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 https://github.com/tarantool/luatest/issues/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; https://github.com/tarantool/luatest/blob/89da427f8bb3bb66e01d2a7b5a9370d0428d8c52/luatest/process.lua#L64-L66
• processing of arguments and environment variables is not necessary: https://github.com/tarantool/luatest/blob/89da427f8bb3bb66e01d2a7b5a9370d0428d8c52/luatest/process.lua#L67-L68
• there are some limitations in popen:new(), you need to use popen:shell();
• you can replace the read function (a more correct option): https://github.com/tarantool/luatest/blob/89da427f8bb3bb66e01d2a7b5a9370d0428d8c52/luatest/ffi_io.lua#L32-L47
• see #312 about this logic (diagram) https://github.com/tarantool/luatest/blob/89da427f8bb3bb66e01d2a7b5a9370d0428d8c52/luatest/process.lua#L51-L59
• ffi.gc works correctly with popen https://github.com/tarantool/luatest/blob/89da427f8bb3bb66e01d2a7b5a9370d0428d8c52/luatest/process.lua#L78-L81

[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.