giles
c273467929
otel/metrics folds spans → {:total-requests :routes}; each route carries a
request count and nearest-rank latency percentiles over its durations. Route
key is the http.route attr (falls back to span name). Includes a small
insertion sort (no sort primitive) and order-preserving distinct.
276 lines
12 KiB
Plaintext
276 lines
12 KiB
Plaintext
;; lib/host/otel.sx — OpenTelemetry in SX, P1: the span model + API.
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;;
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;; A TRACE is a COMPOSITION: a span is {:trace :span :parent :name :t0 :t1 :attrs
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;; :events}, so a trace is a tree of spans (the same shape as an object's :body
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;; composition). Later phases fold that tree into a waterfall (render-fold), OTLP
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;; JSON (export-fold) and metrics (aggregate-fold). This phase gives us the model,
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;; the dynamic parent stack that builds the tree, and a bounded in-memory ring
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;; buffer — spans are cheap timed effects, NOT durable KV rows.
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;; ── monotonic id + clock ─────────────────────────────────────────────
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;; A simple process-monotonic counter gives collision-free ids without needing a
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;; random source (Math.random/Date.now aren't available on this host).
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(define otel/-id-counter 0)
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(define otel/-next-id
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(fn (prefix)
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(begin
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(set! otel/-id-counter (+ otel/-id-counter 1))
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(str prefix otel/-id-counter))))
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(define otel/gen-trace-id (fn () (otel/-next-id "trace-")))
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(define otel/gen-span-id (fn () (otel/-next-id "span-")))
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;; now-ns — real epoch time in NANOSECONDS (the unit OTLP wants for
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;; start/endTimeUnixNano). The OCaml host exposes `clock-milliseconds`
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;; (Unix.gettimeofday, epoch ms); we scale by 1e6. Wall clocks can step
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;; backwards (NTP), so we clamp against a high-water mark: now-ns never
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;; decreases, keeping span durations non-negative even across a clock step.
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(define otel/-last-ns 0)
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(define otel/now-ns
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(fn ()
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(let ((raw (* (clock-milliseconds) 1000000)))
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(let ((t (if (> raw otel/-last-ns) raw otel/-last-ns)))
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(begin
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(set! otel/-last-ns t)
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t)))))
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;; ── the dynamic parent stack ─────────────────────────────────────────
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;; head = the innermost (current) span context {:span id :trace id}. Pushing on
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;; with-span entry / popping on exit is what turns lexical nesting into parent
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;; links, so a trace tree falls out of ordinary call nesting.
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(define otel/-stack (list))
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(define otel/-push! (fn (ctx) (set! otel/-stack (cons ctx otel/-stack))))
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(define otel/-pop! (fn () (set! otel/-stack (rest otel/-stack))))
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(define otel/-top (fn () (if (= (len otel/-stack) 0) nil (first otel/-stack))))
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(define otel/current-span
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(fn () (let ((t (otel/-top))) (if t (get t :span) nil))))
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(define otel/current-trace
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(fn () (let ((t (otel/-top))) (if t (get t :trace) nil))))
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;; ── the bounded ring buffer ──────────────────────────────────────────
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;; Oldest → newest. record! appends and drops from the front once over cap, so the
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;; buffer stays O(cap) no matter how many spans flow through. NOT persisted.
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(define otel/-cap 1000)
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(define otel/-ring (list))
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(define otel/set-cap! (fn (n) (begin (set! otel/-cap n) nil)))
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(define otel/record!
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(fn (span)
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(begin
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(set! otel/-ring (append otel/-ring (list span)))
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(if (> (len otel/-ring) otel/-cap)
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(set! otel/-ring (slice otel/-ring (- (len otel/-ring) otel/-cap)))
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nil)
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span)))
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(define otel/recent (fn () otel/-ring))
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;; Clear the ring AND the parent stack — used between tests / requests.
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(define otel/reset!
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(fn ()
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(begin
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(set! otel/-ring (list))
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(set! otel/-stack (list))
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nil)))
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;; ── -timed: the shared timed-effect core ─────────────────────────────
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;; Records a span around (thunk): a fresh span id, the trace inherited from the
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;; enclosing span (or a new trace at the root), the enclosing span as :parent, and
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;; t0/t1 straddling the call. Pushes its context so nested spans see it as parent,
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;; pops after, then records the finished span. `finalize` maps the thunk's result
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;; to EXTRA attrs merged onto `attrs` (e.g. an http.status only known post-call).
