getBytes(bytesRequested));
}
@NotNull
public String getString(int bytesRequested, String charset) throws IOException
{
byte[] bytes = getBytes(bytesRequested);
try {
return new String(bytes, charset);
} catch (UnsupportedEncodingException e) {
return new String(bytes);
}
}
/**
* Creates a String from the stream, ending where <code>byte=='\0'</code> or where <code>length==maxLength</code>.
*
* @param maxLengthBytes The maximum number of bytes to read. If a zero-byte is not reached within this limit,
* reading will stop and the string will be truncated to this length.
* @return The read string.
* @throws IOException The buffer does not contain enough bytes to satisfy this request.
*/
@NotNull
public String getNullTerminatedString(int maxLengthBytes) throws IOException
{
// NOTE currently only really suited to single-byte character strings
byte[] bytes = new byte[maxLengthBytes];
// Count the number of non-null bytes
int length = 0;
while (length < bytes.length && (bytes[length] = getByte()) != '\0')
length++;
return new String(bytes, 0, length);
}
}