一、前言
前面介绍了Zookeeper的系统模型，下面进一步学习Zookeeper的底层序列化机制，Zookeeper的客户端与服务端之间会进行一系列的网络通信来实现数据传输，Zookeeper使用Jute组件来完成数据的序列化和反序列化操作。
二、Jute
Jute是Zookeeper底层序列化组件，其用于Zookeeper进行网络数据传输和本地磁盘数据存储的序列化和反序列化工作。
2.1 Jute序列化
MockReHeader实体类
package com.hust.grid.leesf.jute.examples; import org.apache.jute.InputArchive;
import org.apache.jute.OutputArchive;
import org.apache.jute.Record; public class MockReHeader implements Record {
private long sessionId;
private String type; public MockReHeader() { } public MockReHeader(long sessionId, String type) {
this.sessionId = sessionId;
this.type = type;
} public void setSessionId(long sessionId) {
this.sessionId = sessionId;
} public void setType(String type) {
this.type = type;
} public long getSessionId() {
return sessionId;
} public String getType() {
return type;
} public void serialize(OutputArchive oa, String tag) throws java.io.IOException {
oa.startRecord(this, tag);
oa.writeLong(sessionId, "sessionId");
oa.writeString(type, "type");
oa.endRecord(this, tag);
} public void deserialize(InputArchive ia, String tag) throws java.io.IOException {
ia.startRecord(tag);
this.sessionId = ia.readLong("sessionId");
this.type = ia.readString("type");
ia.endRecord(tag);
} @Override
public String toString() {
return "sessionId = " + sessionId + ", type = " + type;
}
}
Main
package com.hust.grid.leesf.jute.examples; import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer; import org.apache.jute.BinaryInputArchive;
import org.apache.jute.BinaryOutputArchive;
import org.apache.zookeeper.server.ByteBufferInputStream; public class Main {
public static void main(String[] args) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
BinaryOutputArchive boa = BinaryOutputArchive.getArchive(baos);
new MockReHeader(0x3421eccb92a34el, "ping").serialize(boa, "header"); ByteBuffer bb = ByteBuffer.wrap(baos.toByteArray()); ByteBufferInputStream bbis = new ByteBufferInputStream(bb);
BinaryInputArchive bia = BinaryInputArchive.getArchive(bbis); MockReHeader header2 = new MockReHeader();
System.out.println(header2);
header2.deserialize(bia, "header");
System.out.println(header2);
bbis.close();
baos.close();
}
}
运行结果
sessionId = 0, type = null
sessionId = 14673999700337486, type = ping
说明：可以看到MockReHeader实体类需要实现Record接口并且实现serialize和deserialize方法。
OutputArchive和InputArchive分别是Jute底层的序列化器和反序列化器。
在Zookeeper的src文件夹下有zookeeper.jute文件，其内容如下
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF 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.
*/ module org.apache.zookeeper.data {
class Id {
ustring scheme;
ustring id;
}
class ACL {
int perms;
Id id;
}
// information shared with the client
class Stat {
long czxid; // created zxid
long mzxid; // last modified zxid
long ctime; // created
long mtime; // last modified
int version; // version
int cversion; // child version
int aversion; // acl version
long ephemeralOwner; // owner id if ephemeral, 0 otw
int dataLength; //length of the data in the node
int numChildren; //number of children of this node
long pzxid; // last modified children
}
// information explicitly stored by the server persistently
