前言：
mysql作为常用的数据库，笔者一直以来都觉得比较神秘。
在实际应用中，我们可以通过其Navicat、mysql command-line、java-mysql-jar等方式来与其进行进行连接操作。
在笔者接触到越来越多的中间件应用后，mysql的神秘面纱就被慢慢揭开了。故决定将这个过程通过博客的方式记录下来，并且当前篇文章作为Mycat的前序篇，对于需要学习Mycat的同学来说，也是有必要去了解的。
本文主要通过对mysql-connector-java源码的分析来了解client与mysql-server创建连接握手的基本过程。
1.准备环境
* Windows环境下的mysql服务安装（笔者安装版本为5.7.17）
* jdk1.8.0_131
* mysql-connector-java-5.1.35.jar
* 简单表结构（student）
CREATE TABLE student (
id int(11) NOT NULL AUTO_INCREMENT,
sno varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
sname varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
PRIMARY KEY (id) USING BTREE
);2.代码准备
通过最原始的JDBC的方式来创建于mysql-server的连接。
// 创建mysql连接基本类
public class DBConn {
private static final String jdbcdriver="com.mysql.jdbc.Driver";
// origin
private static final String jdbcurl="jdbc:mysql://localhost:3306/db1?useUnicode=true&characterEncoding=utf-8";
private static final String username="root";
private static final String password="root";
private static final String driver = "com.mysql.jdbc.Driver";
private static final Connection conn = null;
/**
* 连接数据库
* @return
*/
public static Connection conn() {
Connection conn = null;
try {
Class.forName(driver);
try {
conn = DriverManager.getConnection(jdbcurl, username, password);
} catch (SQLException e) {
e.printStackTrace();
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return conn;
}
/**
* 关闭数据库链接
* @return
*/
public static void close() {
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}本文主要就是对DriverManager.getConnection(jdbcurl, username, password)的源码解析
3.创建连接过程分析
3.1 Class.forName(driver)
此时的driver即是com.mysql.jdbc.Driver，Class.forName不需要多介绍，java的一种类加载方式，使用装载当前类的类加载器来装载指定的class类。
该步骤的意义就是将mysql的Driver加载到JVM中。并且会执行Driver的static方法，源码如下：
// com.mysql.jdbc.Driver
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
public Driver() throws SQLException {
}
static {
try {
// 加载后，会默认执行
DriverManager.registerDriver(new Driver());
} catch (SQLException var1) {
throw new RuntimeException("Can't register driver!");
}
}
}
// DriverManager.registerDriver
public static synchronized void registerDriver(java.sql.Driver driver,
DriverAction da)
throws SQLException {
// CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>()
// 直接将Driver包装成DriverInfo添加到DriverManger中
if(driver != null) {
registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
} else {
// This is for compatibility with the original DriverManager
throw new NullPointerException();
}
...
}总结：执行完Class.forName("com.mysql.jdbc.Driver")后，该Driver对象就被添加到DriverManger中
3.2 getConnection
下面就是最关键的这一句代码，DriverManager.getConnection(jdbcurl, username, password);通用的这句创建Connection的代码，可以创建不同Driver类型的连接，还是蛮神奇的，下面我们就来一起看下吧。
// 1.DriverManager.getConnection(String url,String user, String password)
public static Connection getConnection(String url,
String user, String password) throws SQLException {
java.util.Properties info = new java.util.Properties();
// 拼装用户名密码到info中
if (user != null) {
info.put("user", user);
}
if (password != null) {
info.put("password", password);
}
return (getConnection(url, info, Reflection.getCallerClass()));
}
// 2.DriverManager.getConnection(String url, java.util.Properties info, Class<?> caller)
private static Connection getConnection(
String url, java.util.Properties info, Class<?> caller) {
...
for(DriverInfo aDriver : registeredDrivers) {
if(isDriverAllowed(aDriver.driver, callerCL)) {
try {
// 主要就是这一句在创建连接
// 本质上还是调用了具体使用的Driver的connect方法
// 所以就是调用NonRegisteringDriver.connect(String url, Properties info)实现
Connection con = aDriver.driver.connect(url, info);
if (con != null) {
// Success!
println("getConnection returning " + aDriver.driver.getClass().getName());
return (con);
}
} catch (SQLException ex) {
if (reason == null) {
reason = ex;
}
}
...
}
...
