always lowercase the hostnames provided by the hostname helpers

The DHCP RFC doesn't require that the domain name option 15 be
lowercase, which can result in hostname that has uppercase letters. This
isn't a valid hostname and causes setting deserialization to fail.

Author: tzneal

sources/dogtag/bin/imds.rs

@@ -20,7 +20,10 @@ async fn main() -> Result<()> {
         .fetch_hostname()
         .await
         .context(error::ImdsSnafu)?
-        .context(error::NoHostnameSnafu)?;
+        .context(error::NoHostnameSnafu)?
+        // the IMDS client returns a lowercase hostname anyway, but there's some
+        // symmetry in having both helpers lowercase the result always
+        .to_ascii_lowercase();
     println!("{hostname}");
     Ok(())
 }

sources/dogtag/bin/reverse.rs

@@ -25,7 +25,8 @@ async fn main() -> Result<()> {
         .await
         .map_err(|e| error::Error::Lookup {
             source: Box::new(e),
-        })?;
+        })?
+        .to_ascii_lowercase();
     println!("{hostname}");
     Ok(())
 }

sources/imdsclient/src/lib.rs

@@ -242,8 +242,8 @@ impl ImdsClient {
         Ok(self.fetch_string(&hostname_target).await?.and_then(|h| {
             h.split_whitespace()
                 .next()
-                .map(|h| h.trim_end_matches('.'))
-                .map(String::from)
+                // trim any trailing dots and lowercase the result
+                .map(|h| h.trim_end_matches('.').to_ascii_lowercase())
         }))
     }
 
@@ -842,8 +842,9 @@ mod test {
         let base_uri = format!("http://{}", server.addr());
         let token = "some+token";
         let response_code = 200;
+        // should always lowercase the response
         let response_body =
-            r#"ip-10-0-13-37.example.com. ip-10-0-13-37.eu-central-1.compute.internal"#;
+            r#"ip-10-0-13-37.EXAMPLE.com. ip-10-0-13-37.eu-central-1.compute.internal"#;
         server.expect(
             Expectation::matching(request::method_path("PUT", "/latest/api/token"))
                 .times(1)