/*
* Copyright 2012 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;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.buffer.CompositeByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.internal.RecyclableArrayList;
import io.netty.util.internal.StringUtil;
import java.util.List;
/**
* {@link ChannelInboundHandlerAdapter} which decodes bytes in a stream-like fashion from one {@link ByteBuf} to an
* other Message type.
*
* For example here is an implementation which reads all readable bytes from
* the input {@link ByteBuf} and create a new {@link ByteBuf}.
*
* <pre>
* public class SquareDecoder extends {@link ByteToMessageDecoder} {
* {@code @Override}
* public void decode({@link ChannelHandlerContext} ctx, {@link ByteBuf} in, List<Object> out)
* throws {@link Exception} {
* out.add(in.readBytes(in.readableBytes()));
* }
* }
* </pre>
*
* <h3>Frame detection</h3>
* <p>
* Generally frame detection should be handled earlier in the pipeline by adding a
* {@link DelimiterBasedFrameDecoder}, {@link FixedLengthFrameDecoder}, {@link LengthFieldBasedFrameDecoder},
* or {@link LineBasedFrameDecoder}.
* <p>
* If a custom frame decoder is required, then one needs to be careful when implementing
* one with {@link ByteToMessageDecoder}. Ensure there are enough bytes in the buffer for a
* complete frame by checking {@link ByteBuf#readableBytes()}. If there are not enough bytes
* for a complete frame, return without modifying the reader index to allow more bytes to arrive.
* <p>
* To check for complete frames without modifying the reader index, use methods like {@link ByteBuf#getInt(int)}.
* One <strong>MUST</strong> use the reader index when using methods like {@link ByteBuf#getInt(int)}.
* For example calling <tt>in.getInt(0)</tt> is assuming the frame starts at the beginning of the buffer, which
* is not always the case. Use <tt>in.getInt(in.readerIndex())</tt> instead.
* <h3>Pitfalls</h3>
* <p>
* Be aware that sub-classes of {@link ByteToMessageDecoder} <strong>MUST NOT</strong>
* annotated with {@link @Sharable}.
* <p>
* Some methods such as {@link ByteBuf#readBytes(int)} will cause a memory leak if the returned buffer
* is not released or added to the <tt>out</tt> {@link List}. Use derived buffers like {@link ByteBuf#readSlice(int)}
* to avoid leaking memory.
*/
public abstract class ByteToMessageDecoder extends ChannelInboundHandlerAdapter {
/**
* Cumulate {@link ByteBuf}s by merge them into one {@link ByteBuf}'s, using memory copies.
*/
public static final Cumulator MERGE_CUMULATOR = new Cumulator() {
@Override
public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
ByteBuf buffer;
if (cumulation.writerIndex() > cumulation.maxCapacity() - in.readableBytes()
|| cumulation.refCnt() > 1) {
// Expand cumulation (by replace it) when either there is not more room in the buffer
// or if the refCnt is greater then 1 which may happen when the user use slice().retain() or
// duplicate().retain().
//
// See:
// - https://github.com/netty/netty/issues/2327
// - https://github.com/netty/netty/issues/1764
buffer = expandCumulation(alloc, cumulation, in.readableBytes());
} else {
buffer = cumulation;
}
buffer.writeBytes(in);
in.release();
return buffer;
}
};
/**
* Cumulate {@link ByteBuf}s by add them to a {@link CompositeByteBuf} and so do no memory copy whenever possible.
* Be aware that {@link CompositeByteBuf} use a more complex indexing implementation so depending on your use-case
* and the decoder implementation this may be slower then just use the {@link #MERGE_CUMULATOR}.
*/
public static final Cumulator COMPOSITE_CUMULATOR = new Cumulator() {
@Override
public ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in) {
ByteBuf buffer;
if (cumulation.refCnt() > 1) {
// Expand cumulation (by replace it) when the refCnt is greater then 1 which may happen when the user
// use slice().retain() or duplicate().retain().
