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A Contrived Elixir Early-Return Example
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| defmodule ContrivedWebHandler do | |
| def handle(request) do | |
| request | |
| |> rate_limit() | |
| |> validate_csrf() | |
| |> get_user() | |
| |> check_password() | |
| |> ensure_permissions() | |
| |> ensure_quota() | |
| |> check_cache() | |
| |> execute_action() | |
| catch | |
| {:fail, request, user, reason} -> | |
| Logger.error( | |
| message: "error handling request", | |
| user: user, | |
| action: request.action, | |
| resource: request.resource | |
| ) | |
| {:cached, request, user, result} -> | |
| Logger.info( | |
| message: "request found in cache", | |
| user: user, | |
| action: request.action, | |
| resource: request.resource | |
| ) | |
| {:ok, result} | |
| unexpected -> | |
| Logger.error( | |
| message: "unknown return status while handling request", | |
| error: unexpected | |
| ) | |
| end | |
| def rate_limit(request) do | |
| if RateLimiter.limited?(request) do | |
| throw({:fail, request, nil, :rate_limit}) | |
| end | |
| request | |
| end | |
| def validate_csrf(request) do | |
| if CsrfValidator.valid?(request) do | |
| request | |
| else | |
| throw({:fail, request, nil, :bad_csrf_token}) | |
| end | |
| end | |
| def get_user(request) do | |
| if App.authentication_disabled?() do | |
| throw(:ok) | |
| end | |
| case UserService.get_user(request) do | |
| {:ok, user} -> | |
| {request, user} | |
| {:error, reason} -> | |
| throw({:fail, request, nil, reason}) | |
| end | |
| end | |
| def check_password({request, user}) do | |
| case UserService.check_password(user, request.password) do | |
| :ok -> | |
| {request, user} | |
| {:error, reason} -> | |
| throw({:fail, request, user, reason}) | |
| end | |
| end | |
| def ensure_permissions({request, user}) do | |
| cond do | |
| !user.enabled -> | |
| throw({:fail, request, user, :user_disabled}) | |
| user.admin -> | |
| {request, user} | |
| !PermissionChecker.allowed(user, request.action, request.resource) -> | |
| throw({:error, :permission_denied}) | |
| true -> | |
| {request, user} | |
| end | |
| end | |
| def ensure_quota({request, user}) do | |
| if !QuotaChecker.has_quota(user, request.action, request.resource) do | |
| throw({:fail, request, user, :quota_exhausted}) | |
| end | |
| end | |
| def check_cache({request, user}) do | |
| case Cache.get_cached_result(user, request.action, request.resource) do | |
| {:ok, result} -> | |
| throw({:cached, user, request, result}) | |
| {:ok, nil} -> | |
| {request, user} | |
| {:error, reason} -> | |
| throw({:fail, request, user, reason}) | |
| end | |
| end | |
| def execute_action({request, user}) do | |
| Logger.info( | |
| message: "executing action", | |
| user: user, | |
| action: request.action, | |
| resource: request.resource | |
| ) | |
| action_handler = get_action_handler(request.action) | |
| action_handler.(user, request.resource) | |
| end | |
| end |
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