Follow-up

  5993e149 vinyl: sanitize full/empty key stmt detection
  4273ec52 box: introduce JSON Indexes

Historically, we use tuple_field_count to check whether a statement
represents an empty key (match all) or a full key (point lookup): if
the number of fields in a tuple is greater than or equal to the number
of parts in a key definition, it can be used as a full key; if the
number of fields is zero, then the statement represents an empty key.

While this used to be correct not so long ago, appearance of JSON
indexes changed the rules of the game: now a tuple can have nested
indexed fields so that the same field number appears in the key
definition multiple times. This means tuple_field_count can be less
than the number of key parts and hence the full key check won't work
for a statement representing a tuple.

Actually, any tuple in vinyl can be used as a full key as it has all
key parts by definition, there's no need to use tuple_field_count for
such statements - we only need to do that for statements representing
keys. Keeping that in mind, let's introduce helpers for checking
whether a statement can be used as a full/empty key and use them
throughout the code.

Fix test_run:cmd('set variable ...') for string values (PR #146). It is
needed for enabling the use_unix_sockets_iproto option.

Mhash 'random' method is supposed to return a valid node id given
an arbitrary integer, likely generated randomly. But on some
values it was returning 'end' marker despite emptiness of the
container.

This was because of confusion in usage of mh_size() and mh_end().
Mh_size() means real number of objects, stored in the cache,
while mh_end() means hash capacity, or 'number of buckets' as it
is named. Generally capacity is bigger than size, and sometimes
it led to a situation like this:

    size = 1
    capacity = 4
    rnd = 3

    [0]  [1]  [2]  [3]
     -    -    x    -

When code iterates only 'size' times, looking for an element
starting from 'rnd' position, it will not find anything. It
should iterate 'capacity' times instead.

SWIM module API is going to provide a set of clear and pure
functions with appropriately settled const qualifiers. And it
wants to use sio_strfaddr() to provide to user an easy way to
get a pointer to URI of a SWIM member stored in a const memory.

It requires this two-line modification of sio module.

Now there is new member in box.stat.net() called "CONNECTIONS"
which is a number of active iproto connections.

Closes #3905

@TarantoolBot document
Title: box.stat.net
Update the documentation for box.stat.net
to reflect the addition of the field
which reports iproto connections number.

The patch fixes the following test failure:

 | --- app/socket.result	Mon Feb 25 17:32:49 2019
 | +++ app/socket.reject	Mon Feb 25 17:39:51 2019
 | @@ -2827,7 +2827,7 @@
 |  ...
 |  echo_fiber ~= nil
 |  ---
 | -- true
 | +- false
 |  ...
 |  client:write('hello')
 |  ---

This happens, because we don't wait for echo_fiber to start.
Use a channel to make sure it does. Also, increase read/write
timeouts from 0.1 up to 5 seconds - it won't increase the test
runtime, but it will make it more robust.

Closes #4022

This patch fixes the following test failure:

 | --- box/iproto_stress.result	Tue Dec 25 09:56:54 2018
 | +++ box/iproto_stress.reject	Tue Dec 25 10:12:22 2018
 | @@ -80,7 +80,7 @@
 |  ...
 |  n_workers -- 0
 |  ---
 | -- 0
 | +- 340
 |  ...
 |  n_errors -- 0
 |  ---
 | @@ -93,5 +93,3 @@
 |  ---
 |  ...
 |  box.cfg{net_msg_max = net_msg_max}
 | ----
 | -...

The problem is the test is quite cpu intensive so if the host is heavily
loaded (as it is often the case when tests are run on Travis CI), it may
take a few minutes to complete, while the timeout is set to 10 seconds.

To fix it, let's
 - Increase the timeout up to 60 seconds and use test_run.wait_cond
   instead of a homebrew loop.
 - Decrease the number of fibers from 400 down to 100 and adjust
   box.cfg.net_msg_max respectively.

Closes #3911

If a key is frequently updated, iteration to the next key stored in the
memory level can take quite a while, because:

 - In case of GE/GT iterator, vy_mem_iterator_next_key will have to
   iterate the tree from left to right to skip older key versions.

 - In case of LE/LT iterator, vy_mem_iterator_find_lsn will have to
   iterate the tree from right to left to find the newest key version
   visible in the read view.

To avoid that, let's fall back on key lookup if we failed to find an
appropriate statement after one iteration, because in this case there's
a good chance that there's more statements for this key. This should be
fine since a lookup in a memory tree is pretty cheap.

