feat: Add type LocalName

Author: bitfl0wer

src/constraints/types/local_name.rs

@@ -0,0 +1,21 @@
+use regex::Regex;
+
+use crate::types::local_name::{LocalName, REGEX_LOCAL_NAME};
+
+impl super::Constrained for LocalName {
+    fn validate(
+        &self,
+        _target: Option<crate::certs::Target>,
+    ) -> Result<(), crate::errors::ConstraintError> {
+        #[allow(clippy::expect_used)]
+        let regex = Regex::new(REGEX_LOCAL_NAME).expect("This Regex must never be invalid.");
+        if regex.is_match(&self.0) {
+            Ok(())
+        } else {
+            Err(super::ConstraintError::Malformed(Some(format!(
+                "{} is not of allowed regex {REGEX_LOCAL_NAME}",
+                self.0
+            ))))
+        }
+    }
+}

src/constraints/types/mod.rs

@@ -3,6 +3,7 @@
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 mod federation_id;
+mod local_name;
 mod rawr;
 mod service;
 

src/types/local_name.rs

@@ -0,0 +1,34 @@
+use std::str::FromStr;
+
+use crate::Constrained;
+use crate::errors::ConstraintError;
+
+/// Rust-flavor regular expression describing valid format for the local name of a Federation ID.
+pub const REGEX_LOCAL_NAME: &str = r#"\b([a-z0-9._%+-]+)$"#;
+
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(::serde::Serialize))]
+/// A polyproto "Local Name"[(1)](https://polyproto.org/docs/protocols/core/#5-federation-ids-fids)[(2)](https://polyproto.org/docs/protocols/core/#6111-polyproto-distinguished-name-pdn)
+/// is the instance-unique actor handle before the `@` in a [FederationId](crate::types::FederationId).
+///
+/// ## Example
+///
+/// In a `FederationId` of `[email protected]`, the local name would be `xenia`.
+pub struct LocalName(pub(crate) String);
+
+impl LocalName {
+    /// Creates [Self], ensuring that `name` is a valid, acceptable `LocalName`.
+    pub fn new(name: &str) -> Result<Self, ConstraintError> {
+        let local_name = LocalName(name.to_owned());
+        local_name.validate(None)?;
+        Ok(local_name)
+    }
+}
+
+impl FromStr for LocalName {
+    type Err = ConstraintError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        LocalName::new(s)
+    }
+}

src/types/mod.rs

@@ -12,6 +12,8 @@ pub mod encrypted_pkm;
 /// Module defining the [FederationId] type.
 #[cfg(feature = "types")]
 pub mod federation_id;
+/// Module defining the [LocalName] type.
+pub mod local_name;
 /// Module defining the [PolyprotoDistinguishedName] type.
 pub mod pdn;