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otel P3: auto-instrument handlers at the make-app seam

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otel/instrument-routes wraps each flattened Dream route's handler in a timed
span named METHOD /route with {:http.method :http.route :http.status} attrs;
host/make-app applies it so every matched request becomes a trace. Refactored
with-span onto a shared otel/-timed core that takes a finalize fn for
result-derived attrs (the http.status only known post-handler).
This commit is contained in:
giles
2026-07-01 14:37:49 +00:00
parent e521909b21
commit c2def0ea16
3 changed files with 92 additions and 8 deletions
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46
lib/host/tests/otel.sx
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@@ -80,6 +80,52 @@
(host-ot-test "timed span t1 >= t0" (>= (get host-ot-timed :t1) (get host-ot-timed :t0)) true)
(host-ot-test "timed span t0 nanosecond-scale" (> (get host-ot-timed :t0) 1000000000000000) true)
;; ── P3: auto-instrument handlers — a request becomes a trace ────────
;; otel/instrument-routes wraps each route's handler so dispatching a request
;; records a root span named "METHOD /route" with http.method/route/status attrs.
(otel/reset!)
(define host-ot-routes
(list
(dream-get "/feed" (fn (req) (dream-response 200 {} "ok")))
(dream-post "/feed" (fn (req) (dream-response 201 {} "made")))))
(define host-ot-iapp (dream-router (otel/instrument-routes host-ot-routes)))
(host-ot-iapp (dream-request "GET" "/feed" {} ""))
(host-ot-test "one span for one request" (len (otel/recent)) 1)
(define host-ot-is (first (otel/recent)))
(host-ot-test "span name is method+route" (get host-ot-is :name) "GET /feed")
(host-ot-test "http.method attr" (get (get host-ot-is :attrs) :http.method) "GET")
(host-ot-test "http.route attr" (get (get host-ot-is :attrs) :http.route) "/feed")
(host-ot-test "http.status attr" (get (get host-ot-is :attrs) :http.status) 200)
(host-ot-test "request span is a root (no parent)" (get host-ot-is :parent) nil)
(host-ot-test "request span has a trace id" (not (= (get host-ot-is :trace) nil)) true)
;; a second request → its own span + trace, status from its response
(host-ot-iapp (dream-request "POST" "/feed" {} "x"))
(host-ot-test "two requests two spans" (len (otel/recent)) 2)
(define host-ot-is2 (last (otel/recent)))
(host-ot-test "post span name" (get host-ot-is2 :name) "POST /feed")
(host-ot-test "post status attr" (get (get host-ot-is2 :attrs) :http.status) 201)
(host-ot-test "distinct trace per request"
(not (= (get host-ot-is :trace) (get host-ot-is2 :trace))) true)
;; bare-string handler results still get a status (coerced to 200)
(otel/reset!)
(define host-ot-sapp
(dream-router (otel/instrument-routes
(list (dream-get "/plain" (fn (req) "hello"))))))
(host-ot-sapp (dream-request "GET" "/plain" {} ""))
(host-ot-test "string handler status coerced to 200"
(get (get (first (otel/recent)) :attrs) :http.status) 200)
;; ── P3 integration: make-app traces every request ──────────────────
(otel/reset!)
(feed/reset!)
(define host-ot-happ (host/make-app (list host/feed-routes)))
(host-ot-happ (dream-request "GET" "/health" {} ""))
(define host-ot-hs (first (filter (fn (s) (= (get s :name) "GET /health")) (otel/recent))))
(host-ot-test "make-app traces the health request" (not (= host-ot-hs nil)) true)
(host-ot-test "make-app health status 200" (get (get host-ot-hs :attrs) :http.status) 200)
(define
host-ot-tests-run!
(fn