feat(llm): propagate trace context to HTTP requests

packages/llm/src/route/transport/http.ts

@@ -131,31 +131,32 @@ export const httpJson = <Body, Frame>(input: HttpJsonInput<Body, Frame>): HttpJs
   frames: (prepared, request, runtime) =>
     LLMHttpTelemetry.stream(
       prepared.request,
-      Stream.unwrap(
-        runtime.http.execute(prepared.request).pipe(
-          Effect.map((response) =>
-            Stream.unwrap(
-              Effect.gen(function* () {
-                const received = yield* LLMHttpTelemetry.ResponseReceived
-                if (received) yield* received(response.status)
-                const firstChunk = yield* LLMHttpTelemetry.ResponseChunkReceived
-                return prepared.framing.frame(
-                  response.stream.pipe(
-                    Stream.tap(() => firstChunk ?? Effect.void),
-                    Stream.mapError((error) =>
-                      ProviderShared.eventError(
-                        `${request.model.provider}/${request.model.route.id}`,
-                        `Failed to read ${request.model.provider}/${request.model.route.id} stream`,
-                        ProviderShared.errorText(error),
+      (providerRequest) =>
+        Stream.unwrap(
+          runtime.http.execute(providerRequest).pipe(
+            Effect.map((response) =>
+              Stream.unwrap(
+                Effect.gen(function* () {
+                  const received = yield* LLMHttpTelemetry.ResponseReceived
+                  if (received) yield* received(response.status)
+                  const firstChunk = yield* LLMHttpTelemetry.ResponseChunkReceived
+                  return prepared.framing.frame(
+                    response.stream.pipe(
+                      Stream.tap(() => firstChunk ?? Effect.void),
+                      Stream.mapError((error) =>
+                        ProviderShared.eventError(
+                          `${request.model.provider}/${request.model.route.id}`,
+                          `Failed to read ${request.model.provider}/${request.model.route.id} stream`,
+                          ProviderShared.errorText(error),
+                        ),
                       ),
                     ),
-                  ),
-                )
-              }),
+                  )
+                }),
+              ),
             ),
           ),
         ),
-      ),
     ),
 })
 

packages/llm/src/telemetry/http.ts

@@ -2,7 +2,7 @@ export * as LLMHttpTelemetry from "./http"
 
 import { Cause, Clock, Context, Effect, Exit, Option, References, Stream } from "effect"
 import { ParentSpan, type Span } from "effect/Tracer"
-import { HttpClient, HttpClientRequest } from "effect/unstable/http"
+import { HttpClient, HttpClientRequest, HttpTraceContext } from "effect/unstable/http"
 import {
   ATTR_ERROR_TYPE,
   ATTR_HTTP_REQUEST_METHOD,
@@ -40,11 +40,14 @@ const observe = <A, E, R>(effect: Effect.Effect<A, E, R>) =>
     () => Effect.void,
   )
 
-export const stream = <A, R>(request: HttpClientRequest.HttpClientRequest, source: Stream.Stream<A, LLMError, R>) =>
+export const stream = <A, R>(
+  request: HttpClientRequest.HttpClientRequest,
+  source: (request: HttpClientRequest.HttpClientRequest) => Stream.Stream<A, LLMError, R>,
+) =>
   Stream.unwrap(
     Effect.gen(function* () {
       const parent = yield* CurrentModelSpan
-      if (!parent) return source
+      if (!parent) return source(request)
       const url = URL.canParse(request.url) ? new URL(request.url) : undefined
       const port = url?.port
         ? Number(url.port)
@@ -71,12 +74,16 @@ export const stream = <A, R>(request: HttpClientRequest.HttpClientRequest, sourc
       })
       const state: State = { responseReceived: false }
       yield* Effect.addFinalizer((exit) => observe(finalize(span, state, exit)))
-      return observeStream(span, state, source)
+      return observeStream(
+        span,
+        state,
+        source(HttpClientRequest.setHeaders(request, HttpTraceContext.toHeaders(span))),
+      )
     }).pipe(
       Effect.withTracerEnabled(true),
       Effect.catchCauseIf(
         (cause) => !Cause.hasInterrupts(cause),
-        () => Effect.succeed(source),
+        () => Effect.succeed(source(request)),
       ),
     ),
   )

packages/llm/test/telemetry.test.ts

@@ -184,7 +184,8 @@ describe("GenAI telemetry", () => {
           ? span.status.endTime >= http.status.endTime
           : false,
       ).toBeTrue()
-      expect(traceparent).toBeUndefined()
+      expect(traceparent?.split("-")[1]).toBe(http?.traceId)
+      expect(traceparent?.split("-")[2]).toBe(http?.spanId)
     }),
   )
 
@@ -303,7 +304,7 @@ describe("GenAI telemetry", () => {
       yield* Effect.useSpan("ambient", () =>
         Effect.all(
           [
-            LLMHttpTelemetry.stream(HttpClientRequest.post("https://example.test/path"), Stream.empty).pipe(
+            LLMHttpTelemetry.stream(HttpClientRequest.post("https://example.test/path"), () => Stream.empty).pipe(
               Stream.runDrain,
             ),
             LLMWebSocketTelemetry.stream("wss://example.test/path", Stream.empty).pipe(Stream.runDrain),
@@ -524,7 +525,7 @@ describe("GenAI telemetry", () => {
     }),
   )
 
-  it.live("does not mutate provider request headers", () =>
+  it.live("propagates the transport span to provider requests", () =>
     Effect.acquireUseRelease(
       Effect.sync(() => {
         const received: { traceparent?: string; b3?: string } = {}
@@ -564,9 +565,10 @@ describe("GenAI telemetry", () => {
           )
 
           const http = spans.find((span) => span.attributes.get(ATTR_HTTP_REQUEST_METHOD) === "POST")
-          expect(http).toBeDefined()
-          expect(received.traceparent).toBeUndefined()
-          expect(received.b3).toBeUndefined()
+          const traceparent = received.traceparent?.split("-")
+          expect(traceparent?.[1]).toBe(http?.traceId)
+          expect(traceparent?.[2]).toBe(http?.spanId)
+          expect(received.b3).toStartWith(`${http?.traceId}-${http?.spanId}-`)
         }),
       ({ server }) => Effect.promise(() => server.stop(true)),
     ),