stride3d/stride · error · ArgumentException

Expected STREAM-START.

Error message

Expected STREAM-START.

What it means

A new Emitter must receive a StreamStart event as the very first event; it initializes line/column/indent state from it. EmitStreamStart throws ArgumentException if the first event passed to Emit is anything other than StreamStart.

Solutions

1. Emit a StreamStart event first: emitter.Emit(new StreamStart());
2. Build the full event sequence StreamStart -> DocumentStart -> content -> DocumentEnd -> StreamEnd.
3. If using an EmittingEventQueue or serializer, ensure the serializer emits the stream envelope rather than suppressing it.

Example fix

// before
emitter.Emit(new DocumentStart()); // throws
// after
emitter.Emit(new StreamStart());
emitter.Emit(new DocumentStart());

if (!(events.FirstOrDefault() is StreamStart))
    emitter.Emit(new StreamStart()); // ensure stream envelope opens
foreach (var evt in events) emitter.Emit(evt);

bool StartsWithStreamStart(IEnumerable<ParsingEvent> events) => events.FirstOrDefault() is StreamStart;

try { emitter.Emit(evt); }
catch (ArgumentException ex) when (ex.Message == "Expected STREAM-START.") { /* restart with a fresh emitter and emit StreamStart first */ }

When it happens

Trigger: Emitting a DocumentStart, Scalar, or any other event to a fresh Emitter without first emitting StreamStart.

Common situations: Hand-rolling an emitter loop and skipping the stream start; reusing an emitter mid-way after an exception left it in a fresh state; constructing events manually and forgetting StreamStart.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Expected nothing after STREAM-END
• Expected DOCUMENT-START or STREAM-END
• An IObjectNode was expected when processing the path
• An IMemberNode was expected when processing the path
• Unable to load the given stream

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/46c345dcc944b767. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Emitter.cs:644

                    break;

                case EmitterState.YAML_EMIT_END_STATE:
                    throw new YamlException("Expected nothing after STREAM-END");

                default:
                    Debug.Assert(false, "Invalid state.");
                    throw new InvalidOperationException("Invalid state");
            }
        }

        /// <summary>
        /// Expect STREAM-START.
        /// </summary>
        private void EmitStreamStart(ParsingEvent evt)
        {
            if (!(evt is StreamStart))
            {
                throw new ArgumentException("Expected STREAM-START.", "evt");
            }

            indent = -1;
            line = 0;
            column = 0;
            isWhitespace = true;
            isIndentation = true;

            state = EmitterState.YAML_EMIT_FIRST_DOCUMENT_START_STATE;
        }

        /// <summary>
        /// Expect DOCUMENT-START or STREAM-END.
        /// </summary>
        private void EmitDocumentStart(ParsingEvent evt, bool isFirst)
        {
            DocumentStart documentStart = evt as DocumentStart;
            if (documentStart != null)

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