connection: support connection via an existing socket fd

[askalt]

This patch contains several changes:

Now, to connect to the Tarantool, you need to pass an object that satisfies tarantool.Dialer interface.

You can use one of the existing implementations: NetDialer, OpenSslDialer or FdDialer (which connects to the Tarantool using an existing socket fd).

For example:

conn, err := tarantool.Connect(context.Background(), tarantool.NetDialer{
	Address:  "127.0.0.1:3301",
	User:     "user",
	Password: "secret",
}, tarantool.Opts{})

To create a connection pool, you need to pass a map[string]tarantool.Dialer,where each dialer is associated with a unique ID (for example, it can bethe server address). Connections will be distinguished from each other using
these IDs.

For example:

connPool, err := pool.Connect(context.Background(), map[string]tarantool.Dialer{
	"127.0.0.1": tarantool.NetDialer{
		Address:  "127.0.0.1",
		User:     "user",
		Password: "secret",
	},
}, tarantool.Opts{})

The conn.RemoteAddr and conn.LocalAddr functions have been removed. To obtain the connection address, you can use conn.Addr.

Now, NewWatcher checks the actual features of the server, rather than relying
on the features provided by the user during connection creation.

In the case of connection pool, watchers are created for connections that support
this feature.

ClientProtocolInfo, ServerProtocolInfo were removed. Now, there is ProtocolInfo,
which returns the server protocol info.

I didn't forget about (remove if it is not applicable):

• Tests (see documentation for a testing package)
• Changelog (see documentation for changelog format)
• Documentation (see documentation for documentation style guide)

Related issues:
Closes #321

[oleg-jukovec]

Watchers from the pool use conn.Addr() instead of id.

[oleg-jukovec]

Thank you for the patch! Please, squash two commits into one:

connection: make dialer mandatory
+
tests: correct according to the changes

Although correct the commit headers:

connection: make dialer mandatory -> api: make dialer mandatory
dial: add the ability to connect via socket fd -> api: add the ability to connect via socket fd
docs: update according to the changes -> doc: update according to the changes

And move Closes https://github.com/tarantool/go-tarantool/issues/321 to a latest commit.

[DerekBum]

lgtm.

[oleg-jukovec]

Please, rebase the pull request.

[better0fdead]

Hi, thx for patch. Pls, rebase pull request.