dotnet/wpf · error · FileFormatException

SR.XpsValidatingLoaderUnsupportedEncoding

Error message

SR.XpsValidatingLoaderUnsupportedEncoding

What it means

The XPS validating loader only accepts XML parts declared (or detected) as UTF-8 or UTF-16. During Read(), when the XML declaration carries an encoding attribute other than 'utf-8' or 'unicode' (UTF-16), a FileFormatException is thrown because XPS (OPC) mandates one of those two encodings for XML markup parts.

Solutions

1. Re-save the part's XML stream as UTF-8 (or UTF-16) so the XML declaration matches (e.g. XmlWriter with Encoding.UTF8).
2. Remove the bogus encoding attribute or fix it to encoding="utf-8" in the XML declaration.
3. Strip BOM/declaration mismatches: ensure the stream's actual byte encoding matches the declared encoding.
4. Regenerate the XPS document from the source application rather than editing markup by hand.

Example fix

// before
var settings = new XmlWriterSettings { Encoding = Encoding.GetEncoding("windows-1252") };
// after
var settings = new XmlWriterSettings { Encoding = new UTF8Encoding(false) };

using var sr = new StreamReader(part.GetStream());
string head = sr.ReadLine();
var m = System.Text.RegularExpressions.Regex.Match(head ?? "", "encoding=\"([^\"]+)\"");
if (m.Success && !m.Groups[1].Value.Equals("utf-8", StringComparison.OrdinalIgnoreCase) &&
    !m.Groups[1].Value.Equals("unicode", StringComparison.OrdinalIgnoreCase))
    throw new InvalidDataException($"Unsupported XPS part encoding: {m.Groups[1].Value}");

static bool IsSupportedXpsEncoding(XmlReader r) =>
    r.Encoding is UTF8Encoding || r.Encoding is UnicodeEncoding;

try { loader.Load(stream); }
catch (FileFormatException ex) when (ex.Message.Contains("encoding")) { /* re-encode part to UTF-8 and retry, or surface a clear message */ }

When it happens

Trigger: Calling code that opens an XPS/OPC package part whose XML starts with an XML declaration declaring e.g. encoding="utf-16le", "iso-8859-1", "windows-1252" or "us-ascii"; the XpsSchemaValidator's XmlEncodingEnforcingTextReader.Read() checks the declaration's encoding attribute on the first node read and throws.

Common situations: Non-WPF tools generating XPS markup with a default XML serializer encoding; hand-edited FixedPage .fpage files saved with a regional codepage; conversion pipelines that re-serialize XPS parts with XmlWriter configured for a non-UTF-8 encoding.

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

• " }} " element found. Expected fixed page element ( }} ).
• SR.EncodingNotSupported
• SR.InvalidDSContentType
• SR.InvalidSFContentType
• SR.InvalidStoryFragmentsMarkup

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/0cf3f295559f3b55. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/FixedSchema.cs:45

            {
            }

            public override bool Read()
            {
                bool result = base.Read();

                if (result && !_encodingChecked)
                {
                    if (base.NodeType == XmlNodeType.XmlDeclaration)
                    {
                        string encoding = base["encoding"];

                        if (encoding != null)
                        {
                            if (!encoding.Equals(Encoding.Unicode.WebName, StringComparison.OrdinalIgnoreCase) &&
                                        !encoding.Equals(Encoding.UTF8.WebName, StringComparison.OrdinalIgnoreCase))
                            {
                                throw new FileFormatException(SR.XpsValidatingLoaderUnsupportedEncoding);
                            }
                        }
                    }

                    if (!(base.Encoding is UTF8Encoding) && !(base.Encoding is UnicodeEncoding))
                    {
                        throw new FileFormatException(SR.XpsValidatingLoaderUnsupportedEncoding);
                    }

                    _encodingChecked = true;
                }

                return result;
            }

            private bool _encodingChecked;
        }

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