Module `traft::storage` doesn't panic anymore. Instead, it gracefully
returns errors. All unwraps are moved to the calling functions.

Also, the code is supplemented by tests, and debug logs are removed.

1. Merge `on_ready` handler with the `loop_fn` body into
   the larger `raft_main` function.

2. Get rid of debug logs.

1. Prefer using `"str".into()` since it's briefer.
2. Preserve `"str".to_owned()` if type inference can't help.

1. Fix PICOLIB_AUTORUN env var naming.
2. Add an assertion that it works as expected.
3. Show output if listing tests fails.
3. Run inner tests with listen port :0 to avoid
   "address already in use" errors.

It's a part of networking development.

Also, this patch refactors error handling introduced in previous commit
(see 96aba97a). A single struct is replaced with the enum, common for
all `try_from` functions.

1. Replace `From` trait for raft::Entry with the `TryFrom`. Fairly
   handle its errors in the storage.

2. Replace some other unwraps with "expect" with a more clear message.

3. Support all of `raft::EntryType` variants.

Run it:

```
PICODATA_RAFT_ID=2 cargo run run
```

This is a pre-requisite for further two-node configuration development.
This is a temporary hack until fair joining is implemented.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/16

1. Trait `From` for `traft::row::Entry` now accepts a value instead of a
   reference in order to avoid unnecessary clones. A caller makes a
   clone itself if necessary.

2. Trait `From` implementation for `traft::Message` now accepts a
   reference instead of a value. Anyway, it uses msgpack under the hood
   and doesn't affect performance.

1. Remove `get_stash` function - it doesn't show anything interesting.
2. Adjust logging levels.

Also split log level initialization away from schema.

For ambiguous concepts (such as Entry, Message) use prefix notation instead of suffixes.

This patch eliminates raw raft node dereferencing and redundant use of
`borrow_mut()`.  Instead, `traft::Node` provides a safe API that
communicates with the raw node through the fiber channel.

Also, functions `node::new` and `node::start` are merged because keeping
them distinct makes no sense.

As we recently discovered, Tarantool has a peculiarity - when calling
stored procedures with `{language = "C"}` option, it disregards the
shared object (`.so` / `.dylib`) already loaded by Lua and makes the
second independent `dlopen`. As a result, Lua and C stored procedures
can't share state, because even static variables point to different
memory locations.

As a workaround, this patch provides the API for hiding the state inside
`lua_State`. Under the hood, the stash consumes a custom struct and
leaks the wrapping box. Inside Lua, it's represented by a userdata,
which the `access()` function provides access to.

Use publicly available `tarantool::global_lua` instead of the self-made
implementation.

Tarantool specificities make it difficult to set up usual rust tests.
Picolib is coupled with tarantool symbols and compiled as a dylib, so
it can't be linked to a stand-alone binary.

This patch introduces another way of testing.

All tests (called inner) are already built into dylib and exposed in
the tarantool console:

```
tarantool> picolib.test
---
- test_version: 'function: 0x41f32400'
  test_traft_storage_RaftEntryRow: 'function: 0x41f32550'
...
```

The new integration test `inner.rs` iterates over them and runs each
one in a separate tarantool instance.

See also: commit 6610e5cb

Sergey V authored 3 years ago and Yaroslav Dynnikov committed 3 years ago

Originally it was `picolib::traft::storage::Message`.
Now it's simply `picolib::Message`.

Move tarantool+slog related stuff to a separate module `tlog`.
Introduce the `tlog!` macro for easier logging.

The clap module we use for parsing command-line arguments allows
specifying `default_value`. Unfortunately, it makes impossible to tell
if an argument was actually passed. So it always overrides env var with
a default value, which is undesirable.

1. Change raft_state schema. Now it's more suitable for updating
   individual fields of the raft hard state.

   Close https://gitlab.com/picodata/picodata/picodata/-/issues/13

2. Persist commit and applied indices.

   Close https://gitlab.com/picodata/picodata/picodata/-/issues/14

3. Rearrange storage code. High cohesion, low coupling, as they
   teach us.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/12

This patch implements the Storage trait without MemStorage from example.
All data is persisted it tarantool spaces.

Also, Rust modules are slightly reorganized.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/11

Close https://gitlab.com/picodata/picodata/picodata/-/issues/10

Close https://gitlab.com/picodata/picodata/picodata/-/issues/9

- There's a fiber which ticks logical clock.
- There's a `raft_propose` API exposed in the Tarantool console.

Close https://gitlab.com/picodata/picodata/picodata/-/issues/7
Close https://gitlab.com/picodata/picodata/picodata/-/issues/8