Factor out event reification

In order to provide event records to subscribers, we must convert the
accumulated events of the form (table, objref, time) into event records.

The process of doing this is simple for objects in the database. The
only difference is that deletion events do not provide a snapshot (as
the object has been deleted). To avoid repeating ourselves, we define an
"events_of" function that accumulates event records. The function takes
an argument that specifies whether an attempt to provide a snapshot
should be performed.

The reification of events associated with messages - which are not
stored in the database - is untouched. This relies on a callback
instated elsewhere.

Signed-off-by: Colin James <[email protected]>

Author: Colin James

ocaml/xapi/xapi_event.ml

@@ -651,39 +651,32 @@ let from_inner __context session subs from from_t timer batching =
     ; snapshot
     }
   in
-  let events =
-    List.fold_left
-      (fun acc x ->
-        let ev = event_of `del x in
-        if Subscription.event_matches subs ev then ev :: acc else acc
-      )
-      [] deletes
-  in
-  let events =
-    List.fold_left
-      (fun acc (table, objref, mtime) ->
+  let events_of ~kind ?(with_snapshot = true) entries acc =
+    let rec go events ((table, obj, _time) as entry) =
+      let snapshot =
         let serialiser = Eventgen.find_get_record table in
-        try
-          let xml = serialiser ~__context ~self:objref () in
-          let ev = event_of `_mod ?snapshot:xml (table, objref, mtime) in
-          if Subscription.event_matches subs ev then ev :: acc else acc
-        with _ -> acc
-      )
-      events mods
+        if with_snapshot then
+          serialiser ~__context ~self:obj ()
+        else
+          None
+      in
+      let event = event_of kind ?snapshot entry in
+      if Subscription.event_matches subs event then
+        event :: events
+      else
+        events
+    in
+    List.fold_left go acc entries
   in
   let events =
-    List.fold_left
-      (fun acc (table, objref, ctime) ->
-        let serialiser = Eventgen.find_get_record table in
-        try
-          let xml = serialiser ~__context ~self:objref () in
-          let ev = event_of `add ?snapshot:xml (table, objref, ctime) in
-          if Subscription.event_matches subs ev then ev :: acc else acc
-        with _ -> acc
-      )
-      events creates
+    [] (* Accumulate the events for objects stored in the database. *)
+    |> events_of ~kind:`del ~with_snapshot:false deletes
+    |> events_of ~kind:`_mod mods
+    |> events_of ~kind:`add creates
   in
   let events =
+    (* Messages require a special casing as their contents are not
+       stored in the database. *)
     List.fold_left
       (fun acc mev ->
         let event =