A particular sentry + finch setup that results in sentry entering a possibly infinite error loop with some possible workarounds.

error_loop.exs

Mix.install([:sentry, :finch, :jason])

defmodule Sentry.FinchClient do
  @moduledoc false
  # adapts https://github.com/getsentry/sentry-elixir/blob/master/lib/sentry/hackney_client.ex
  @behaviour Sentry.HTTPClient

  @finch_name S.Finch

  @impl true
  def child_spec do
    child_spec = {Finch, name: @finch_name, pools: %{default: [size: 1, count: 1]}}
    Supervisor.child_spec(child_spec, [])
  end

  @impl true
  def post(url, headers, body) do
    req = Finch.build(:post, url, headers, body)

    case Finch.request(req, @finch_name, receive_timeout: 5000) do
      {:ok, %Finch.Response{status: status, body: body, headers: headers}} ->
        {:ok, status, headers, body}

      {:error, _reason} = failure ->
        failure
    end
  end
end

Application.put_all_env(
  sentry: [
    client: Sentry.FinchClient,
    environment_name: :test,
    included_environments: [:test],
    dsn: System.fetch_env!("SENTRY_DSN")
  ]
)

Application.put_env(:logger, Sentry.LoggerBackend, capture_log_messages: true)

Logger.add_backend(Sentry.LoggerBackend)
:ok = Application.ensure_started(:sentry)

Enum.each(1..1000, fn i -> Sentry.capture_message("event #{i}") end)

receive do
  :never -> :ok
end

Possible fix #3

Sentry package could add try/catch around calling the custom client. Pseudocode

Current

# Somewhere in sentry package

if custom_client do
  custom_client.post(url, headers, body) # If this throws, things go bad
end

Proposed

# Somewhere in sentry package

if custom_client do
  try do
    custom_client.post(url, headers, body)
  catch
    e -> {:error, e}
  end
end

This way, no matter what the client does, the error loop is prevented. We should ask - is there any reason for the Sentry package to report an exception that happened in the custom client?

I don't think so, and I think the error should be suppressed. If the client throws, it means sentry cannot report the error. It seems absurd to me to report an error that happened during reporting an error.