Awesome

cargo-osha

A program to list unsafe code in a Rust project. Not actually a cargo plugin (yet).

Right now this is a proof of concept. I wanted to play with a tool like this to see if it was feasible. I don't really intend to be actively developing it. If someone wants to work on it, or a similar tool, go ahead with my blessing.

Example

Example from winit, a crate that does a large amount of platform-specific FFI:

> cargo run -- winit/src/**.rs
...
Unsafe functions: 20/85
Unsafe expressions: 222/16847
Unsafe traits: 0/14
Unsafe methods: 14/460
Unsafe impls: 21/136

So, out of 85 functions in the files, 20 of them are marked unsafe. Out of 460 methods, 14 of them are unsafe, and so on.

Example from ggez, a crate that mostly uses dependencies that provide safe wrappers, and so needs little unsafe code itself:

> cargo run -- ggez/src/**.rs
...
Unsafe functions: 0/101
Unsafe expressions: 0/6786
Unsafe traits: 0/7
Unsafe methods: 0/312
Unsafe impls: 1/122

Usage

Right now it only provides a simple command line program that reads in N Rust source files. Doesn't walk dependencies or anything, you have to provide all files on the command line. It has no command line flags worth speaking of.

The code itself is nigh trivial, just read the source. It uses syn to walk a Rust source code file and counts up the occurances of unsafe in various places. There may be some it misses, just open an issue or whatever.

Should be split into a library someday maybe.

On Unsafe

Number of lines of code inside the unsafe blocks themselves isn't a useful estimate.

-- /u/kibwen

I don't think any sort of counting can help.

-- /u/DGolubets

Unsafe isn't your enemy. Unsafe is your friend... you know, the friend who lives in the country and has a giant pickup truck and 37 guns. You might not bring him to your sister's wedding, but if you need something blown up, he is THERE for you.

-- me

This tool isn't intended to "measure unsafety", it's intended to be a quick and dirty investigation, because partial information is better than no information. /u/annodomini on Reddit said it best:

It's a quick metric for doing a preliminary overview, not a replacement for doing proper auditing.

Taking a look at the output of cargo-osha posted elsewhere in the thread, there are 1025 unsafe expressions in actix-web, out of a total of 37602. That tells me that there's a pretty large auditing job to do, just to determine what invariants need to apply for those 1025 unsafe expressions to be valid, let alone auditing any of the code within privacy boundaries that the unsafe code relies on to uphold those invariants.

If a crate has two or three unsafe expressions, that tells me that it could be relatively quick to audit those expressions, figure out the invariants they rely on, and then audit everything in the code base that could impact those invariants; for instance, if it relies on invariants about length and capacity, then from there you just have to audit things that touch length and capacity. Or in some cases, the unsafe code doesn't really depend on any other invariants, and can be audited in isolation.

On the other hand, if you have 1025 unsafe expressions, that's a huge job to audit all of those plus everything that could impact whether those are actually valid or not.

Why the name?

In the USA, OSHA (Operational Safety and Health Administration) is the part of the government responsible for workplace safety. It's their job to make sure that construction workers wear hard hats, miners don't breathe asbestos, factory workers aren't crushed by machinery, and all that sort of useful stuff. OSHA has an impossible job, because if they did it perfectly then nothing would ever get done, but the world is still a much better place because they exist.

Apologies for the obscure name to the rest of the world!