Implement Connector and DriverContext interface

[shogo82148]

Description

Implemented the Connector interface and DriverContext interface in go 1.10.
fixes #671

#705 also implements Connector interface, while the context support is incomplete.

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[nemith]

See #705

[shogo82148]

I did. but #705 is missing some features.

• MySQLDriver doesn't implement driver.DriverContext.
• It is not able to cancel the context during handshaking.

[dolmen]

• To simplify the API, the Connector should be merged with Config: just implement the Connect and Driver methods directly on *Config. OpenConnector would become a one-line wrapper around ParseDSN.

• Rename connector.go to connector_go1.10.go, driver_go110.go to driver_go1.10.go, driver_go110_test.go to driver_go1.10_test.go because the Go toolchain has special support for this naming scheme. This makes the // +build go1.10 lines redundant, so remove them. (see also Rename go version dependent sources using idiomatic naming #822 that applies this to all existing files)

• You duplicated the content of Driver.Open method in Connect. This open the way to maintainance nightmare (bug could be fixed in one place but forgotten in the other). A refactoring is necessary to remove this duplication. I propose to move the common bits as a private method of Config.

[dolmen]

Do not merge master into your own branch. Instead, use rebase!

[methane]

Do not merge master into your own branch. Instead, use rebase!

We use "squash and merge". So no need to rebase.
I prefer "merge master" over rebase, because it makes clear what changed from last review.

[methane]

For new code, use current year.

[shogo82148]

Will we? #822 (comment)
If we drop Go 1.7, I can rewrite MySQLDriver.Open the following.

// Open new Connection.
// See https://github.com/go-sql-driver/mysql#dsn-data-source-name for how
// the DSN string is formated
func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
	c, err := ParseDSN(dsn)
	if err != nil {
		return nil, err
	}
	return c.Connect(context.Background())
}

This is more simple solution for duplicated code.

[shogo82148]

The context package has been supported from Go 1.6, and Go 1.6 has been dropped.
So I can rewrite MySQLDriver.Open as #778 (comment), and I did it. ee66ae6

[cbandy]

Before this change, a connection would get its own *Config from ParseDSN. Here, each connection returned by Connect shares a pointer to the one Config. Is that intentional/desirable?

[julienschmidt]

Ideally all connections would share one immutable copy.
One goal of the connector interface was to avoid having to parse and allocate a new config for each connection.

[cbandy]

This looks new during Connect. What does it do?

[shogo82148]

It cancels opening new connection, if the context is canceled.
See #608 please.

Other methods which supports the context have this lines. (e.g.

mysql/connection_go18.go

Lines 84 to 87 in 2307b45

	if err := mc.watchCancel(ctx); err != nil {
	return nil, err
	}
	defer mc.finish()

)
I did not need it because MySQLDriver.Open did not correspond to the context so far, but since Config.Connect become to correspond to the context, I added this

[cbandy]

Is there anything I can do to help this along?

[cbandy]

The conflict appears to be this small change in driver.go: 7ac0064#diff-749da71b40f8ff06fc9e78ce917b0cce

[shogo82148]

I resolved the conflict. Check it, please.

[methane]

I don't like Config implements Connector interface.

type Connector struct {
    cfg *Config  // immutable private copy.
}

func NewConnector(cfg *Config) *Connector {
  copyCfg := *cfg
  // deep copy some members
  return &Connector{cfg: cfg}
}

func (c *Connector) Connect(ctx context.Context) (driver.Conn, error) {
    // ...
}

This allows future optimization for us. For example, we can use one dedicated killing connection,
instead of connect when cancelling.

[shogo82148]

It sounds good.
I will add the Connector struct.

[nemith]

Since this is the real solution to ":" in username any chance we can get this into the driver?