Since all decoding functions except xrow_decode_header() decode a packet
body, let's pass an xrow_header object to xrow_on_decode_error() instead
of raw pointers to msgpack data. This will simplify packet body decoding
functions a bit while in xrow_decode_header() we can use dump_row_hex()
directly without hurting readability.

While we are at it, make dump_row_hex() static, because it's not used
outside its compilation unit.

xrow_header_has_key() isn't used anywhere.

The purpose of iproto_dml_body_has_key() is unclear - we use it to skip
unknown DML keys, but we would skip them anyway in the switch-case down
the code path, like we do while decoding other requests. The only useful
thing it does is implicitly checks that the key has type MP_UINT, but we
can do that explicitly instead.

xrow_header_decode() checks that the packet body is a valid msgpack and
there's no outstanding data beyond the packet end so we don't need to
redo this checks while decoding the body (e.g. in xrow_decode_dml()).

Prior to this patch, an assertion was thrown if a tuple with an invalid
id was inserted into the _priv system space. This bug appeared only in
the debug build.

Closes #6295

Closes #4909

Fixed error in implementation of `ev_io_closing`: this function
is called to do same work as `fd_kill` and should call it after
checking fd (in `coio_close` we pass invalid event value, that
leads to assertion in new libev version).

Implement ability to pass timeout to 'fiber:join' function.
If timeout expired, join fails with 'timed out' error.

Closes #6203

@TarantoolBot document
Title: ability to set timeout for 'fiber:join' function was implemented
Implement ability to pass timeout to 'fiber:join' function.
If timeout expired, join fails with 'timed out' error.

Add new  metrics `REQUESTS_IN_PROGRESS` and `REQUESTS_IN_STREAM_QUEUE`
to `box.stat.net`, which contain detailed statistics for iproto requests.
These metrics contains same counters as other metrics in `box.stat.net`:
current, rps and total.

Part of #6293

@TarantoolBot document
Title: detailed iproto requests statistics was implemented
Add new  metrics `REQUESTS_IN_PROGRESS` and `REQUESTS_IN_STREAM_QUEUE`
to `box.stat.net`, which contain detailed statistics for iproto requests.
These metrics contains same counters as other metrics in `box.stat.net`:
current, rps and total.
```
-- statistics for requests currently being processed in tx thread.
REQUESTS_IN_PROGRESS:
current: -- count of requests currently being processed in the tx thread
rps: -- count of requests processed by the tx thread per second
total: -- total count of requests processed by tx thread

-- statistics for requests placed in queues of streams.
REQUESTS_IN_STREAM_QUEUE:
current: -- count of requests currently waiting in queues of streams
rps: -- count of requests placed in streams queues per second
total: -- total count of requests, which was placed in queues of streams
          for all time
```

In next patch new rmean for iproto thread statistic, that collected
in tx thread will be implemented. We need rename IPROTO_LAST constant
to make next patch more clear.

There was several different function to get iproto statistic,
one function for one metric. Since we wan't to add some new
metrics it will be better to implement one function for getting
all iproto statistic not add several new functions.

Currently first element in queue of pending requests in
stream is a request which was pushed to tx thread for
processing. In this patch special pointer to this request
(stream->current) was implemented and queue of pending
requests now really contains only pending requests.

OSX workflows use brew for install openssl.
There was a new release of openssl@3.0 and
homebrew updated the openssl formula.

Close #6468

It never returns NULL anymore, because it uses xmalloc for memory
allocations.

It never returns NULL anymore, because it uses xmalloc for memory
allocations.

An mhash is used for allocating system objects. Failing to grow it is
likely to render the Tarantool instance unusuable so better fail early.

Checks of mh(new) and mh(put) return value will be removed in follow-up
patches.

We want to use the xmalloc helper throughout the code, not only in
the core lib. Move its definition to trivia/util.h and use fprintf+exit
instead of say/panic in order not to create circular dependencies.

No need to pass them around when we can embed them in netbox_transport.
This is a step towards rewriting the netbox state machine in C.

Part of #6291

There's no need to optimize out fiber.wakeup:
 - we already have C function calls on the code path;
 - fiber.wakeup is pretty cheap to be called unconditionally.

This is a preparation for moving send/recv buffers to C.

Let's recycle buffers in the same place where we reset the transport:
when switching the state to 'closed', 'error', or 'error_reconnect'.

This is a preparation for moving send/recv buffers to C.

In future we will store watchers in this struct. Besides, we can already
move send/recv buffers there. So 'registry' is not an appropriate name.
Let's rename it to 'transport' - the name which is already used in
net.box for a net.box connection implementation object.

It stores a socket, not a net.box connection. Let's rename it to sock to
avoid confusion.

Exporting symbols of a third party library is not a best practice,
as we know from [1]. Let's wrap the msgpack symbols that need to
be exported with the "tnt_" prefix.

While working on the patch, it was decided to export the msgpack
symbols that are used in "msgpuckffi.lua".
In test shared libraries where the symbols "mp_***_{decimal,uuid}"
are used, they are replaced to exported "tnt_mp_***_{decimal,uuid}",
because in the case of linking with "libcore.a" the "libcore.a"
needs to be rebuild with the "-fPIC" flag, that seems as overkill
for tests.

1. https://github.com/tarantool/memcached/issues/59

Closes #5932

Before this change `./test-run.py -j -1` always give zero exit code even
when there were failed tests. It is the regression from
2.6.0-104-g43482eedc.

The `-j -1` is the test-run mode, when it does not execute any
parallelization code: don't spawn worker processes and proceed with
tests one-by-one from a single process. It was kept just in case, when
the parallelization was implemented. AFAIS, it is barely used.

