dotnet/wpf · error · ArgumentException

bogus GorillaEncodingType passed to Uncompress

Error message

bogus GorillaEncodingType passed to Uncompress

What it means

GorillaCodec.Uncompress switches on the GorillaEncodingType to set the bit mask and decode strategy; an unrecognized type reaches the default case and throws ArgumentException with this message. Like its Compress/GetDataFromReader counterparts, it defends the decompression path against encodings it does not implement.

Solutions

1. Validate the encoding type against known GorillaEncodingType members before calling Uncompress.
2. Default Unknown encodings to a concrete supported member if the data format allows (e.g. re-encode as OneByte).
3. Treat payloads with unsupported encodings as corrupt ISF: catch ArgumentException and reject or re-acquire the ink data.
4. Verify the producer wrote a supported encoding; convert the data with a compatible library version if needed.

Example fix

// before
codec.Uncompress(encodingFromHeader, reader, count, out output);
// after
if (encodingFromHeader == GorillaEncodingType.Unknown)
    throw new InvalidDataException("ISF uses unsupported Gorilla encoding");
codec.Uncompress(encodingFromHeader, reader, count, out output);

if (encodingType == GorillaEncodingType.Unknown || !Enum.IsDefined(typeof(GorillaEncodingType), encodingType))
    throw new InvalidDataException("Unsupported Gorilla encoding in ISF payload");

bool IsDecodable(GorillaEncodingType t) => Enum.IsDefined(typeof(GorillaEncodingType), t) && t != GorillaEncodingType.Unknown;

try { codec.Uncompress(encodingType, reader, units, out output); }
catch (ArgumentException ex) when (ex.Message.Contains("Uncompress")) { /* treat ink data as corrupt; re-import or fail gracefully */ }

When it happens

Trigger: Calling Uncompress with an invalid GorillaEncodingType — usually a value read from ISF-encoded stroke data that is Unknown/0 or outside the supported set, or a raw int cast without validation.

Common situations: Decoding stroke packet data from another application or older ISF writer using an unsupported Gorilla encoding; custom decompression code caching an invalid enum; uninitialized encoding fields.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• bogus GorillaEncodingType passed to compress
• bogus GorillaEncodingType passed to GetDataFromReader
• Decompression of packet data failed.
• input or compressed data was null in Compress
• invalid huffman encoded data

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/e2a9a11c20f969ff. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/InkSerializedFormat/GorillaCodec.cs:623

                        bitsToWrite = Native.BitsPerShort;
                        //shorts are decoded as unsigned values, no mask required
                        bitMask = 0;
                        break;
                    }
                case GorillaEncodingType.Byte:
                    {
                        if (bitCount == 0)
                        {
                            bitCount = Native.BitsPerByte;
                        }
                        bitsToWrite = Native.BitsPerByte;
                        //bytes are decoded as unsigned values, no mask required
                        bitMask = 0;
                        break;
                    }
                default:
                    {
                        throw new ArgumentException(StrokeCollectionSerializer.ISFDebugMessage("bogus GorillaEncodingType passed to Uncompress"));
                    }
            }
            List<byte> output = new List<byte>((bitsToWrite / 8) * unitsToDecode);
            BitStreamWriter writer = new BitStreamWriter(output);
            uint bitData = 0;

            while (!reader.EndOfStream && unitsToDecode > 0)
            {
                //we're going to cast to an uint anyway, just read as one
                bitData = reader.ReadUInt32(bitCount);
                // Construct the item
                bitData = ((bitData & bitMask) != 0) ? bitMask | bitData : bitData;
                writer.WriteReverse(bitData, bitsToWrite);
                unitsToDecode--;
            }

            return output.ToArray();
        }

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