class StatPersisted {
long czxid; // created zxid
long mzxid; // last modified zxid
long ctime; // created
long mtime; // last modified
int version; // version
int cversion; // child version
int aversion; // acl version
long ephemeralOwner; // owner id if ephemeral, 0 otw
long pzxid; // last modified children
} // information explicitly stored by the version 1 database of servers
class StatPersistedV1 {
long czxid; //created zxid
long mzxid; //last modified zxid
long ctime; //created
long mtime; //last modified
int version; //version
int cversion; //child version
int aversion; //acl version
long ephemeralOwner; //owner id if ephemeral. 0 otw
}
} module org.apache.zookeeper.proto {
class ConnectRequest {
int protocolVersion;
long lastZxidSeen;
int timeOut;
long sessionId;
buffer passwd;
}
class ConnectResponse {
int protocolVersion;
int timeOut;
long sessionId;
buffer passwd;
}
class SetWatches {
long relativeZxid;
vector<ustring>dataWatches;
vector<ustring>existWatches;
vector<ustring>childWatches;
}
class RequestHeader {
int xid;
int type;
}
class MultiHeader {
int type;
boolean done;
int err;
}
class AuthPacket {
int type;
ustring scheme;
buffer auth;
}
class ReplyHeader {
int xid;
long zxid;
int err;
}
class GetDataRequest {
ustring path;
boolean watch;
}
class SetDataRequest {
ustring path;
buffer data;
int version;
}
class SetDataResponse {
org.apache.zookeeper.data.Stat stat;
}
class GetSASLRequest {
buffer token;
}
class SetSASLRequest {
buffer token;
}
class SetSASLResponse {
buffer token;
}
class CreateRequest {
ustring path;
buffer data;
vector<org.apache.zookeeper.data.ACL> acl;
int flags;
}
class DeleteRequest {
ustring path;
int version;
}
class GetChildrenRequest {
ustring path;
boolean watch;
}
class GetChildren2Request {
ustring path;
boolean watch;
}
class CheckVersionRequest {
ustring path;
int version;
}
class GetMaxChildrenRequest {
ustring path;
}
class GetMaxChildrenResponse {
int max;
}
class SetMaxChildrenRequest {
ustring path;
int max;
}
class SyncRequest {
ustring path;
}
class SyncResponse {
ustring path;
}
class GetACLRequest {
ustring path;
}
class SetACLRequest {
ustring path;
vector<org.apache.zookeeper.data.ACL> acl;
int version;
}
class SetACLResponse {
org.apache.zookeeper.data.Stat stat;
}
class WatcherEvent {
int type; // event type
int state; // state of the Keeper client runtime
ustring path;
}
class ErrorResponse {
int err;
}
class CreateResponse {
ustring path;
}
class ExistsRequest {
ustring path;
boolean watch;
}
class ExistsResponse {
org.apache.zookeeper.data.Stat stat;
}
class GetDataResponse {
buffer data;
org.apache.zookeeper.data.Stat stat;
}
class GetChildrenResponse {
vector<ustring> children;
}
class GetChildren2Response {
vector<ustring> children;
org.apache.zookeeper.data.Stat stat;
}
class GetACLResponse {
vector<org.apache.zookeeper.data.ACL> acl;
org.apache.zookeeper.data.Stat stat;
}
} module org.apache.zookeeper.server.quorum {
class LearnerInfo {
long serverid;
int protocolVersion;
}
class QuorumPacket {
int type; // Request, Ack, Commit, Ping
long zxid;
buffer data; // Only significant when type is request
