Re: [pve-devel] [PATCH proxmox v3 2/2] network-types: add hostname type

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Tue, Apr 01, 2025 at 04:52:44PM +0200, Stefan Hanreich wrote:
> Add a type for representing Linux hostnames. These are the same
> constraints as the installer enforces [1]. Lowercasing is fine as
> well, since practically everything treats hostnames case-insensitively
> as RFC 952 stipulates:
> 
> > No distinction is made between upper and lower case.
> 
> [1] https://git.proxmox.com/?p=pve-installer.git;a=blob;f=Proxmox/Sys/Net.pm;h=81cb15f0042b195461324fffeca53d732133629e;hb=HEAD#l11
> [2] https://www.rfc-editor.org/rfc/rfc952.txt
> 
> Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
> ---
> 
> Notes:
>     sending this separately because this contains the new types, that
>     haven't been a part of proxmox-ve-rs before.
>     
>     Changes from v2:
>     * improved hostname validation (thanks @Maximiliano @Christoph)
>     * added additional unit tests
>     
>     Changes from v1:
>     * added unit tests
> 
>  proxmox-network-types/src/hostname.rs | 103 ++++++++++++++++++++++++++
>  proxmox-network-types/src/lib.rs      |   1 +
>  2 files changed, 104 insertions(+)
>  create mode 100644 proxmox-network-types/src/hostname.rs
> 
> diff --git a/proxmox-network-types/src/hostname.rs b/proxmox-network-types/src/hostname.rs
> new file mode 100644
> index 00000000..4b2f7ede
> --- /dev/null
> +++ b/proxmox-network-types/src/hostname.rs
> @@ -0,0 +1,103 @@
> +use std::fmt::Display;
> +
> +use serde::{Deserialize, Serialize};
> +use thiserror::Error;
> +
> +#[derive(Error, Debug)]
> +pub enum HostnameError {
> +    #[error("the hostname must be from 1 to 63 characters long")]
> +    InvalidLength,
> +    #[error("the hostname has an invalid format")]
> +    InvalidFormat,
> +}
> +
> +/// Hostname of a Debian system

^ Why debian specific? Should this then not be in a different namespace
or have a different name?

> +///
> +/// It checks for the following conditions:
> +/// * At most 63 characters long.
> +/// * It must not start or end with a hyphen.
> +/// * Must only contain ASCII alphanumeric characters as well as hyphens.
> +/// * It must not be purely numerical.
> +#[derive(Debug, Deserialize, Serialize, Clone, Eq, Hash, PartialOrd, Ord, PartialEq)]
> +pub struct Hostname(String);
> +
> +impl std::str::FromStr for Hostname {
> +    type Err = HostnameError;
> +
> +    fn from_str(hostname: &str) -> Result<Self, Self::Err> {
> +        Self::new(hostname)
> +    }
> +}
> +
> +impl AsRef<str> for Hostname {
> +    fn as_ref(&self) -> &str {
> +        &self.0
> +    }
> +}
> +
> +impl Display for Hostname {
> +    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
> +        self.0.fmt(f)
> +    }
> +}
> +
> +impl Hostname {
> +    /// Constructs a new hostname from a string
> +    ///
> +    /// This function accepts characters in any case, but the resulting hostname will be
> +    /// lowercased.
> +    pub fn new(name_ref: impl AsRef<str>) -> Result<Self, HostnameError> {

Nit: I'd recommend using a `check()` function which does not create the
`Hostname` itself, because then:

- in `FromStr` we know we have a reference (&str) and need to clone.
- We could add a `TryFrom<&str>` wich just uses `.parse()`
- We could add a `TryFrom<String>` which avoids the clone.

But...

> +        let name: &str = name_ref.as_ref();
> +
> +        if name.is_empty() || name.len() > 63 {
> +            return Err(HostnameError::InvalidLength);
> +        }
> +
> +        if !(name.starts_with(|c: char| c.is_ascii_alphanumeric())
> +            && name.ends_with(|c: char| c.is_ascii_alphanumeric())) {
> +            return Err(HostnameError::InvalidFormat);
> +        }
> +
> +        if !name.chars().all(|c| c.is_ascii_alphanumeric() || c == '-') {
> +            return Err(HostnameError::InvalidFormat);
> +        }
> +
> +        if name.chars().all(|c| c.is_ascii_digit()) {
> +            return Err(HostnameError::InvalidFormat);
> +        }
> +
> +        Ok(Self(name.to_lowercase()))

...do we really want/need to do this? (Note that if we really do this,
it should IMO be documented on the *type*, too, not just this method.)

I mean, I'm not completely against it, but if we "normalize", would we
not technically also have to punycode non-ascii hostnames?

(But at the very least it seems that punycode does case-folding... at
least a quick online-punycode conversion tool seems to convert both 'Ө'
and 'ө' to 'xn--j6a')

> +    }
> +}
> +
> +#[cfg(test)]
> +mod tests {
> +    use super::*;
> +
> +    #[test]
> +    fn test_parse_hostname() {
> +        for valid_hostname in [
> +            "debian",
> +            "0host",
> +            "some-host-123",
> +            "63characterlonghostnamexxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
> +        ] {
> +            Hostname::new(valid_hostname).expect("valid hostname");
> +        }
> +
> +        for invalid_hostname in [
> +            "-debian",
> +            "0host-",
> +            "some/host",
> +            "",
> +            "123",
> +            "64characterlonghostnamexxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
> +            "🆒"
> +        ] {
> +            Hostname::new(invalid_hostname).expect_err("invalid hostname");
> +        }
> +
> +        let uppercased_hostname = Hostname::new("UPPERCASE").expect("valid hostname");
> +        assert_eq!(uppercased_hostname.as_ref(), "uppercase");
> +    }
> +}
> diff --git a/proxmox-network-types/src/lib.rs b/proxmox-network-types/src/lib.rs
> index b952d71c..f4812146 100644
> --- a/proxmox-network-types/src/lib.rs
> +++ b/proxmox-network-types/src/lib.rs
> @@ -1,2 +1,3 @@
> +pub mod hostname;
>  pub mod ip_address;
>  pub mod mac_address;
> -- 
> 2.39.5


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