spf: allow for underscores in domain names when including

Use the more relaxed form of Name parsing so that domains
with underscores (which are in common use with email) do
not generate an error at runtime when processing spf
include rules.

crates/kumo-spf/src/lib.rs

@@ -177,7 +177,7 @@ impl<'a> SpfContext<'a> {
     }
 
     pub async fn check(&self, resolver: &dyn Resolver, initial: bool) -> SpfResult {
-        let name = match Name::from_utf8(self.domain) {
+        let name = match Name::from_str_relaxed(self.domain) {
             Ok(name) => name,
             Err(_) => {
                 // Per <https://www.rfc-editor.org/rfc/rfc7208#section-4.3>, invalid

crates/kumo-spf/src/record.rs

@@ -4,7 +4,6 @@ use dns_resolver::Resolver;
 use hickory_resolver::Name;
 use std::fmt;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
-use std::str::FromStr;
 
 #[derive(Debug, Default)]
 pub(crate) struct Record {
@@ -229,7 +228,7 @@ impl Directive {
             }
             .matches(cx.client_ip, IpAddr::V6(*ip6_network)),
             Mechanism::Ptr { domain } => {
-                let domain = match Name::from_str(&cx.domain(domain.as_ref())?) {
+                let domain = match Name::from_str_relaxed(&cx.domain(domain.as_ref())?) {
                     Ok(domain) => domain,
                     Err(err) => {
                         return Err(SpfResult {

crates/kumo-spf/src/tests.rs

@@ -124,6 +124,30 @@ async fn mx() {
     );
 }
 
+#[tokio::test]
+async fn underscores() {
+    let resolver = TestResolver::default()
+        .with_zone(EXAMPLE_COM)
+        .with_txt(
+            "under_score.com",
+            "v=spf1 ip4:192.0.2.128/28 -all".to_string(),
+        )
+        .with_txt(
+            "example.com",
+            "v=spf1 include:under_score.com -all".to_string(),
+        );
+
+    let result = evaluate_ip(Ipv4Addr::from([192, 0, 2, 65]), &resolver).await;
+    k9::assert_equal!(
+        &result,
+        &SpfResult {
+            disposition: SpfDisposition::Fail,
+            context: "matched '-all' directive".to_owned(),
+        },
+        "{result:?}"
+    );
+}
+
 /// https://www.rfc-editor.org/rfc/rfc7208#appendix-A.1
 #[tokio::test]
 async fn ip4() {