Introduce Laravel Precognition

src/Illuminate/Foundation/Http/FormRequest.php

@@ -10,6 +10,7 @@
 use Illuminate\Contracts\Validation\Validator;
 use Illuminate\Http\Request;
 use Illuminate\Routing\Redirector;
+use Illuminate\Support\Collection;
 use Illuminate\Validation\ValidatesWhenResolvedTrait;
 use Illuminate\Validation\ValidationException;
 
@@ -109,8 +110,14 @@ protected function getValidatorInstance()
      */
     protected function createDefaultValidator(ValidationFactory $factory)
     {
+        $rules = $this->container->call([$this, 'rules']);
+
+        if ($this->isPrecognitive()) {
+            $rules = $this->filterPrecognitiveRules($rules);
+        }
+
         return $factory->make(
-            $this->validationData(), $this->container->call([$this, 'rules']),
+            $this->validationData(), $rules,
             $this->messages(), $this->attributes()
         )->stopOnFirstFailure($this->stopOnFirstFailure);
     }

src/Illuminate/Foundation/Http/Kernel.php

@@ -71,6 +71,7 @@ class Kernel implements KernelContract
      * @var string[]
      */
     protected $middlewarePriority = [
+        \Illuminate\Foundation\Http\Middleware\HandlePrecognitiveRequests::class,
         \Illuminate\Cookie\Middleware\EncryptCookies::class,
         \Illuminate\Session\Middleware\StartSession::class,
         \Illuminate\View\Middleware\ShareErrorsFromSession::class,

src/Illuminate/Foundation/Http/Middleware/HandlePrecognitiveRequests.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Illuminate\Foundation\Http\Middleware;
+
+use Illuminate\Container\Container;
+use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Foundation\Precognition;
+use Illuminate\Foundation\Routing\PrecognitionCallableDispatcher;
+use Illuminate\Foundation\Routing\PrecognitionControllerDispatcher;
+use Illuminate\Http\Response;
+use Illuminate\Routing\Contracts\CallableDispatcher as CallableDispatcherContract;
+use Illuminate\Routing\Contracts\ControllerDispatcher as ControllerDispatcherContract;
+
+class HandlePrecognitiveRequests
+{
+    /**
+     *The container instance.
+     *
+     * @var \Illuminate\Container\Container
+     */
+    protected $container;
+
+    /**
+     * Create a new middleware instance.
+     *
+     * @param  \Illuminate\Container\Container  $container
+     * @return void
+     */
+    public function __construct(Container $container)
+    {
+        $this->container = $container;
+    }
+
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Closure  $next
+     * @return \Illuminate\Http\Response
+     */
+    public function handle($request, $next)
+    {
+        if (! $request->isAttemptingPrecognition()) {
+            return $this->appendVaryHeader($request, $next($request));
+        }
+
+        $this->prepareForPrecognition($request);
+
+        return tap($next($request), function ($response) use ($request) {
+            $this->appendVaryHeader($request, $response->header('Precognition', 'true'));
+        });
+    }
+
+    /**
+     * Prepare to handle a precognitive request.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return void
+     */
+    protected function prepareForPrecognition($request)
+    {
+        $request->attributes->set('precognitive', true);
+
+        $this->container->bind(CallableDispatcherContract::class, fn ($app) => new PrecognitionCallableDispatcher($app));
+        $this->container->bind(ControllerDispatcherContract::class, fn ($app) => new PrecognitionControllerDispatcher($app));
+    }
+
+    /**
+     * Append the appropriate "Vary" header to the given response.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Illuminate\Http\Response  $response
+     * @return  \Illuminate\Http\Response  $response
+     */
+    protected function appendVaryHeader($request, $response)
+    {
+        return $response->header('Vary', implode(', ', array_filter([
+            $response->headers->get('Vary'),
+            'Precognition',
+        ])));
+    }
+}

