Support federated tracing v1

.formatter.exs

@@ -2,5 +2,5 @@
 [
   inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"],
   line_length: 120,
-  import_deps: [:absinthe]
+  import_deps: [:absinthe, :protobuf]
 ]

CONTRIBUTING.md

@@ -9,6 +9,19 @@ To get started with the project, run `mix deps.get` in the root directory to ins
 ```sh
 $ mix deps.get
 ```
+
+To run tests:
+
+```sh
+$ mix test
+```
+
+To generate tracing proto:
+
+```sh
+$ protoc --elixir_out=./lib/absinthe/federation reports.proto
+```
+
 ### Commit message convention
 
 We follow the [conventional commits specification](https://www.conventionalcommits.org/en) for our commit messages:

README.md

@@ -121,6 +121,49 @@ defmodule MySchema do
 end
 ```
 
+## Tracing
+
+### Register Middlware
+
+```elixir
+defmodule MyApp.MySchema do
+  use Absinthe.Schema
+  use Absinthe.Federation.Schema
++ use Absinthe.Federation.Tracing
+
+  query do
+    ...
+  end
+end
+```
+
+If you have a custom middleware stack, add the federation tracing middleware to the **beginning** of your middleware stack:
+
+```elixir
+def middleware(middleware, _field, _object),
+  do: [Absinthe.Federation.Tracing.Middleware] ++ [...your other middlewares]
+```
+
+### Register the Pipeline
+
+Specify the pipeline in your Absinthe.Plug endpoint:
+
+```elixir
+forward "/graphql", Absinthe.Plug,
+  schema: MyApp.MySchema,
+  pipeline: {Absinthe.Federation.Tracing.Pipeline, :plug}
+```
+
+If you have your own pipeline function, you can add the phases directly:
+
+```elixir
+def my_pipeline_creator(config, pipeline_opts) do
+  config.schema_mod
+  |> Absinthe.Pipeline.for_document(pipeline_opts)
+  |> add_my_phases() # w.e your custom phases are
+  |> Absinthe.Federation.Tracing.Pipeline.add_phases(pipeline_opts) # Add at the end
+end
+```
 ## More Documentation
 
 See additional documentation, including guides, in the [Absinthe.Federation hexdocs](https://hexdocs.pm/absinthe_federation).

lib/absinthe/federation/plug.ex

@@ -0,0 +1,27 @@
+defmodule Absinthe.Federation.Plug do
+  @behaviour Plug
+  import Plug.Conn
+
+  @impl Plug
+  defdelegate init(opts), to: Absinthe.Plug
+
+  @impl Plug
+  @spec call(Plug.Conn.t(), map) :: Plug.Conn.t() | no_return
+  def call(conn, config) do
+    IO.inspect(config, label: "config.before")
+
+    config =
+      conn
+      |> get_req_header("apollo-federation-include-trace")
+      |> case do
+        [include_trace] ->
+          put_in(config, [:context, :apollo_federation_include_trace], include_trace)
+
+        _ ->
+          config
+      end
+      |> IO.inspect(label: "config.after")
+
+    Absinthe.Plug.call(conn, config)
+  end
+end