streams: interactive transactions and streams support

[AnaNek]

The main purpose of streams is transactions via iproto.
Since v. 2.10.0, Tarantool supports streams and
interactive transactions over them. Each stream
can start its own transaction, so they allows
multiplexing several transactions over one connection.

API for this feature is the following:

* `NewStream()` method to create a stream object for `Connection`
   and `NewStream(userMode Mode)` method to create a stream object
   for `ConnectionPool`
*  stream object `Stream` with `Do() method and
   new request objects to work with stream,
  `BeginRequest` - start transaction via iproto stream;
  `CommitRequest` - commit transaction;
  `RollbackRequest` - rollback transaction.

Closes #101

[oleg-jukovec]

Thank you for the request pool and the work done. Great job!

It seems to me that the only problem is that we don't need to extend the Request interface. I don't see any advantages of it.

I didn't look at the tests very carefully, I will do it after the correction the Request interface.

[oleg-jukovec]

Good news! You can rebase to the master branch.

[oleg-jukovec]

Thanks for the corrections!

It's not your fault but you need to sync with #180 :

1. Do we need special methods like NewStream, NewPreparedStatement which will return a Stream and PreparedStatement object? Or we need a regular Begin request:

func (conn *Connection) Begin(args) (Response, error)
func (conn *Connection) BeginTyped(args) error
func (conn *Connection) BeginAsync(args) *Future

I'll agree to whatever you choose, but you have to choose the same with @vr009 .

2. I think we need *Async versions of methods Begin, Rollback, Commit (not sure about *Typed). It should be synchronized with sql: support prepared statements #180 Execute and Unprepare too. Please contact with @vr009 .

Please don't take it personally. It's just a problem of implementation a similar feature (from an API point of view) at the same time by two different people. The confusion was compounded by the request objects. It's not your fault. It's just circumstance.

[oleg-jukovec]

You could rebase to the master branch.

[oleg-jukovec]

Thank you for the great work! I don't see any critical issues.

So LGTM after resolving the conversations. Also it will be greate if you split long test cases into several shortest ones.

[DifferentialOrange]

2. I think we need *Async versions

So how's it ended?

[oleg-jukovec]

So how's it ended?

It was decided to use request objects + Connection.Do()/Stream.Do(), without specific calls.

[oleg-jukovec]

Unfortunately, you are unlucky and we merged a pull request with context support #173 .

Most likely rebase would be easy and you will need just to add Context() call for new requests objects.