move validation to Domain ctor

src/authoritative_name_server.rs

@@ -1,4 +1,5 @@
-use std::{net::Ipv4Addr, process::Child};
+use std::net::Ipv4Addr;
+use std::process::Child;
 
 use crate::{container::Container, Domain, Result, CHMOD_RW_EVERYONE};
 
@@ -14,15 +15,12 @@ impl AuthoritativeNameServer {
         container.status_ok(&["mkdir", "-p", "/etc/nsd/zones"])?;
 
         let zone_path = "/etc/nsd/zones/main.zone";
-        container.cp(
-            "/etc/nsd/nsd.conf",
-            &nsd_conf(domain.fqdn()),
-            CHMOD_RW_EVERYONE,
-        )?;
+        container.cp("/etc/nsd/nsd.conf", &nsd_conf(domain), CHMOD_RW_EVERYONE)?;
 
-        let zone_file_contents = match domain {
-            Domain::Root => root_zone(),
-            Domain::Tld { domain } => tld_zone(domain),
+        let zone_file_contents = if domain.is_root() {
+            root_zone()
+        } else {
+            tld_zone(domain)
         };
 
         container.cp(zone_path, &zone_file_contents, CHMOD_RW_EVERYONE)?;
@@ -43,13 +41,12 @@ impl Drop for AuthoritativeNameServer {
     }
 }
 
-fn tld_zone(domain: &str) -> String {
-    assert!(domain.ends_with('.'));
-    assert!(!domain.starts_with('.'));
+fn tld_zone(domain: Domain) -> String {
+    assert!(!domain.is_root());
 
     minijinja::render!(
         include_str!("templates/tld.zone.jinja"),
-        tld => domain,
+        tld => domain.as_str()
     )
 }
 
@@ -57,12 +54,10 @@ fn root_zone() -> String {
     minijinja::render!(include_str!("templates/root.zone.jinja"),)
 }
 
-fn nsd_conf(domain: &str) -> String {
-    assert!(domain.ends_with('.'));
-
+fn nsd_conf(domain: Domain) -> String {
     minijinja::render!(
         include_str!("templates/nsd.conf.jinja"),
-        domain => domain
+        domain => domain.as_str()
     )
 }
 
@@ -72,7 +67,7 @@ mod tests {
 
     #[test]
     fn tld_setup() -> Result<()> {
-        let tld_ns = AuthoritativeNameServer::start(Domain::Tld { domain: "com." })?;
+        let tld_ns = AuthoritativeNameServer::start(Domain("com.")?)?;
         let ip_addr = tld_ns.ipv4_addr();
 
         let client = Container::run()?;
@@ -87,7 +82,7 @@ mod tests {
 
     #[test]
     fn root_setup() -> Result<()> {
-        let root_ns = AuthoritativeNameServer::start(Domain::Root)?;
+        let root_ns = AuthoritativeNameServer::start(Domain::ROOT)?;
         let ip_addr = root_ns.ipv4_addr();
 
         let client = Container::run()?;

src/domain.rs

@@ -0,0 +1,32 @@
+use crate::Result;
+
+#[derive(Clone, Copy)]
+pub struct Domain<'a> {
+    inner: &'a str,
+}
+
+// TODO likely needs further validation
+#[allow(non_snake_case)]
+pub fn Domain(input: &str) -> Result<Domain<'_>> {
+    if !input.ends_with('.') {
+        return Err("domain must end with a `.`".into());
+    }
+
+    if input != "." && input.starts_with('.') {
+        return Err("non-root domain cannot start with a `.`".into());
+    }
+
+    Ok(Domain { inner: input })
+}
+
+impl<'a> Domain<'a> {
+    pub const ROOT: Domain<'static> = Domain { inner: "." };
+
+    pub fn is_root(&self) -> bool {
+        self.inner == "."
+    }
+
+    pub fn as_str(&self) -> &'a str {
+        self.inner
+    }
+}

src/lib.rs

@@ -1,4 +1,5 @@
 pub use crate::authoritative_name_server::AuthoritativeNameServer;
+pub use crate::domain::Domain;
 pub use crate::recursive_resolver::RecursiveResolver;
 
 pub type Error = Box<dyn std::error::Error>;
@@ -8,18 +9,5 @@ const CHMOD_RW_EVERYONE: &str = "666";
 
 mod authoritative_name_server;
 pub mod container;
+mod domain;
 mod recursive_resolver;
-
-pub enum Domain<'a> {
-    Root,
-    Tld { domain: &'a str },
-}
-
-impl Domain<'_> {
-    fn fqdn(&self) -> &str {
-        match self {
-            Domain::Root => ".",
-            Domain::Tld { domain } => domain,
-        }
-    }
-}

src/recursive_resolver.rs

@@ -52,14 +52,14 @@ impl Drop for RecursiveResolver {
 
 #[cfg(test)]
 mod tests {
-    use crate::AuthoritativeNameServer;
+    use crate::{AuthoritativeNameServer, Domain};
 
     use super::*;
 
     #[test]
     #[ignore = "FIXME"]
     fn can_resolve() -> Result<()> {
-        let root_ns = AuthoritativeNameServer::start(crate::Domain::Root)?;
+        let root_ns = AuthoritativeNameServer::start(Domain::ROOT)?;
         let roots = &[RootServer {
             name: "my.root-server.com".to_string(),
             ip_addr: root_ns.ipv4_addr(),