Add replace or push functionality

rcgen/src/lib.rs

@@ -349,6 +349,30 @@ impl DistinguishedName {
 		self.entries.push_front((ty, s.into()));
 	}
 
+	/// Replaces the *fist occurrence* of a type with a new value.
+	/// This is a convenience function to avoid duplicating values.
+	///
+	/// If there are multiple occurrences of a type there is currently no way of changing the besides iterating over the types and values of an existing instance and creating a new instance.
+	///
+	/// ```
+	/// # use rcgen::{DistinguishedName, DnType, DnValue};
+	/// let mut dn = DistinguishedName::new();
+	/// dn.push(DnType::CommonName, DnValue::PrintableString("Master Cert".try_into().unwrap()));
+	/// assert_eq!(dn.get(&DnType::CommonName).get(0), Some(&DnValue::PrintableString("Master Cert".try_into().unwrap())).as_ref());
+	/// dn.push(DnType::CommonName, DnValue::PrintableString("Other Master Cert".try_into().unwrap()));
+	/// assert_eq!(dn.get(&DnType::CommonName).get(0), Some(&DnValue::PrintableString("Other Master Cert".try_into().unwrap())).as_ref());
+	/// ```
+	pub fn replace_or_push(&mut self, ty: DnType, s: impl Into<DnValue>) {
+		for (dn_type, dn_value) in self.entries.iter_mut() {
+			if *dn_type == ty {
+				*dn_value = s.into();
+				return;
+			}
+		}
+
+		self.push(ty, s)
+	}
+
 	#[cfg(feature = "x509-parser")]
 	fn from_name(name: &x509_parser::x509::X509Name) -> Result<Self, Error> {
 		use x509_parser::der_parser::asn1_rs::Tag;