aya-log panics when logging [u8;6] without format argument

[arctic-alpaca]

Using aya-log to log a [u8;6] compiles and leads to a runtime panic if no format argument (e.g. :mac) is provided.

Example:
info!(&ctx, "received a packet: {}", [0_u8;6]);

Error:
thread 'tokio-runtime-worker' panicked at 'called `Result::unwrap()` on an `Err` value: ()', /home/arctic-alpaca/.cargo/registry/src/github.com-1ecc6299db9ec823/aya-log-0.1.13/src/lib.rs:110:45

Used a newly created xdp project from the template to reproduce.

[alessandrod]

@vadorovsky when you get a chance could you look into this?

[Hanaasagi]

@alessandrod @vadorovsky Hi, I think I understand why the error was thrown. Firstly, the write function is implemented for the [u8; 6] type, as shown here:

aya/aya-log-common/src/lib.rs

Lines 191 to 195 in 23ce42d

	impl WriteToBuf for [u8; 6] {
	fn write(&self, buf: &mut [u8]) -> Result<usize, ()> {
	TagLenValue::<Argument>::new(Argument::ArrU8Len6, self).write(buf)
	}
	}

This writes the type of the field and some other information, which is then retrieved when formatting the string, as shown here:

aya/aya-log/src/lib.rs

Lines 463 to 465 in 23ce42d

	Argument::ArrU8Len6 => {
	let value: [u8; 6] = attr.value.try_into().map_err(|_| ())?;
	full_log_msg.push_str(&value.format(last_hint.take())?);

Because {} is used in info!(&ctx, "received a packet: {}", [0_u8;6]);, the last_hint variable is None, and an error is thrown when formatting, as shown here:

aya/aya-log/src/lib.rs

Lines 217 to 231 in 23ce42d

	impl Format for [u8; 6] {
	fn format(&self, last_hint: Option<DisplayHint>) -> Result<String, ()> {
	match last_hint {
	Some(DisplayHint::Default) => Err(()),
	Some(DisplayHint::LowerHex) => Err(()),
	Some(DisplayHint::UpperHex) => Err(()),
	Some(DisplayHint::Ipv4) => Err(()),
	Some(DisplayHint::Ipv6) => Err(()),
	Some(DisplayHint::LowerMac) => Ok(LowerMacFormatter::format(*self)),
	Some(DisplayHint::UpperMac) => Ok(UpperMacFormatter::format(*self)),
	_ => Err(()),
	}
	}
	}

And currently, it seems that only {:mac} or {:MAC} can be used for output. I think we could add a DebugFormatter with {:?} format syntax or modify the DefaultFormatter to support this.

[Hanaasagi]

Please give me some feedback. If it would be helpful, I would be happy to take on the responsibility of addressing this issue.

[alessandrod]

I think the issue is here

aya/aya-log/src/lib.rs

Line 115 in 23ce42d

log_buf(buf, &*log).unwrap();

? We shouldn't unwrap

[Hanaasagi]

Indeed, unwrap is not appropriate here, but it is not the root cause of this bug because Err has already occurred. As I mentioned in my previous response, the error thrown by info!(&ctx, "received a packet: {}", [0_u8;6]); is due to the lack of a defined DefaultFormatter processing logic for the [u8;6] type. Therefore, I think resolving this issue depends on whether code like info!("{}", [0_u8;6]) is supported.

• If it is valid, then a DefaultFormatter should be added for the [u8;6] type, for example:

impl Formatter<[u8; 6]> for DefaultFormatter; {
    fn format(v: [u8; 6]) -> String {
        // e.g.
        format!("{:?}", v)
    }
}

• If it is invalid, then the timing of throwing the error should be moved to the proc macro. The error should be thrown during compile time rather than runtime.

Here is an example code that moves the error timing to compile time:

main...Hanaasagi:aya:example

[vadorovsky]

@Hanaasagi that's right, thanks for debugging that!

I think we shouldn't support info!("{}", [0_u8;6]) - std formatter in Rust doesn't support it either:

error[[E0277]](https://doc.rust-lang.org/stable/error_codes/E0277.html): `[u8; 6]` doesn't implement `std::fmt::Display`
 --> src/main.rs:2:20
  |
2 |     println!("{}", [0u8; 6]);
  |                    ^^^^^^^^ `[u8; 6]` cannot be formatted with the default formatter

So I like your second option - moving the error to proc macro. Happy to see that you started working on it! Would you like to submit a pull request?

[Hanaasagi]

Sure, I will open a pull request to validate this in proc macro.