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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.channel.socket.ChannelInputShutdownEvent;
import io.netty.util.internal.StringUtil;
import java.util.List;
//字节到消息类型的解码器
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) {
try {
final ByteBuf buffer;
//这个逻辑cumulation.writerIndex() > cumulation.maxCapacity() - in.readableBytes()
//转换为这个逻辑好理解in.readableBytes() > cumulation.maxCapacity() - in.writerIndex()
//条件1、cumulation的容量不够存储in的可读字节
//条件2、cumulation的引用数大于1，即用户调用了retain()方法
//条件3、cumulation变为只读的
if (cumulation.writerIndex() > cumulation.maxCapacity() - in.readableBytes()
|| cumulation.refCnt() > 1 || cumulation.isReadOnly()) {
// 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() or if its read-only.
//
// See:
// - https://github.com/netty/netty/issues/2327
// - https://github.com/netty/netty/issues/1764
buffer = expandCumulation(alloc, cumulation, in.readableBytes());
} else {
//将cumulation赋值到一个临时变量
buffer = cumulation;
}
//把in的字节写入到buffer中并返回
buffer.writeBytes(in);
return buffer;
} finally {
// We must release in in all cases as otherwise it may produce a leak if writeBytes(...) throw
// for whatever release (for example because of OutOfMemoryError)
//必须释放in
in.release();
}
}
};
/**
* 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;
try {
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);
} else {
CompositeByteBuf composite;
if (cumulation instanceof CompositeByteBuf) {
composite = (CompositeByteBuf) cumulation;
} else {
composite = alloc.compositeBuffer(Integer.MAX_VALUE);
composite.addComponent(true, cumulation);
}
composite.addComponent(true, in);
in = null;
buffer = composite;
}
return buffer;
} finally {
if (in != null) {
// We must release if the ownership was not transfered as otherwise it may produce a leak if
// writeBytes(...) throw for whatever release (for example because of OutOfMemoryError).
in.release();
}
}
}
};
private static final byte STATE_INIT = 0;
private static final byte STATE_CALLING_CHILD_DECODE = 1;
private static final byte STATE_HANDLER_REMOVED_PENDING = 2;
ByteBuf cumulation;
private Cumulator cumulator = MERGE_CUMULATOR;
private boolean singleDecode;
private boolean decodeWasNull;
private boolean first;
/**
* A bitmask where the bits are defined as
* <ul>
* <li>{@link #STATE_INIT}</li>
* <li>{@link #STATE_CALLING_CHILD_DECODE}</li>
* <li>{@link #STATE_HANDLER_REMOVED_PENDING}</li>
* </ul>
*/
private byte decodeState = STATE_INIT;
private int discardAfterReads = 16;
private int numReads;
protected ByteToMessageDecoder() {
ensureNotSharable();
}
/**
* 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;
}
/**
* Set the number of reads after which {@link ByteBuf#discardSomeReadBytes()} are called and so free up memory.
* The default is {@code 16}.
*/
public void setDiscardAfterReads(int discardAfterReads) {
if (discardAfterReads <= 0) {
throw new IllegalArgumentException("discardAfterReads must be > 0");
}
this.discardAfterReads = discardAfterReads;
}
/**
* 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 {
if (decodeState == STATE_CALLING_CHILD_DECODE) {
decodeState = STATE_HANDLER_REMOVED_PENDING;
return;
}
ByteBuf buf = cumulation;
if (buf != null) {
// Directly set this to null so we are sure we not access it in any other method here anymore.
cumulation = null;
int readable = buf.readableBytes();
if (readable > 0) {
ByteBuf bytes = buf.readBytes(readable);
buf.release();
ctx.fireChannelRead(bytes);
} else {
buf.release();
}
numReads = 0;
ctx.fireChannelReadComplete();
}
handlerRemoved0(ctx);
}
protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception { }
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
if (msg instanceof ByteBuf) {
//创建一个List,它实现了AbstractList接口.
CodecOutputList out = CodecOutputList.newInstance();
try {
ByteBuf data = (ByteBuf) msg;
first = cumulation == null;
if (first) {
//第一次调用讲data赋值给cumulation
cumulation = data;
} else {
//如果之前的cumulation不为null则需要将新的data与cumulation合并
cumulation = cumulator.cumulate(ctx.alloc(), cumulation, data);
}
//调用解码逻辑
callDecode(ctx, cumulation, out);
} catch (DecoderException e) {
throw e;
} catch (Exception e) {
throw new DecoderException(e);
} finally {
//如果不为空，并且不在可读，说明子类已经读完全部字节
if (cumulation != null && !cumulation.isReadable()) {
//释放资源
numReads = 0;
cumulation.release();
cumulation = null;
//读取次数达到一定阈值16次,则丢西已经度过的字节，释放一些空间
} else if (++ numReads >= discardAfterReads) {
// We did enough reads already try to discard some bytes so we not risk to see a OOME.
