From 0e74c9ec6147fdc48b0066d23b4f56d64593164a Mon Sep 17 00:00:00 2001
From: Nathaniel McCallum <nathaniel@profian.com>
Date: Sun, 20 Feb 2022 14:56:02 -0500
Subject: [PATCH] Add AlgorithmIdentifier::oids() helper function

Signed-off-by: Nathaniel McCallum <nathaniel@profian.com>
---
 spki/src/algorithm.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/spki/src/algorithm.rs b/spki/src/algorithm.rs
index b138e5075..146fe6420 100644
--- a/spki/src/algorithm.rs
+++ b/spki/src/algorithm.rs
@@ -74,6 +74,26 @@ impl<'a> AlgorithmIdentifier<'a> {
     pub fn parameters_oid(&self) -> Result<ObjectIdentifier> {
         Ok(ObjectIdentifier::try_from(self.parameters_any()?)?)
     }
+
+    /// Convert to a pair of [`ObjectIdentifier`]s.
+    ///
+    /// This method is helpful for decomposing in match statements. Note in
+    /// particular that `NULL` parameters are treated the same as missing
+    /// parameters.
+    ///
+    /// Returns an error if parameters are present but not an OID.
+    pub fn oids(&self) -> der::Result<(ObjectIdentifier, Option<ObjectIdentifier>)> {
+        Ok((
+            self.oid,
+            match self.parameters {
+                None => None,
+                Some(p) => match p {
+                    Any::NULL => None,
+                    _ => Some(p.oid()?),
+                },
+            },
+        ))
+    }
 }
 
 impl<'a> Decodable<'a> for AlgorithmIdentifier<'a> {