Preserve otel event-derived errors when raw events are dropped

Author: sorenbs

README.md

@@ -204,6 +204,11 @@ It means:
   default rollups
 - the canonical routing key is `traceId`
 
+See [docs/profile-otel-traces.md](./docs/profile-otel-traces.md) for the
+profile and OTLP receiver contract, and
+[docs/request-observability.md](./docs/request-observability.md) for
+cross-stream lookup over `evlog` events and `otel-traces` spans.
+
 ## Profile Versus Schema
 
 What belongs in a profile:

src/profiles/otelTraces/normalize.ts

@@ -558,6 +558,7 @@ export function normalizeOtelDecodedSpanResult(
   const endTimestamp = isoFromUnixNano(endUnixNano);
 
   const normalizedEvents: CanonicalOtelSpan["events"] = [];
+  const eventDerivationInput: DecodedOtelEvent[] = [];
   let droppedEvents = Math.max(0, Math.trunc(input.droppedEventsCount ?? 0));
   const eventNames: string[] = [];
   for (const event of input.events) {
@@ -574,6 +575,12 @@ export function normalizeOtelDecodedSpanResult(
     });
     const eventName = normalizeString(event.name) ?? "";
     eventNames.push(eventName);
+    eventDerivationInput.push({
+      timeUnixNano: normalizeNanoString(event.timeUnixNano),
+      name: eventName,
+      attributes: eventAttrs.attributes,
+      droppedAttributesCount: eventAttrs.dropped,
+    });
     normalizedEvents.push({
       timestamp: isoFromUnixNano(normalizeNanoString(event.timeUnixNano)),
       timeUnixNano: normalizeNanoString(event.timeUnixNano),
@@ -622,7 +629,7 @@ export function normalizeOtelDecodedSpanResult(
   const spanAttrs = attrsRes.attributes;
   const service = getString(resourceAttrs, "service.name");
   const statusCode = normalizeStatusCode(input.status?.code);
-  const exception = extractExceptionFromEvents(normalizedEvents);
+  const exception = extractExceptionFromEvents(eventDerivationInput);
   const attrErrorType = getString(spanAttrs, "exception.type", "error.type");
   const attrErrorMessage = getString(spanAttrs, "exception.message", "error.message");
   const attrErrorStack = getString(spanAttrs, "exception.stacktrace", "error.stacktrace");

test/profile_otel_traces.test.ts

@@ -371,7 +371,7 @@ describe("otel-traces profile", () => {
             kind: "server",
             startUnixNano: "1772020800000000000",
             endUnixNano: "1772020800123000000",
-            status: { code: "error", message: "failed" },
+            status: { code: "error" },
             resource: {
               attributes: {
                 "service.name": "checkout",
@@ -528,6 +528,7 @@ describe("otel-traces profile", () => {
                 timeUnixNano: "1772020800100000000",
                 name: "exception",
                 attributes: {
+                  "exception.type": "Error",
                   "exception.message": "checkout failed",
                 },
               },
@@ -548,7 +549,7 @@ describe("otel-traces profile", () => {
         environment: "prod",
         requestId: "req_preserve_1",
         http: { method: "GET", route: "/checkout", statusCode: 500 },
-        error: { isError: true, message: "failed" },
+        error: { isError: true, type: "Error", message: "checkout failed" },
         eventNames: ["exception"],
       });
 
@@ -568,7 +569,7 @@ describe("otel-traces profile", () => {
         environment: "prod",
         requestId: "req_preserve_1",
         http: { method: "GET", route: "/checkout", statusCode: 500 },
-        error: { isError: true, message: "failed" },
+        error: { isError: true, type: "Error", message: "checkout failed" },
         eventNames: ["exception"],
       });
     } finally {