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Java example source code file (ProtobufVarint32LengthFieldPrepender.java)

This example Java source code file (ProtobufVarint32LengthFieldPrepender.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bytebuf, channelhandlercontext, ioexception, messagetobyteencoder, override, protobufvarint32lengthfieldprepender, sharable

The ProtobufVarint32LengthFieldPrepender.java Java example source code

/*
 * Copyright 2015 The Netty Project
 *
 * The Netty Project 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 io.netty.handler.codec.protobuf;

import java.io.IOException;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

/**
 * An encoder that prepends the the Google Protocol Buffers
 * <a href="http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints">Base
 * 128 Varints</a> integer length field. For example:
 * <pre>
 * BEFORE ENCODE (300 bytes)       AFTER ENCODE (302 bytes)
 * +---------------+               +--------+---------------+
 * | Protobuf Data |-------------->| Length | Protobuf Data |
 * |  (300 bytes)  |               | 0xAC02 |  (300 bytes)  |
 * +---------------+               +--------+---------------+
 * </pre> *
 *
 * @see {@link CodedOutputStream} or (@link CodedOutputByteBufferNano)
 */
@Sharable
public class ProtobufVarint32LengthFieldPrepender extends MessageToByteEncoder<ByteBuf> {

    @Override
    protected void encode(
            ChannelHandlerContext ctx, ByteBuf msg, ByteBuf out) throws Exception {
        int bodyLen = msg.readableBytes();
        int headerLen = computeRawVarint32Size(bodyLen);
        out.ensureWritable(headerLen + bodyLen);
        writeRawVarint32(out, bodyLen);
        out.writeBytes(msg, msg.readerIndex(), bodyLen);
    }

    /**
     * Writes protobuf varint32 to (@link ByteBuf).
     * @param out to be written to
     * @param value to be written
     * @throws IOException
     */
    static void writeRawVarint32(ByteBuf out, int value) throws IOException {
        while (true) {
            if ((value & ~0x7F) == 0) {
                out.writeByte(value);
                return;
            } else {
                out.writeByte((value & 0x7F) | 0x80);
                value >>>= 7;
            }
        }
    }

    /**
     * Computes size of protobuf varint32 after encoding.
     * @param value which is to be encoded.
     * @return size of value encoded as protobuf varint32.
     */
    static int computeRawVarint32Size(final int value) {
        if ((value & (0xffffffff <<  7)) == 0) {
            return 1;
        }
        if ((value & (0xffffffff << 14)) == 0) {
            return 2;
        }
        if ((value & (0xffffffff << 21)) == 0) {
            return 3;
        }
        if ((value & (0xffffffff << 28)) == 0) {
            return 4;
        }
        return 5;
    }
}

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