Telemetry metadata doesn't have data about response in case of error

[fuelen]

When a middleware returns an error, then metadata.env struct doesn't have status, body, headers etc, while these fields were available in the middleware. I'd expect to have this data in telemetry handler, as it helps in debugging.

Script:

Mix.install([:tesla, :telemetry])

:telemetry.attach_many(
  "tesla.request",
  [[:tesla, :request, :stop]],
  fn _event, measurements, metadata, _ ->
    dbg(metadata)
  end,
  nil
)

defmodule ExpectOKMiddleware do
  @behaviour Tesla.Middleware

  @impl Tesla.Middleware
  def call(env, next, _opts) do
    with {:ok, env} <- Tesla.run(env, next) do
      if dbg(env).status == 200 do
        {:ok, env}
      else
        {:error, {:unexpected_response, "not ok :("}}
      end
    end
  end
end

client = Tesla.client([Tesla.Middleware.Telemetry, {Tesla.Middleware.BaseUrl, "https://hex.pm/api"}, ExpectOKMiddleware])
client |> Tesla.get("/packages/tesla") |> dbg()

output:

[tesla_test.exs:18: ExpectOKMiddleware.call/3]
env #=> %Tesla.Env{
  method: :get,
  url: "https://hex.pm/api/packages/tesla",
  query: [],
  headers: [
    {"cache-control", "max-age=0, private, must-revalidate"},
    {"date", "Fri, 24 Nov 2023 14:41:30 GMT"},
    {"via", "1.1 google"},
    {"server", "Cowboy"},
    {"vary", "accept-encoding"},
    {"content-length", "56"},
    {"content-type", "application/vnd.hex+json; charset=utf-8"},
    {"strict-transport-security", "max-age=31536000"},
    {"x-request-id", "F5qWJEjGVwCUrFsJ5ONB"},
    {"alt-svc", "h3=\":443\"; ma=2592000,h3-29=\":443\"; ma=2592000"}
  ],
  body: "{\"message\":\"User-Agent header is required\",\"status\":400}",
  status: 400,
  opts: [],
  __module__: Tesla,
  __client__: %Tesla.Client{
    fun: nil,
    pre: [
      {Tesla.Middleware.Telemetry, :call, [[]]},
      {Tesla.Middleware.BaseUrl, :call, ["https://hex.pm/api"]},
      {ExpectOKMiddleware, :call, [[]]}
    ],
    post: [],
    adapter: nil
  }
}

[tesla_test.exs:7: (file)]
metadata #=> %{
  env: %Tesla.Env{
    method: :get,
    url: "/packages/tesla",
    query: [],
    headers: [],
    body: nil,
    status: nil,
    opts: [],
    __module__: Tesla,
    __client__: %Tesla.Client{
      fun: nil,
      pre: [
        {Tesla.Middleware.Telemetry, :call, [[]]},
        {Tesla.Middleware.BaseUrl, :call, ["https://hex.pm/api"]},
        {ExpectOKMiddleware, :call, [[]]}
      ],
      post: [],
      adapter: nil
    }
  },
  error: {:unexpected_response, "not ok :("}
}

[tesla_test.exs:28: (file)]
client #=> %Tesla.Client{
  fun: nil,
  pre: [
    {Tesla.Middleware.Telemetry, :call, [[]]},
    {Tesla.Middleware.BaseUrl, :call, ["https://hex.pm/api"]},
    {ExpectOKMiddleware, :call, [[]]}
  ],
  post: [],
  adapter: nil
}
|> Tesla.get("/packages/tesla") #=> {:error, {:unexpected_response, "not ok :("}}