//
// See:
// - https://github.com/netty/netty/issues/2327
// - https://github.com/netty/netty/issues/1764
buffer = expandCumulation(alloc, cumulation, in.readableBytes());
buffer.writeBytes(in);
in.release();
} else {
CompositeByteBuf composite;
if (cumulation instanceof CompositeByteBuf) {
composite = (CompositeByteBuf) cumulation;
} else {
int readable = cumulation.readableBytes();
composite = alloc.compositeBuffer();
composite.addComponent(cumulation).writerIndex(readable);
}
composite.addComponent(in).writerIndex(composite.writerIndex() + in.readableBytes());
buffer = composite;
}
return buffer;
}
};
ByteBuf cumulation;
private Cumulator cumulator = MERGE_CUMULATOR;
private boolean singleDecode;
private boolean first;
protected ByteToMessageDecoder() {
CodecUtil.ensureNotSharable(this);
}
/**
* If set then only one message is decoded on each {@link #channelRead(ChannelHandlerContext, Object)}
* call. This may be useful if you need to do some protocol upgrade and want to make sure nothing is mixed up.
*
* Default is {@code false} as this has performance impacts.
*/
public void setSingleDecode(boolean singleDecode) {
this.singleDecode = singleDecode;
}
/**
* If {@code true} then only one message is decoded on each
* {@link #channelRead(ChannelHandlerContext, Object)} call.
*
* Default is {@code false} as this has performance impacts.
*/
public boolean isSingleDecode() {
return singleDecode;
}
/**
* Set the {@link Cumulator} to use for cumulate the received {@link ByteBuf}s.
*/
public void setCumulator(Cumulator cumulator) {
if (cumulator == null) {
throw new NullPointerException("cumulator");
}
this.cumulator = cumulator;
}
/**
* Returns the actual number of readable bytes in the internal cumulative
* buffer of this decoder. You usually do not need to rely on this value
* to write a decoder. Use it only when you must use it at your own risk.
* This method is a shortcut to {@link #internalBuffer() internalBuffer().readableBytes()}.
*/
protected int actualReadableBytes() {
return internalBuffer().readableBytes();
}
/**
* Returns the internal cumulative buffer of this decoder. You usually
* do not need to access the internal buffer directly to write a decoder.
* Use it only when you must use it at your own risk.
*/
protected ByteBuf internalBuffer() {
if (cumulation != null) {
return cumulation;
} else {
return Unpooled.EMPTY_BUFFER;
}
}
@Override
public final void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
ByteBuf buf = internalBuffer();
int readable = buf.readableBytes();
if (readable > 0) {
ByteBuf bytes = buf.readBytes(readable);
buf.release();
ctx.fireChannelRead(bytes);
ctx.fireChannelReadComplete();
} else {
buf.release();
}
cumulation = null;
handlerRemoved0(ctx);
}
/**
* Gets called after the {@link ByteToMessageDecoder} was removed from the actual context and it doesn't handle
* events anymore.
*/
protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception { }
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
if (msg instanceof ByteBuf) {
RecyclableArrayList out = RecyclableArrayList.newInstance();
try {
ByteBuf data = (ByteBuf) msg;
first = cumulation == null;
if (first) {
cumulation = data;
} else {
cumulation = cumulator.cumulate(ctx.alloc(), cumulation, data);
}
callDecode(ctx, cumulation, out);
} catch (DecoderException e) {
throw e;
} catch (Throwable t) {
throw new DecoderException(t);
} finally {
if (cumulation != null && !cumulation.isReadable()) {
cumulation.release();
cumulation = null;
}
int size = out.size();
for (int i = 0; i < size; i ++) {
ctx.fireChannelRead(out.get(i));
}
out.recycle();
}
} else {
ctx.fireChannelRead(msg);
}
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
if (cumulation != null && !first && cumulation.refCnt() == 1) {
// discard some bytes if possible to make more room in the
// buffer but only if the refCnt == 1 as otherwise the user may have
// used slice().retain() or duplicate().retain().
