trace directive does not set traceparent header by default

[Jiehong]

Hello,

I'm trying to use the trace directive, but it's doing less than it should.

Eg:

:8081 {
  handle /hello {
  tracing {
    span app
  }
  respond 200 "hi"
  }
}

Looking at the spec for open telemetry traceparent header: https://www.w3.org/TR/trace-context/#traceparent-header

I'd expect:

• generate a new traceparent if not present in the incoming request (it does!)
• use the incoming traceparent header and create a new span id (it does!)
• the traceparent header is returned in the http response (it does not)

So, using caddy as the front gateway, I do no receive a traceparent, but it does not send a traceparent header to backends behind.

The workaround is to write that header myself for each handler, hard-coding the flag:

:8081 {
  handle /hello {
  tracing {
    span app
  }
  header traceparent 00-{http.vars.trace_id}-{http.vars.span_id}-01
  respond 200 "hi"
  }
}

I'd expect tracing to automatically set the traceparent header in the header (to have it in the response, or to have it in the request sent via reverse_proxy)

[Jiehong]

Also, it seems that tracing does not always respect json logging.

Eg:

2025/07/21 14:15:41.311 INFO    traces export: context deadline exceeded: rpc error: code = Unavailable desc = connection error: desc = "transport: Error while dialing: dial tcp [::1]:4317: connect: connection refused"