egametang/ET · error · Exception

from bson error: {type.FullName} {stream.Position} {stream.L

Error message

from bson error: {type.FullName} {stream.Position} {stream.Length}

What it means

Thrown by MongoHelper.Deserialize(Type, Stream) (line 153) wrapping BsonSerializer.Deserialize(stream, type). Fails when the stream does not contain a complete/valid BSON document for the type, the stream position is wrong, or the type is unregistered. Inner exception IS preserved.

Source

Thrown at Packages/cn.etetet.core/Scripts/Core/Share/Serialize/MongoHelper.cs:153

                using MemoryStream memoryStream = new(bytes, index, count);
                
                return BsonSerializer.Deserialize(memoryStream, type);
            }
            catch (Exception e)
            {
                throw new Exception($"from bson error: {type.FullName} {bytes.Length} {index} {count}", e);
            }
        }

        public static object Deserialize(Type type, Stream stream)
        {
            try
            {
                return BsonSerializer.Deserialize(stream, type);
            }
            catch (Exception e)
            {
                throw new Exception($"from bson error: {type.FullName} {stream.Position} {stream.Length}", e);
            }
        }

        public static T Deserialize<T>(byte[] bytes)
        {
            try
            {
                using MemoryStream memoryStream = new(bytes);
                
                return (T)BsonSerializer.Deserialize(memoryStream, typeof (T));
            }
            catch (Exception e)
            {
                throw new Exception($"from bson error: {typeof (T).FullName} {bytes.Length}", e);
            }
        }

        public static T Deserialize<T>(byte[] bytes, int index, int count)

View on GitHub (pinned to 5cab01f7a8)

Solutions

Ensure stream.Position points at the document start and the stream contains at least one full document.
Buffer/await until the full document length (from its 4-byte prefix) is available.
Check the inner exception; register the type's serializer if missing.
Prefer the byte[] overload when you already have buffered bytes.

Defensive patterns

Strategy: validation

Validate before calling

if (type == null) throw new ArgumentNullException(nameof(type));
if (stream == null || !stream.CanRead) throw new ArgumentException("stream not readable", nameof(stream));
if (stream.Position >= stream.Length) throw new EndOfStreamException("stream empty at position");

Try / catch

try { return MongoHelper.Deserialize(type, stream); }
catch (Exception e) { Log.Error($"Deserialize({type}) stream pos={stream.Position} len={stream.Length} failed: {e}"); throw; }

Prevention

Do not deserialize from a stream until the whole document is buffered.
Reset stream.Position to the document start before each call.
Register the target type's serializer.

When it happens

Trigger: Stream position not at the start of a document, stream shorter than one BSON document, type mismatch, or a non-readable stream.

Common situations: Deserializing from a NetworkStream before the full document arrived, reusing a stream without rewinding, Mongo cursor reads, decompressed-buffer reads with wrong position.

Related errors

AI-assisted analysis of egametang/ET@5cab01f7a8 (2026-08-13). Data as JSON: /api/errors/eae39f389b7a0759. Report an issue: GitHub.