optional reshape/1 added to: impl, conf, attr (#39)

* optional `reshape/1` added to: impl, conf, attr

* optional `reshape/1` added to: impl, conf, attr

lib/telemetria.ex

@@ -33,6 +33,11 @@ defmodule Telemetria do
     see `:throttle` setting in `Telemetria.Options`
   - **`locals: [atom()]`** — the list of names of local variables to be exported
     to the telemetry call
+  - **`transform: [{:args, (list() -> list())}, {:result, (any() -> any())}]`** — 
+    the functions to be called on the incoming attributes and/or result to reshape them
+  - **`reshape: (map() -> map())`** — the function to be called on the resulting attributes
+    to reshape them before sending to the actual telemetry handler; the default application-wide
+    reshaper might be set in `:telemetria, :reshaper` config
 
   ### Example
 
@@ -130,6 +135,8 @@ defmodule Telemetria do
   @type event_prefix :: [atom()]
   @type handler_config :: term()
 
+  @default_reshaper Application.compile_env(:telemetria, :reshaper)
+
   @doc false
   defmacro __using__(opts) do
     initial_ast =
@@ -331,6 +338,9 @@ defmodule Telemetria do
       locals =
         context |> get_in([:options, :locals]) |> Kernel.||([])
 
+      reshape =
+        context |> get_in([:options, :reshape]) |> Kernel.||(@default_reshaper)
+
       {clause_args, context} = Keyword.pop(context, :arguments, [])
       args = Keyword.merge(args, clause_args)
 
@@ -363,7 +373,7 @@ defmodule Telemetria do
 
             Telemetria.Throttler.execute(
               unquote(group),
-              {block_ctx, %{system_time: now, consumed: benchmark}, attributes}
+              {block_ctx, %{system_time: now, consumed: benchmark}, attributes, unquote(reshape)}
             )
           end
 

lib/telemetria/backend.ex

@@ -31,6 +31,11 @@ defmodule Telemetria.Backend do
   @doc "The implementation will be called when the block context is to be updated"
   @callback update(block_context(), block_metadata()) :: block_context()
 
+  @doc "The implementation will be called to reshape the event before sending it to the actual handler"
+  @callback reshape(block_metadata()) :: block_metadata()
+
+  @optional_callbacks reshape: 1
+
   @implementation Telemetria.Application.backend()
 
   case @implementation do
@@ -41,18 +46,31 @@ defmodule Telemetria.Backend do
       defdelegate return(block_context, context), to: @implementation
       @doc false
       defdelegate update(block_context, updates), to: @implementation
+      @doc false
+      def reshape(updates) do
+        if function_exported?(@implementation, :reshape, 1),
+          do: apply(@implementation, :reshape, [updates]),
+          else: updates
+      end
 
     list when is_list(list) ->
-      def entry(block_id) do
-        Enum.each(@implementation, & &1.entry(block_id))
+      if Enum.any?(@implementation, &function_exported?(&1, :reshape, 1)) do
+        IO.warn("[telemetría] `reshape/1` is ignored when several backends are specified")
       end
 
-      def return(block_context, context) do
-        Enum.each(@implementation, & &1.return(block_context, context))
-      end
+      @doc false
+      def entry(block_id),
+        do: Enum.each(@implementation, & &1.entry(block_id))
 
-      def update(block_context, updates) do
-        Enum.each(@implementation, & &1.update(block_context, updates))
-      end
+      @doc false
+      def return(block_context, context),
+        do: Enum.each(@implementation, & &1.return(block_context, context))
+
+      @doc false
+      def update(block_context, updates),
+        do: Enum.each(@implementation, & &1.update(block_context, updates))
+
+      @doc false
+      def reshape(updates), do: updates
   end
 end

lib/telemetria/backend/open_telemetry.ex

@@ -35,15 +35,17 @@ case {Telemetria.Application.open_telemetry?(), Code.ensure_compiled(OpenTelemet
 
       @impl true
       def return(block_ctx, context) do
-        attributes = Estructura.Flattenable.flatten(context, jsonify: true)
-
-        Span.set_attributes(block_ctx, attributes)
+        Span.set_attributes(block_ctx, context)
         Span.end_span(block_ctx)
         OpenTelemetry.Ctx.detach(block_ctx)
 
         :ok
       end
 
+      @impl true
+      def reshape(updates),
+        do: Estructura.Flattenable.flatten(updates, jsonify: true) |> IO.inspect()
+
       defp fix_block_id(block_id) when is_list(block_id), do: Enum.join(block_id, ".")
       defp fix_block_id(block_id), do: block_id
     end

lib/telemetria/backend/telemetry.ex

@@ -18,6 +18,9 @@ case {Telemetria.Application.telemetry?(), Code.ensure_compiled(:telemetry)} do
         {measurements, metadata} = Map.pop(context, :measurements, %{})
         :telemetry.execute(block_id, measurements, metadata)
       end
+
+      @impl true
+      def reshape(updates), do: updates
     end
 
   _ ->

lib/telemetria/throttler.ex

@@ -67,13 +67,21 @@ defmodule Telemetria.Throttler do
     Logger.warning("Wrong config for group: #{group}, skipping")
   end
 
-  defp do_execute(group, {event, measurements, metadata}) do
-    context =
+  defp do_execute(group, {event, measurements, metadata, reshaper}) do
+    {context, updates} =
       metadata
       |> Map.put(:telemetria_group, group)
       |> Map.put(:measurements, measurements)
+      |> Map.pop(:context, %{})
 
-    Telemetria.Backend.return(event, context)
+    updates = if is_function(reshaper, 1), do: reshaper.(updates), else: updates
+
+    updates =
+      updates
+      |> Map.put(:context, context)
+      |> Telemetria.Backend.reshape()
+
+    Telemetria.Backend.return(event, updates)
   end
 
   defp do_execute(group, [event]),

test/support/telemetria_tester.ex

@@ -53,7 +53,8 @@ defmodule Test.Telemetria.Example do
               transform: [
                 args: {__MODULE__, :transform_args},
                 result: &__MODULE__.transform_result/1
-              ]
+              ],
+              reshape: &Test.Telemetria.Example.reshape/1
   defp annotated_2(i) when (is_integer(i) and i == 42) or is_nil(i), do: i || 42
 
   @telemetria level: :error, if: &Test.Telemetria.S.allow?/1
@@ -84,4 +85,6 @@ defmodule Test.Telemetria.Example do
   def transform_args(args), do: inspect(args)
 
   def transform_result(result), do: inspect(result)
+
+  def reshape(outcome), do: Map.take(outcome, [:args, :result, :locals])
 end