Usual `./test-run.py` or `./test-run.py -j N` invocations are not
affected. Tarantool's CI is not affected.

See https://github.com/tarantool/test-run/pull/313 for details.

If we insert a tuple in space with an index that is being built in background,
new tuple will or will not be inserted into new index depending on the result of
lexicographical comparison with tuple which was inserted into new index last.
The problem is hash index is unordered, so background build will not work properly
if primary key is HASH index.

To avoid this, disable building index in background if primary index is hash.

Closes #5977

The test uses error injection.

Follow-up 0428bbce ("vinyl: fix use of
dropped space in deferred DELETE handler").

For deferred DELETE statements to be recovered after restart, we write
them to a special 'blackhole' system space, _vinyl_deferred_delete,
which doesn't store any data, but is logged in the WAL, as a normal
space. In the on_replace trigger installed for this space, we insert
deferred DELETE statements into the memory (L0) level of the LSM tree
corresponding to the space for which the statement was generated. We
also wait for L0 quota in the trigger. The problem is a space can be
dropped while we are waiting for quota, in which case the trigger
function will crash once it resumes execution.

To fix this, let's wait for quota before we write the information about
the deferred DELETE statement to the _vinyl_deferred_delete space and
check if the LSM tree was dropped after yield. This way, everything will
work as expected even if a new space is created with the same id,
because we don't yield after checking quota.

Closes #6448

Will come in handy for testing #6448.

@TarantoolBot document
Title: Document box.stat.vinyl().regulator.blocked_writers

The new stat counter shows the number of fibers that are blocked waiting
for Vinyl level0 memory quota.

The struct is empty.

Use a special luaL_serializer with encode_error_as_ext disabled.
Default options are propagated to it via an update trigger.

This is a preparation for merging serializer_opts into luaL_serializer.

It's not needed now, because error marshaling is enabled automatically
if the connector supports it (IPROTO_FEATURE_ERROR_EXTENSION is set in
IPROTO_ID features).

Closes #6428

@TarantoolBot document
Title: Drop error_marshaling_enabled session setting

box.session.setting.error_marshaling_enabled was used to enable encoding
errors returned by CALL/EVAL in the extended format (as the MP_ERROR
MsgPack extension). Now, the feature is enabled automatically if the
connector supports it (sets IPROTO_FEATURE_ERROR_EXTENSION in IPROTO_ID
features).

The new IPROTO protocol feature IPROTO_FEATURE_ERROR_EXTENSION enables
encoding errors returned by CALL/EVAL commands as the MP_ERROR MsgPack
extension. Note, the MP_ERROR extension can still be disabled globally
by setting msgpack.cfg.encode_error_as_ext to false. If an IPROTO client
doesn't set the feature bit, errors will be encoded as generic cdata
objects (converted to strings by default).

Needed for #6428

@TarantoolBot document
Title: Document IPROTO_FEATURE_ERROR_EXTENSION

A new feature bit for the IPROTO_ID command was added:

```
IPROTO_FEATURE_ERROR_EXTENSION = 2
```

The protocol version was incremented - now it equals 2.

If a network client sets this bit, errors returned by CALL/EVAL will be
encoded as the MP_ERROR MsgPack extension (unless disabled globally by
msgpack.cfg.encode_error_as_ext). If the bit is unset, errors will be
encoded according to the serialization rules used for generic cdata
objects (converted to strings by default).

The built-in net.box connector sets this feature bit.

The server sets this feature bit if it supports the MP_ERROR MsgPack
extension so a net.box client can explicitly request the feature upon
connecting to a server:

```lua
net.box.connect(uri, {required_protocol_features = {'error_extension'}})
```

This patch adds a new msgpack.cfg: encode_error_as_ext. Setting it makes
msgpack and msgpackffi modules encode errors as the MP_ERROR msgpack
extension. If the flag is unset, msgpack.encode behavior depends on
encode_load_metatables, encode_use_tostring, and encode_invalid_as_nil
options, see luaL_convertfield(), while msgpackffi.encode() will always
encode errors as strings. The latter needs to be fixed, but it's out of
the scope of this work and tracked separately, see #4499.

The new option is enabled by default.

Interaction with box.session.settings.error_marshaling_enabled: errors
are encoded as the MP_ERROR msgpack extension when returned via IPROTO
iff both error_marshaling_enabled and encode_error_as_ext are set.

Closes #6433

@TarantoolBot document
Title: Document msgpack.cfg.encode_error_as_ext

The new option determines how error objects (see box.error.new) are
encoded in the msgpack format:
 - If it's set, errors are encoded as the MP_ERROR msgpack extension.
   This is the default behavior.
 - If it's unset, the encoded format depends on other msgpack
   configuration options (encode_load_metatables, encode_use_tostring,
   encode_invalid_as_nil). With the otherwise default configuration,
   they are encoded as strings (see error.message).

Functions affected by the default configuration (msgpack.cfg):
 - msgpack and msgpackffi modules
 - Storing errors in tuples and spaces (box.tuple.new)
 - Returning errors from IPROTO CALL/EVAL

error_to_mpstream and error_to_mpstream_noext have a lot in common.
Factor it out into helper functions.

The function doesn't iterate over the stack of errors so it should have
suffix '_one', like mp_encode_error_one.

It's customary for mp_encode_* functions to take a pointer to the buffer
and return a pointer following the end of encoded data.
mp_encode_error_one takes (char **) and advances it. Fix it to be
consistent with other mp_encode_* functions.

There's no reason not to enable extended errors for CALL_16.
Enable the feature and add a test.

Needed for #6433

There's no way to encode an error yet so the test just hard-codes
msgpack data. It will be fixed in the future, once we allow to encode
errors with msgpack/msgpackffi.

Needed for #6433

It's not used anymore.