Phoenix and multiple webhooks ignored


I have an elixir phoneix application that receives Stripe webhooks to update payment status in the database, I have a problem, sometimes my webhook endpoint does not return a response to stripe so the webhook will be failed.

When I looked in the logs : I found that sometimes the request does not pass through the Plug (in the Plug I check the signature of the webhook), and then the request can reach the Controller function.

The Plug code :

def call(%{request_path: "/webhooks/stripe"} = conn, _) do
    check_signature(conn, "secret")

  defp check_signature(conn, signing_secret) do
      # Stripe.Webhook.construct_event(body, stripe_signature, signing_secret)
      # etc..
      IO.puts("signature OK")
      Plug.Conn.assign(conn, :stripe_event, stripe_event)
      {:error, error} ->
        |> send_resp(:bad_request, "Stripe signature error: #{error}")
        |> halt()
      _ -> conn
      |> send_resp(:bad_request, "Stripe signature error")
      |> halt()

So in the logs the request can be terminated in the Plug and the last log entry is “signature OK”

Why do you think is that ?

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Well it seems like the plug is executed successfully then. You’ll have to post more code that is supposed to be executed after it to troubleshoot further.

Here is the function in the controller :

  def webhooks_payment(%Plug.Conn{assigns: %{stripe_event: stripe_event}} = conn, _params) do
    IO.puts("webhooks_payment controller reached")
    case handle_payment_intent_event(stripe_event) do
      {:ok, _result} ->
        IO.puts("webhooks_payment controller ok")

      {:error, error} ->
        IO.puts("webhooks_payment controller error")
        handle_error(conn, error)

I put 2 screenshots to show how sometimes it can reach the controller function and sometimes it doesn’t even log the entry message.

  • If the app is working on the request (still in Plug) and another webhook is received, will that block the current one ?

What do you think @dimitarvp ? I don’t think it’s a networking problem (k8s istio ingress) becuase the request can reach the Plug but not pass to the Controller

Any ideas please ?

That does seem quite mysterious…

Maybe add an IO.inspect(stripe_event) after this or wrap the assignment like so

|> IO.inspect(label: "conn before when signature OK")
|> Plug.Conn.assign(:stripe_event, stripe_event)
|> IO.inspect(label: "conn after when signature OK")

to determine if there’s anything unexpected going on with the conn that do not reach the function in the controller.

The request could also potentially be reaching the controller and just not matching on webhooks_payment if there’s no catchall function head e.g.
def webhooks_payment(conn, params), do: IO.inspect(conn, label: "conn from catchall webhooks_payments")

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