Rewrite Process in Popen

[olegrok]

Also such approach should preserve backward compatibility (old versions should use old code). But new Tarantool versions 2.4 should works fine. Maybe it will fix #120 .

[ochaplashkin]

During solution #252 , we tried to rewrite the module, but decided to postpone it indefinitely.
These are notes about what we managed to find out (for the future):

• list of possible problems with popen;
• ffi pipe and popen popen are not compatible (by interfaces);
• output_beatifier:hijack_output(...) not needed because POPEN will do it;
  

  luatest/luatest/process.lua

  Lines 64 to 66 in 89da427

  	if output_beautifier then
  	output_beautifier:hijack_output()
  	end

• processing of arguments and environment variables is not necessary:
  

  luatest/luatest/process.lua

  Lines 67 to 68 in 89da427

  	local argv = to_const_char(args)
  	local envp = to_const_char(env_list)

• there are some limitations in popen:new(), you need to use popen:shell();
• you can replace the read function (a more correct option):
  

  luatest/luatest/ffi_io.lua

  Lines 32 to 47 in 89da427

  	function export.read_fd(fd, chunks, options)
  	local buffer_size = options and options.buffer_size or export.READ_BUFFER_SIZE
  	local timeout = options and options.timeout or export.READ_TIMEOUT
  	chunks = chunks or {}
  	local buffer
  	while socket.iowait(fd, 'R', timeout) ~= '' do
  	timeout = 0 -- next iowait must return immediately
  	buffer = buffer or ffi.new('char[?]', buffer_size)
  	local count = ffi.C.read(fd, buffer, buffer_size)
  	if count < 0 then
  	error('read pipe failed: ' .. errno.strerror())
  	end
  	table.insert(chunks, ffi.string(buffer, count))
  	end
  	return chunks
  	end

• see Fix detect tarantool crash at exit #312 about this logic (diagram)
  

  luatest/luatest/process.lua

  Lines 51 to 59 in 89da427

  	local pid = ffi.C.fork()
  	if pid == -1 then
  	error('fork failed: ' .. pid)
  	elseif pid > 0 then
  	if output_beautifier then
  	output_beautifier:enable({track_pid = pid})
  	end
  	return self:from({pid = pid, ignore_gc = options.ignore_gc, output_beautifier = output_beautifier})
  	end

• ffi.gc works correctly with popen
  

  luatest/luatest/process.lua

  Lines 78 to 81 in 89da427

  	ffi.gc(self._pid_ull, function(x)
  	local pid = tonumber(ffi.cast(ffi.typeof(0ULL), x))
  	log.debug("Killing GC'ed process " .. pid)
  	Process.kill_pid(pid, nil, {quiet = true})

[olegrok]

ffi pipe and popen popen are not compatible (by interfaces);

This issue was written when 1.10 was relevant. Currently it's not so. You don't need to care about ffi and popen compatibility.