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;; Returns the thunk's value unchanged.
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(define otel/-timed
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(fn (name attrs finalize thunk)
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(let ((parent-ctx (otel/-top)))
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(let ((trace (if parent-ctx (get parent-ctx :trace) (otel/gen-trace-id)))
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(span (otel/gen-span-id))
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(parent (if parent-ctx (get parent-ctx :span) nil)))
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(let ((t0 (begin (otel/-push! {:span span :trace trace}) (otel/now-ns))))
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(let ((result (thunk)))
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(let ((t1 (otel/now-ns)))
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(begin
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(otel/-pop!)
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(otel/record!
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{:trace trace :span span :parent parent :name name
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:t0 t0 :t1 t1
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:attrs (merge attrs (finalize result))
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:events (list)})
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result))))))))
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;; with-span — a plain timed span; no result-derived attrs.
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(define otel/with-span
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(fn (name attrs thunk)
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(otel/-timed name attrs (fn (r) {}) thunk)))
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;; ── auto-instrument HTTP handlers ─────────────────────────────────────
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;; A trace is a composition; a request handler is a timed effect. Wrap one Dream
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;; route's handler so dispatching it records a root span "METHOD /route" with
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;; {:http.method :http.route :http.status}. The status is only known after the
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;; handler runs, so it's a finalize attr; the result is coerced the same way the
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;; router coerces it, so a bare-string handler still reports 200. The raw handler
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;; result is returned untouched so dr/run-route's own coercion is unchanged.
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(define otel/instrument-route
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(fn (r)
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(let ((method (dream-route-method r))
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(path (dream-route-path r))
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(handler (dream-route-handler r)))
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(dream-route method path
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(fn (req)
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(otel/-timed
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(str method " " path)
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{:http.method method :http.route path}
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(fn (resp) {:http.status (dream-status (dream-coerce-response resp))})
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(fn () (handler req))))))))
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;; Flatten nested route groups and instrument each route — the host/make-app seam.
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(define otel/instrument-routes
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(fn (routes) (map otel/instrument-route (dr/flatten-routes routes))))
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;; ── P4: render-fold → SVG waterfall ───────────────────────────────────
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;; A trace is a tree of spans; a waterfall is a fold over that tree into SVG (the
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;; same discipline as the compose render-fold: walk the structure, emit per node).
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;; Layout: x ∝ (t0 − trace.t0), width ∝ duration, y ∝ depth (ancestor count via
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;; parent links). Geometry is computed as plain rect data first (otel/waterfall-
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;; rects, testable), then folded into <svg> markup (otel/waterfall).
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(define otel/-row-h 18)
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(define otel/-svg-w 640)
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(define otel/-pad 4)
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;; all spans belonging to one trace, from the ring.
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(define otel/trace-spans
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(fn (trace-id) (filter (fn (s) (= (get s :trace) trace-id)) (otel/recent))))
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(define otel/-span-by-id
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(fn (spans id) (first (filter (fn (s) (= (get s :span) id)) spans))))
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;; depth = number of ancestors reachable via :parent within this trace's spans.
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(define otel/-depth
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(fn (s spans)
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(if (nil? (get s :parent))
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0
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(let ((p (otel/-span-by-id spans (get s :parent))))
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(if (nil? p) 0 (+ 1 (otel/-depth p spans)))))))
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;; trace start = earliest t0; end = latest t1 (folds over the spans).
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(define otel/-min-t0
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(fn (spans) (reduce (fn (m s) (min m (get s :t0))) (get (first spans) :t0) spans)))
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(define otel/-max-t1
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(fn (spans) (reduce (fn (m s) (max m (get s :t1))) (get (first spans) :t1) spans)))
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;; a rect per span: {:span :name :depth :x :y :w}. x/width are scaled to the
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;; drawable width; a zero-duration span still gets a 1px sliver so it's visible.
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(define otel/waterfall-rects
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(fn (trace-id)
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(let ((spans (otel/trace-spans trace-id)))
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(if (empty? spans)
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(list)
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(let ((t0 (otel/-min-t0 spans))
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(t1 (otel/-max-t1 spans))
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(iw (- otel/-svg-w (* 2 otel/-pad))))
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(let ((total (if (> (- t1 t0) 0) (- t1 t0) 1)))
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(map
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(fn (s)
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(let ((d (otel/-depth s spans))
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(dur (- (get s :t1) (get s :t0))))
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(let ((raw-w (* (/ dur total) iw)))
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{:span (get s :span)
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:name (get s :name)
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:depth d
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:x (+ otel/-pad (* (/ (- (get s :t0) t0) total) iw))
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:y (+ otel/-pad (* d otel/-row-h))
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:w (if (> raw-w 1) raw-w 1)})))
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spans)))))))
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;; one <g> (bar + label) per rect.
