It sounds like a lack of funding (i.e. the grant ran out) was the real issue. Given how high profile curl is, this raises the question of how sustainable rewrite-in-rust efforts driven by grants (or other short-term funding) are, if they don't have an existing rust community to take advantage of the grant.

This wasn't a rewrite-in-Rust effort, and I think that's the problem. Nothing valuable from curl has been rewritten in Rust.

Only some existing Rust code has been added to curl, but the Rust ecosystem already has a better, safer way of using that code.

Curl is not planning to ever require Rust, so the rewrites are limited only to optional components, and can't fully guarantee that the code is safe. The Rust components are required to expose an unsafe unchecked C interface for the rest of curl. C compilers are unable to enforce the safety invariants of the interface, like the Rust compiler would in a program fully written in Rust.

Probably I misread the original announcement, but I got the impression this was a pilot to adding more rust to curl (and is exactly what a rewrite would start to look like)?

The original announcement explicitly said it's not a rewrite, multiple times: https://daniel.haxx.se/blog/2020/10/09/rust-in-curl-with-hyp...

> A rewrite of curl to another language is not considered

> This is not converting curl to Rust.

> Don’t be fooled into believing that we are getting rid of C in curl by taking this step.

Curl plans to live and die with C: https://daniel.haxx.se/blog/2017/03/27/curl-is-c/

This has been reaffirmed recently in https://daniel.haxx.se/blog/2024/08/06/libcurl-is-24-years-o...

> There was never any consideration to use another language than C for the library […] Not then, not now.

Not only curl is rejecting possibility of being rewritten in Rust, it's also committed to supporting completely-Rust-free curl, because they pride themselves on supporting a lot of retro/niche platforms that Rust doesn't exist on.

I think you're right. Curl is a rich source of C era vulnerabilities (memory safety, weak typing, etc.). Anyone using Rust has already decided they don't want anything to do with that.

Except when they use `unsafe`, which they do, a lot.

Can you back up that claim? In my experience, the vast majority of Rust is safe, or built on communally-audited safe abstractions over unsafe code.

Using communally audited abstractions over unsafe code means you’re using unsafe a lot.

If there was some way to prove that the abstraction is safe, then that would be fine. But the inadequacy of communal auditing is the reason why C has security issues.

The area of Rust code that is unsafe is much, much smaller than the amount in equivalent C code, making it much more tractable to audit. I won't pretend that it's perfect, but it's not remotely comparable to C.

There’s no easy bound on the set of code you’d have to audit to confirm that even one use of unsafe is in fact safe.

It's literally THE unsafe part of the code. It's the only part of code that can invoke UB.

  fn do_something() {
      unsafe { ... }
  }

  // Somewhere in the program
  do_something();

Doesn't matter where "do_something" is used and how much. The only possibly problematic part of this code is the unsafe block. You only audit it.

But if you can manually identify an invariant inside an abstraction it can greatly improve performance for callers/users, additionally, tools like Kani use comprehensible macros to facilitate automatically proving safety of `unsafe` code. Not to mention built in linting, package management, docs, and FP that rust/std provides. Lots has been said about unsafe rust, but the most basic libc tools require the whole cascade of upstream callers to check safety, it's basically backwards from the ground up from a resources and an outcomes perspective.

Use of unsafe is very rare (except for FFI to C where it's unavoidable). I've written tens of thousands of lines of Rust and used `unsafe` exactly once.

Exactly the same experience : my toy compiler project has 10477 lines of Rust code, and there is only one line with unsafe:

  let is_tty = unsafe { libc::isatty(libc::STDERR_FILENO) } != 0; 

Here's the source, just in case: https://github.com/burjui/rambo/

In fact, there are exactly two "unsafe" blocks in all of my Rust projects, and the second one is not even needed anymore because of the language and ecosystem improvements, but the project is basically abandoned, so I'm probably not gonna fix it. There's just no need for unsafe in the vast majority of code.

I don't know where Rust critics get their statistics; probably from picking their noses, judging by their arguments. Most don't seem to even have read the official docs, the bare minimum required to form any conclusions at all about the language. I guess they don't read much Rust code and think there is no way we can write even semi-decently performing high-level code without resorting to unsafe hacks or calling C, because that's the way it's done in other languages.