Support new options on opentelemetry_tesla

README.md

@@ -151,7 +151,22 @@ end
 )
 ```
 
-`Hardhat` wraps each request in an [OpenTelemetry](`Tesla.Middleware.OpenTelemetry`) span and propagates the trace context to the destination host. It does not currently expose the ability to change the span name in the trace, but it will observe any [path parameters](`Hardhat.Middleware.PathParams`) you interpolate into the URL so that similar spans can be easily aggregated.
+`Hardhat` wraps each request in an [OpenTelemetry](`Tesla.Middleware.OpenTelemetry`) span and propagates the trace context to the destination host. It will observe any [path parameters](`Hardhat.Middleware.PathParams`) you interpolate into the URL so that similar spans can be easily aggregated. To disable propagation or change other behavior of the tracing, override the `opentelemetry_opts/0` function:
+
+```elixir
+defmodule NoPropagationClient do
+  use Hardhat
+
+  def opentelemety_opts do
+    [
+      # Disable trace propagation for talking to a third-party API
+      propagator: :none
+    ]
+  end
+end
+```
+
+For more information about the options available to tracing, see `Hardhat.Defaults.opentelemetry_opts/0` or `Tesla.Middleware.OpenTelemetry`.
 
 ## Failure detection
 

lib/hardhat/builder.ex

@@ -83,6 +83,11 @@ defmodule Hardhat.Builder do
         []
       end
 
+      @doc false
+      def opentelemetry_opts() do
+        []
+      end
+
       @doc false
       def install_regulator() do
         Regulator.install(
@@ -103,7 +108,8 @@ defmodule Hardhat.Builder do
                      retry_opts: 0,
                      should_retry: 1,
                      regulator_opts: 0,
-                     should_regulate: 1
+                     should_regulate: 1,
+                     opentelemetry_opts: 0
     end
   end
 
@@ -155,7 +161,15 @@ defmodule Hardhat.Builder do
 
       unquote(circuit_breaker)
       plug(Tesla.Middleware.Telemetry)
-      plug(Tesla.Middleware.OpenTelemetry)
+
+      plug(
+        Tesla.Middleware.OpenTelemetry,
+        Keyword.merge(
+          Hardhat.Defaults.opentelemetry_opts(),
+          __MODULE__.opentelemetry_opts()
+        )
+      )
+
       plug(Hardhat.Middleware.PathParams)
     end
   end

lib/hardhat/defaults.ex

@@ -156,4 +156,21 @@ defmodule Hardhat.Defaults do
   def should_regulate({:ok, %Tesla.Env{} = env}) do
     env.status >= 500 || env.status == 429
   end
+
+  @doc """
+  Default options for the `Tesla.Middleware.OpenTelemetry` middleware.
+
+  The options include:
+  * `:span_name` - override span name. Can be a `String` for a static span name,
+     or a function that takes the `Tesla.Env` and returns a `String`. The
+     default span name is chosen by the middleware.
+  * `:propagator` - configures trace headers propagators. Setting it to `:none`
+     disables propagation. Any module that implements `:otel_propagator_text_map`
+     can be used. Defaults to calling `:opentelemetry.get_text_map_injector/0`
+  * `:mark_status_ok` - configures spans with a list of expected HTTP error codes to be
+     marked as ok, not as an error-containing spans. The default is empty.
+  """
+  def opentelemetry_opts do
+    []
+  end
 end

test/middleware/opentelemetry_test.exs

@@ -6,6 +6,14 @@ defmodule Hardhat.OpentelemetryTest do
     use Hardhat
   end
 
+  defmodule NoPropagationClient do
+    use Hardhat
+
+    def opentelemetry_opts do
+      [propagator: :none]
+    end
+  end
+
   for {name, spec} <- Record.extract_all(from_lib: "opentelemetry/include/otel_span.hrl") do
     Record.defrecord(name, spec)
   end
@@ -17,6 +25,7 @@ defmodule Hardhat.OpentelemetryTest do
   setup do
     bypass = Bypass.open()
     pool = start_supervised!(TestClient)
+    start_supervised!(NoPropagationClient)
     :application.stop(:opentelemetry)
     :application.set_env(:opentelemetry, :tracer, :otel_tracer_default)
     :application.set_env(:opentelemetry, :traces_exporter, {:otel_exporter_pid, self()})
@@ -54,4 +63,18 @@ defmodule Hardhat.OpentelemetryTest do
 
     assert_receive {:span, span(name: "/user/:id", attributes: _)}, 1000
   end
+
+  test "does not propagate trace when disabled", %{bypass: bypass} do
+    parent = self()
+
+    Bypass.expect_once(bypass, fn conn ->
+      send(parent, {:traceheader, Plug.Conn.get_req_header(conn, "traceparent")})
+      Plug.Conn.resp(conn, 200, "Hello, world")
+    end)
+
+    assert {:ok, _conn} =
+             NoPropagationClient.get("http://localhost:#{bypass.port}/")
+
+    assert_receive {:traceheader, []}, 1000
+  end
 end