dotnet/wpf · error · NotSupportedException

SR.WriteNotSupported

Error message

SR.WriteNotSupported

What it means

DeobfuscatingStream is a read-only stream that decrypts obfuscated XPS package content on read. Its Write override unconditionally throws NotSupportedException (SR.WriteNotSupported) after checking disposal — writes are simply not a supported operation on this stream.

Solutions

1. Write to an underlying writable FileStream and wrap it for obfuscation instead
2. Only read from DeobfuscatingStream; use CanWrite to branch before writing
3. Check stream.CanWrite before calling write APIs

Example fix

// before
dest = new DeobfuscatingStream(...);
dest.Write(data, 0, data.Length);
// after
using var dest = File.Create(path);
dest.Write(data, 0, data.Length);

if (!stream.CanWrite) throw/log instead of writing;

static bool IsWritable(Stream s) => s.CanWrite;

try { stream.Write(buf, 0, buf.Length); } catch (NotSupportedException) { /* write to underlying FileStream instead */ }

When it happens

Trigger: Calling Write (or a wrapper that writes, e.g. StreamWriter/CopyTo into it) on a DeobfuscatingStream instance.

Common situations: Passing the deobfuscating stream to APIs that both read and write (e.g. Stream.CopyTo in the wrong direction), or trying to modify an obfuscated XPS file in place.

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

• Stream does not support SetLength.
• SR.DocumentStreamMustBeFileSource
• SR.DocumentStreamMustBeTemporary
• SR.PackageControllerStreamCorruption
• SR.ReachSerialization_NotSupported

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/def39aea7bb62cb7. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/IO/Packaging/DeobfuscatingStream.cs:72

            // Read in the raw data from the underlying stream
            int bytesRead = _obfuscatedStream.Read(buffer, offset, count);

            // Apply de-obfuscatation as necessary
            Deobfuscate(buffer, offset, bytesRead, readPosition);

            return bytesRead;
        }

        /// <summary>
        /// Write
        /// </summary>
        /// <remarks>This is a read-only stream; throw now supported exception</remarks>
        public override void Write(byte[] buffer, int offset, int count)
        {
            CheckDisposed();

            throw new NotSupportedException(SR.WriteNotSupported);
        }

        /// <summary>
        /// Seek
        /// </summary>
        /// <param name="offset">offset</param>
        /// <param name="origin">origin</param>
        public override long Seek(long offset, SeekOrigin origin)
        {
            CheckDisposed();

            return _obfuscatedStream.Seek(offset, origin);
        }

        /// <summary>
        /// SetLength
        /// </summary>
        /// <remarks>This is a read-only stream; throw now supported exception</remarks>

View on GitHub (pinned to 81131a70a4)