数据库路由中间件MyCat - 源代码篇（4）
2. 前端连接建立与认证
Created with Raphaël 2.1.0 MySql连接建立以及认证过程 client client MySql MySql 1.TCP连接请求 2.接受TCP连接 3.TCP连接建立 4.握手包HandshakePacket 5.认证包AuthPacket 6.如果验证成功，则返回OkPacket 7.默认会发送查询版本信息的包 8.返回结果包
2.5 (7~8) 默认会发送查询版本信息的包,返回结果包
MySql客户端在连接建立后，默认会发送查询版本信息的包，这其实就是一个SQL查询请求了。只不过这个请求不用路由到后台某个数据库^_^。
连接成功建立后，连接绑定的RW线程会监听上面的读事件。在客户端发送查询版本信息的包之后，会触发RW线程去读取对应连接，过程与之前接收AuthPacket类似：
RW类代码片段
//监听到有效读
if (key.isValid() && key.isReadable()) {
try {
//异步读取数据并处理数据
con.asynRead();
} catch (IOException e) {
con.close("program err:" + e.toString());
continue;
} catch (Exception e) {
LOGGER.debug("caught err:", e);
con.close("program err:" + e.toString());
continue;
}
}
之后的读取过程也是调用AbstractConnection的asynRead()方法，进行异步读取。过程就不再赘述，读取到的数据交由FrontendCommandHandler处理。
查询版本信息的包（是一种CommandPacket）内容：
CommandPacket：
- packet length (3)
- packet number (1)
- command (1)
- statement (null terminated string)
FrontendCommandHandler的处理方法：
@Override
public void handle(byte[] data)
{
if(source.getLoadDataInfileHandler()!=null&&source.getLoadDataInfileHandler().isStartLoadData())
{
MySQLMessage mm = new MySQLMessage(data);
int packetLength = mm.readUB3();
if(packetLength+4==data.length)
{
source.loadDataInfileData(data);
}
return;
}
switch (data[4])
{
case MySQLPacket.COM_INIT_DB:
commands.doInitDB();
source.initDB(data);
break;
case MySQLPacket.COM_QUERY:
commands.doQuery();
source.query(data);
break;
case MySQLPacket.COM_PING:
commands.doPing();
source.ping();
break;
case MySQLPacket.COM_QUIT:
commands.doQuit();
source.close("quit cmd");
break;
case MySQLPacket.COM_PROCESS_KILL:
commands.doKill();
source.kill(data);
break;
case MySQLPacket.COM_STMT_PREPARE:
commands.doStmtPrepare();
source.stmtPrepare(data);
break;
case MySQLPacket.COM_STMT_EXECUTE:
commands.doStmtExecute();
source.stmtExecute(data);
break;
case MySQLPacket.COM_STMT_CLOSE:
commands.doStmtClose();
source.stmtClose(data);
break;
case MySQLPacket.COM_HEARTBEAT:
commands.doHeartbeat();
source.heartbeat(data);
break;
default:
commands.doOther();
source.writeErrMessage(ErrorCode.ER_UNKNOWN_COM_ERROR,
"Unknown command");
}
}
根据CommandPacket的第五字节判断command类型，不同类型有不同的处理。
首先querycommand计数加1，之后调用对应FrontendConnection的query(byte[])方法：
public void query(byte[] data) {
if (queryHandler != null) {
// 取得语句|get sql
MySQLMessage mm = new MySQLMessage(data);
//从第六字节开始读取|read from the 6th byte
mm.position(5);
String sql = null;
try {
sql = mm.readString(charset);
} catch (UnsupportedEncodingException e) {
writeErrMessage(ErrorCode.ER_UNKNOWN_CHARACTER_SET, "Unknown charset '" + charset + "'");
return;
}
if (sql == null || sql.length() == 0) {
writeErrMessage(ErrorCode.ER_NOT_ALLOWED_COMMAND, "Empty SQL");
return;
}
// sql = StringUtil.replace(sql, "`", "");
// 移除末尾';'|remove last ';'
if (sql.endsWith(";")) {
sql = sql.substring(0, sql.length() - 1);
}
// 记录SQL|record SQL
this.setExecuteSql(sql);
// 执行查询
queryHandler.setReadOnly(privileges.isReadOnly(user));
queryHandler.query(sql);
} else {
writeErrMessage(ErrorCode.ER_UNKNOWN_COM_ERROR, "Query unsupported!");
}
}
执行查询，调用对应的FrontendQueryHandler：
这里，很明显，是ServerQueryHandler。
public void query(String sql) {
ServerConnection c = this.source;
if (LOGGER.isDebugEnabled()) {
LOGGER.debug(new StringBuilder().append(c).append(sql).toString());
}
//
int rs = ServerParse.parse(sql);
int sqlType = rs & 0xff;
switch (sqlType) {
case ServerParse.EXPLAIN:
ExplainHandler.handle(sql, c, rs >>> 8);
break;
case ServerParse.EXPLAIN2:
Explain2Handler.handle(sql, c, rs >>> 8);
break;
case ServerParse.SET:
SetHandler.handle(sql, c, rs >>> 8);
break;
case ServerParse.SHOW:
ShowHandler.handle(sql, c, rs >>> 8);
break;
case ServerParse.SELECT:
if(QuarantineHandler.handle(sql, c)){
SelectHandler.handle(sql, c, rs >>> 8);
}
break;
case ServerParse.START:
StartHandler.handle(sql, c, rs >>> 8);
break;
case ServerParse.BEGIN:
BeginHandler.handle(sql, c);
break;
case ServerParse.SAVEPOINT:
SavepointHandler.handle(sql, c);
break;
case ServerParse.KILL:
KillHandler.handle(sql, rs >>> 8, c);
break;
case ServerParse.KILL_QUERY:
LOGGER.warn(new StringBuilder().append("Unsupported command:").append(sql).toString());
c.writeErrMessage(ErrorCode.ER_UNKNOWN_COM_ERROR,"Unsupported command");
break;
case ServerParse.USE:
UseHandler.handle(sql, c, rs >>> 8);
break;
case ServerParse.COMMIT:
c.commit();
break;
case ServerParse.ROLLBACK:
c.rollback();
break;
case ServerParse.HELP:
LOGGER.warn(new StringBuilder().append("Unsupported command:").append(sql).toString());
c.writeErrMessage(ErrorCode.ER_SYNTAX_ERROR, "Unsupported command");
break;
case ServerParse.MYSQL_CMD_COMMENT:
c.write(c.writeToBuffer(OkPacket.OK, c.allocate()));
break;
case ServerParse.MYSQL_COMMENT:
c.write(c.writeToBuffer(OkPacket.OK, c.allocate()));
break;
case ServerParse.LOAD_DATA_INFILE_SQL:
c.loadDataInfileStart(sql);
break;
default:
if(readOnly){
LOGGER.warn(new StringBuilder().append("User readonly:").append(sql).toString());
c.writeErrMessage(ErrorCode.ER_USER_READ_ONLY, "User readonly");
break;
}
if(QuarantineHandler.handle(sql, c)){
c.execute(sql, rs & 0xff);
}
}
}
针对每种command，都有不同的handler和处理方式。之后如何处理，就在之后的SQL解析器等章节进行分析。