vector<org.apache.zookeeper.data.Id> authinfo;
}
} module org.apache.zookeeper.server.persistence {
class FileHeader {
int magic;
int version;
long dbid;
}
} module org.apache.zookeeper.txn {
class TxnHeader {
long clientId;
int cxid;
long zxid;
long time;
int type;
}
class CreateTxnV0 {
ustring path;
buffer data;
vector<org.apache.zookeeper.data.ACL> acl;
boolean ephemeral;
}
class CreateTxn {
ustring path;
buffer data;
vector<org.apache.zookeeper.data.ACL> acl;
boolean ephemeral;
int parentCVersion;
}
class DeleteTxn {
ustring path;
}
class SetDataTxn {
ustring path;
buffer data;
int version;
}
class CheckVersionTxn {
ustring path;
int version;
}
class SetACLTxn {
ustring path;
vector<org.apache.zookeeper.data.ACL> acl;
int version;
}
class SetMaxChildrenTxn {
ustring path;
int max;
}
class CreateSessionTxn {
int timeOut;
}
class ErrorTxn {
int err;
}
class Txn {
int type;
buffer data;
}
class MultiTxn {
vector<org.apache.zookeeper.txn.Txn> txns;
}
}
其定义了所有的实体类的所属包名、类名及类的所有成员变量和类型，该文件会在源代码编译时，Jute会使用不同的代码生成器为这些类定义生成实际编程语言的类文件，如java语言生成的类文件保存在src/java/generated目录下，每个类都会实现Record接口。
三、通信协议
基于TCP/IP协议，Zookeeper实现了自己的通信协议来玩按成客户端与服务端、服务端与服务端之间的网络通信，对于请求，主要包含请求头和请求体，对于响应，主要包含响应头和响应体。
3.1 请求协议
对于请求协议而言，如下为获取节点数据请求的完整协议定义
class RequestHeader {
int xid;
int type;
}
从zookeeper.jute中可知RequestHeader包含了xid和type，xid用于记录客户端请求发起的先后序号，用来确保单个客户端请求的响应顺序，type代表请求的操作类型，如创建节点（OpCode.create）、删除节点（OpCode.delete）、获取节点数据（OpCode.getData）。
协议的请求主体内容部分，包含了请求的所有操作内容，不同的请求类型请求体不同。对于会话创建而言，其请求体如下
class ConnectRequest {
int protocolVersion;
long lastZxidSeen;
int timeOut;
long sessionId;
buffer passwd;
}
Zookeeper客户端和服务器在创建会话时，会发送ConnectRequest请求，该请求包含协议版本号protocolVersion、最近一次接收到服务器ZXID lastZxidSeen、会话超时时间timeOut、会话标识sessionId和会话密码passwd。
对于获取节点数据而言，其请求体如下
class GetDataRequest {
ustring path;
boolean watch;
}
Zookeeper客户端在向服务器发送节点数据请求时，会发送GetDataRequest请求，该请求包含了数据节点路径path、是否注册Watcher的标识watch。
对于更新节点数据而言，其请求体如下
class SetDataRequest {
ustring path;
buffer data;
int version;
}
Zookeeper客户端在向服务器发送更新节点数据请求时，会发送SetDataRequest请求，该请求包含了数据节点路径path、数据内容data、节点数据的期望版本号version。
针对不同的请求类型，Zookeeper都会定义不同的请求体，可以在zookeeper.jute中查看。
3.2 响应协议
对于响应协议而言，如下为获取节点数据响应的完整协议定义
响应头中包含了每个响应最基本的信息，包括xid、zxid和err：
class ReplyHeader {
int xid;
long zxid;
int err;
}
xid与请求头中的xid一致，zxid表示Zookeeper服务器上当前最新的事务ID，err则是一个错误码，表示当请求处理过程出现异常情况时，就会在错误码中标识出来，常见的包括处理成功（Code.OK）、节点不存在（Code.NONODE）、没有权限（Code.NOAUTH）。
协议的响应主体内容部分，包含了响应的所有数据，不同的响应类型请求体不同。对于会话创建而言，其响应体如下
class ConnectResponse {
int protocolVersion;
int timeOut;
long sessionId;
buffer passwd;
}
针对客户端的会话创建请求，服务端会返回客户端一个ConnectResponse响应，该响应体包含了版本号protocolVersion、会话的超时时间timeOut、会话标识sessionId和会话密码passwd。
对于获取节点数据而言，其响应体如下
class GetDataResponse {
buffer data;
org.apache.zookeeper.data.Stat stat;
}
针对客户端的获取节点数据请求，服务端会返回客户端一个GetDataResponse响应，该响应体包含了数据节点内容data、节点状态stat。
对于更新节点数据而言，其响应体如下
class SetDataResponse {
org.apache.zookeeper.data.Stat stat;
}
针对客户端的更新节点数据请求，服务端会返回客户端一个SetDataResponse响应，该响应体包含了最新的节点状态stat。
针对不同的响应类型，Zookeeper都会定义不同的响应体，可以在zookeeper.jute中查看。
四、总结
本篇博客讲解了Zookeeper中的序列化机制和客户端与服务端、服务端与服务端的通信协议，内容相对较为简单，容易理解，谢谢各位园友的观看~