squash! Add Absinthe.Plug integration test.

WIP: promising lead on #11

Author: Garth Kidd

test/opencensus_absinthe_test.exs

@@ -55,6 +55,62 @@ defmodule Opencensus.AbsintheTest do
       pipeline: {__MODULE__, :traced_pipeline}
     )
 
+    def call(conn, opts) do
+      span_ctx = :ocp.current_span_ctx() |> IO.inspect(label: "#{__MODULE__}.call/2 span_ctx")
+
+      try do
+        conn
+        |> super(opts)
+        |> assign(:called_all_plugs, true)
+        |> IO.inspect(label: "#{__MODULE__}.call/2 conn AFTER")
+      rescue
+        err ->
+          {err, :ocp.current_span_ctx()} |> IO.inspect(label: "#{__MODULE__}.call/2 err")
+          reraise(err, [], __STACKTRACE__)
+      after
+        unwind_span_failures(span_ctx)
+        :ocp.with_span_ctx(span_ctx)
+      end
+    end
+
+    defmodule SpanContext do
+      require Record
+      @fields Record.extract(:span_ctx, from_lib: "opencensus/include/opencensus.hrl")
+      Record.defrecordp(:span_ctx, @fields)
+      defstruct Keyword.keys(@fields)
+
+      def from(record) when Record.is_record(record, :span_ctx),
+        do: struct!(__MODULE__, span_ctx(record))
+
+      def from(:undefined), do: nil
+    end
+
+    @spec unwind_span_failures(:opencensus.span_ctx() | %SpanContext{}) :: nil
+    defp unwind_span_failures(target_span_ctx) when is_tuple(target_span_ctx) do
+      target_span_ctx
+      |> SpanContext.from()
+      |> dead_child_spans(:ocp.current_span_ctx())
+      |> IO.inspect(label: "dead spans")
+      |> Enum.each(&:oc_trace.finish_span(&1))
+    end
+
+    @spec dead_child_spans(%SpanContext{}, :opencensus.span_ctx(), [:opencensus.span_ctx()]) :: [
+            :opencensus.span_ctx()
+          ]
+    defp dead_child_spans(target, span_ctx, spans \\ [])
+
+    defp dead_child_spans(%SpanContext{}, :undefined, _), do: []
+
+    defp dead_child_spans(%SpanContext{} = target, span_ctx, spans) do
+      %{span_id: span_id, trace_id: trace_id} = target
+
+      case SpanContext.from(span_ctx) do
+        %{span_id: ^span_id} -> spans
+        %{trace_id: ^trace_id} -> [span_ctx | spans]
+        _ -> []
+      end
+    end
+
     def traced_pipeline(config, pipeline_opts \\ []) do
       config
       |> Absinthe.Plug.default_pipeline(pipeline_opts)