binlogsyncer: Format config in logs

[dveeden]

Example code:

package main

import "github.com/go-mysql-org/go-mysql/replication"

func main() {
	cfg := replication.BinlogSyncerConfig{
		ServerID: 100,
		Flavor:   "mysql",
		Host:     "127.0.0.1",
		Port:     3306,
		User:     "root",
		Password: "secret",
	}
	replication.NewBinlogSyncer(cfg)
}

Without this PR:

[2023/01/27 11:58:30] [info] binlogsyncer.go:173 create BinlogSyncer with config {100 mysql 127.0.0.1 3306 root    false false <nil> false UTC false 0 0s 0s 0 false false 0 <nil> 0xc0000ac180 0x52a420 <nil> false}

With this PR:

[2023/01/27 11:56:31] [info] binlogsyncer.go:170 create BinlogSyncer with config {"ServerID":100,"Flavor":"mysql","Host":"127.0.0.1","Port":3306,"User":"root","Password":"\u003chidden\u003e","Localhost":"","Charset":"","SemiSyncEnabled":false,"RawModeEnabled":false,"TLSConfig":null,"ParseTime":false,"TimestampStringLocation":null,"UseDecimal":false,"RecvBufferSize":0,"HeartbeatPeriod":0,"ReadTimeout":0,"MaxReconnectAttempts":0,"DisableRetrySync":false,"VerifyChecksum":false,"DumpCommandFlag":0,"Logger":{"Advanced":null}}

And the value after formatting:

{
  "ServerID": 100,
  "Flavor": "mysql",
  "Host": "127.0.0.1",
  "Port": 3306,
  "User": "root",
  "Password": "<hidden>",
  "Localhost": "",
  "Charset": "",
  "SemiSyncEnabled": false,
  "RawModeEnabled": false,
  "TLSConfig": null,
  "ParseTime": false,
  "TimestampStringLocation": null,
  "UseDecimal": false,
  "RecvBufferSize": 0,
  "HeartbeatPeriod": 0,
  "ReadTimeout": 0,
  "MaxReconnectAttempts": 0,
  "DisableRetrySync": false,
  "VerifyChecksum": false,
  "DumpCommandFlag": 0,
  "Logger": {
    "Advanced": null
  }
}

1. This more clearly identifies fields in the config
2. This more explicitly shows that the password was masked

Another option would be to do this:

diff --git a/replication/binlogsyncer.go b/replication/binlogsyncer.go
index 9c88aa8..e0164c0 100644
--- a/replication/binlogsyncer.go
+++ b/replication/binlogsyncer.go
@@ -170,7 +170,7 @@ func NewBinlogSyncer(cfg BinlogSyncerConfig) *BinlogSyncer {
        // Clear the Password to avoid outputing it in log.
        pass := cfg.Password
        cfg.Password = ""
-       cfg.Logger.Infof("create BinlogSyncer with config %v", cfg)
+       cfg.Logger.Infof("create BinlogSyncer with config %#v", cfg)
        cfg.Password = pass
 
        b := new(BinlogSyncer)

which results in:

[2023/01/27 11:59:52] [info] binlogsyncer.go:173 create BinlogSyncer with config replication.BinlogSyncerConfig{ServerID:0x64, Flavor:"mysql", Host:"127.0.0.1", Port:0xcea, User:"root", Password:"", Localhost:"", Charset:"", SemiSyncEnabled:false, RawModeEnabled:false, TLSConfig:(*tls.Config)(nil), ParseTime:false, TimestampStringLocation:(*time.Location)(nil), UseDecimal:false, RecvBufferSize:0, HeartbeatPeriod:0, ReadTimeout:0, MaxReconnectAttempts:0, DisableRetrySync:false, VerifyChecksum:false, DumpCommandFlag:0x0, Option:(func(*client.Conn) error)(nil), Logger:(*log.Logger)(0xc0000ac180), Dialer:(client.Dialer)(0x52a420), RowsEventDecodeFunc:(func(*replication.RowsEvent, []uint8) error)(nil), DiscardGTIDSet:false}

But I think JSON is more useful here.

It would also be possible to do this on top of the PR:

diff --git a/replication/binlogsyncer.go b/replication/binlogsyncer.go
index ad4592c..23ede39 100644
--- a/replication/binlogsyncer.go
+++ b/replication/binlogsyncer.go
@@ -38,7 +38,7 @@ type BinlogSyncerConfig struct {
        // User is for MySQL user.
        User string
        // Password is for MySQL password.
-       Password string
+       Password string `json:"-"`
 
        // Localhost is local hostname if register salve.
        // If not set, use os.Hostname() instead.
@@ -159,9 +159,6 @@ func NewBinlogSyncer(cfg BinlogSyncerConfig) *BinlogSyncer {
                cfg.Dialer = dialer.DialContext
        }
 
-       // Clear the Password to avoid outputing it in log.
-       pass := cfg.Password
-       cfg.Password = "<hidden>"
        jsonCfg, err := json.Marshal(cfg)
        if err != nil {
                cfg.Logger.Warnf("Failed to encode config as JSON: %s", err)
@@ -169,8 +166,6 @@ func NewBinlogSyncer(cfg BinlogSyncerConfig) *BinlogSyncer {
        }
        cfg.Logger.Infof("create BinlogSyncer with config %s", jsonCfg)
 
-       cfg.Password = pass
-
        b := new(BinlogSyncer)
 
        b.cfg = cfg

This would remove the password from the config and remove the need to replace it. But this might limit future use of JSON encoded BinlogSyncerConfig.

[dveeden]

@lance6716 @atercattus PTAL