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, opts) do span_name = get_span_name(env, Keyword.get(opts, :span_name)) OpenTelemetry.Tracer.with_span span_name, %{kind: :client} do env |> Tesla.put_headers(:otel_propagator_text_map.inject([])) |> Tesla.run(next) |> set_span_attributes() |> handle_result() end end 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 end end defp set_span_attributes({_, %Tesla.Env{} = env} = result) do OpenTelemetry.Tracer.set_attributes(build_attrs(env)) result end defp set_span_attributes(result) do result end defp handle_result({:ok, %Tesla.Env{status: status} = env}) when status > 400 do OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, "")) {:ok, env} end defp handle_result({:error, {Tesla.Middleware.FollowRedirects, :too_many_redirects}} = result) do OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, "")) result end defp handle_result({:ok, env}) do {:ok, env} end defp handle_result(result) do OpenTelemetry.Tracer.set_status(OpenTelemetry.status(:error, "")) result end defp build_attrs(%Tesla.Env{ method: method, url: url, status: status_code, headers: headers, query: query }) do url = Tesla.build_url(url, query) uri = URI.parse(url) attrs = %{ "http.method": http_method(method), "http.url": url, "http.target": uri.path, "http.host": uri.host, "http.scheme": uri.scheme, "http.status_code": status_code } maybe_append_content_length(attrs, headers) end defp maybe_append_content_length(attrs, headers) do case Enum.find(headers, fn {k, _v} -> k == "content-length" end) do nil -> attrs {_key, content_length} -> Map.put(attrs, :"http.response_content_length", content_length) end end defp http_method(method) do method |> Atom.to_string() |> String.upcase() end end