[WIP] Implementation of a Node.js Backend Service for Handling Transparent Span Transmission #242
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Coding agent has begun work on Implementation of a Node.js Backend Service for Handling Transparent Span Transmission and will replace this description as work progresses.
See problem context
The following is a snapshot of a chat conversation between a user and an AI coding assistant. Prioritize later messages in the conversation.
User: @workspace /explain 现在的设计能不能实现 Langfuese Observation 被解析为 ReadableSpan然后被透明传输到后端的设计？
AI: 当前结构无法直接把 Langfuse 的 Observation 视作
AI: 并交给
AI: 。Exporter 只会处理由
AI: 生成并送入
AI: 的 OpenTelemetry span，而
AI: 里通过
AI: 产生的是 Langfuse 自有对象，与 OTel span 管道隔离。
AI: 只是让 Langfuse 能共享同一个 Provider，并不会把 Observation 注入 OTel。若要“透明传输”，需要在回调里显式把每个 Observation 映射成 OTel span（或另写一个针对 Observation 的 exporter）后再交给 Provider 处理。
User: https://github.com/langfuse/langfuse-js/tree/main/packages/tracing/src
阅读这个仓库下的代码，然后给出解决方案
AI: 先梳理 Langfuse tracing 包和我们现有追踪初始化，再把两边打通：
packages/tracing/src关键实现做了梳理，确认 Observation -> OpenTelemetry Span 的映射路径。init-tracing.ts/TransparentBrowserExporter设计，提出如何复用同一个TracerProvider，让 Langfuse Observation 产出的ReadableSpan自动进入我们的透明传输链路。核心发现
startObservation等 API 最终都会调用getLangfuseTracer()→Tracer.startSpan()（见AI: 第 112 行起）。返回的
LangfuseSpan等对象只是对 OTelSpan的包装，内部持有otelSpan；结束时会直接调用otelSpan.end()。setLangfuseTracerProvider会把我们自定义的TracerProvider存进全局状态，后续getLangfuseTracer()就会从这里取（AI: 第 119 行起）。
BatchSpanProcessor+TransparentBrowserExporter的BasicTracerProvider传进去，Langfuse 生成的所有 Observation 都会作为普通ReadableSpan交给 exporter，无需再做二次转换。LangfuseSpanProcessor（来自@langfuse/otel），OTel 允许挂多个 Processor。推荐方案
初始化阶段共用 Provider
initTracing中我们已经构造了BasicTracerProvider并调用了setLangfuseTracerProvider(provider)——保留这一步即可。initTracing总是在调用createLangfuseCallback之前执行。这样 Langfuse callback 内部所有startObservation都会复用同一个 provider。Exporter 链路
BatchSpanProcessor→TransparentBrowserExporter会收到所有ReadableSpan，包括我们在业务里手工启动的 span、Langfuse Planner / Agent / Generation Observation。provider.addSpanProcessor(new LangfuseSpanProcessor({ … }))。它与我们的透明 exporter 互不干扰。可选：在 Transparent exporter 中识别 Langfuse 元数据
LangfuseOtelSpanAttributes枚举)。回调层的小改动（若需要同步 Langfuse 的 sessionId 到 span）
createLangfuseCallback已尝试从taskPrompt/context提取sessionId并写到root.updateTrace。startObservation前针对agentContext写一个小工具，为当前活动 span 调用span.setAttribute(LangfuseOtelSpanAttributes.TRACE_SESSION_ID, sessionId)。这属于可选增量。测试验证
packages/eko-core/example/nodejs_debug下运行一次 Task，观察我们的后端是否成功收到 Planner/Generation 等 span，或在浏览器端用navigator.sendBeacon调试TransparentBrowserExporterpayload。LangfuseSpanProcessor并确认它和透明 exporter 都能拿到同一批ReadableSpan。质量门
需求覆盖
User: 请检查当前的exporter实现，这个透明传输的设计是否合理，是否会漏掉属性？
AI: 先快速复盘
TransparentBrowserExporter的结构，再对照ReadableSpan的字段检查有没有被忽略的关键信息，最后给出改进建议。检查结果
traceId、spanId、name、kind、startTime、endTime、attributes、status、events、resource、instrumentationScope）都有覆盖，Langfuse 写入到 attributes 的内容会被完整保留。ReadableSpan里的以下信息：links：链路信息在链状工作流里很常用，丢掉后无法还原代理-工具之间的关联。droppedAttributesCount、droppedEventsCount、droppedLinksCount：会影响排障时对采样/丢弃行为的认知。duration（虽然可由 start/end 复算，但直接带上可省一步）。span.spanContext()里的traceFlags、traceState也没带，如果后端要继续分发或做抽样判定会有信息缺口。json.length计算字符数，遇上非 ASCII 或JSON.stringify的 Unicode 转义时会和真实字节数不一致，可能提前或延后触发限额。useSendBeacon控制项也清楚。建议
toTransportSpan里补上上述遗漏字段，例如：links: span.linksdroppedCounts三个字段duration或后端再算traceFlags: span.spanContext().traceFlags、traceState: span.spanContext().traceState?.serialize?.()new TextEncoder().encode(json).length计算；Node 环境可以回退到Buffer.byteLength(json, "utf8")。ReadableSpan的浅拷贝（去掉函数字段）或遵循 OTLP JSON 约定格式；这样能减少后续维护时同步字段的工作量。需求覆盖
User: 那就直接发送ReadableSpan的浅拷贝也行，或者用OTPL JSON。总之要保证后端能够很容易的解析成Langfuse对应的Observation。
AI:
AI:
User: [I] ~/Project/eko/packages/eko-core x> pnpm run build feat/eko-debugger *
src/index.ts → dist/index.cjs.js...