 - Don't pass iterator_type to vy_mem_iterator_seek and functions called
   by it. Instead pass only a key and jump to the first statement
   following the key according to the iterator search criteria. Turns
   out this is enough for memory iterator implementation.
 - Fold EQ check in vy_mem_iterator_seek to avoid code duplication.
 - Drop vy_mem_iterator_start and use vy_mem_iterator_seek directly.

This patch fixes the following test failure:

 | --- box/push.result	Thu Jan 24 13:10:04 2019
 | +++ var/001_box/push.result	Thu Jan 24 13:13:08 2019
 | @@ -536,17 +536,3 @@
 |  ---
 |  ...
 |  chan_disconnected:get()
 | ----
 | -- true
 | -...
 | -chan_push:put(true)
 | ----
 | -- true
 | -...
 | -chan_push:get()
 | ----
 | -- Session is closed
 | -...
 | -box.schema.func.drop('do_long_and_push')
 | ----
 | -...

The problem occurs because the main fiber may close the connection
before do_long_and_push sets the session.on_disconnect trigger, in
which case chan_disconnected:get() will never return. Fix this by
setting the trigger in the main fiber and adding another channel
to wait for do_long_and_push function to start. Also, don't forget
to clear the trigger once the test is complete.

Fixes commit 43af2de2 ("session: outdate a session of a closed
connection").

Closes #3947

Due to the fact that in the case of multikey indexes, the size of
the field map may depend on a particular tuple, the
tuple_int_field_map function has been reworked in such a way as
to allocate the field map of the required size and return it.

Needed for #1257

* Added basic luacov support.
* Added use_unix_sockets_iproto option.
* Fixed TARANTOOL_SRC_DIR on >=tarantool-2.1.1-322-g3f5f59bb5.
  - It is important for app-tap/http_client.test.lua, it fails now.
* Renamed pre_cleanup to pretest_clean.
* pretest_clean: clean up _cluster space.

The bug was introduced in d735b6bf (move
'uri' lib to src/lib/).

lcov reports the following warnings:

Cannot open source file src/uri.rl
Cannot open source file src/uri.c

coveralls-lcov then fails with this message:

coveralls-lcov --service-name travis-ci --service-job-id 498721113 --repo-token [FILTERED] coverage.info
/var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:63:in `initialize': No such file or directory @ rb_sysopen - /tarantool/src/lib/uri/CMakeFiles/uri.dir/src/uri.c (Errno::ENOENT)
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:63:in `open'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:63:in `generate_source_file'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:16:in `block in convert'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:15:in `each'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/converter.rb:15:in `convert'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/lib/coveralls/lcov/runner.rb:68:in `run'
	from /var/lib/gems/2.3.0/gems/coveralls-lcov-1.5.1/bin/coveralls-lcov:5:in `<top (required)>'
	from /usr/local/bin/coveralls-lcov:22:in `load'
	from /usr/local/bin/coveralls-lcov:22:in `<main>'

So coverage target in Travis-CI fails and a coverage does not reported
to coveralls.io.

The bug was introduced in d735b6bf (move
'uri' lib to src/lib/).

'Info' is a header-only library consisting of one file. It is
going to be used by SWIM, stored in src/lib, but src/lib can not
depend on src/. This commit moves 'info' to lib/info.

Needed for #3234

Core is supposed to be the most basic library, providing only
really common features used everywhere like fiber, diag, memory,
logging. Which can't be said about collations - they are used
only by high level things - SQL, Lua utf8, comparators.

Collations are built now as 'lib/coll' library.

The patch is not necessary for anything, but it is a right thing
to do, while some activity is happening there.

Error "syntax error after column name" does not make any sense.
Let's remove it.

Part of ...3965

Macros SQL_*_BKPT were used in debug mode to log errors that
occurred during the execution of VDBE. They are not used now.
This patch removes them.

Part of #3965

@TarantoolBot document
Title: changes in EXPLAIN and PRAGMA

The most important change is that the column names for
the result of the "EXPLAIN ...", "EXPLAIN QUERY PLAN ..."
and "PRAGMA ..." commands are now defined.
Example:
box.cfg{listen = 3302}
cn = require('net.box').connect(box.cfg.listen)
cn:execute('EXPLAIN SELECT 1;')

In addition, the 'case_sensitive_like', 'parser_trace' and
'sql_default_engine' pragmas now return their values if
they are executed without arguments. For the first two
pragmas, this value is their state, and for the latter,
the default engine currently set in SQL.
Example:
box.sql.execute('PRAGMA case_sensitive_like;')

And the last change is that now the execution of the
“PRAGMA” command without determining which pragma to
execute returns status for all flag-type pragmas.
Flag-type pragmas are pragmas that have TRUE or FALSE as
status.
Example:
box.sql.execute('PRAGMA;')

Currently, EXPLAIN and PRAGMA do not set the column types for the
result. This is incorrect, since any returned row must have a
column type. This patch defines the types for these columns.

