A header you
can take apart.
Fifty-five characters, four fields, and a rule for each. Type one, break one, or send it on a hop — every answer on this page comes from the library, compiled to JavaScript and running in this tab.
- Fields
- four, separated by dashes
- Ids
- 16 and 8 octets, lowercase hex
- Answers
- from
parse,start,inject
Edit it, or start from one of these:
Reading…
What the next hop sends.
The same trace id, a new span id. One header is replaced, the other travels as it arrived.
Press “send it to the next hop”.
Three steps, in this order.
A hop reads, joins and writes. The page above calls the same three functions a server does; nothing in the browser reimplements them.
Read
parse accepts the header or refuses it with the offset
and the shape it wanted. A hop that only wants to get on with the
request calls extract, which starts a new trace instead
of failing.
fn read(header : StringView) -> @trace.TraceContext raise {
@propagate.parse(header)
}Join
The new span takes the trace id and the vendor state from the parent. Its own span id is minted, and the sampler is asked once, with the parent in hand.
fn join(
tracer : @trace.Tracer,
parent : @trace.TraceContext,
now : () -> Int64,
) -> @trace.Span raise {
tracer.start(
"GET /orders/42",
parent=parent,
kind=@trace.Server,
at=now(),
)
}Write
inject replaces the two propagation headers on the
outgoing request, so the sender's context cannot survive beside the
one this hop decided on.
fn write(
request_headers : Array[(String, String)],
span : @trace.Span,
) -> Array[(String, String)] {
@propagate.inject(request_headers, {
context: Some(span.context()),
baggage: @propagate.empty_baggage,
})
}