[opentelemetry-tesla] add custom span name override as middleware opt (#105)

* fix remove extra bracket in mix.exs

* use capture log for less verbose test output

* add span_name opt for overriding span name

* add moduledoc

* allow function for span_name opt

instrumentation/opentelemetry_tesla/lib/middleware/opentelemetry_tesla_middleware.ex

@@ -1,9 +1,24 @@
 defmodule Tesla.Middleware.OpenTelemetry do
+  @moduledoc """
+  Creates OpenTelemetry spans and injects tracing headers into HTTP requests
+
+  When used with `Tesla.Middleware.PathParams`, the span name will be created
+  based on the provided path. Without it, the span name follow OpenTelemetry
+  standards and use just the method name, if not being overriden by opts.
+
+  NOTE: This middleware needs to come before `Tesla.Middleware.PathParams`
+
+  ## Options
+
+    - `: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`
+
+  """
   require OpenTelemetry.Tracer
   @behaviour Tesla.Middleware
 
-  def call(env, next, _options) do
+  def call(env, next, opts) do
-    span_name = get_span_name(env)
+    span_name = get_span_name(env, Keyword.get(opts, :span_name))
 
     OpenTelemetry.Tracer.with_span span_name, %{kind: :client} do
       env
@@ -14,7 +29,15 @@ defmodule Tesla.Middleware.OpenTelemetry do
     end
   end
 
-  defp get_span_name(env) do
+  defp get_span_name(_env, span_name) when is_binary(span_name) do
+    span_name
+  end
+
+  defp get_span_name(env, span_name_fun) when is_function(span_name_fun, 1) do
+    span_name_fun.(env)
+  end
+
+  defp get_span_name(env, _) do
     case env.opts[:path_params] do
       nil -> "HTTP #{http_method(env.method)}"
       _ -> URI.parse(env.url).path

instrumentation/opentelemetry_tesla/test/middleware/opentelemetry_tesla_middleware_test.exs

@@ -25,7 +25,8 @@ defmodule Tesla.Middleware.OpenTelemetryTest do
     {:ok, bypass: bypass}
   end
 
-  test "it records a generic span name if opentelemetry middleware is configured before path params middleware",
+  describe "span name" do
+    test "uses generic route name when opentelemetry middleware is configured before path params middleware",
         %{
           bypass: bypass
         } do
@@ -59,6 +60,108 @@ defmodule Tesla.Middleware.OpenTelemetryTest do
       assert_receive {:span, span(name: "/users/:id", attributes: _attributes)}
     end
 
+    test "uses low-cardinality method name when path params middleware is not used",
+        %{
+          bypass: bypass
+        } do
+      defmodule TestClient do
+        def get(client) do
+          Tesla.get(client, "/users/")
+        end
+
+        def client(url) do
+          middleware = [
+            {Tesla.Middleware.BaseUrl, url},
+            Tesla.Middleware.OpenTelemetry
+          ]
+
+          Tesla.client(middleware)
+        end
+      end
+
+      Bypass.expect_once(bypass, "GET", "/users/", fn conn ->
+        Plug.Conn.resp(conn, 204, "")
+      end)
+
+      bypass.port
+      |> endpoint_url()
+      |> TestClient.client()
+      |> TestClient.get()
+
+      assert_receive {:span, span(name: "HTTP GET", attributes: _attributes)}
+    end
+
+    test "uses custom span name when passed in middleware opts",
+        %{
+          bypass: bypass
+        } do
+      defmodule TestClient do
+        def get(client) do
+          params = [id: '3']
+
+          Tesla.get(client, "/users/:id", opts: [path_params: params])
+        end
+
+        def client(url) do
+          middleware = [
+            {Tesla.Middleware.BaseUrl, url},
+            {Tesla.Middleware.OpenTelemetry, span_name: "POST :my-high-cardinality-url"},
+            Tesla.Middleware.PathParams
+          ]
+
+          Tesla.client(middleware)
+        end
+      end
+
+      Bypass.expect_once(bypass, "GET", "/users/3", fn conn ->
+        Plug.Conn.resp(conn, 204, "")
+      end)
+
+      bypass.port
+      |> endpoint_url()
+      |> TestClient.client()
+      |> TestClient.get()
+
+      assert_receive {:span, span(name: "POST :my-high-cardinality-url", attributes: _attributes)}
+    end
+
+    test "uses custom span name function when passed in middleware opts",
+        %{
+          bypass: bypass
+        } do
+      defmodule TestClient do
+        def get(client) do
+          params = [id: '3']
+
+          Tesla.get(client, "/users/:id", opts: [path_params: params])
+        end
+
+        def client(url) do
+          middleware = [
+            {Tesla.Middleware.BaseUrl, url},
+            {Tesla.Middleware.OpenTelemetry, span_name: fn env ->
+              "#{String.upcase(to_string(env.method))} potato"
+            end},
+            Tesla.Middleware.PathParams
+          ]
+
+          Tesla.client(middleware)
+        end
+      end
+
+      Bypass.expect_once(bypass, "GET", "/users/3", fn conn ->
+        Plug.Conn.resp(conn, 204, "")
+      end)
+
+      bypass.port
+      |> endpoint_url()
+      |> TestClient.client()
+      |> TestClient.get()
+
+      assert_receive {:span, span(name: "GET potato", attributes: _attributes)}
+    end
+  end
+
   test "Records spans for Tesla HTTP client", %{bypass: bypass} do
     defmodule TestClient do
       def get(client) do
@@ -311,9 +414,9 @@ defmodule Tesla.Middleware.OpenTelemetryTest do
               ]
             }} =
              Tesla.Middleware.OpenTelemetry.call(
-               %Tesla.Env{url: ""},
+               _env = %Tesla.Env{url: ""},
-               [],
+               _next = [],
-               "http://example.com"
+               _opts = []
              )
 
     assert is_binary(traceparent)

instrumentation/opentelemetry_tesla/test/test_helper.exs

@@ -1 +1 @@
-ExUnit.start()
+ExUnit.start(capture_log: true)