shengminw opened a new issue, #4468:
URL: https://github.com/apache/rocketmq/issues/4468
## Optimize broker buffer length initialization
The format of the message written to the CommitLog, except for the message
body, also includes many other information.
CommitLog storage format：
```java
// 1 TOTALSIZE
this.byteBuf.writeInt(msgLen);
// 2 MAGICCODE
this.byteBuf.writeInt(CommitLog.MESSAGE_MAGIC_CODE);
// 3 BODYCRC
this.byteBuf.writeInt(msgInner.getBodyCRC());
// 4 QUEUEID
this.byteBuf.writeInt(msgInner.getQueueId());
// 5 FLAG
this.byteBuf.writeInt(msgInner.getFlag());
// 6 QUEUEOFFSET, need update later
this.byteBuf.writeLong(0);
// 7 PHYSICALOFFSET, need update later
this.byteBuf.writeLong(0);
// 8 SYSFLAG
this.byteBuf.writeInt(msgInner.getSysFlag());
// 9 BORNTIMESTAMP
this.byteBuf.writeLong(msgInner.getBornTimestamp());
// 10 BORNHOST
ByteBuffer bornHostBytes = msgInner.getBornHostBytes();
this.byteBuf.writeBytes(bornHostBytes.array());
// 11 STORETIMESTAMP
this.byteBuf.writeLong(msgInner.getStoreTimestamp());
// 12 STOREHOSTADDRESS
ByteBuffer storeHostBytes = msgInner.getStoreHostBytes();
this.byteBuf.writeBytes(storeHostBytes.array());
// 13 RECONSUMETIMES
this.byteBuf.writeInt(msgInner.getReconsumeTimes());
// 14 Prepared Transaction Offset
this.byteBuf.writeLong(msgInner.getPreparedTransactionOffset());
// 15 BODY
this.byteBuf.writeInt(bodyLength);
if (bodyLength > 0)
this.byteBuf.writeBytes(msgInner.getBody());
// 16 TOPIC
this.byteBuf.writeByte((byte) topicLength);
this.byteBuf.writeBytes(topicData);
// 17 PROPERTIES
this.byteBuf.writeShort((short) propertiesLength);
if (propertiesLength > 0)
this.byteBuf.writeBytes(propertiesData);
```
However, the length of the encdoer buffer is equal to the maximum length of
the message body, which may cause the buffer to exceed the bounds during
messageBodySize is on the boundry of maxMessageBodySize.
```java
private final ByteBuf byteBuf;
private final int maxMessageBodySize;
MessageExtEncoder(final int maxMessageBodySize) {
ByteBufAllocator alloc = UnpooledByteBufAllocator.DEFAULT;
byteBuf = alloc.directBuffer(maxMessageBodySize);
this.maxMessageBodySize = maxMessageBodySize;
}
```
I think the initial buffer length needs to be extended to ensure robustness
when sending long messages.
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