nostr: add RelayUrl::domain method

Adds a method to retrieve the domain from a `RelayUrl` when applicable.

Pull-Request: #914
Signed-off-by: Yuki Kishimoto <[email protected]>

Author: yukibtc

CHANGELOG.md

@@ -43,6 +43,7 @@
 
 - nostr: add NIP-88 support ([Yuki Kishimoto] at https://github.com/rust-nostr/nostr/pull/892)
 - nostr: add `Nip11GetOptions` ([Yuki Kishimoto] at https://github.com/rust-nostr/nostr/pull/913)
+- nostr: add `RelayUrl::domain` method ([Yuki Kishimoto] at https://github.com/rust-nostr/nostr/pull/914)
 
 ### Fixed
 

crates/nostr/src/types/url.rs

@@ -146,6 +146,26 @@ impl RelayUrl {
             .is_some_and(|host| host.ends_with(".onion"))
     }
 
+    /// If this URL has a host, and it is a domain name (not an IP address), return it.
+    /// Non-ASCII domains are punycode-encoded per IDNA if this is the host
+    /// of a special URL, or percent encoded for non-special URLs.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use nostr::types::url::{Error, RelayUrl};
+    ///
+    /// let url = RelayUrl::parse("wss://127.0.0.1:7777").unwrap();
+    /// assert_eq!(url.domain(), None);
+    ///
+    /// let url = RelayUrl::parse("wss://relay.example.com").unwrap();
+    /// assert_eq!(url.domain(), Some("relay.example.com"));
+    /// ```
+    #[inline]
+    pub fn domain(&self) -> Option<&str> {
+        self.url.domain()
+    }
+
     /// Return the serialization of this relay URL without the trailing slash.
     ///
     /// This method will always remove the trailing slash.
@@ -387,4 +407,19 @@ mod tests {
         let non_onion_url = RelayUrl::parse("ws://127.0.0.1:7777").unwrap();
         assert!(!non_onion_url.is_onion());
     }
+
+    #[test]
+    fn test_domain() {
+        let url = RelayUrl::parse("wss://example.com").unwrap();
+        assert_eq!(url.domain(), Some("example.com"));
+
+        let url = RelayUrl::parse("wss://relay.example.com/").unwrap();
+        assert_eq!(url.domain(), Some("relay.example.com"));
+
+        let url = RelayUrl::parse("wss://example.com/path/to/resource").unwrap();
+        assert_eq!(url.domain(), Some("example.com"));
+
+        let url = RelayUrl::parse("wss://127.0.0.1:7777").unwrap();
+        assert_eq!(url.domain(), None);
+    }
 }