}
// 3.NonRegisteringDriver.connect(String url, Properties info)
public Connection connect(String url, Properties info) throws SQLException {
...
Properties props = null;
if ((props = this.parseURL(url, info)) == null) {
return null;
} else if (!"1".equals(props.getProperty("NUM_HOSTS"))) {
return this.connectFailover(url, info);
} else {
try {
// 在这里创建Connection
com.mysql.jdbc.Connection newConn
= ConnectionImpl.getInstance(this.host(props), this.port(props), props, this.database(props), url);
return newConn;
...
}
}
// 4.ConnectionImpl.getInstance
protected static Connection getInstance(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url) throws SQLException {
return (Connection)(!Util.isJdbc4() ?
new ConnectionImpl(hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url) :
// 看JDBC版本，笔者这里是JDBC4，故使用com.mysql.jdbc.JDBC4Connection来连接
(Connection)Util.handleNewInstance(JDBC_4_CONNECTION_CTOR, new Object[]{hostToConnectTo, portToConnectTo, info, databaseToConnectTo, url}, (ExceptionInterceptor)null));
}
// 5.com.mysql.jdbc.JDBC4Connection实例创建
public class JDBC4Connection extends ConnectionImpl {
// JDBC4Connection中的构造方法直接使用ConnectionImplement的构造方法
}
// 6.com.mysql.jdbc.ConnectionImpl构造方法
public ConnectionImpl(String hostToConnectTo, int portToConnectTo, Properties info, String databaseToConnectTo, String url) throws SQLException {
...
this.port = portToConnectTo;
this.database = databaseToConnectTo;
this.myURL = url;
this.user = info.getProperty("user");
this.password = info.getProperty("password");
...
try {
this.dbmd = this.getMetaData(false, false);
this.initializeSafeStatementInterceptors();
// 在这里创建socket连接
this.createNewIO(false);
this.unSafeStatementInterceptors();
} catch (SQLException var11) {
...
}
}
// 7.ConnectionImpl.createNewIO
public void createNewIO(boolean isForReconnect) throws SQLException {
synchronized(this.getConnectionMutex()) {
Properties mergedProps = this.exposeAsProperties(this.props);
// 是否高可用，如果配置了高可用，针对不可用时会重试多次，本文中分析一次连接即可
if (!this.getHighAvailability()) {
this.connectOneTryOnly(isForReconnect, mergedProps);
} else {
this.connectWithRetries(isForReconnect, mergedProps);
}
}
}
// 8.ConnectionImpl.connectOneTryOnly(boolean isForReconnect, Properties mergedProps)
private void connectOneTryOnly(boolean isForReconnect, Properties mergedProps) throws SQLException {
Object var3 = null;
try {
// 核心连接方法
this.coreConnect(mergedProps);
// 赋值其他参数
this.connectionId = this.io.getThreadId();
this.isClosed = false;
boolean oldAutoCommit = this.getAutoCommit();
int oldIsolationLevel = this.isolationLevel;
boolean oldReadOnly = this.isReadOnly(false);
String oldCatalog = this.getCatalog();
this.io.setStatementInterceptors(this.statementInterceptors);
this.initializePropsFromServer();
if (isForReconnect) {
this.setAutoCommit(oldAutoCommit);
if (this.hasIsolationLevels) {
this.setTransactionIsolation(oldIsolationLevel);
}
this.setCatalog(oldCatalog);
this.setReadOnly(oldReadOnly);
}
...
// 9.ConnectionImpl.coreConnect(Properties mergedProps)
private void coreConnect(Properties mergedProps) throws SQLException, IOException {
...
this.port = newPort;
this.host = newHost;
this.sessionMaxRows = -1;
// 创建长连接
this.io = new MysqlIO(newHost, newPort, mergedProps, this.getSocketFactoryClassName(), this.getProxy(), this.getSocketTimeout(), this.largeRowSizeThreshold.getValueAsInt());
// 三次握手完成后，进行信息交换，完成用户名密码验证
this.io.doHandshake(this.user, this.password, this.database);
}3.3 MySQLIO
从3.2的代码流程来看，最终创建长连接的代码在于MysqlIO的构造方法中。下面我们来详细看下
// MysqlIO.java
public MysqlIO(String host, int port, Properties props, String socketFactoryClassName, MySQLConnection conn, int socketTimeout, int useBufferRowSizeThreshold) throws IOException, SQLException {
this.connection = conn;
...
this.reusablePacket = new Buffer(1024);
this.sendPacket = new Buffer(1024);
// 基本参数全部赋予MysqlIO
this.port = port;
this.host = host;
this.socketFactoryClassName = socketFactoryClassName;
this.socketFactory = this.createSocketFactory();
...
try {
// 通过socketFactory.connect来创建长连接
this.mysqlConnection = this.socketFactory.connect(this.host, this.port, props);
...
