dotnet/wpf · error · FileFormatException

Feature name in the transform's primary stream is

Error message

Feature name in the transform's primary stream is '{0}', but expected '{1}'.

What it means

This FileFormatException is thrown when the FeatureIdentifier stored in a transform's primary stream does not match the expected DataSpaceVersionIdentifier. The transform metadata belongs to an unknown or different feature, so the library refuses to process it. Comparison is case-insensitive ordinal per the data-space spec.

Solutions

Open the package with the software version that wrote the transform (the identifier is product-specific).
Re-save the package from the original application so the expected feature identifier is written.
Inspect the transform's primary stream to confirm the mismatched identifier string.
Catch FileFormatException and report an unsupported/incompatible package format to the user.

Defensive patterns

Strategy: try-catch

Validate before calling

// Only accept packages produced by the expected writer/version:
if (!IsFromTrustedProducer(path)) throw new InvalidDataException("Package produced by an unsupported implementation.");

Type guard

bool UsesExpectedFeatureIdentifier(string featureId, string expectedId) => string.Equals(featureId, expectedId, StringComparison.OrdinalIgnoreCase);

Try / catch

try { package = Package.Open(path); }
catch (FileFormatException ex) when (ex.Message.Contains("Feature name")) { Console.Error.WriteLine($"Unsupported transform feature: {ex.Message}"); throw; }

Prevention

Open packages with the same product/version that wrote them.
Re-export packages to a supported format before cross-tool consumption.
Log the feature identifier from the exception for diagnostics.

When it happens

Trigger: Opening a package whose transform's primary stream ("/_metadata/DataSpaces/TransformInfo/...") records a FeatureIdentifier other than the expected DataSpace version identifier; raised in DataSpaceManager while reading the transform's file format version block.

Common situations: Packages written by other/older implementations using different transform feature identifiers, hand-edited or repackaged files where the identifier was changed, or reading a file that mixes transform formats.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/1a2979596210e6f9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/System/IO/Packaging/CompoundFile/DataSpaceManager.cs:1594

    /// If the format version information in the stream is corrupt.
    /// </exception>
    private void ReadDataSpaceVersionInformation(StorageInfo dataSpaceStorage)
    {
        if (_fileFormatVersion == null)
        {
            if (dataSpaceStorage.StreamExists( DataSpaceVersionName ))
            {
                StreamInfo versionStreamInfo = dataSpaceStorage.GetStreamInfo( DataSpaceVersionName );
                using (Stream versionStream = versionStreamInfo.GetStream(FileMode.Open))
                {
                    _fileFormatVersion = FormatVersion.LoadFromStream(versionStream);

                    // Transform Identifier: we preserve casing, but do case-insensitive comparison
                    //Case-insensitive comparison. As per recommendations, we convert both strings
                    //to Upper case and then compare with StringComparison.Ordinal
                    if (!string.Equals(_fileFormatVersion.FeatureIdentifier, DataSpaceVersionIdentifier, StringComparison.OrdinalIgnoreCase))
                    {
                        throw new FileFormatException(
                                            SR.Format(SR.InvalidTransformFeatureName,
                                            _fileFormatVersion.FeatureIdentifier,
                                            DataSpaceVersionIdentifier));
                    }
                    // If we ever write this version number out again, we will want to record
                    // the fact that it was done by the current version of the Dataspace software.
                    _fileFormatVersion.WriterVersion = DataSpaceCurrentWriterVersion;
                }
            }
        }
    }

    /// <summary>
    /// If the DataSpace version information was not present in the file, we initialize it with the
    /// values for the current DataSpace software.
    /// If the information was present we should have already read it as a part of the ReadDataSpaceMap.
    /// </summary>
    private void EnsureDataSpaceVersionInformation()

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