Closes #3832

Currently box.sql.execute ('PRAGMA') returns nothing, but prints
list of pragmas and their statuses to stdout. Such strategy is
considered to be wrong since output of this command would be
unavailable for users who redirect stdout, use net box connection
etc. This patch makes the command to return result as the rest of
SQL commands. The result contains only FLAG-type pragmas and their
statuses.

Currently PRAGMA case_sensitive_like returns nothing. This seems
wrong, since other similar pragmas return their status. Fixed in
the current patch.

After this patch, "PRAGMA sql_default_engine" called without
arguments will return currently set sql_default_engine.

Currently PRAGMA parser_trace returns an empty table. This seems
wrong, since other similar pragmas return their status. Fixed in
the current patch.

Some macros in pragma.c and pragma.h are obsolete because the
values they are checking are no longer used or their usage makes
no sense. Let's remove them.

For the same reason why 'uri' was moved to src/lib - SWIM needs
core and uuid, and SWIM will live in src/lib.

This commit follows 'uri' relocation as a separate one because
'uri' relocation required some changes in the files, moved by
this commit.

Needed for #3234

Http_parser in fact does not depend on anything, even on the core.
As a rule, such basic libraries are stored in src/lib.

The patch is not necessary for anything, but it is a right thing
to do, while some activity is happening there.

Http_parser is a standalone library, which in fact does not
require httpc. And because of that it is going to be moved into
lib/http_parser.

URI and core libraries are going to be used by SWIM, stored in
src/lib. But src/lib can not depend on src/. This patch pushes
URI library down to src/lib - the lowest level of source
dependencies.

Needed for #3234

Memtx uses separate mempools for iterators of different types.
Due to the fact that there will be more iterators of different
sizes in a series of upcoming changes, let's always allocate the
iterator of the largest size.
No changes have been made to the rtree iterators pool because the
size of these structures is significantly larger.

Needed for #3961

This can't entail any consequences, because socket fd is set to -1 in
this case, but this just looks a bit messy. Let's clean it up.

Follow-up commit 305dbcf6 ("iproto: close socket explicitly before
wal_dir at exit").

When we replaced SQLite's ephemeral spaces with our ones, one
optimization concerning ORDER BY clause was disabled. It allows to
reduce number of fields in format of ephemeral space or sorter table.
To illustrate how it works, consider example:

CREATE TABLE t (id INT PRIMARY KEY, b INT);
SELECT * FROM t ORDER BY b;

To sort entries from t, ephemeral space with format [b, id, b] is
created. One can see, that such format contains duplicate of b column.
To avoid such situation, SQLite provides optimization which removes
duplicates. Meanwhile, it doesn't change already set format of ephemeral
(or sorter) space (and SQLite tolerates that format difference). That's
why it was turned off. However, such optimization turns out to be not
optional but required: some column values shouldn't be computed twice.
For instance:

SELECT random() AS x FROM t ORDER BY x;

Without filtering fields from ephemeral space format, it would be like:
[random(), random()]. In other words, results would be sorted by first
call to random() function, but resulting set would consist of values
given by second call of random(). So, to enable it, we should reduce
field count in format of ephemeral space by number of matches between
SELECT and ORDER BY column lists.

Also, type of return value for random() function has been fixed.

Closes #3783

Refactored memtx_tree code so that memtx_tree.h, memtx_rtree.h,
memtx_bitset.h, memtx_hash.h contained only the signature of the
tree object constructor while all implementation details were in
corresponding *.c files.

Needed for #3961

Introduce a macro BPS_TREE_IDENTICAL for BPS TREE class. This
makes possible to define custom comparators for stucture-based
leafs.
Previously, a C++ comparison operator "!=" override was used for
this purpose. Due to the fact that we are not going to rework on
C++ C-only components of Tarantool like memtx_tree, we needed a
way to make complex structures comparisons using preprocessor.

Needed for #3961

The bps_tree.h header defines the macro _api_name, but does not
undefine it at the end. Fixed.

tarantool instance didn't close socket explicitly
which could cause hot standby instance to fail to bind
in case it tries to bind before socket is closed by OS.
Now it is fixed by closing socket explicitly before wal_dir.

Closes #3967

Add preprocessing of the request headers. Each header must be 'string' or 'table'
with '__tostring' metamethod.

Closes #3679