From 1232f3b7a583484cd8eda4874cfcdee0c724fa75 Mon Sep 17 00:00:00 2001
From: Peter Dettman <peter.dettman@bouncycastle.org>
Date: Fri, 24 May 2024 22:21:22 +0700
Subject: Add helper methods for optional tagged fields

---
 crypto/src/asn1/Asn1Utilities.cs | 52 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

(limited to 'crypto/src')

diff --git a/crypto/src/asn1/Asn1Utilities.cs b/crypto/src/asn1/Asn1Utilities.cs
index eacbf499a..ea61ab01a 100644
--- a/crypto/src/asn1/Asn1Utilities.cs
+++ b/crypto/src/asn1/Asn1Utilities.cs
@@ -649,5 +649,57 @@ namespace Org.BouncyCastle.Asn1
         {
             return TryParseExplicitBaseObject(taggedObjectParser, Asn1Tags.ContextSpecific, tagNo, out baseObject);
         }
+
+        #region Sequence cursor
+
+        public static TResult ReadOptionalContextTagged<TState, TResult>(Asn1Sequence sequence, ref int sequencePosition,
+            int tagNo, TState state, Func<Asn1TaggedObject, TState, TResult> constructor)
+            where TResult : class
+        {
+            return ReadOptionalTagged(sequence, ref sequencePosition, Asn1Tags.ContextSpecific, tagNo, state,
+                constructor);
+        }
+
+        public static TResult ReadOptionalTagged<TState, TResult>(Asn1Sequence sequence, ref int sequencePosition, int tagClass,
+            int tagNo, TState state, Func<Asn1TaggedObject, TState, TResult> constructor)
+            where TResult : class
+        {
+            if (sequencePosition < sequence.Count &&
+                sequence[sequencePosition] is Asn1TaggedObject taggedObject &&
+                taggedObject.HasTag(tagClass, tagNo))
+            {
+                sequencePosition++;
+                return constructor(taggedObject, state);
+            }
+
+            return null;
+        }
+
+        public static bool TryReadOptionalContextTagged<TState, TResult>(Asn1Sequence sequence,
+            ref int sequencePosition, int tagNo, TState state, out TResult result,
+            Func<Asn1TaggedObject, TState, TResult> constructor)
+        {
+            return TryReadOptionalTagged(sequence, ref sequencePosition, Asn1Tags.ContextSpecific, tagNo,
+                state, out result, constructor);
+        }
+
+        public static bool TryReadOptionalTagged<TState, TResult>(Asn1Sequence sequence, ref int sequencePosition,
+            int tagClass, int tagNo, TState state, out TResult result,
+            Func<Asn1TaggedObject, TState, TResult> constructor)
+        {
+            if (sequencePosition < sequence.Count &&
+                sequence[sequencePosition] is Asn1TaggedObject taggedObject &&
+                taggedObject.HasTag(tagClass, tagNo))
+            {
+                sequencePosition++;
+                result = constructor(taggedObject, state);
+                return true;
+            }
+
+            result = default;
+            return false;
+        }
+
+        #endregion
     }
 }
-- 
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