//
// See:
// - https://github.com/netty/netty/issues/2327
// - https://github.com/netty/netty/issues/1764
cumulation.discardSomeReadBytes();
}
ctx.fireChannelReadComplete();
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
RecyclableArrayList out = RecyclableArrayList.newInstance();
try {
if (cumulation != null) {
callDecode(ctx, cumulation, out);
decodeLast(ctx, cumulation, out);
} else {
decodeLast(ctx, Unpooled.EMPTY_BUFFER, out);
}
} catch (DecoderException e) {
throw e;
} catch (Exception e) {
throw new DecoderException(e);
} finally {
try {
if (cumulation != null) {
cumulation.release();
cumulation = null;
}
int size = out.size();
for (int i = 0; i < size; i++) {
ctx.fireChannelRead(out.get(i));
}
if (size > 0) {
// Something was read, call fireChannelReadComplete()
ctx.fireChannelReadComplete();
}
ctx.fireChannelInactive();
} finally {
// recycle in all cases
out.recycle();
}
}
}
/**
* Called once data should be decoded from the given {@link ByteBuf}. This method will call
* {@link #decode(ChannelHandlerContext, ByteBuf, List)} as long as decoding should take place.
*
* @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
* @param in the {@link ByteBuf} from which to read data
* @param out the {@link List} to which decoded messages should be added
*/
protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
try {
while (in.isReadable()) {
int outSize = out.size();
int oldInputLength = in.readableBytes();
decode(ctx, in, out);
// Check if this handler was removed before continuing the loop.
// If it was removed, it is not safe to continue to operate on the buffer.
//
// See https://github.com/netty/netty/issues/1664
if (ctx.isRemoved()) {
break;
}
if (outSize == out.size()) {
if (oldInputLength == in.readableBytes()) {
break;
} else {
continue;
}
}
if (oldInputLength == in.readableBytes()) {
throw new DecoderException(
StringUtil.simpleClassName(getClass()) +
".decode() did not read anything but decoded a message.");
}
if (isSingleDecode()) {
break;
}
}
} catch (DecoderException e) {
throw e;
} catch (Throwable cause) {
throw new DecoderException(cause);
}
}
/**
* Decode the from one {@link ByteBuf} to an other. This method will be called till either the input
* {@link ByteBuf} has nothing to read when return from this method or till nothing was read from the input
* {@link ByteBuf}.
*
* @param ctx the {@link ChannelHandlerContext} which this {@link ByteToMessageDecoder} belongs to
* @param in the {@link ByteBuf} from which to read data
* @param out the {@link List} to which decoded messages should be added
* @throws Exception is thrown if an error accour
*/
protected abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
/**
* Is called one last time when the {@link ChannelHandlerContext} goes in-active. Which means the
* {@link #channelInactive(ChannelHandlerContext)} was triggered.
*
* By default this will just call {@link #decode(ChannelHandlerContext, ByteBuf, List)} but sub-classes may
* override this for some special cleanup operation.
*/
protected void decodeLast(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
decode(ctx, in, out);
}
static ByteBuf expandCumulation(ByteBufAllocator alloc, ByteBuf cumulation, int readable) {
ByteBuf oldCumulation = cumulation;
cumulation = alloc.buffer(oldCumulation.readableBytes() + readable);
cumulation.writeBytes(oldCumulation);
oldCumulation.release();
return cumulation;
}
/**
* Cumulate {@link ByteBuf}s.
*/
public interface Cumulator {
/**
* Cumulate the given {@link ByteBuf}s and return the {@link ByteBuf} that holds the cumulated bytes.
* The implementation is responsible to correctly handle the life-cycle of the given {@link ByteBuf}s and so
* call {@link ByteBuf#release()} if a {@link ByteBuf} is fully consumed.
*/
ByteBuf cumulate(ByteBufAllocator alloc, ByteBuf cumulation, ByteBuf in);
}
}