src/Illuminate/Foundation/Precognition.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Illuminate\Foundation;
+
+use Illuminate\Http\Response;
+
+class Precognition
+{
+    /**
+     * Get the "after" validation hook that can be used for precognition requests.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @return \Closure
+     */
+    public static function afterValidationHook($request)
+    {
+        return function ($validator) use ($request) {
+            if ($validator->messages()->isEmpty() && $request->headers->has('Precognition-Validate-Only')) {
+                abort(204);
+            }
+        };
+    }
+}

src/Illuminate/Foundation/Providers/FoundationServiceProvider.php

@@ -4,6 +4,7 @@
 
 use Illuminate\Contracts\Foundation\MaintenanceMode as MaintenanceModeContract;
 use Illuminate\Foundation\MaintenanceModeManager;
+use Illuminate\Foundation\Precognition;
 use Illuminate\Foundation\Vite;
 use Illuminate\Http\Request;
 use Illuminate\Log\Events\MessageLogged;
@@ -73,7 +74,15 @@ public function register()
     public function registerRequestValidation()
     {
         Request::macro('validate', function (array $rules, ...$params) {
-            return validator()->validate($this->all(), $rules, ...$params);
+            $rules = $this->isPrecognitive()
+                ? $this->filterPrecognitiveRules($rules)
+                : $rules;
+
+            return tap(validator($this->all(), $rules, ...$params), function ($validator) {
+                if ($this->isPrecognitive()) {
+                    $validator->after(Precognition::afterValidationHook($this));
+                }
+            })->validate();
         });
 
         Request::macro('validateWithBag', function (string $errorBag, array $rules, ...$params) {

src/Illuminate/Foundation/Routing/PrecognitionCallableDispatcher.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Illuminate\Foundation\Routing;
+
+use Illuminate\Http\Response;
+use Illuminate\Routing\CallableDispatcher;
+use Illuminate\Routing\Route;
+
+class PrecognitionCallableDispatcher extends CallableDispatcher
+{
+    /**
+     * Dispatch a request to a given callable.
+     *
+     * @param  \Illuminate\Routing\Route  $route
+     * @param  callable  $callable
+     * @return mixed
+     */
+    public function dispatch(Route $route, $callable)
+    {
+        $this->resolveParameters($route, $callable);
+
+        abort(204);
+    }
+}

src/Illuminate/Foundation/Routing/PrecognitionControllerDispatcher.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace Illuminate\Foundation\Routing;
+
+use Illuminate\Http\Response;
+use Illuminate\Routing\ControllerDispatcher;
+use Illuminate\Routing\Route;
+use RuntimeException;
+
+class PrecognitionControllerDispatcher extends ControllerDispatcher
+{
+    /**
+     * Dispatch a request to a given controller and method.
+     *
+     * @param  \Illuminate\Routing\Route  $route
+     * @param  mixed  $controller
+     * @param  string  $method
+     * @return void
+     */
+    public function dispatch(Route $route, $controller, $method)
+    {
+        $this->ensureMethodExists($controller, $method);
+
+        $this->resolveParameters($route, $controller, $method);
+
+        abort(204);
+    }
+
+    /**
+     * Ensure that the given method exists on the controller.
+     *
+     * @param  object  $controller
+     * @param  string  $method
+     * @return $this
+     */
+    protected function ensureMethodExists($controller, $method)
+    {
+        if (method_exists($controller, $method)) {
+            return $this;
+        }
+
+        $class = $controller::class;
+
+        throw new RuntimeException("Attempting to predict the outcome of the [{$class}::{$method}()] method but the method is not defined.");
+    }
+}

src/Illuminate/Foundation/Validation/ValidatesRequests.php

@@ -3,6 +3,7 @@
 namespace Illuminate\Foundation\Validation;
 
 use Illuminate\Contracts\Validation\Factory;
+use Illuminate\Foundation\Precognition;
 use Illuminate\Http\Request;
 use Illuminate\Validation\ValidationException;
 