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(define otel/-rect->g
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(fn (r)
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(quasiquote
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(g
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(rect :x (unquote (get r :x)) :y (unquote (get r :y))
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:width (unquote (get r :w)) :height (unquote (- otel/-row-h 2))
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:fill "#4c78a8" :rx 2)
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(text :x (unquote (+ (get r :x) 3)) :y (unquote (+ (get r :y) 12))
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:font-size 10 :fill "#ffffff" (unquote (get r :name)))))))
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;; max depth across rects (0 when empty) → svg height.
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(define otel/-max-depth
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(fn (rects) (reduce (fn (m r) (max m (get r :depth))) 0 rects)))
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;; the trace as an inline <svg> waterfall.
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(define otel/waterfall
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(fn (trace-id)
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(let ((rects (otel/waterfall-rects trace-id)))
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(let ((h (+ (* 2 otel/-pad) (* (+ (otel/-max-depth rects) 1) otel/-row-h))))
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(quasiquote
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(svg :width (unquote otel/-svg-w) :height (unquote h)
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:xmlns "http://www.w3.org/2000/svg"
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(splice-unquote (map otel/-rect->g rects))))))))
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;; count nodes whose head symbol prints as `head` — a small SVG-tree assertion aid.
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(define otel/-tree-count
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(fn (tree head)
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(if (list? tree)
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(let ((self (if (and (not (empty? tree)) (= (str (first tree)) head)) 1 0)))
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(reduce (fn (acc n) (+ acc (otel/-tree-count n head))) self tree))
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0)))
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;; ── P5: metrics (aggregate-fold) ──────────────────────────────────────
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;; Fold the recent spans into per-route request counts + a latency histogram
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;; (p50/p95/p99 from durations). No `sort` primitive here, so percentiles ride a
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;; tiny insertion sort; nearest-rank keeps the maths exact for the tests.
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(define otel/-insert
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(fn (x sorted)
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(if (empty? sorted)
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(list x)
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(if (<= x (first sorted))
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(cons x sorted)
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(cons (first sorted) (otel/-insert x (rest sorted)))))))
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(define otel/-sort-nums
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(fn (lst) (reduce (fn (acc x) (otel/-insert x acc)) (list) lst)))
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;; nearest-rank percentile of an ASCENDING list: rank = ceil(p/100 · N), 1-based.
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(define otel/-percentile
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(fn (sorted p)
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(if (empty? sorted)
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0
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(let ((n (len sorted)))
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(let ((idx (- (ceil (* (/ p 100) n)) 1)))
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(let ((i (if (< idx 0) 0 (if (>= idx n) (- n 1) idx))))
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(nth sorted i)))))))
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;; a span's route label: the http.route attr, else the span name.
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(define otel/-span-route
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(fn (s) (or (get (get s :attrs) :http.route) (get s :name))))
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(define otel/-span-dur (fn (s) (- (get s :t1) (get s :t0))))
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;; distinct values, order-preserving.
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(define otel/-distinct
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(fn (lst)
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(reduce
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(fn (acc x) (if (some (fn (y) (= y x)) acc) acc (append acc (list x))))
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(list)
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lst)))
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;; the aggregate for one route: count + latency percentiles over its durations.
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(define otel/route-metrics
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(fn (spans route)
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(let ((rs (filter (fn (s) (= (otel/-span-route s) route)) spans)))
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(let ((durs (otel/-sort-nums (map otel/-span-dur rs))))
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{:route route
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:count (len rs)
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:p50 (otel/-percentile durs 50)
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:p95 (otel/-percentile durs 95)
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:p99 (otel/-percentile durs 99)}))))
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;; fold spans → {:total-requests N :routes (per-route metrics …)}.
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(define otel/metrics
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(fn (spans)
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(let ((routes (otel/-distinct (map otel/-span-route spans))))
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{:total-requests (len spans)
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:routes (map (fn (r) (otel/route-metrics spans r)) routes)})))
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;; convenience: metrics over the current ring.
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(define otel/metrics-recent (fn () (otel/metrics (otel/recent))))
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