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Fix base64 deserialization when JSON encoder escapes forward slashes (#1342)

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
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Copilot 2026-02-23 14:20:25 -05:00 • committed by GitHub
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126
tests/ModelContextProtocol.Tests/Protocol/ResourceContentsTests.cs
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@ -1,4 +1,5 @@
using ModelContextProtocol.Protocol;
using System.Text;
using System.Text.Json;
namespace ModelContextProtocol.Tests.Protocol;
@ -489,4 +490,129 @@ public static class ResourceContentsTests
Assert.DoesNotContain("mimeType", json);
}
[Fact]
public static void BlobResourceContents_Deserialization_HandlesEscapedForwardSlashInBase64()
{
// Base64 uses '/' which some JSON encoders escape as '\/' (valid JSON).
// The converter must unescape before storing the base64 UTF-8 bytes.
byte[] originalBytes = [0xFF, 0xD8, 0xFF, 0xE0]; // sample bytes that produce '/' in base64
string base64 = Convert.ToBase64String(originalBytes); // "/9j/4A=="
Assert.Contains("/", base64);
// Simulate a JSON encoder that escapes '/' as '\/'
string json = $$"""{"uri":"file:///test.bin","blob":"{{base64.Replace("/", "\\/")}}","mimeType":"application/octet-stream"}""";
var deserialized = JsonSerializer.Deserialize<ResourceContents>(json, McpJsonUtilities.DefaultOptions);
var blob = Assert.IsType<BlobResourceContents>(deserialized);
Assert.Equal(base64, System.Text.Encoding.UTF8.GetString(blob.Blob.ToArray()));
Assert.Equal(originalBytes, blob.DecodedData.ToArray());
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_FromBytes_RoundtripsCorrectly(byte[] originalBytes)
{
string expectedBase64 = Convert.ToBase64String(originalBytes);
var blob = BlobResourceContents.FromBytes(originalBytes, "file:///test.bin", "application/octet-stream");
Assert.Equal("file:///test.bin", blob.Uri);
Assert.Equal("application/octet-stream", blob.MimeType);
Assert.Equal(originalBytes, blob.DecodedData.ToArray());
Assert.Equal(expectedBase64, Encoding.UTF8.GetString(blob.Blob.ToArray()));
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_BlobSetter_RoundtripsCorrectly(byte[] originalBytes)
{
string base64 = Convert.ToBase64String(originalBytes);
byte[] base64Utf8 = Encoding.UTF8.GetBytes(base64);
var blob = new BlobResourceContents { Blob = base64Utf8, Uri = "file:///test.bin" };
Assert.Equal(base64Utf8, blob.Blob.ToArray());
Assert.Equal(originalBytes, blob.DecodedData.ToArray());
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_JsonRoundtrip_PreservesData(byte[] originalBytes)
{
string base64 = Convert.ToBase64String(originalBytes);
byte[] base64Utf8 = Encoding.UTF8.GetBytes(base64);
var original = new BlobResourceContents
{
Blob = base64Utf8,
Uri = "file:///test.bin",
MimeType = "application/octet-stream"
};
string json = JsonSerializer.Serialize<ResourceContents>(original, McpJsonUtilities.DefaultOptions);
var deserialized = Assert.IsType<BlobResourceContents>(
JsonSerializer.Deserialize<ResourceContents>(json, McpJsonUtilities.DefaultOptions));
Assert.Equal(base64Utf8, deserialized.Blob.ToArray());
Assert.Equal(originalBytes, deserialized.DecodedData.ToArray());
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_FromBytes_JsonRoundtrip_PreservesData(byte[] originalBytes)
{
string expectedBase64 = Convert.ToBase64String(originalBytes);
var original = BlobResourceContents.FromBytes(originalBytes, "file:///test.bin", "application/octet-stream");
string json = JsonSerializer.Serialize<ResourceContents>(original, McpJsonUtilities.DefaultOptions);
var deserialized = Assert.IsType<BlobResourceContents>(
JsonSerializer.Deserialize<ResourceContents>(json, McpJsonUtilities.DefaultOptions));
Assert.Equal(expectedBase64, Encoding.UTF8.GetString(deserialized.Blob.ToArray()));
Assert.Equal(originalBytes, deserialized.DecodedData.ToArray());
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_EscapedJsonRoundtrip_PreservesData(byte[] originalBytes)
{
string base64 = Convert.ToBase64String(originalBytes);
string json = $$"""{"uri":"file:///test.bin","blob":"{{base64.Replace("/", "\\/")}}","mimeType":"application/octet-stream"}""";
var deserialized = Assert.IsType<BlobResourceContents>(
JsonSerializer.Deserialize<ResourceContents>(json, McpJsonUtilities.DefaultOptions));
Assert.Equal(base64, Encoding.UTF8.GetString(deserialized.Blob.ToArray()));
Assert.Equal(originalBytes, deserialized.DecodedData.ToArray());
}
[Fact]
public static void BlobResourceContents_BlobSetterInvalidatesCachedDecodedData()
{
byte[] bytes1 = [1, 2, 3];
var blob = BlobResourceContents.FromBytes(bytes1, "file:///test.bin");
Assert.Equal(bytes1, blob.DecodedData.ToArray());
byte[] newBytes = [4, 5, 6];
string newBase64 = Convert.ToBase64String(newBytes);
blob.Blob = Encoding.UTF8.GetBytes(newBase64);
Assert.Equal(newBytes, blob.DecodedData.ToArray());
}
[Theory]
[MemberData(nameof(ContentBlockTests.Base64TestData), MemberType = typeof(ContentBlockTests))]
public static void BlobResourceContents_FromBytes_LazilyEncodesBlob(byte[] originalBytes)
{
var blob = BlobResourceContents.FromBytes(originalBytes, "file:///test.bin");
// Access DecodedData first without touching Blob
Assert.Equal(originalBytes, blob.DecodedData.ToArray());
// Now access Blob and verify lazy encoding
string expectedBase64 = Convert.ToBase64String(originalBytes);
Assert.Equal(expectedBase64, Encoding.UTF8.GetString(blob.Blob.ToArray()));
}
}