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

["Christoph Heiss" <c.heiss@proxmox.com>]

On Tue Apr 1, 2025 at 3:21 PM CEST, Stefan Hanreich wrote:
> Add a type for representing Linux hostnames. These are the same
> constraints as the installer enforces [1].

Actually, the regex is not *fully* complete, see parse_fqdn() in the
same file in [1].

[..]
> [1] https://git.proxmox.com/?p=pve-installer.git;a=blob;f=Proxmox/Sys/Net.pm;h=81cb15f0042b195461324fffeca53d732133629e;hb=HEAD#l11
>
[..]
> diff --git a/proxmox-network-types/src/hostname.rs b/proxmox-network-types/src/hostname.rs
> new file mode 100644
> index 00000000..f183aecb
> --- /dev/null
> +++ b/proxmox-network-types/src/hostname.rs
[..]
> +/// Hostname of a Linux machine
> +///
> +/// A hostname is at most 63 characters long and must only contain lowercase alphanumeric
> +/// characters as well as hyphens. It must not start or end with a hyphen.

This should probably also reject purely numeric hostnames, as mentioned
in Bugzilla #1054 [0]. This isn't a requirement per any RFC, but seems
to can cause subtle bugs. It's enforced in the installer too.

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=1054

> +#[derive(Debug, Deserialize, Serialize, Clone, Eq, Hash, PartialOrd, Ord, PartialEq)]
> +pub struct Hostname(String);
> +
[..]
> +
> +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: impl AsRef<str>) -> Result<Self, HostnameError> {
> +        let name_ref = name.as_ref();
> +
> +        if !(1..63).contains(&name_ref.len()) {

This actually fails for hostnames exactly 63 characters long (which
should be accepted), as `..` is non-inclusive :^)

E.g. the following tests, adapted from proxmox-installer-common/utils.rs
in pve-installer:

  #[cfg(test)]
  mod tests {
      use super::*;

      #[test]
      fn too_long() {
          assert!(Hostname::new(format!("{}.com", "a".repeat(63))).is_ok());
          assert!(Hostname::new(format!("{}.com", "a".repeat(64))).is_err());
      }
  }

> +            return Err(HostnameError::InvalidLength);
> +        }
> +
> +        let host_name = name_ref.to_lowercase();
> +
> +        let mut characters = host_name.chars();
> +
> +        // first character must not be a hyphen
> +        // SAFETY: ok because of length check
> +        if !characters.next().unwrap().is_alphanumeric() {

This should rather use .is_ascii_alphanumeric(). Otherwise any
alphanumeric Unicode character is accepted [1], but hostnames may be
ASCII only, as per e.g. RFC 952 ("ASSUMPTIONS") and hostname(7) [2].

[1] https://doc.rust-lang.org/std/primitive.char.html#method.is_alphabetic
[2] https://manpages.debian.org/bookworm/manpages/hostname.7.en.html

> +            return Err(HostnameError::InvalidSymbols);
> +        }
> +
> +        if !characters.all(|c| c.is_alphanumeric() || c == '-') {

^ same as above.

> +            return Err(HostnameError::InvalidSymbols);
> +        }
> +
> +        // last character must not be a hyphen
> +        // SAFETY: ok because of length check
> +        if !host_name.chars().next_back().unwrap().is_alphanumeric() {

^ same as above.



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