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next

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The React Framework

nextjs.org

vercel/next.js

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import type { TraceContextHeaders } from '../lib/trace/tracer'; /** * The trace context of the span that the middleware span and the downstream * request (the render) share as their parent, given the middleware's active * context (before the middleware span starts). * * When the active context is the one the request carries (an incoming * `traceparent`, or the one next-server's middleware-invoke pass wrote onto * the request), the received `traceparent` / `tracestate` are returned * verbatim, so the middleware never changes them. Otherwise (an active host * span, or a root span inserted by the middleware adapter) the active * context is returned. */ export declare function getSharedParentTraceContext(requestHeaders: Headers, activeTraceContext: TraceContextHeaders | undefined): TraceContextHeaders | undefined; /** * Makes sure the downstream request of a middleware response that continues * the request (`NextResponse.next()` or a rewrite) carries the trace context * of the middleware span's parent, so the render is a sibling of the * middleware span in the same trace. It is passed as `traceparent` / * `tracestate` request-header overrides, which every host applies to the * downstream request: hosts that invoke middleware separately from the render * (deployments, adapters, direct entrypoints) as well as next-server's router * server. * * `traceparent` and `tracestate` are forwarded as a pair: the downstream * request never carries one trace context's `traceparent` with another's * `tracestate`. Request-header overrides replace the whole downstream request * header set, so: * - Without user overrides (or with an empty list, which hosts ignore): * nothing is added when the request already carries that trace context. * Otherwise every request header the middleware received is listed * (unchanged) alongside the trace context, except a received `tracestate` * when the trace context has none. * - With user overrides, they are kept and the trace context headers are * added. A `traceparent` the user explicitly set (to a value other than the * one the middleware received) wins, together with whatever `tracestate` * the user set (if any). Otherwise (`traceparent` copied unchanged from the * request, e.g. via `new Headers(request.headers)`, or omitted) both are set * to the trace context, dropping a user `tracestate` when it has none. */ export declare function forwardTraceContextToRequest(responseHeaders: Headers, requestHeaders: Headers, traceContext: TraceContextHeaders | undefined): void;