Create connection from socket fd

[locker]

Currently, to create a connection, the user has to specify a URI. The connector creates a socket and connects it to the given URI under the hood. There are use cases when the user doesn't have a URI but does have a connected socket fd. For example, a socket fd could be inherited from the parent process on fork. We need a way to wrap a raw socket fd number in a connection object.

For more details see the IPROTO over socketpair design document.

[oleg-jukovec]

The implementation on Tarantool:
tarantool/tarantool#8984

[oleg-jukovec]

Possibly changes from the public interface:

1. Just parse fd from URI

Let's just support a new uri format (we need to find a suitable URL scheme) for file descriptors and use it with connect:

conn, err := tarantool.Connect(ctx, "fd://236", opts)

2. Replace address and most of connect options by the Dialer interface

Use a Dialer{} interface instead of address:

// For regular connections:
//dialer := tarantool.TtDialer{
//    Username: "foo",
//    Password: "bar",
//}
// For TLS connections:
//dialer := tarantool.TlsDialer{
//    Username: "foo",
//    Password: "bar",
//    KeyFile: "foo/bar/file.key",
//}
dialer := tarantool.FdDialer{
    Fd: 233,
}
dialer := tarantool.Connect(ctx, dialer, opts)

Advantages

• Flexible and testable interface.

Disadvantages

• This requires refactoring before the task (1-3 days.).
• Users may not like too big changes in the public API.
• The change requires update the Connect/ConnectWithOpts of the pool package too.