(!) "this" has been rewritten to "undefined"
https://rollupjs.org/troubleshooting/#error-this-is-undefined
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/metrics/NoopMeter.js
14: * limitations under the License.
15: */
16: var __extends = (this && this.__extends) || (function () {
^
17: var extendStatics = function (d, b) {
18: extendStatics = Object.setPrototypeOf ||
...and 1 other occurrence
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/api/diag.js
14: * limitations under the License.
15: */
16: var __read = (this && this.__read) || function (o, n) {
^
17: var m = typeof Symbol === "function" && o[Symbol.iterator];
18: if (!m) return o;
...and 3 other occurrences
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/api/context.js
14: * limitations under the License.
15: */
16: var __read = (this && this.__read) || function (o, n) {
^
17: var m = typeof Symbol === "function" && o[Symbol.iterator];
18: if (!m) return o;
...and 3 other occurrences
...and 3 other files
(!) Circular dependencies
../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/schemas.js -> ../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/iso.js -> ../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/schemas.js
../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/index.js -> ../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/aws_crc32.js -> ../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/index.js
src/agent/llm.ts -> src/memory/index.ts -> src/agent/llm.ts
(!) Mixing named and default exports
https://rollupjs.org/configuration-options/#output-exports
The following entry modules are using named and default exports together:
src/index.ts
Consumers of your bundle will have to use chunk.default to access their default export, which may not be what you want. Use
output.exports: "named"to disable this warning.created dist/index.cjs.js in 1.7s
src/index.ts → dist/index.esm.js...
(!) "this" has been rewritten to "undefined"
https://rollupjs.org/troubleshooting/#error-this-is-undefined
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/metrics/NoopMeter.js
14: * limitations under the License.
15: */
16: var __extends = (this && this.__extends) || (function () {
^
17: var extendStatics = function (d, b) {
18: extendStatics = Object.setPrototypeOf ||
...and 1 other occurrence
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/api/context.js
14: * limitations under the License.
15: */
16: var __read = (this && this.__read) || function (o, n) {
^
17: var m = typeof Symbol === "function" && o[Symbol.iterator];
18: if (!m) return o;
...and 3 other occurrences
../../node_modules/.pnpm/@opentelemetry[email protected]/node_modules/@opentelemetry/api/build/esm/api/diag.js
14: * limitations under the License.
15: */
16: var __read = (this && this.__read) || function (o, n) {
^
17: var m = typeof Symbol === "function" && o[Symbol.iterator];
18: if (!m) return o;
...and 3 other occurrences
...and 3 other files
(!) Circular dependencies
../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/schemas.js -> ../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/iso.js -> ../../node_modules/.pnpm/[email protected]/node_modules/zod/v4/classic/schemas.js
../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/index.js -> ../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/aws_crc32.js -> ../../node_modules/.pnpm/@[email protected]/node_modules/@aws-crypto/crc32/build/module/index.js
src/agent/llm.ts -> src/memory/index.ts -> src/agent/llm.ts
created dist/index.esm.js in 1.2s
[I] ~/Project/eko/packages/eko-core x> feat/eko-debugger *
这是构建结果
AI: 先把 exporter 改成按原始
AI: 结构序列化，确保后端能直接当作 Langfuse Observation 解析；主要动作：
TransparentBrowserExporter里补齐traceFlags/traceState、AI: 、
AI: 、
dropped*Count等字段，并把AI: 、父上下文都序列化。
getByteLength，浏览器用TextEncoder、Node 用Buffer.byteLength，保证批大小限制按真实字节计算。构建结果
pnpm --filter eko-core build✅（Rollup 只提示 opentelemetry 自带的"this" has been rewritten、循环依赖、mixed exports，这些是既有依赖的已知告警）。需求覆盖
AI: /OTLP JSON，让后端易于恢复 Langfuse Observation” → ✅ 已改写 exporter 并验证可以编译。
如还想进一步贴近 OTLP，可把
toTransportSpan改成产出标准 OTLP JSON 的ResourceSpans结构；后端若已有解析器，可以直接复用。User: 非常好，我现在要用Node来做一个后端服务来处理这些被透明传输来的Span了。
我的想法是这个API会先转成Span对象，然后构建对应的Observation，然后使用opentelemetry node sdk，配合langfuse otel 中的 LangfuseSpanProcesser来将透明传输到我这个API端点的内容传输的到Langfuse。
User: 非常好，我现在要用Node来做一个后端服务来处理这些被透明传输来的Span了。
我的想法是这个API会先转成Span对象，然后构建对应的Observation，然后使用opentelemetry node sdk，配合langfuse otel 中的 LangfuseSpanProcesser来将透明传输到我这个API端点的内容传输的到Langfuse。
你现在最好是找一个合适的文件夹来创建这个后端服务。
TITLE: Implementation of a Node.js Backend Service for Handling Transparent Span Transmission
USER INTENT: The user aims to create a Node.js backend service that processes spans transmitted transparently from the frontend, converting them into observations and sending them to Langfuse using the OpenTelemetry Node SDK.
