feat:add code comments & refactor mysql config constant (#826)

* feat:add code comments & refactor mysql config constant

* feat: modify code comments

Author: CocaineCong

canal/config.go

@@ -8,11 +8,12 @@ import (
 	"time"
 
 	"github.com/BurntSushi/toml"
-	"github.com/go-mysql-org/go-mysql/client"
-	"github.com/go-mysql-org/go-mysql/mysql"
 	"github.com/pingcap/errors"
 	"github.com/siddontang/go-log/log"
 	"github.com/siddontang/go-log/loggers"
+
+	"github.com/go-mysql-org/go-mysql/client"
+	"github.com/go-mysql-org/go-mysql/mysql"
 )
 
 type DumpConfig struct {
@@ -91,13 +92,13 @@ type Config struct {
 	// Set TLS config
 	TLSConfig *tls.Config
 
-	//Set Logger
+	// Set Logger
 	Logger loggers.Advanced
 
-	//Set Dialer
+	// Set Dialer
 	Dialer client.Dialer
 
-	//Set Localhost
+	// Set Localhost
 	Localhost string
 }
 
@@ -121,19 +122,18 @@ func NewConfig(data string) (*Config, error) {
 	return &c, nil
 }
 
+// NewDefaultConfig initiates some default config for Canal
 func NewDefaultConfig() *Config {
 	c := new(Config)
 
-	c.Addr = "127.0.0.1:3306"
-	c.User = "root"
-	c.Password = ""
-
+	c.Addr = mysql.DEFAULT_ADDR
+	c.User = mysql.DEFAULT_USER
+	c.Password = mysql.DEFAULT_PASSWORD
 	c.Charset = mysql.DEFAULT_CHARSET
 	c.ServerID = uint32(rand.New(rand.NewSource(time.Now().Unix())).Intn(1000)) + 1001
+	c.Flavor = mysql.DEFAULT_FLAVOR
 
-	c.Flavor = "mysql"
-
-	c.Dump.ExecutionPath = "mysqldump"
+	c.Dump.ExecutionPath = mysql.DEFAULT_DUMP_EXECUTION_PATH
 	c.Dump.DiscardErr = true
 	c.Dump.SkipMasterData = false
 

mysql/const.go

@@ -170,11 +170,19 @@ const (
 )
 
 const (
+	DEFAULT_ADDR                  = "127.0.0.1:3306"
+	DEFAULT_USER                  = "root"
+	DEFAULT_PASSWORD              = ""
+	DEFAULT_FLAVOR                = "mysql"
 	DEFAULT_CHARSET               = "utf8"
 	DEFAULT_COLLATION_ID   uint8  = 33
 	DEFAULT_COLLATION_NAME string = "utf8_general_ci"
 )
 
+const (
+	DEFAULT_DUMP_EXECUTION_PATH = "mysqldump"
+)
+
 // Like vitess, use flavor for different MySQL versions,
 const (
 	MySQLFlavor   = "mysql"

mysql/position.go

@@ -6,12 +6,14 @@ import (
 	"strings"
 )
 
-// For binlog filename + position based replication
+// Position for binlog filename + position based replication
 type Position struct {
 	Name string
 	Pos  uint32
 }
 
+// Compare the position information between the p and o,
+// if p > o return 1 means the position of p is further back than o.
 func (p Position) Compare(o Position) int {
 	// First compare binlog name
 	nameCmp := CompareBinlogFileName(p.Name, o.Name)
@@ -32,6 +34,9 @@ func (p Position) String() string {
 	return fmt.Sprintf("(%s, %d)", p.Name, p.Pos)
 }
 
+// CompareBinlogFileName compares the binlog filename of a and b.
+// if a>b will return 1.
+// if b>a will return -1.
 func CompareBinlogFileName(a, b string) int {
 	// sometimes it's convenient to construct a `Position` literal with no `Name`
 	if a == "" && b == "" {
@@ -61,9 +66,11 @@ func CompareBinlogFileName(a, b string) int {
 		return n[:i], seq
 	}
 
+	// get the basename(aBase) and the serial number(aSeq)
 	aBase, aSeq := splitBinlogName(a)
 	bBase, bSeq := splitBinlogName(b)
 
+	// aBase and bBase generally will be equal if they are both from the same database configuration.
 	if aBase > bBase {
 		return 1
 	} else if aBase < bBase {