// 创建输入输出流
if (this.connection.getUseReadAheadInput()) {
this.mysqlInput = new ReadAheadInputStream(this.mysqlConnection.getInputStream(), 16384, this.connection.getTraceProtocol(), this.connection.getLog());
} else if (this.connection.useUnbufferedInput()) {
this.mysqlInput = this.mysqlConnection.getInputStream();
} else {
this.mysqlInput = new BufferedInputStream(this.mysqlConnection.getInputStream(), 16384);
}
this.mysqlOutput = new BufferedOutputStream(this.mysqlConnection.getOutputStream(), 16384);
}
...
}
// StandardSocketFactory.connect
public Socket connect(String hostname, int portNumber, Properties props) throws SocketException, IOException {
if (props != null) {
this.host = hostname;
this.port = portNumber;
...
if (this.host != null) {
while(i < possibleAddresses.length) {
try {
// new Socket();创建原生的Socket
this.rawSocket = this.createSocket(props);
this.configureSocket(this.rawSocket, props);
InetSocketAddress sockAddr = new InetSocketAddress(possibleAddresses[i], this.port);
if (localSockAddr != null) {
this.rawSocket.bind(localSockAddr);
}
// 原生的socket连接到mysql-server
this.rawSocket.connect(sockAddr, this.getRealTimeout(connectTimeout));
break;
}
...
}
}
}总结：最终我们可以看到，客户端与mysql-server的连接，还是通过原生的Socket来创建的。并且通过创建Socket的inputStream和outputStream来发送和接收消息。
3.4 MysqlIO.doHandshark()
相比较常规的client-server连接而言，mysql的连接创建，在三次握手之后，还需要执行一个doHandshark()方法，该方法本质上是来验证客户端输入的对应库的用户名密码等信息。
具体协议内容参考dev.mysql.com/doc/internals/en/connection-phase-packets.html#Protocol::HandsharkV10
整个过程可以分为三个阶段：
* mysql-server发送handshark信息，里面包括mysql的基本信息，加密seed等
* client根据seed信息对password进行加密，将用户名密码等信息发送给mysql-server
* mysql-server对接收到的加密密码进行密码比对，匹配后则返回okay包
下面通过代码来分析下handshark过程：
1）mysql-server发送handshark信息
这里可以直接参考mycat的代码，下面就是mycat中HandsharkPacket.java
可以直接看到server发送的消息体信息
// HandsharkPacket.write()
public void write(FrontendConnection c) {
ByteBuffer buffer = c.allocate();
BufferUtil.writeUB3(buffer, calcPacketSize());
buffer.put(packetId);
buffer.put(protocolVersion);
BufferUtil.writeWithNull(buffer, serverVersion);
BufferUtil.writeUB4(buffer, threadId);
BufferUtil.writeWithNull(buffer, seed);
BufferUtil.writeUB2(buffer, serverCapabilities);
buffer.put(serverCharsetIndex);
BufferUtil.writeUB2(buffer, serverStatus);
buffer.put(FILLER_13);
// buffer.position(buffer.position() + 13);
BufferUtil.writeWithNull(buffer, restOfScrambleBuff);
c.write(buffer);
}2）client解析handshark信息
就是解析上面mysql-server发送的HandsharkPacket包信息
// MysqlIO.doHandshake
void doHandshake(String user, String password, String database) throws SQLException {
this.checkPacketSequence = false;
this.readPacketSequence = 0;
// 在这里获取server发送来的hardshark包信息
Buffer buf = this.readPacket();
this.protocolVersion = buf.readByte();
...
// 读取包字段 serverVersion threadId seed ...
this.serverVersion = buf.readString("ASCII", this.getExceptionInterceptor());
this.threadId = buf.readLong();
this.seed = buf.readString("ASCII", this.getExceptionInterceptor());
...
}
// MysqlIO.readPacket
protected final Buffer readPacket() throws SQLException {
try {
...