TASK DESCRIPTION: The user wants to set up a backend service that:
EXISTING:
TransparentBrowserExporter.ReadableSpanstructures or OTLP JSON to the backend.PENDING:
CODE STATE:
RELEVANT CODE/DOCUMENTATION SNIPPETS:
LangfuseSpanProcessorfrom the Langfuse OpenTelemetry integration, which will be used in the backend service.ReadableSpanand its attributes, which will be relevant for processing spans in the backend.OTHER NOTES:
Original prompt
非常好，我现在要用Node来做一个后端服务来处理这些被透明传输来的Span了。
我的想法是这个API会先转成Span对象，然后构建对应的Observation，然后使用opentelemetry node sdk，配合langfuse otel 中的 LangfuseSpanProcesser来将透明传输到我这个API端点的内容传输的到Langfuse。
你现在最好是找一个合适的文件夹来创建这个后端服务。
The following is a snapshot of a chat conversation between a user and an AI coding assistant. Prioritize later messages in the conversation.
User: @workspace /explain 现在的设计能不能实现 Langfuese Observation 被解析为 ReadableSpan然后被透明传输到后端的设计？
AI: 当前结构无法直接把 Langfuse 的 Observation 视作
AI: 并交给
AI: 。Exporter 只会处理由
AI: 生成并送入
AI: 的 OpenTelemetry span，而
AI: 里通过
AI: 产生的是 Langfuse 自有对象，与 OTel span 管道隔离。
AI: 只是让 Langfuse 能共享同一个 Provider，并不会把 Observation 注入 OTel。若要“透明传输”，需要在回调里显式把每个 Observation 映射成 OTel span（或另写一个针对 Observation 的 exporter）后再交给 Provider 处理。
User: https://github.com/langfuse/langfuse-js/tree/main/packages/tracing/src
阅读这个仓库下的代码，然后给出解决方案
AI: 先梳理 Langfuse tracing 包和我们现有追踪初始化，再把两边打通：
packages/tracing/src关键实现做了梳理，确认 Observation -> OpenTelemetry Span 的映射路径。init-tracing.ts/TransparentBrowserExporter设计，提出如何复用同一个TracerProvider，让 Langfuse Observation 产出的ReadableSpan自动进入我们的透明传输链路。核心发现
startObservation等 API 最终都会调用getLangfuseTracer()→Tracer.startSpan()（见AI: 第 112 行起）。返回的
LangfuseSpan等对象只是对 OTelSpan的包装，内部持有otelSpan；结束时会直接调用otelSpan.end()。setLangfuseTracerProvider会把我们自定义的TracerProvider存进全局状态，后续getLangfuseTracer()就会从这里取（AI: 第 119 行起）。
BatchSpanProcessor+TransparentBrowserExporter的BasicTracerProvider传进去，Langfuse 生成的所有 Observation 都会作为普通ReadableSpan交给 exporter，无需再做二次转换。LangfuseSpanProcessor（来自@langfuse/otel），OTel 允许挂多个 Processor。推荐方案
初始化阶段共用 Provider
initTracing中我们已经构造了BasicTracerProvider并调用了setLangfuseTracerProvider(provider)——保留这一步即可。initTracing总是在调用createLangfuseCallback之前执行。这样 Langfuse callback 内部所有startObservation都会复用同一个 provider。Exporter 链路
BatchSpanProcessor→TransparentBrowserExporter会收到所有ReadableSpan，包括我们在业务里手工启动的 span、Langfuse Planner / Agent / Generation Observation。provider.addSpanProcessor(new LangfuseSpanProcessor({ … }))。它与我们的透明 exporter 互不干扰。可选：在 Transparent exporter 中识别 Langfuse 元数据
LangfuseOtelSpanAttributes枚举)。回调层的小改动（若需要同步 Langfuse 的 sessionId 到 span）
createLangfuseCallback已尝试从taskPrompt/context提取sessionId并写到root.updateTrace。startObservation前针对agentContext写一个小工具，为当前活动 span 调用span.setAttribute(LangfuseOtelSpanAttributes.TRACE_SESSION_ID, sessionId)。这属于可选增量。测试验证
packages/eko-core/example/nodejs_debug下运行一次 Task，观察我们的后端是否成功收到 Planner/Generation 等 span，或在浏览器端用navigator.sendBeacon调试TransparentBrowserExporterpayload。LangfuseSpanProcessor并确认它和透明 exporter 都能拿到同一批ReadableSpan。质量门
需求覆盖
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