From 1ac44c4dd80f77e16a8f31bd45ea13832c68eda7 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Thu, 4 Dec 2025 11:30:49 -0500
Subject: [PATCH] feat client: add exporter_stdout

---
 src/client/exporter_stdout.ml | 62 +++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 src/client/exporter_stdout.ml

diff --git a/src/client/exporter_stdout.ml b/src/client/exporter_stdout.ml
new file mode 100644
index 00000000..4e8ec5c2
--- /dev/null
+++ b/src/client/exporter_stdout.ml
@@ -0,0 +1,62 @@
+(** A simple exporter that prints on stdout *)
+
+open Common_
+open Opentelemetry_util
+open Opentelemetry_emitter
+
+open struct
+  let pp_span out (sp : OTEL.Span.t) =
+    let open OTEL in
+    Format.fprintf out
+      "@[<2>SPAN@ trace_id: %a@ span_id: %a@ name: %S@ start: %a@ end: %a@]@."
+      Trace_id.pp
+      (Trace_id.of_bytes sp.trace_id)
+      Span_id.pp
+      (Span_id.of_bytes sp.span_id)
+      sp.name Timestamp_ns.pp_debug sp.start_time_unix_nano
+      Timestamp_ns.pp_debug sp.end_time_unix_nano
+
+  let pp_vlist mutex pp out l =
+    if l != [] then (
+      let@ () = Util_mutex.protect mutex in
+      Format.fprintf out "@[<v>";
+      List.iteri
+        (fun i x ->
+          if i > 0 then Format.fprintf out "@,";
+          pp out x)
+        l;
+      Format.fprintf out "@]@."
+    )
+end
+
+let stdout : OTEL.Exporter.t =
+  let open Opentelemetry_util in
+  let out = Format.std_formatter in
+  let mutex = Mutex.create () in
+
+  let closed = Atomic.make false in
+
+  let mk_emitter pp_signal =
+    let emit l =
+      if Atomic.get closed then raise Emitter.Closed;
+      pp_vlist mutex pp_signal out l
+    in
+    let enabled () = not (Atomic.get closed) in
+    let tick ~now:_ = () in
+    let flush_and_close () =
+      if not (Atomic.exchange closed true) then
+        let@ () = Util_mutex.protect mutex in
+        Format.pp_print_flush out ()
+    in
+    let closed () = Atomic.get closed in
+
+    { Emitter.emit; closed; enabled; tick; flush_and_close }
+  in
+
+  {
+    emit_spans = mk_emitter pp_span;
+    emit_logs = mk_emitter Proto.Logs.pp_log_record;
+    emit_metrics = mk_emitter Proto.Metrics.pp_metric;
+    on_tick = Cb_set.create ();
+    cleanup = (fun ~on_done () -> on_done ());
+  }