/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.lucene.store;
import java.io.IOException;
import java.util.Map;
import java.util.Set;
import org.apache.lucene.util.BitUtil;
import org.apache.lucene.util.BytesRef;
/**
* Abstract base class for performing write operations of Lucene's low-level
* data types.
* <p>{@code DataOutput} may only be used from one thread, because it is not
* thread safe (it keeps internal state like file position).
*/
public abstract class DataOutput {
/** Writes a single byte.
* <p>
* The most primitive data type is an eight-bit byte. Files are
* accessed as sequences of bytes. All other data types are defined
* as sequences of bytes, so file formats are byte-order independent.
*
* @see IndexInput#readByte()
*/
public abstract void writeByte(byte b) throws IOException;
/** Writes an array of bytes.
* @param b the bytes to write
* @param length the number of bytes to write
* @see DataInput#readBytes(byte[],int,int)
*/
public void writeBytes(byte[] b, int length) throws IOException {
writeBytes(b, 0, length);
}
/** Writes an array of bytes.
* @param b the bytes to write
* @param offset the offset in the byte array
* @param length the number of bytes to write
* @see DataInput#readBytes(byte[],int,int)
*/
public abstract void writeBytes(byte[] b, int offset, int length) throws IOException;
/** Writes an int as four bytes.
* <p>
* 32-bit unsigned integer written as four bytes, high-order bytes first.
*
* @see DataInput#readInt()
*/
public void writeInt(int i) throws IOException {
writeByte((byte)(i >> 24));
writeByte((byte)(i >> 16));
writeByte((byte)(i >> 8));
writeByte((byte) i);
}
/** Writes a short as two bytes.
* @see DataInput#readShort()
*/
public void writeShort(short i) throws IOException {
writeByte((byte)(i >> 8));
writeByte((byte) i);
}
/** Writes an int in a variable-length format. Writes between one and
* five bytes. Smaller values take fewer bytes. Negative numbers are
* supported, but should be avoided.
* <p>VByte is a variable-length format for positive integers is defined where the
* high-order bit of each byte indicates whether more bytes remain to be read. The
* low-order seven bits are appended as increasingly more significant bits in the
* resulting integer value. Thus values from zero to 127 may be stored in a single
* byte, values from 128 to 16,383 may be stored in two bytes, and so on.</p>
* <p>VByte Encoding Example</p>
* <table cellspacing="0" cellpadding="2" border="0" summary="variable length encoding examples">
* <tr valign="top">
* <th align="left">Value</th>
* <th align="left">Byte 1</th>
* <th align="left">Byte 2</th>
* <th align="left">Byte 3</th>
* </tr>
* <tr valign="bottom">
* <td>0</td>
* <td><code>00000000</code></td>
* <td></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>1</td>
* <td><code>00000001</code></td>
* <td></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>2</td>
* <td><code>00000010</code></td>
* <td></td>
* <td></td>
* </tr>
* <tr>
* <td valign="top">...</td>
* <td valign="bottom"></td>
* <td valign="bottom"></td>
* <td valign="bottom"></td>
* </tr>
* <tr valign="bottom">
* <td>127</td>
* <td><code>01111111</code></td>
* <td></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>128</td>
* <td><code>10000000</code></td>
* <td><code>00000001</code></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>129</td>
* <td><code>10000001</code></td>
* <td><code>00000001</code></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>130</td>
* <td><code>10000010</code></td>
* <td><code>00000001</code></td>
* <td></td>
* </tr>
* <tr>
* <td valign="top">...</td>
* <td></td>
* <td></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>16,383</td>
* <td><code>11111111</code></td>
* <td><code>01111111</code></td>
* <td></td>
* </tr>
* <tr valign="bottom">
* <td>16,384</td>
* <td><code>10000000</code></td>
* <td><code>10000000</code></td>
* <td><code>00000001</code></td>
* </tr>
* <tr valign="bottom">
* <td>16,385</td>
* <td><code>10000001</code></td>
* <td><code>10000000</code></td>
* <td><code>00000001</code></td>
* </tr>
* <tr>
* <td valign="top">...</td>
* <td valign="bottom"></td>
* <td valign="bottom"></td>
* <td valign="bottom"></td>
* </tr>
* </table>
* <p>This provides compression while still being efficient to decode.</p>
*
* @param i Smaller values take fewer bytes. Negative numbers are
* supported, but should be avoided.
