Introduce Credentials struct.

src/proto/server/credentials.rs

@@ -0,0 +1,55 @@
+//! Defines the `Credentials` struct, for use when logging in to a server.
+
+/// Credentials for logging in a client to a server.
+#[derive(Debug, Eq, PartialEq)]
+pub struct Credentials {
+  user_name: String,
+  password: String,
+}
+
+impl Credentials {
+  /// Attempts to build credentials.
+  ///
+  /// Returns `None` if `password` is empty, `Some(credentials)` otherwise.
+  pub fn new(user_name: String, password: String) -> Option<Credentials> {
+    if password.is_empty() {
+      return None;
+    }
+
+    Some(Credentials {
+      user_name,
+      password,
+    })
+  }
+
+  /// The user name to log in as.
+  pub fn user_name(&self) -> &str {
+    &self.user_name
+  }
+
+  /// The password to log in with.
+  pub fn password(&self) -> &str {
+    &self.password
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use super::Credentials;
+
+  #[test]
+  fn empty_password() {
+    assert_eq!(Credentials::new("alice".to_string(), String::new()), None);
+  }
+
+  #[test]
+  fn new_success() {
+    let user_name = "alice".to_string();
+    let password = "sekrit".to_string();
+
+    let credentials = Credentials::new(user_name, password).unwrap();
+
+    assert_eq!(credentials.user_name(), "alice");
+    assert_eq!(credentials.password(), "sekrit");
+  }
+}

src/proto/server/mod.rs

@@ -1,9 +1,11 @@
 mod client;
 mod constants;
+mod credentials;
 mod request;
 mod response;
 #[cfg(test)]
 mod testing;
 
+pub use self::credentials::Credentials;
 pub use self::request::*;
 pub use self::response::*;