:badarith error

[OvermindDL1]

In the logs I keep getting a :badarith error randomly between 2 to 30 seconds, the stacktrace is (reformatted for readability):

** (ErlangError) erlang error:
[
  reason: :badarith,
  mfa: {Wobserver.Web.Client, :websocket_handle, 3},
  stacktrace: [
    {Wobserver.System.Scheduler, :"-utilization/0-fun-0-", 1, [file: 'lib/wobserver/system/scheduler.ex', line: 37]},
    {Enum, :"-map/2-lists^map/1-0-", 2, [file: 'lib/enum.ex', line: 1229]},
    {Wobserver.System, :overview, 0, [file: 'lib/wobserver/system.ex', line: 54]},
    {Wobserver.Web.Client, :client_handle, 2, [file: 'lib/wobserver/web/client.ex', line: 47]},
    {Wobserver.Web.Client, :websocket_handle, 3, [file: 'lib/wobserver/web/client.ex', line: 5]},
    {:cowboy_websocket, :handler_call, 7, [file: 'c:/Users/<user>/Projects/my_server/deps/cowboy/src/cowboy_websocket.erl', line: 588]},
    {:cowboy_protocol, :execute, 4, [file: 'c:/Users/<user>/Projects/my_server/deps/cowboy/src/cowboy_protocol.erl', line: 442]}
  ],
  msg: {:text, "{\"command\":\"system\",\"data\":null}"},
  req: [
    socket: #Port<0.89433>,
    transport: :ranch_tcp,
    connection: :keepalive,
    pid: #PID<0.1515.0>,
    method: "GET",
    version: :"HTTP/1.1",
    peer: {{10, 1, 2, 158}, 64429},
    host: "<user>",
    host_info: :undefined,
    port: 80,
    path: "/observer/ws",
    path_info: :undefined,
    qs: "",
    qs_vals: :undefined,
    bindings: [],
    headers: [
      {"host", "<user>"},
      {"user-agent", "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:51.0) Gecko/20100101 Firefox/51.0"},
      {"accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"},
      {"accept-language", "en-US,en;q=0.5"}, {"accept-encoding", "gzip, deflate"},
      {"sec-websocket-version", "13"}, {"origin", "http://<user>"},
      {"sec-websocket-extensions", "permessage-deflate"},
      {"sec-websocket-key", "S82iJ2lUI+jBYrl9P6icQQ=="},
      {"cookie", "_my_server_key=snip"},
      {"connection", "keep-alive, Upgrade"},
      {"pragma", "no-cache"},
      {"cache-control", "no-cache"},
      {"upgrade", "websocket"}
    ],
    p_headers: [
      {"sec-websocket-extensions", [{"permessage-deflate", []}]},
      {"upgrade", ["websocket"]},
      {"connection", ["keep-alive", "upgrade"]}
    ],
    cookies: :undefined,
    meta: [websocket_version: 13, websocket_compress: false],
    body_state: :waiting,
    buffer: "",
    multipart: :undefined,
    resp_compress: false,
    resp_state: :done,
    resp_headers: [],
    resp_body: "",
    onresponse: :already_called
  ],
  state: %{proxy: nil, state: %{}}
]
  (cowboy) c:/Users/<user>/Projects/my_server/deps/cowboy/src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

Specifically it is complaining about the division on line 37 in the lib/wobserver/system/scheduler.ex file, the whole function is:

  def utilization do
    ensure_started()

    case last_utilization() do
      false ->
        get_utilization()
        |> Enum.map(fn {_, u, t} ->u / t end)
      last ->
        get_utilization()
        |> Enum.zip(last)
        |> Enum.map(fn {{_, u0, t0}, {_, u1, t1}} -> (u1 - u0) / (t1 - t0) end)
    end
  end

I also see the error happen on the other Enum.map line as well, specifically it seems t can be 0 in the first Enum.map and t1-t0 can be 0 in the other Enum.map at times, checks probably need to be added to do an alternative action instead.

[IanLuites]

Rookie mistake.... I remember thinking: I need to write a 0 check for this.

Will fix.

[OvermindDL1]

Rookie mistake.... I remember thinking: I need to write a 0 check for this.

Heh, we've all done those plenty. ^.^

[IanLuites]

Fixed in release v0.1.7.