@@ -22,10 +23,22 @@ public function validateWith($validator, Request $request = null)
         $request = $request ?: request();
 
         if (is_array($validator)) {
-            $validator = $this->getValidationFactory()->make($request->all(), $validator);
+            $rules = $request->isPrecognitive()
+                ? $request->filterPrecognitiveRules($validator)
+                : $validator;
+
+            $validator = $this->getValidationFactory()->make($request->all(), $rules);
+        } elseif ($request->isPrecognitive()) {
+            $validator->setRules(
+                $request->filterPrecognitiveRules($validator->getRules())
+            );
         }
 
-        return $validator->validate();
+        return tap($validator, function ($validator) use ($request) {
+            if ($request->isPrecognitive()) {
+                $validator->after(Precognition::afterValidationHook($request));
+            }
+        })->validate();
     }
 
     /**
@@ -42,9 +55,19 @@ public function validateWith($validator, Request $request = null)
     public function validate(Request $request, array $rules,
                              array $messages = [], array $customAttributes = [])
     {
-        return $this->getValidationFactory()->make(
+        $rules = $request->isPrecognitive()
+            ? $request->filterPrecognitiveRules($rules)
+            : $rules;
+
+        $validator = $this->getValidationFactory()->make(
             $request->all(), $rules, $messages, $customAttributes
-        )->validate();
+        );
+
+        return tap($validator, function ($validator) use ($request) {
+            if ($request->isPrecognitive()) {
+                $validator->after(Precognition::afterValidationHook($request));
+            }
+        })->validate();
     }
 
     /**

src/Illuminate/Foundation/helpers.php

@@ -17,6 +17,7 @@
 use Illuminate\Foundation\Mix;
 use Illuminate\Http\Exceptions\HttpResponseException;
 use Illuminate\Queue\CallQueuedClosure;
+use Illuminate\Routing\Router;
 use Illuminate\Support\Facades\Date;
 use Illuminate\Support\HtmlString;
 use Symfony\Component\HttpFoundation\Response;
@@ -601,6 +602,35 @@ function policy($class)
     }
 }
 
+if (! function_exists('precognitive')) {
+    /**
+     * Handle a Precognition controller hook.
+     *
+     * @param  null|callable  $callable
+     * @return mixed
+     */
+    function precognitive($callable = null)
+    {
+        $callable ??= function () {
+            //
+        };
+
+        $payload = $callable(function ($default, $precognition = null) {
+            $response = request()->isPrecognitive()
+                ? ($precognition ?? $default)
+                : $default;
+
+            abort(Router::toResponse(request(), value($response)));
+        });
+
+        if (request()->isPrecognitive()) {
+            abort(204);
+        }
+
+        return $payload;
+    }
+}
+
 if (! function_exists('public_path')) {
     /**
      * Get the path to the public folder.

src/Illuminate/Http/Concerns/CanBePrecognitive.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace Illuminate\Http\Concerns;
+
+use Illuminate\Support\Collection;
+
+trait CanBePrecognitive
+{
+    /**
+     * Filter the given array of rules into an array of rules that are included in precognitive headers.
+     *
+     * @param  array  $rules
+     * @return array
+     */
+    public function filterPrecognitiveRules($rules)
+    {
+        if (! $this->headers->has('Precognition-Validate-Only')) {
+            return $rules;
+        }
+
+        return Collection::make($rules)
+            ->only(explode(',', $this->header('Precognition-Validate-Only')))
+            ->all();
+    }
+
+    /**
+     * Determine if the request is attempting to be precognitive.
+     *
+     * @return bool
+     */
+    public function isAttemptingPrecognition()
+    {
+        return $this->header('Precognition') === 'true';
+    }
+
+    /**
+     * Determine if the request is precognitive.
+     *
+     * @return bool
+     */
+    public function isPrecognitive()
+    {
+        return $this->attributes->get('precognitive', false);
+    }
+}

src/Illuminate/Http/Request.php

@@ -22,7 +22,8 @@
  */
 class Request extends SymfonyRequest implements Arrayable, ArrayAccess
 {
-    use Concerns\InteractsWithContentTypes,
+    use Concerns\CanBePrecognitive,
+        Concerns\InteractsWithContentTypes,
         Concerns\InteractsWithFlashData,
         Concerns\InteractsWithInput,
         Macroable;