1 files changed, 55 insertions, 61 deletions

diff --git a/crypto/src/asn1/cms/MetaData.cs b/crypto/src/asn1/cms/MetaData.cs
index a0d783d59..5754fd6f1 100644
--- a/crypto/src/asn1/cms/MetaData.cs
+++ b/crypto/src/asn1/cms/MetaData.cs
@@ -19,46 +19,59 @@ namespace Org.BouncyCastle.Asn1.Cms
             return new MetaData(Asn1Sequence.GetInstance(taggedObject, declaredExplicit));
         }
 
-        private DerBoolean hashProtected;
-		private DerUtf8String fileName;
-		private DerIA5String  mediaType;
-		private Attributes otherMetaData;
-
-		public MetaData(
-			DerBoolean		hashProtected,
-			DerUtf8String	fileName,
-			DerIA5String	mediaType,
-			Attributes		otherMetaData)
-		{
-			this.hashProtected = hashProtected;
-			this.fileName = fileName;
-			this.mediaType = mediaType;
-			this.otherMetaData = otherMetaData;
-		}
+        public static MetaData GetOptional(Asn1Encodable element)
+        {
+            if (element == null)
+                throw new ArgumentNullException(nameof(element));
 
-		private MetaData(Asn1Sequence seq)
-		{
-			this.hashProtected = DerBoolean.GetInstance(seq[0]);
-
-			int index = 1;
-
-			if (index < seq.Count && seq[index] is DerUtf8String utf8)
-			{
-				this.fileName = utf8;
-				++index;
-			}
-			if (index < seq.Count && seq[index] is DerIA5String ia5)
-			{
-				this.mediaType = ia5;
-                ++index;
-            }
-            if (index < seq.Count)
-			{
-				this.otherMetaData = Attributes.GetInstance(seq[index++]);
-			}
-		}
+            if (element is MetaData metaData)
+                return metaData;
+
+            Asn1Sequence asn1Sequence = Asn1Sequence.GetOptional(element);
+            if (asn1Sequence != null)
+                return new MetaData(asn1Sequence);
+
+            return null;
+        }
+
+        private readonly DerBoolean m_hashProtected;
+        private readonly DerUtf8String m_fileName;
+        private readonly DerIA5String m_mediaType;
+        private readonly Attributes m_otherMetaData;
+
+        public MetaData(DerBoolean hashProtected, DerUtf8String fileName, DerIA5String mediaType,
+            Attributes otherMetaData)
+        {
+            m_hashProtected = hashProtected ?? throw new ArgumentNullException(nameof(hashProtected));
+            m_fileName = fileName;
+            m_mediaType = mediaType;
+            m_otherMetaData = otherMetaData;
+        }
+
+        private MetaData(Asn1Sequence seq)
+        {
+            int count = seq.Count, pos = 0;
+            if (count < 1 || count > 4)
+                throw new ArgumentException("Bad sequence size: " + count, nameof(seq));
+
+            m_hashProtected = DerBoolean.GetInstance(seq[pos++]);
+            m_fileName = Asn1Utilities.ReadOptional(seq, ref pos, DerUtf8String.GetOptional);
+            m_mediaType = Asn1Utilities.ReadOptional(seq, ref pos, DerIA5String.GetOptional);
+            m_otherMetaData = Asn1Utilities.ReadOptional(seq, ref pos, Attributes.GetOptional);
+
+            if (pos != count)
+                throw new ArgumentException("Unexpected elements in sequence", nameof(seq));
+        }
 
-		/**
+        public virtual bool IsHashProtected => m_hashProtected.IsTrue;
+
+        public virtual DerUtf8String FileName => m_fileName;
+
+        public virtual DerIA5String MediaType => m_mediaType;
+
+        public virtual Attributes OtherMetaData => m_otherMetaData;
+
+        /**
 		 * <pre>
 		 * MetaData ::= SEQUENCE {
 		 *   hashProtected        BOOLEAN,
@@ -69,31 +82,12 @@ namespace Org.BouncyCastle.Asn1.Cms
 		 * </pre>
 		 * @return
 		 */
-		public override Asn1Object ToAsn1Object()
+        public override Asn1Object ToAsn1Object()
 		{
-			Asn1EncodableVector v = new Asn1EncodableVector(hashProtected);
-			v.AddOptional(fileName, mediaType, otherMetaData);
+            Asn1EncodableVector v = new Asn1EncodableVector(4);
+            v.Add(m_hashProtected);
+			v.AddOptional(m_fileName, m_mediaType, m_otherMetaData);
 			return new DerSequence(v);
 		}
-
-		public virtual bool IsHashProtected
-		{
-			get { return hashProtected.IsTrue; }
-		}
-
-		public virtual DerUtf8String FileName
-		{
-			get { return fileName; }
-		}
-
-		public virtual DerIA5String MediaType
-		{
-			get { return mediaType; }
-		}
-
-		public virtual Attributes OtherMetaData
-		{
-			get { return otherMetaData; }
-		}
 	}
 }