Java tutorial
/* * 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 com.google.protobuf.CodedOutputStream; import com.google.protobuf.nano.CodedOutputByteBufferNano; 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 Google Protocol Buffers * <a href="https://developers.google.com/protocol-buffers/docs/encoding?csw=1#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 CodedOutputStream * @see 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 */ static void writeRawVarint32(ByteBuf out, int value) { 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; } }