ChromeTrace

Category: Observability

Source: chrome_trace.dart

Functions

`String spansToChromeTrace(

Iterable<Map<String, dynamic>> spans, { required String sessionId, String processName = 'glue', String? version, })`

Converts a stream of serialized span maps — the JSONL shape produced by ObservabilitySpan.toMap (and written by FileSink) — into a JSON string in Chrome Trace Event Format, which Firefox Profiler imports natively via src/profile-logic/import/chrome.ts.

Mapping rules:

• Each completed span -> one X (Complete) event with ts and dur in microseconds since epoch. Spans missing end_time are dropped (they were in-flight when the log was sampled and have no duration).
• Spans sharing a trace_id share a tid. Firefox Profiler renders overlapping intervals on the same tid as visually nested, which matches parent/child span semantics. Each new trace_id gets the next integer tid in first-seen order.
• Per-span events[] entries -> i (Instant) events on the same tid, scoped to the thread (s: "t").
• Span kind -> Chrome cat. Categories drive marker colors in the UI.
• M metadata events name the process and each thread (after the trace's root span — the one with no parent_span_id within the trace, falling back to the earliest-started span).
• Spans with status_code == "error" get args.data.glue.status = "error" so the UI tooltip surfaces failures without polluting marker names.

The output uses the envelope form {"traceEvents": [...], "displayTimeUnit": "ms", "otherData": {...}} rather than a bare array, so [sessionId] and [version] show up in the profiler's "Profile Info" panel.

List<Map<String, dynamic>> parseSpansJsonl(String jsonl)

Reads a list of newline-delimited JSON span records from [jsonl] — the shape produced by FileSink and stored in $GLUE_HOME/logs/spans-*.jsonl. Malformed or empty lines are silently skipped, matching how SessionStore.loadConversation reads its sibling JSONL file.