// See https://github.com/netty/netty/issues/4275
numReads = 0;
discardSomeReadBytes();
}
int size = out.size();
decodeWasNull = !out.insertSinceRecycled();
//把解析出来的消息循环调用下一个handler
fireChannelRead(ctx, out, size);
//回收资源
out.recycle();
}
} else {
ctx.fireChannelRead(msg);
}
}
//把消息循环调用到下一个handler
static void fireChannelRead(ChannelHandlerContext ctx, List<Object> msgs, int numElements) {
if (msgs instanceof CodecOutputList) {
fireChannelRead(ctx, (CodecOutputList) msgs, numElements);
} else {
for (int i = 0; i < numElements; i++) {
ctx.fireChannelRead(msgs.get(i));
}
}
}
//把消息循环调用到下一个handler
static void fireChannelRead(ChannelHandlerContext ctx, CodecOutputList msgs, int numElements) {
for (int i = 0; i < numElements; i ++) {
ctx.fireChannelRead(msgs.getUnsafe(i));
}
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
numReads = 0;
discardSomeReadBytes();
if (decodeWasNull) {
decodeWasNull = false;
if (!ctx.channel().config().isAutoRead()) {
ctx.read();
}
}
ctx.fireChannelReadComplete();
}
//释放一些空间
protected final void discardSomeReadBytes() {
//只有在refCnt()引用次数为1时才释放，否则可以子类正在使用已经读取过的字节.
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();
}
}
//连接断开处理逻辑
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
channelInputClosed(ctx, true);
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
if (evt instanceof ChannelInputShutdownEvent) {
// The decodeLast method is invoked when a channelInactive event is encountered.
// This method is responsible for ending requests in some situations and must be called
// when the input has been shutdown.
channelInputClosed(ctx, false);
}
super.userEventTriggered(ctx, evt);
}
private void channelInputClosed(ChannelHandlerContext ctx, boolean callChannelInactive) throws Exception {
CodecOutputList out = CodecOutputList.newInstance();
try {
channelInputClosed(ctx, out);
} catch (DecoderException e) {
throw e;
} catch (Exception e) {
throw new DecoderException(e);
} finally {
try {
//释放资源
if (cumulation != null) {
cumulation.release();
cumulation = null;
}
//调用下一个handler
int size = out.size();
fireChannelRead(ctx, out, size);
//触发ChannelReadComplete事件
if (size > 0) {
// Something was read, call fireChannelReadComplete()
ctx.fireChannelReadComplete();
}
//触发ChannelInactive事件
if (callChannelInactive) {
ctx.fireChannelInactive();
}
} finally {
// Recycle in all cases
out.recycle();
}
}
}
/**
* Called when the input of the channel was closed which may be because it changed to inactive or because of
* {@link ChannelInputShutdownEvent}.
*/
void channelInputClosed(ChannelHandlerContext ctx, List<Object> out) throws Exception {
if (cumulation != null) {
//调用解码逻辑
callDecode(ctx, cumulation, out);
//调用解码逻辑-子类可以释放资源
decodeLast(ctx, cumulation, out);
} else {
//传入对象-子类释放资源
decodeLast(ctx, Unpooled.EMPTY_BUFFER, out);
}
}
//解码逻辑
protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
try {
//如果in还有可读字节则循环
while (in.isReadable()) {
int outSize = out.size();
//如果out内有数据则调用下一个handle然后清空out
if (outSize > 0) {
fireChannelRead(ctx, out, outSize);
out.clear();
if (ctx.isRemoved()) {
break;
}
outSize = 0;
}
//拿到in的可读字节长度
int oldInputLength = in.readableBytes();
//调用子类解码逻辑
decodeRemovalReentryProtection(ctx, in, out);
//检查
if (ctx.isRemoved()) {
break;
}
//没有解析出新的消息
if (outSize == out.size()) {
//如果可读字节在交给子类读取后没有变化则结束循环,否则进行下一轮循环.
if (oldInputLength == in.readableBytes()) {
break;
} else {
continue;
}
}
//如果解析出新消息，但是可读字节长度没变说明解析又错误
if (oldInputLength == in.readableBytes()) {
throw new DecoderException(
StringUtil.simpleClassName(getClass()) +
".decode() did not read anything but decoded a message.");
}
//是否只解析1次
if (isSingleDecode()) {
break;
}
}
} catch (DecoderException e) {
throw e;
} catch (Exception cause) {
throw new DecoderException(cause);
}
}
//子类解析ByteBuf，将解析出的对象放入out中.
protected abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
//子类解析
final void decodeRemovalReentryProtection(ChannelHandlerContext ctx, ByteBuf in, List<Object> out)
throws Exception {
//把状态设置为STATE_CALLING_CHILD_DECODE=表示子类正在解析中
decodeState = STATE_CALLING_CHILD_DECODE;
try {
//子类解析
decode(ctx, in, out);
} finally {
//判断状态是否为移除
boolean removePending = decodeState == STATE_HANDLER_REMOVED_PENDING;
//把状态设置为初始状态
decodeState = STATE_INIT;
if (removePending) {
//调用移除逻辑
handlerRemoved(ctx);
}
}
}
/**
* 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 {
if (in.isReadable()) {
// Only call decode() if there is something left in the buffer to decode.
// See https://github.com/netty/netty/issues/4386
decodeRemovalReentryProtection(ctx, in, out);
}
}
static ByteBuf expandCumulation(ByteBufAllocator alloc, ByteBuf cumulation, int readable) {
//cumulation赋值到临时变量
ByteBuf oldCumulation = cumulation;
//创建一个新的ByteBuf对象,（其实就是扩容了)
cumulation = alloc.buffer(oldCumulation.readableBytes() + readable);
//把原来旧的oldCumulation内字节进入到cumulation当中并返回
cumulation.writeBytes(oldCumulation);
//释放旧的
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);
}
}