Elixir getting error from controller: Expected action/2 to return a Plug.Conn

Question

I have this small controller to handle user registration

def create(conn, %{"user" => user_params}) do
   changeset = User.changeset(%User{}, user_params)

    IO.inspect(user_params)

    errors = []

    cond do
      user_params["name"] === nil              -> errors = ["Name cannot be empty" | errors ]
      String.length(user_params["name"]) >= 50 -> errors = ["Name cannot be longer than 50 characters" | errors ]
      String.length(user_params["name"]) <= 3  -> errors = ["Name cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["email"] === nil              -> errors = ["Email cannot be empty" | errors ]
      String.length(user_params["email"]) >= 50 -> errors = ["Email cannot be longer than 50 characters" | errors ]
      String.length(user_params["email"]) <= 5  -> errors = ["Email cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["username"] === nil              -> errors = ["Username cannot be empty" | errors ]
      String.length(user_params["username"]) >= 30 -> errors = ["Username cannot be longer than 30 characters" | errors ] 
      String.length(user_params["username"]) <= 3  -> errors =  ["Username cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["password"]  === nil             ->         errors = ["Password cannot be empty" | errors ]
      user_params["passwordC"] === nil             ->         errors = ["Password Confirmation cannot be empty" | errors ]
      String.length(user_params["password"]) >= 30 ->         errors = ["Password cannot be longer than 30 characters" | errors ]
      String.length(user_params["password"]) <= 3  ->         errors = ["Password cannot be shorter than 3 characters" | errors ]
      user_params["password"] !== user_params["passwordC"] -> errors = ["Passwords do not match" | errors ]
    end

    cond do
      (length errors) >= 1 -> conn |> json %{success: false, errors: errors}
      (length errors) == 0 -> conn |> json %{success: true} 
    end
end

I get the json response, but I keep raising this exception:

Request: POST /auth/register
** (exit) an exception was raised:
    ** (RuntimeError) expected action/2 to return a Plug.Conn, all plugs must receive a connection (conn) and return a connection
        (bdo_pug) web/controllers/user_controller.ex:1: BdoPug.UserController.phoenix_controller_pipeline/2
        (bdo_pug) lib/phoenix/router.ex:261: BdoPug.Router.dispatch/2
        (bdo_pug) web/router.ex:1: BdoPug.Router.do_call/2
        (bdo_pug) lib/bdo_pug/endpoint.ex:1: BdoPug.Endpoint.phoenix_pipeline/1
        (bdo_pug) lib/plug/debugger.ex:93: BdoPug.Endpoint."call (overridable 3)"/2
        (bdo_pug) lib/phoenix/endpoint/render_errors.ex:34: BdoPug.Endpoint.call/2
        (plug) lib/plug/adapters/cowboy/handler.ex:15: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

I've googled it and it keeps telling me I need to return the conn which I believe I am. Any information would be great thanks.

The entire controller for extra detail

defmodule BdoPug.UserController do
  use BdoPug.Web, :controller

  alias BdoPug.User

  plug :scrub_params, "user" when action in [:create, :update]

  def new(conn, _params) do
    changeset = User.changeset(%User{})
    render(conn, "new.html", changeset: changeset)
  end

  def create(conn, %{"user" => user_params}) do
    changeset = User.changeset(%User{}, user_params)

    errors = []

    cond do
      user_params["name"] === nil              -> errors = ["Name cannot be empty" | errors ]
      String.length(user_params["name"]) >= 50 -> errors = ["Name cannot be longer than 50 characters" | errors ]
      String.length(user_params["name"]) <= 3  -> errors = ["Name cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["email"] === nil              -> errors = ["Email cannot be empty" | errors ]
      String.length(user_params["email"]) >= 50 -> errors = ["Email cannot be longer than 50 characters" | errors ]
      String.length(user_params["email"]) <= 5  -> errors = ["Email cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["username"] === nil              -> errors = ["Username cannot be empty" | errors ]
      String.length(user_params["username"]) >= 30 -> errors = ["Username cannot be longer than 30 characters" | errors ] 
      String.length(user_params["username"]) <= 3  -> errors =  ["Username cannot be shorter than 3 characters" | errors ]
    end
    cond do
      user_params["password"]  === nil             ->         errors = ["Password cannot be empty" | errors ]
      user_params["passwordC"] === nil             ->         errors = ["Password Confirmation cannot be empty" | errors ]
      String.length(user_params["password"]) >= 30 ->         errors = ["Password cannot be longer than 30 characters" | errors ]
      String.length(user_params["password"]) <= 3  ->         errors = ["Password cannot be shorter than 3 characters" | errors ]
      user_params["password"] !== user_params["passwordC"] -> errors = ["Passwords do not match" | errors ]
    end

    cond do
      (length errors) >= 1 -> conn |> json %{success: false, errors: errors}
      (length errors) == 0 -> conn |> json %{success: true} 
    end

    """
    case Repo.insert(changeset) do
      {:ok, _user} ->
        conn
        |> put_flash(:info, "User created successfully.")
        |> redirect(to: user_path(conn, :index))
      {:error, changeset} ->
        render(conn, "new.html", changeset: changeset)
    end
    """
  end

  def loginView(conn, _params) do
    render(conn, "loginView.html")
  end

  def loginPost(conn, %{"user" => user_params}) do

  end
end

Answer 1

It seems like you wrapped the auto-generated case statement in """ . In Elixir, """ is the start of a HEREDOC, so you've essentially created one large string at the end of your function. Elixir functions return the last value in the function body which is either a raw value or the result of a function. So instead of returning the Plug.Conn struct expected by the calling function, it's returning the string of the HEREDOC since that's the last value.