feat(dagcid): disallow libp2p-key CIDs in DagCid

src/DagCid.cs

@@ -1,4 +1,5 @@
-using Newtonsoft.Json;
+using System;
+using Newtonsoft.Json;
 
 namespace Ipfs
 {
@@ -10,11 +11,32 @@ namespace Ipfs
     /// </remarks>
     public record DagCid
     {
+        private Cid _value = null!;
+
         /// <summary>
         /// The <see cref="Cid"/> value of this DAG link.
         /// </summary>
+        /// <exception cref="ArgumentException">
+        /// Thrown when attempting to set a CID with ContentType "libp2p-key", 
+        /// as IPLD links must be immutable and libp2p-key CIDs represent mutable IPNS addresses.
+        /// </exception>
         [JsonProperty("/")]
-        public required Cid Value { get; set; }
+        public required Cid Value 
+        { 
+            get => _value;
+            set
+            {
+                if (value.ContentType == "libp2p-key")
+                {
+                    throw new ArgumentException(
+                        "Cannot store CID-encoded libp2p key as DagCid link. " +
+                        "IPLD links must be immutable, but libp2p-key CIDs represent mutable IPNS addresses. " +
+                        "Use the resolved content CID instead.",
+                        nameof(value));
+                }
+                _value = value;
+            }
+        }
 
         /// <summary>
         /// Implicit casting of a <see cref="DagCid"/> to a <see cref="Cid"/>.
@@ -25,8 +47,23 @@ public record DagCid
         /// <summary>
         /// Explicit casting of a <see cref="Cid"/> to a <see cref="DagCid"/>.
         /// </summary>
-        /// <param name="cid">The <see cref="Cid"/> to cast.</param>"
-        public static explicit operator DagCid(Cid cid) => new DagCid { Value = cid, };
+        /// <param name="cid">The <see cref="Cid"/> to cast.</param>
+        /// <exception cref="ArgumentException">
+        /// Thrown when attempting to cast a CID with ContentType "libp2p-key", 
+        /// as IPLD links must be immutable and libp2p-key CIDs represent mutable IPNS addresses.
+        /// </exception>
+        public static explicit operator DagCid(Cid cid) 
+        {
+            if (cid.ContentType == "libp2p-key")
+            {
+                throw new ArgumentException(
+                    "Cannot cast CID-encoded libp2p key to DagCid. " +
+                    "IPLD links must be immutable, but libp2p-key CIDs represent mutable IPNS addresses. " +
+                    "Use the resolved content CID instead.",
+                    nameof(cid));
+            }
+            return new DagCid { Value = cid, };
+        }
 
         /// <summary>
         /// Returns the string representation of the <see cref="DagCid"/>.

test/DagCidTest.cs

@@ -0,0 +1,112 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+
+namespace Ipfs
+{
+    [TestClass]
+    public class DagCidTest
+    {
+        [TestMethod]
+        public void Value_ValidCid_SetsSuccessfully()
+        {
+            // Arrange
+            Cid validCid = "QmXg9Pp2ytZ14xgmQjYEiHjVjMFXzCVVEcRTWJBmLgR39V";
+
+            // Act & Assert
+            var dagCid = new DagCid { Value = validCid };
+            Assert.AreEqual(validCid, dagCid.Value);
+        }
+
+        [TestMethod]
+        public void Value_LibP2pKeyCid_ThrowsArgumentException()
+        {
+            // Arrange - using real IPNS key CID that should have libp2p-key content type
+            Cid libp2pKeyCid = "k51qzi5uqu5dlvj2baxnqndepeb86cbk3ng7n3i46uzyxzyqj2xjonzllnv0v8";
+
+            // Verify this CID actually has libp2p-key content type
+            Assert.AreEqual("libp2p-key", libp2pKeyCid.ContentType);
+
+            // Act & Assert
+            var exception = Assert.ThrowsException<ArgumentException>(() => 
+                new DagCid { Value = libp2pKeyCid });
+
+            Assert.IsTrue(exception.Message.Contains("Cannot store CID-encoded libp2p key as DagCid link"));
+            Assert.IsTrue(exception.Message.Contains("IPLD links must be immutable"));
+            Assert.AreEqual("value", exception.ParamName);
+        }
+
+        [TestMethod]
+        public void Value_LibP2pKeyCid_SetAfterConstruction_ThrowsArgumentException()
+        {
+            // Arrange
+            Cid validCid = "QmXg9Pp2ytZ14xgmQjYEiHjVjMFXzCVVEcRTWJBmLgR39V";
+            // Using another real IPNS key CID
+            Cid libp2pKeyCid = "k51qzi5uqu5dlvj2baxnqndepeb86cbk3ng7n3i46uzyxzyqj2xjonzllnv0v8";
+
+            var dagCid = new DagCid { Value = validCid };
+
+            // Act & Assert
+            var exception = Assert.ThrowsException<ArgumentException>(() => 
+                dagCid.Value = libp2pKeyCid);
+
+            Assert.IsTrue(exception.Message.Contains("Cannot store CID-encoded libp2p key as DagCid link"));
+            Assert.AreEqual("value", exception.ParamName);
+        }
+
+        [TestMethod]
+        public void ExplicitCast_ValidCid_CastsSuccessfully()
+        {
+            // Arrange
+            Cid validCid = "QmXg9Pp2ytZ14xgmQjYEiHjVjMFXzCVVEcRTWJBmLgR39V";
+
+            // Act
+            var dagCid = (DagCid)validCid;
+
+            // Assert
+            Assert.AreEqual(validCid, dagCid.Value);
+        }
+
+        [TestMethod]
+        public void ExplicitCast_LibP2pKeyCid_ThrowsArgumentException()
+        {
+            // Arrange - using real IPNS key CID that should have libp2p-key content type
+            Cid libp2pKeyCid = "k51qzi5uqu5dlvj2baxnqndepeb86cbk3ng7n3i46uzyxzyqj2xjonzllnv0v8";
+
+            // Act & Assert
+            var exception = Assert.ThrowsException<ArgumentException>(() => 
+                (DagCid)libp2pKeyCid);
+
+            Assert.IsTrue(exception.Message.Contains("Cannot cast CID-encoded libp2p key to DagCid"));
+            Assert.IsTrue(exception.Message.Contains("IPLD links must be immutable"));
+            Assert.AreEqual("cid", exception.ParamName);
+        }
+
+        [TestMethod]
+        public void ImplicitCast_DagCidToCid_WorksCorrectly()
+        {
+            // Arrange
+            Cid originalCid = "QmXg9Pp2ytZ14xgmQjYEiHjVjMFXzCVVEcRTWJBmLgR39V";
+            var dagCid = new DagCid { Value = originalCid };
+
+            // Act
+            Cid convertedCid = dagCid;
+
+            // Assert
+            Assert.AreEqual(originalCid, convertedCid);
+        }
+
+        [TestMethod]
+        public void ToString_ReturnsValueToString()
+        {
+            // Arrange
+            Cid cid = "QmXg9Pp2ytZ14xgmQjYEiHjVjMFXzCVVEcRTWJBmLgR39V";
+            var dagCid = new DagCid { Value = cid };
+
+            // Act
+            var result = dagCid.ToString();
+
+            // Assert
+            Assert.AreEqual(cid.ToString(), result);
+        }
+    }
+}