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The official Couchbase JVM Core IO Library
/*
* Copyright (c) 2019 Couchbase, Inc.
*
* 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.
*/
package com.couchbase.client.core.util;
import com.couchbase.client.core.deps.io.netty.buffer.ByteBuf;
import com.couchbase.client.core.deps.io.netty.buffer.Unpooled;
import java.io.ByteArrayOutputStream;
import java.util.function.IntConsumer;
import java.util.function.IntSupplier;
/**
* Encodes and decodes the unsigned LEB128 (Little Endian Base 128) format.
* See LEB128.
*/
public class UnsignedLEB128 {
private UnsignedLEB128() {
throw new AssertionError("not instantiable");
}
/**
* Reads an unsigned LEB128 value from the buffer. If this methods throws an exception
* the reader index remains unchanged, otherwise the index advances past the value.
*
* @return the decoded value
* @throws ArithmeticException if the decoded value is longer than 64 bits.
* @throws IndexOutOfBoundsException if the buffer's readable bytes do not contain a complete value.
*/
public static long read(ByteBuf buf) {
final int readerMark = buf.readerIndex();
try {
return read(buf::readByte);
} catch (Exception e) {
buf.readerIndex(readerMark);
throw e;
}
}
/**
* Advances the buffer's reader index past the unsigned LEB128 value at the reader index.
* If this method throws an exception, the reader index will be unchanged.
*
* @return the number of bytes skipped.
* @throws IndexOutOfBoundsException if the buffer's readable bytes do not contain a complete value.
*/
public static int skip(ByteBuf buf) {
final int readerMark = buf.readerIndex();
int bytesSkipped = 0;
try {
do {
bytesSkipped++;
} while ((buf.readByte() & 0x80) != 0);
} catch (Exception e) {
buf.readerIndex(readerMark);
throw e;
}
return bytesSkipped;
}
/**
* Writes the unsigned LEB128 representation of the value to the buffer.
*/
public static void write(ByteBuf buf, long value) {
write(value, buf::writeByte);
}
/**
* Returns a byte array containing the unsigned LEB128 representation of the given value.
*/
public static byte[] encode(long value) {
ByteArrayOutputStream result = new ByteArrayOutputStream();
write(value, result::write);
return result.toByteArray();
}
/**
* Given a byte array starting with an unsigned LEB128 value, returns the decoded form
* of that value.
*
* @throws ArithmeticException if the decoded value is larger than 64 bits.
* @throws IndexOutOfBoundsException if the input does not contain a complete LEB128 value
*/
public static long decode(byte[] bytes) {
return read(Unpooled.wrappedBuffer(bytes));
}
private static long read(IntSupplier byteSource) {
long result = 0;
for (int i = 0; ; i++) {
final int b = byteSource.getAsInt();
final long low7Bits = b & 0x7f;
final boolean done = (b & 0x80) == 0;
// The first 9 groups of 7 bits are guaranteed to fit (9 * 7 = 63 bits).
// That leaves room for only the low-order bit from the 10th group (which has index 9)
if (i == 9 && (b & 0xfe) != 0) {
throw new ArithmeticException("Value is larger than 64-bits");
}
result |= low7Bits << (7 * i);
if (done) {
return result;
}
}
}
private static void write(long value, IntConsumer byteSink) {
while (true) {
final int b = (int) (value & 0x7f);
value >>>= 7;
if (value == 0) {
byteSink.accept(b);
return;
}
byteSink.accept(b | 0x80);
}
}
}