* @throws IOException If there is an I/O error writing to the underlying medium.
* @see DataInput#readVInt()
*/
public final void writeVInt(int i) throws IOException {
while ((i & ~0x7F) != 0) {
writeByte((byte)((i & 0x7F) | 0x80));
i >>>= 7;
}
writeByte((byte)i);
}
/**
* Write a {@link BitUtil#zigZagEncode(int) zig-zag}-encoded
* {@link #writeVInt(int) variable-length} integer. This is typically useful
* to write small signed ints and is equivalent to calling
* <code>writeVInt(BitUtil.zigZagEncode(i))</code>.
* @see DataInput#readZInt()
*/
public final void writeZInt(int i) throws IOException {
writeVInt(BitUtil.zigZagEncode(i));
}
/** Writes a long as eight bytes.
* <p>
* 64-bit unsigned integer written as eight bytes, high-order bytes first.
*
* @see DataInput#readLong()
*/
public void writeLong(long i) throws IOException {
writeInt((int) (i >> 32));
writeInt((int) i);
}
/** Writes an long in a variable-length format. Writes between one and nine
* bytes. Smaller values take fewer bytes. Negative numbers are not
* supported.
* <p>
* The format is described further in {@link DataOutput#writeVInt(int)}.
* @see DataInput#readVLong()
*/
public final void writeVLong(long i) throws IOException {
if (i < 0) {
throw new IllegalArgumentException("cannot write negative vLong (got: " + i + ")");
}
writeSignedVLong(i);
}
// write a potentially negative vLong
private void writeSignedVLong(long i) throws IOException {
while ((i & ~0x7FL) != 0L) {
writeByte((byte)((i & 0x7FL) | 0x80L));
i >>>= 7;
}
writeByte((byte)i);
}
/**
* Write a {@link BitUtil#zigZagEncode(long) zig-zag}-encoded
* {@link #writeVLong(long) variable-length} long. Writes between one and ten
* bytes. This is typically useful to write small signed ints.
* @see DataInput#readZLong()
*/
public final void writeZLong(long i) throws IOException {
writeSignedVLong(BitUtil.zigZagEncode(i));
}
/** Writes a string.
* <p>
* Writes strings as UTF-8 encoded bytes. First the length, in bytes, is
* written as a {@link #writeVInt VInt}, followed by the bytes.
*
* @see DataInput#readString()
*/
public void writeString(String s) throws IOException {
final BytesRef utf8Result = new BytesRef(s);
writeVInt(utf8Result.length);
writeBytes(utf8Result.bytes, utf8Result.offset, utf8Result.length);
}
private static int COPY_BUFFER_SIZE = 16384;
private byte[] copyBuffer;
/** Copy numBytes bytes from input to ourself. */
public void copyBytes(DataInput input, long numBytes) throws IOException {
assert numBytes >= 0: "numBytes=" + numBytes;
long left = numBytes;
if (copyBuffer == null)
copyBuffer = new byte[COPY_BUFFER_SIZE];
while(left > 0) {
final int toCopy;
if (left > COPY_BUFFER_SIZE)
toCopy = COPY_BUFFER_SIZE;
else
toCopy = (int) left;
input.readBytes(copyBuffer, 0, toCopy);
writeBytes(copyBuffer, 0, toCopy);
left -= toCopy;
}
}
/**
* Writes a String map.
* <p>
* First the size is written as an {@link #writeVInt(int) vInt},
* followed by each key-value pair written as two consecutive
* {@link #writeString(String) String}s.
*
* @param map Input map.
* @throws NullPointerException if {@code map} is null.
*/
public void writeMapOfStrings(Map<String,String> map) throws IOException {
writeVInt(map.size());
for (Map.Entry<String, String> entry : map.entrySet()) {
writeString(entry.getKey());
writeString(entry.getValue());
}
}
/**
* Writes a String set.
* <p>
* First the size is written as an {@link #writeVInt(int) vInt},
* followed by each value written as a
* {@link #writeString(String) String}.
*
* @param set Input set.
* @throws NullPointerException if {@code set} is null.
*/
public void writeSetOfStrings(Set<String> set) throws IOException {
writeVInt(set.size());
for (String value : set) {
writeString(value);
}
}
}