stride3d/stride · error · NotSupportedException

Operation 'SetPosition' is not supported

Error message

Operation 'SetPosition' is not supported

What it means

LZ4Stream is a sequential (non-seekable) compression stream, so assigning its Position property is not a meaningful operation and throws NotSupportedException with operation name 'SetPosition'. Seeking backwards would require decompressing from the start; the stream simply does not support it.

Solutions

  1. Do not assign Position on LZ4Stream; restructure the code to read strictly forward
  2. If rewind is needed, close and recreate the LZ4Stream over a fresh copy of the underlying stream
  3. Check stream.CanSeek before seeking and take a non-seekable code path

Example fix

// before
lz4Stream.Position = 0;
// after
if (lz4Stream.CanSeek) lz4Stream.Position = 0; else lz4Stream = new LZ4Stream(new MemoryStream(rawData), mode);
Defensive patterns

Strategy: type-guard

Validate before calling

if (!stream.CanSeek) throw new InvalidOperationException("Position assignment requires a seekable stream; this LZ4 stream is sequential");

Type guard

static bool SupportsPositionSet(Stream s) => s.CanSeek;

Try / catch

try { lz4Stream.Position = 0; }
catch (NotSupportedException) { // non-seekable: recreate stream instead
  lz4Stream.Dispose(); lz4Stream = new LZ4Stream(new MemoryStream(rawData), CompressionMode.Decompress); }

Prevention

When it happens

Trigger: Assigning to stream.Position on an LZ4Stream, e.g. `lz4Stream.Position = 0;`, or any API internally that sets Position to rewind the stream.

Common situations: Copying code that works on FileStream/MemoryStream (where Position assignment rewinds) onto an LZ4-wrapped stream; deserialization code that tries to seek back to re-read a header.

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 stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/61a539b11237f5b9. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Serialization/Serialization/LZ4/LZ4Stream.cs:347

    }

    /// <inheritdoc/>
    public override void Flush()
    {
        if (bufferOffset > 0 && CanWrite) FlushCurrentChunk();
    }

    /// <inheritdoc/>
    public override long Length
    {
        get { return length; }
    }

    /// <inheritdoc/>
    public override long Position
    {
        get { return position; }
        set { throw NotSupported("SetPosition"); }
    }

    /// <inheritdoc/>
    public override int ReadByte()
    {
        if (!CanRead) throw NotSupported("Read");

        if (bufferOffset >= bufferLength && !AcquireNextChunk())
            return -1; // that's just end of stream

        position++;

        return dataBuffer[bufferOffset++];
    }

    /// <inheritdoc/>
    public override unsafe int Read(byte[] buffer, int offset, int count)
    {

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