Oban Met generating JSON encoding error

I see this error locally when running my application. mix deps shows versions:

  • oban 2.19.1
  • oban_met 0.1.11
  • oban_pro 1.5.0
  • oban_web 2.10.2
  • telemetry 1.3.0
  • telemetry_metrics 1.1.0
  • telemetry_poller 1.1.0
[error] GenServer {Oban.Registry, {Oban, Oban.Met.Listener}} terminating
** (Protocol.UndefinedError) protocol JSON.Encoder not implemented for type Oban.Met.Values.Gauge (a struct), the protocol must be explicitly implemented.

If you have a struct, you can derive the implementation specifying which fields should be encoded to JSON:

    @derive {JSON.Encoder, only: [....]}
    defstruct ...

It is also possible to encode all fields, although this should be used carefully to avoid accidentally leaking private information when new fields are added:

    @derive JSON.Encoder
    defstruct ...

Finally, if you don't own the struct you want to encode to JSON, you may use Protocol.derive/3 placed outside of any module:

    Protocol.derive(JSON.Encoder, NameOfTheStruct, only: [...])
    Protocol.derive(JSON.Encoder, NameOfTheStruct). This protocol is implemented for the following type(s): Atom, BitString, Date, DateTime, Decimal, Duration, Float, Integer, List, Map, NaiveDateTime, Oban.Pro.Producer, Oban.Pro.Producer.Meta.GlobalLimit, Oban.Pro.Producer.Meta.GlobalLimit.Partition, Oban.Pro.Producer.Meta.RateLimit, Oban.Pro.Producer.Meta.RateLimit.Partition, Time

Got value:

    %Oban.Met.Values.Gauge{data: [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]}

    (elixir 1.18.2) lib/json.ex:1: JSON.Encoder.impl_for!/1
    (elixir 1.18.2) lib/json.ex:109: JSON.Encoder.encode/2
    (elixir 1.18.2) src/elixir_json.erl:323: :elixir_json."-do_encode_map/2-lc$^0/1-0-"/2
    (elixir 1.18.2) src/elixir_json.erl:323: :elixir_json.do_encode_map/2
    (elixir 1.18.2) src/elixir_json.erl:308: :elixir_json.do_encode_list/2
    (elixir 1.18.2) src/elixir_json.erl:323: :elixir_json."-do_encode_map/2-lc$^0/1-0-"/2
    (elixir 1.18.2) src/elixir_json.erl:323: :elixir_json."-do_encode_map/2-lc$^0/1-0-"/2
    (elixir 1.18.2) src/elixir_json.erl:323: :elixir_json.do_encode_map/2
    (oban 2.19.1) lib/oban/notifier.ex:307: Oban.Notifier.encode/1
    (elixir 1.18.2) lib/enum.ex:1714: Enum."-map/2-lists^map/1-1-"/2
    (oban 2.19.1) lib/oban/notifier.ex:202: anonymous fn/4 in Oban.Notifier.notify/3
    (telemetry 1.3.0) /Users/me/code/myapp/deps/telemetry/src/telemetry.erl:324: :telemetry.span/3
    (oban_met 0.1.11) lib/oban/met/listener.ex:82: Oban.Met.Listener.handle_info/2
    (stdlib 6.2) gen_server.erl:2345: :gen_server.try_handle_info/3
    (stdlib 6.2) gen_server.erl:2433: :gen_server.handle_msg/6
    (stdlib 6.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
Last message: :report

Oban added a transparent switch between Jason and JSON, which must also be respected by the other packages. In this case, oban_met is behind a version.

Upgrading oban_web (Changelog — Oban Web v2.11.0) and oban_met (Changelog — Oban Met v1.0.1) to the latest versions will fix the issue:

{:oban_web, "~> 2.11"},
{:oban_met, "~> 1.0"}

Understood. The newer oban_web requires phoenix_live_view 1.0, which is a bigger lift to upgrade to. (We even have a couple of deps that require an older version of LV.) I guess we’ll have to prioritize that or else use an older version of Oban until we can.

There are minimal changes in Web v2.11 to support LV 1.0. The newer oban_web may work with a slightly older version of phoenix_live_view if you want to try an override: true.

Thanks, that will let us limp along for a bit. Specifying the oban versions you showed and {:phoenix_live_view, "~> 0.20.17", override: true} fixes the decoding errors. It means that the Oban Web dashboard just displays {@inner_content} , but we can work to get on LiveView 1.0 before the next deploy.