Fetch: set the parent context of the fetch (#73)

* Fetch: set the parent context of the fetch * changeset
vercel · Mar 29, 2024 · 5019762 · 5019762
1 parent ca0db56
commit 5019762
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Showing 3 changed files with 42 additions and 6 deletions.
diff --git a/.changeset/afraid-dodos-marry.md b/.changeset/afraid-dodos-marry.md
@@ -0,0 +1,5 @@
+---
+"@vercel/otel": patch
+---
+
+(fix) Use the fetch's span context for propagation, not parent's.
diff --git a/packages/otel/src/instrumentations/fetch.ts b/packages/otel/src/instrumentations/fetch.ts
@@ -3,6 +3,7 @@ import {
   SpanStatusCode,
   propagation,
   context,
+  trace as traceApi,
 } from "@opentelemetry/api";
 import type {
   Attributes,
@@ -272,6 +273,8 @@ export class FetchInstrumentation implements Instrumentation {
       const spanName =
         init?.opentelemetry?.spanName ?? `fetch ${req.method} ${req.url}`;
 
+      const parentContext = context.active();
+
       const span = tracer.startSpan(
         spanName,
         {
@@ -283,15 +286,16 @@ export class FetchInstrumentation implements Instrumentation {
             ...init?.opentelemetry?.attributes,
           },
         },
-        context.active()
+        parentContext
       );
       if (!span.isRecording() || !isSampled(span.spanContext().traceFlags)) {
         span.end();
         return originalFetch(input, init);
       }
 
       if (shouldPropagate(url, init)) {
-        propagation.inject(context.active(), req.headers, HEADERS_SETTER);
+        const fetchContext = traceApi.setSpan(parentContext, span);
+        propagation.inject(fetchContext, req.headers, HEADERS_SETTER);
       }
 
       if (attributesFromRequestHeaders) {

diff --git a/tests/e2e/test/vercel-deployment/render-outbound.test.ts b/tests/e2e/test/vercel-deployment/render-outbound.test.ts
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { SpanKind, SpanStatusCode } from "@opentelemetry/api";
+import type { ITrace } from "collector";
 import { describe } from "../../lib/with-bridge";
 import { expectTrace } from "../../lib/expect-trace";
 
@@ -59,13 +60,26 @@ describe("vercel deployment: outbound", {}, (props) => {
       ],
     });
 
+    let fetchSpan: ITrace["spans"][0] | undefined;
+    collector.getAllTraces().forEach((trace) => {
+      trace.spans.forEach((span) => {
+        if (span.name === `fetch POST http://localhost:${bridge.port}/`) {
+          fetchSpan = span;
+        }
+      });
+    });
+    expect(fetchSpan).toBeDefined();
+    if (!fetchSpan) {
+      throw new Error("already asserted");
+    }
+
     const fetches = bridge.fetches;
     expect(fetches).toHaveLength(1);
 
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     const fetch = fetches[0]!;
-    expect(fetch.headers.get("traceparent")).toMatch(
-      /00-[0-9a-fA-F]{32}-[0-9a-fA-F]{16}-01/
+    expect(fetch.headers.get("traceparent")).toEqual(
+      `00-${fetchSpan.traceId}-${fetchSpan.spanId}-01`
     );
   });
 
@@ -124,13 +138,26 @@ describe("vercel deployment: outbound", {}, (props) => {
       ],
     });
 
+    let fetchSpan: ITrace["spans"][0] | undefined;
+    collector.getAllTraces().forEach((trace) => {
+      trace.spans.forEach((span) => {
+        if (span.name === `fetch POST http://localhost:${bridge.port}/`) {
+          fetchSpan = span;
+        }
+      });
+    });
+    expect(fetchSpan).toBeDefined();
+    if (!fetchSpan) {
+      throw new Error("already asserted");
+    }
+
     const fetches = bridge.fetches;
     expect(fetches).toHaveLength(1);
 
     // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
     const fetch = fetches[0]!;
-    expect(fetch.headers.get("traceparent")).toMatch(
-      /00-[0-9a-fA-F]{32}-[0-9a-fA-F]{16}-01/
+    expect(fetch.headers.get("traceparent")).toEqual(
+      `00-${fetchSpan.traceId}-${fetchSpan.spanId}-01`
     );
   });