Lots of libc

[Arcterus]

Is there a reason why there are so many calls to libc functions when there are equivalent functions in safe Rust? For example it seems like libc::setenv() could be replaced with env::set_var() and libc::chdir() could be replaced with env::set_current_dir().

[mssun]

Thanks, @Arcterus. I don't have a very strong reason to only use libc functions. But I do meet following problems:

• nix (https://github.com/nix-rust/nix) is a good wrapper for libc functions, but it's not completed . Some function are still missing (e.g., getpwnam is missing nix-rust/nix#862)
• std functions are good, but we still need libc for others
• I'm not sure libc::setenv() and env::set_var() have exact same function (they are probably same). If not same, I don't know if using std will bring side effects.

If I try my best to avoid libc and use nix and std, the code will mix everything together which looks ugly. I tend to use nix and std functions only. But before nix is completed, I have to use libc.

Anyway, for this case (libc::setenv() vs env::set_var()), I read the code https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/os.rs#L467. You are right, I think it's better to use env::set_var. (At least from the perspective of maintenance, but looks like it uses extra memory)

If you have other suggestion, feel free to comment. Many thanks.

[Arcterus]

Usually I think it's better to use std when possible, as that way we can reduce the amount of unsafe code and make it easier to track down related bugs. I can see how the allocations may be an issue though (set_current_dir() similarly seems to allocate to handle the C string). My goal with this issue is basically to lessen the amount of code that requires unsafe.

A better way to replace the libc stuff might be to take the libc::chdir(), libc::setenv()s, and libc::execl() and replace them with Command (using .current_dir(), .env(), and .exec()). However, I assume they will also allocate to make sure the given strings have an ending null byte.

[mssun]

Agree. I saw you fork the repo and made some modification. Free feel to send PRs.

[Arcterus]

My fork won't compile yet because I need to get some changes merged into rust-users (so I can access the user's password).