Module trace 

W3C trace context, and the request identifier that travels beside it.

A request that arrives with a traceparent header is part of a trace somebody else started: a gateway, a client library, another service. Its trace id is kept so the lines this server logs – and, once spans are exported, the spans themselves – join that trace rather than starting an unrelated one. A request without one starts a trace of its own.

Hand-written rather than taken from the opentelemetry crates, which this side does not otherwise need: parsing traceparent is a fixed-width format of four fields, and the rules for refusing one are short enough to read here. See https://www.w3.org/TR/trace-context/.

Nothing here generates an identifier. That needs randomness, and where it comes from is a host’s business – the server has a thread to keep a generator on, a Cloudflare Worker has the JavaScript runtime’s. So this module only parses, validates and formats, and builds on wasm32 as it does everywhere else.

Structs

SpanId

A span id: eight bytes, never all zero. Here, the id of the caller’s span that this request is a child of.

TraceContext

The trace a request belongs to.

TraceId

A trace id: sixteen bytes, never all zero.

Constants

MAX_REQUEST_ID_LEN

The longest x-request-id taken from a client. Long enough for any identifier scheme in use – a UUID is 36, a ULID 26, a Heroku or Envoy id well under this – and short enough that the header cannot be used to make every log line carry a payload.

Functions

parse_traceparent

Parse a traceparent value: version-traceid-parentid-flags, as lowercase hex.

valid_request_id

Whether a client’s x-request-id can be used as given: between one and MAX_REQUEST_ID_LEN bytes, every one of them visible ASCII.