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

[Stefan Hanreich]

Thanks for your review - comments inline

On 4/4/25 09:31, Wolfgang Bumiller wrote:
> 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 at 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?

As Christoph mentioned, Debian explicitly forbids numeric-only
hostnames. They are technically valid, just *strongly* discouraged since
depending on the implementation they are interpreted as IPs rather than
hostnames. 0 or 1 or 234728934 for instance is a valid IPv4 after all
(ping accepts them as input for instance).

Since we're debian-based I figured I'd add it to the validation since
it's very much relevant for our use-case here. I have nothing against
changing the name though to DebianHostname.

>> +///
>> +/// 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.)

The idea was that, since hostnames are treated case-insensitively by
basically every application, it would make no sense to create two
*different* hostnames, that would be the same in practice. It's
something we could maybe move to a (Partial)Eq implementation and remove
the lowercasing here?

> 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')

I see your point, but I decided to stick to what the installer allows
for hostnames, which is ASCII-only characters without doing any punycode
conversion (correct me if I'm wrong there, but I don't remember this
being the case).

>> +    }
>> +}
>> +
>> +#[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