mysql Client进行一次查询需要三个核心操作，获得连接、测试连是否可用、发送请求：
代码语言：javascript复制conn, _ := client.Connect("127.0.0.1:3306", "root", "", "test")
conn.Ping()
r, _ := conn.Execute(`insert into table (id, name) values (1, "abc")`)首先我们看下获取连接的过程：github.com/go-mysql-org/go-mysql@v1.7.0/client/conn.go
代码语言：javascript复制func Connect(addr string, user string, password string, dbName string, options ...func(*Conn)) (*Conn, error) {
dialer := &net.Dialer{}
return ConnectWithDialer(ctx, "", addr, user, password, dbName, dialer.DialContext, options...)func ConnectWithDialer(ctx context.Context, network string, addr string, user string, password string, dbName string, dialer Dialer, options ...func(*Conn)) (*Conn, error) {
c := new(Conn)
conn, err := dialer(ctx, network, addr)
if err = c.handshake(); err != nil {
握手过程中需要进行身份认证：
代码语言：javascript复制 func (c *Conn) handshake() error {
if err = c.readInitialHandshake(); err != nil {
if err := c.writeAuthHandshake(); err != nil {
if err := c.handleAuthResult(); err != nil {标识连接的过程如下：
代码语言：javascript复制type Conn struct {
*packet.Conn
user string
password string
db string
tlsConfig *tls.Config
proto string
// server capabilities
capability uint32
// client-set capabilities only
ccaps uint32
attributes map[string]string
status uint16
charset string
salt []byte
authPluginName string
connectionID uint32
}认证完成后就可以获得server端分配的本次连接的连接ID：github.com/go-mysql-org/go-mysql@v1.7.0/client/auth.go
代码语言：javascript复制func (c *Conn) readInitialHandshake() error {
data, err := c.ReadPacket()
return errors.Annotate(c.handleErrorPacket(data), "read initial handshake error")
c.connectionID = binary.LittleEndian.Uint32(data[pos : pos 4])
pos = 4一般通过conn.Ping()命令测试连接的可用性
代码语言：javascript复制func (c *Conn) Ping() error {
if err := c.writeCommand(COM_PING); err != nil {
if _, err := c.readOK(); err != nil {可以看到它是一个单独的命令，mysql的命令列表如下：
代码语言：javascript复制const (
COM_SLEEP byte = iota
COM_QUIT
COM_INIT_DB
COM_QUERY
COM_FIELD_LIST
COM_CREATE_DB
COM_DROP_DB
COM_REFRESH
COM_SHUTDOWN
COM_STATISTICS
COM_PROCESS_INFO
COM_CONNECT
COM_PROCESS_KILL
COM_DEBUG
COM_PING
COM_TIME
COM_DELAYED_INSERT
COM_CHANGE_USER
COM_BINLOG_DUMP
COM_TABLE_DUMP
COM_CONNECT_OUT
COM_REGISTER_SLAVE
COM_STMT_PREPARE
COM_STMT_EXECUTE
COM_STMT_SEND_LONG_DATA
COM_STMT_CLOSE
COM_STMT_RESET
COM_SET_OPTION
COM_STMT_FETCH
COM_DAEMON
COM_BINLOG_DUMP_GTID
COM_RESET_CONNECTION
)执行请求的场景可以分为两种：不带参数的请求和带参数的请求：github.com/go-mysql-org/go-mysql@v1.7.0/client/conn.go，不带参数的请求直接执行，带参数的需要先预编译，然后执行。
代码语言：javascript复制func (c *Conn) Execute(command string, args ...interface{}) (*Result, error) {
if len(args) == 0 {
return c.exec(command)
if s, err := c.Prepare(command); err != nil {
r, err = s.Execute(args...)执行的过程就是向server发送COM_QUERY命令
代码语言：javascript复制func (c *Conn) exec(query string) (*Result, error) {
if err := c.writeCommandStr(COM_QUERY, query); err != nil {
return c.readResult(false)github.com/go-mysql-org/go-mysql@v1.7.0/client/req.go
代码语言：javascript复制func (c *Conn) writeCommandStr(command byte, arg string) error {
return c.writeCommandBuf(command, utils.StringToByteSlice(arg))
}func (c *Conn) writeCommandBuf(command byte, arg []byte) error {
err := c.WritePacket(data.B)github.com/go-mysql-org/go-mysql@v1.7.0/packet/conn.go
代码语言：javascript复制func (c *Conn) WritePacket(data []byte) error {预编译的请求发送在github.com/go-mysql-org/go-mysql@v1.7.0/client/stmt.go，对应命令：COM_STMT_PREPARE
代码语言：javascript复制func (c *Conn) Prepare(query string) (*Stmt, error) {
if err := c.writeCommandStr(COM_STMT_PREPARE, query); err != nil {
data, err := c.ReadPacket()
s := new(Stmt)func (c *Conn) writeCommandStr(command byte, arg string) error {
return c.writeCommandBuf(command, utils.StringToByteSlice(arg))func (s *Stmt) Execute(args ...interface{}) (*Result, error) {
if err := s.write(args...); err != nil {
return s.conn.readResult(true)发送命令的过程如下，它先填充字段类型信息，然后填充字段的值，然后进行发送：
代码语言：javascript复制func (s *Stmt) write(args ...interface{}) error {
for i := range args {
switch v := args[i].(type) {
case int8:
paramTypes[i<<1] = MYSQL_TYPE_TINY
paramValues[i] = []byte{byte(v)}
s.conn.ResetSequence()
return s.conn.WritePacket(data)
}每次发生之前都会重置序列号。
代码语言：javascript复制func (c *Conn) ResetSequence() {
c.Sequence = 0
}mysql的类型信息定义如下：
代码语言：javascript复制
const (
MYSQL_TYPE_DECIMAL byte = iota
MYSQL_TYPE_TINY
MYSQL_TYPE_SHORT
MYSQL_TYPE_LONG
MYSQL_TYPE_FLOAT
MYSQL_TYPE_DOUBLE
MYSQL_TYPE_NULL
MYSQL_TYPE_TIMESTAMP
MYSQL_TYPE_LONGLONG
MYSQL_TYPE_INT24
MYSQL_TYPE_DATE
MYSQL_TYPE_TIME
MYSQL_TYPE_DATETIME
MYSQL_TYPE_YEAR
MYSQL_TYPE_NEWDATE
MYSQL_TYPE_VARCHAR
MYSQL_TYPE_BIT
//mysql 5.6
MYSQL_TYPE_TIMESTAMP2
MYSQL_TYPE_DATETIME2
MYSQL_TYPE_TIME2
)
const (
MYSQL_TYPE_JSON byte = iota 0xf5
MYSQL_TYPE_NEWDECIMAL
MYSQL_TYPE_ENUM
MYSQL_TYPE_SET
MYSQL_TYPE_TINY_BLOB
MYSQL_TYPE_MEDIUM_BLOB
MYSQL_TYPE_LONG_BLOB
MYSQL_TYPE_BLOB
MYSQL_TYPE_VAR_STRING
MYSQL_TYPE_STRING
MYSQL_TYPE_GEOMETRY
)总结一下，mysql client的实现起来很简单，建立连接，按照mysql协议编码，发送请求到服务端。
