CP-53161: Baggage threaded through smapi and back into xapi (#6278)

It continues the path of threading the `trace_context` across different
components. Specifically, from `xapi` to `smapi` and back to `xapi`.

Additional improvement: the tracecontext is passed even when `smapi`
component is experimental and it does not create spans. Therefore, it is
not creating orphaned spans from http requests made to xapi.

BVT+BST: 213297

Author: edwintorok

ocaml/libs/tracing/dune

@@ -1,7 +1,7 @@
 (library
  (name tracing)
  (modules tracing)
- (libraries re uri yojson xapi-log xapi-stdext-threads threads.posix)
+ (libraries astring re uri yojson xapi-log xapi-stdext-threads threads.posix)
  (preprocess
   (pps ppx_deriving_yojson))
  (public_name xapi-tracing))
@@ -33,7 +33,7 @@
 (library
  (name tracing_propagator)
  (modules propagator)
- (libraries astring http-lib tracing))
+ (libraries http-lib tracing))
 
 (test
  (name test_tracing)

ocaml/libs/tracing/propagator.ml

@@ -54,25 +54,11 @@ module Http = struct
     | xs ->
         Some xs
 
-  let parse input =
-    let open Astring.String in
-    let trim_pair (key, value) = (trim key, trim value) in
-    input
-    |> cuts ~sep:";"
-    |> List.map (cut ~sep:"=" >> Option.map trim_pair)
-    |> List.filter_map Fun.id
-
   let inject_into ctx req =
     let open Tracing in
     let traceparent = (hdr_traceparent, TraceContext.traceparent_of ctx) in
     let baggage =
-      let encoded =
-        let encode =
-          List.map (fun (k, v) -> Printf.sprintf "%s=%s" k v)
-          >> String.concat ";"
-        in
-        TraceContext.baggage_of ctx |> Option.map encode
-      in
+      let encoded = TraceContext.encode_baggage ctx in
       (hdr_baggage, encoded)
     in
     let entries = [traceparent; baggage] in
@@ -102,7 +88,7 @@ module Http = struct
     let traceparent = List.assoc_opt hdr_traceparent headers in
     let baggage =
       let* all = alloc_assoc hdr_baggage headers in
-      Some (List.concat_map parse all)
+      Some (List.concat_map TraceContext.parse all)
     in
     let open TraceContext in
     empty |> maybe with_traceparent traceparent |> maybe with_baggage baggage

ocaml/libs/tracing/tracing.ml

@@ -18,6 +18,8 @@ open D
 
 let fail fmt = Printf.ksprintf failwith fmt
 
+let ( >> ) f g x = g (f x)
+
 let failures = Atomic.make 0
 
 let not_throttled () =
@@ -228,6 +230,20 @@ module TraceContext = struct
 
   let baggage_of ctx = ctx.baggage
 
+  let parse input =
+    let open Astring.String in
+    let trim_pair (key, value) = (trim key, trim value) in
+    input
+    |> cuts ~sep:";"
+    |> List.map (cut ~sep:"=" >> Option.map trim_pair)
+    |> List.filter_map Fun.id
+
+  let encode_baggage ctx =
+    let encode =
+      List.map (fun (k, v) -> Printf.sprintf "%s=%s" k v) >> String.concat ";"
+    in
+    ctx |> baggage_of |> Option.map encode
+
   let to_json_string t = Yojson.Safe.to_string (to_yojson t)
 
   let of_json_string s = of_yojson (Yojson.Safe.from_string s)
@@ -810,6 +826,8 @@ let with_child_trace ?attributes ?trace_context parent ~name f =
 module EnvHelpers = struct
   let traceparent_key = "TRACEPARENT"
 
+  let baggage_key = "BAGGAGE"
+
   let of_traceparent traceparent =
     match traceparent with
     | None ->
@@ -834,8 +852,23 @@ module EnvHelpers = struct
     | None ->
         []
     | Some span ->
-        Some (span |> Span.get_context |> SpanContext.to_traceparent)
-        |> of_traceparent
+        let baggage_env =
+          span
+          |> Span.get_context
+          |> SpanContext.context_of_span_context
+          |> TraceContext.encode_baggage
+          |> Option.fold ~none:[] ~some:(fun baggage ->
+                 [String.concat "=" [baggage_key; baggage]]
+             )
+        in
+        let traceparent_env =
+          span
+          |> Span.get_context
+          |> SpanContext.to_traceparent
+          |> Option.some
+          |> of_traceparent
+        in
+        List.concat [baggage_env; traceparent_env]
 end
 
 module Propagator = struct

ocaml/libs/tracing/tracing.mli

@@ -95,6 +95,10 @@ module TraceContext : sig
 
   val baggage_of : t -> baggage option
 
+  val parse : string -> baggage
+
+  val encode_baggage : t -> string option
+
   val to_json_string : t -> string
 
   val of_json_string : string -> (t, string) result

python3/examples/XenAPI/XenAPI.py

@@ -118,6 +118,15 @@ def with_tracecontext(self):
 
             for k, v in headers.items():
                 self.add_extra_header(k, v)
+        else:
+            headers ={}
+            traceparent = os.getenv("TRACEPARENT", None)
+            if traceparent:
+                self.add_extra_header("traceparent", traceparent)
+
+        baggage = os.getenv("BAGGAGE", None)
+        if baggage:
+            self.add_extra_header("baggage", baggage)
 
     def with_originator(self):
         originator_k = "ORIGINATOR"

python3/packages/observer.py

@@ -210,6 +210,13 @@ def create_tracer_from_config(path):
             if "=" in item
         )
 
+        baggage = os.getenv("BAGGAGE")
+        if baggage:
+            update = dict(
+                item.split("=", 1) for item in baggage.split(";") if "=" in item
+            )
+            otel_resource_attrs.update(update)
+
         service_name = config.get(
             "otel_service_name", otel_resource_attrs.get("service.name", "unknown")
         )