// 获取包长度（占用3byte）
int packetLength = (this.packetHeaderBuf[0] & 255) + ((this.packetHeaderBuf[1] & 255) << 8) + ((this.packetHeaderBuf[2] & 255) << 16);
...
// 获取sequenceId信息（占用1byte）
byte multiPacketSeq = this.packetHeaderBuf[3];
...
// 包体信息读取到buffer中
byte[] buffer = new byte[packetLength + 1];
int numBytesRead = this.readFully(this.mysqlInput, buffer, 0, packetLength);
...
} 3）client根据seed信息加密password后，发送包信息给server
// MysqlIO.proceedHandshakeWithPluggableAuthentication
private void proceedHandshakeWithPluggableAuthentication(String user, String password, String database, Buffer challenge) throws SQLException {
if (this.authenticationPlugins == null) {
this.loadAuthenticationPlugins();
}
int passwordLength = 16;
int userLength = user != null ? user.length() : 0;
int databaseLength = database != null ? database.length() : 0;
...
while(0 < counter--) {
String enc;
// client发送验证包信息时，done为null
if (done == null) {
if (challenge != null) {
...
plugin = this.getAuthenticationPlugin(enc);
if (plugin == null) {
plugin = this.getAuthenticationPlugin(this.defaultAuthenticationPluginProtocolName);
}
// 拼装参数
this.checkConfidentiality(plugin);
fromServer = new Buffer(StringUtils.getBytes(this.seed));
}
}else {
...
}
...
try {
// 进行password加密操作，默认使用MysqlNativePasswordPlugin执行
// Security.scramble411(pwd, fromServer.readString(), this.connection.getPasswordCharacterEncoding())
plugin.setAuthenticationParameters(user, password);
done = plugin.nextAuthenticationStep(fromServer, toServer);
} catch (SQLException var19) {
throw SQLError.createSQLException(var19.getMessage(), var19.getSQLState(), var19, this.getExceptionInterceptor());
}
if (toServer.size() > 0) {
if (challenge == null) {
...
} else if (challenge.isAuthMethodSwitchRequestPacket()) {
...
} else if (!challenge.isRawPacket() && !old_raw_challenge) {
enc = this.getEncodingForHandshake();
last_sent = new Buffer(packLength);
last_sent.writeLong(this.clientParam);
last_sent.writeLong((long)this.maxThreeBytes);
this.appendCharsetByteForHandshake(last_sent, enc);
last_sent.writeBytesNoNull(new byte[23]);
last_sent.writeString(user, enc, this.connection);
...
// client发送用户名密码等相关信息到server端
this.send(last_sent, last_sent.getPosition());
}
4）mysql-server验证用户名密码成功后，返回OK包至client，client解析响应包
// MysqlIO.proceedHandshakeWithPluggableAuthentication
private void proceedHandshakeWithPluggableAuthentication(String user, String password, String database, Buffer challenge) throws SQLException {
if (this.authenticationPlugins == null) {
this.loadAuthenticationPlugins();
}
...
while(0 < counter--) {
String enc;
// 此时done=true，执行else逻辑
if (done == null) {
...
}else {
// 解析回执包之后，
challenge = this.checkErrorPacket();
old_raw_challenge = false;
++this.packetSequence;
++this.compressedPacketSequence;
// 验证是否OK包，正确的话，client与mysql-server的连接完成
if (challenge.isOKPacket()) {
if (!done) {
throw SQLError.createSQLException(Messages.getString("Connection.UnexpectedAuthenticationApproval", new Object[]{plugin.getProtocolPluginName()}), this.getExceptionInterceptor());
}
plugin.destroy();
break;
}
}
}
// MysqlIO.checkErrorPacket
private Buffer checkErrorPacket(int command) throws SQLException {
Buffer resultPacket = null;
this.serverStatus = 0;
try {
// 解析回执包
resultPacket = this.reuseAndReadPacket(this.reusablePacket);
} catch (SQLException var4) {
throw var4;
} catch (Exception var5) {
throw SQLError.createCommunicationsException(this.connection, this.lastPacketSentTimeMs, this.lastPacketReceivedTimeMs, var5, this.getExceptionInterceptor());
}
this.checkErrorPacket(resultPacket);
return resultPacket;
}
总结：client与mysql-server的连接，除了常规的Socket连接三次握手之外，还多了一步，验证client的用户名密码正确性，只有输入正确的用户名密码，当前连接才算建立完成。
最后用一张图，来总结下整个过程。
