I'm sorry, I don't really follow this explanation at all.
The purpose of middleware, as I understand it, is a means of structuring
the processing of HTTP requests into discrete (reusable) units.
Authenticating a user is probably a domain concern.
Uploading or viewing a blog post are definitely domain concerns.
Those things belong in controllers - the glue between your domain model and
the HTTP model.
Middleware should end with e.g. routing and the controller framework - at
that point we're out of the HTTP domain, into the application domain.
What you describe, in my opinion, sounds like overuse of middleware, or a
pretty big stretch at least?
The way I understand middleware, this is where systematic processing of
HTTP requests take place, where routing (in some form) determines which
controller to run, and then at that point, the controller provides the
integration between the HTTP world and your domain - but this
integration-layer is isn't systematic, it doesn't deal with HTTP requests
at large, it only deals with one very specific HTTP request.
In other words, middleware classifies and filters requests - whereas
controllers take a classified, filtered request, to which they must respond.
Middleware that involves domain knowledge, such as blog posts and
transactions on those, can't be applied to HTTP requests in general,
because they're coupled to your domain - from the description, I would
classify those as controllers, which do not belong in a middleware stack.
I mean, that's my understanding - I realize all this stuff is pretty
fluent, but I do get the impression that there's bit of a tendency to try
to use middleware as an "application framework", turning everything into
middleware in the name of reuse. But the way I understand it (from the way
I've seen it used on other platforms) it's an HTTP abstraction, not a
general-purpose framework for anything and everything you can think of.
I think that middleware fills a gap by providing a modular abstraction for
classifying and filtering requests, which we didn't have before.
I've never viewed it as any kind of framework for more than that.
On Fri, Apr 21, 2017 at 8:03 PM, Rivera, John <rive...@buffalo.edu> wrote:
> Sure — here’s an example.
>
> Let’s say you have a UploadBlogPost and a ViewBlogPost request. Let’s say
> the UploadBlogPost request takes an unique id and the post’s body and
> sticks it into a database. And let’s say ViewBlogPost takes an id, and
> returns the blog post associated with that id.
>
> The UploadBlogPost request shouldn’t be sent in by just anybody. And what
> if the unique id isn’t so unique after all? So we write up, let’s say, an
> AuthenticatedRequest decorator and a TransactionalRequest decorator. The
> ViewBlogPost request, however, can be sent in by anybody, and it is
> read-only, so it doesn’t have to be transactional, either.
>
> So for UploadBlogPost, you’d have the dependency injection container
> return a new AuthenticatedRequest(new TransactionalRequest(new
> UploadBlogPostHandler))); and new ViewBlogPost(); respectively. That’s what
> I meant by fine-tuned — you do not want none of that if ( $request
> instanceof UploadBlogPost) { … } else if ( $request instanceof ViewBlogPost
> ) { … } nastiness.
>
> On the other hand, we want to log all requests that comes in, right? And
> what if that AuthenticatedRequest decorator throws an
> UserNotAuthenticatedException? We’d want to handle that before that thing
> bubbles up beyond the router, right? So those are things that apply to the
> application in its entirety — no matter what request comes in, we’ll always
> need those middlewares ready for action.
>
> That’s where PSR-15 may make more sense. Let’s say we have this in the
> index.php file — a simplified example, not necessarily correctly
> implementing PSR-15, but you get the idea:
>
> $stack = new Stack();
> $stack->add(function ($request, $response) { */ does the logging goodness
> */});
> $stack->add(function ($request, $response) { */ sends the request off to
> its handler. If the handler doesn’t like it, catch the exception and… */ });
> $stack->add(function ($request, $response) { */ … send it to here, where
> the exception is handled. */ });
>
> It wouldn’t make sense for a framework to provide fine-tuned middleware
> support, but a ‘one-size-fits-all’ middleware inter-op does make sense.
> PSR-15 allows a framework to “run” any middleware you may build without a
> mess of if-else statements.
>
> The above example is probably not how I’d write it ‘in the real world’,
> but I hope you get the idea of what I’m trying to say :)
>
> John
>
> On Apr 21, 2017, at 1:41 PM, Rasmus Schultz <ras...@mindplay.dk> wrote:
>
> I'm not sure what you mean by "fine-grained" middleware?
>
> This "fine-grained" middleware performs request-to-response processing the
> same as "general" middleware - they have the same method signature.
>
> This is pretty abstract, so can you support this point of view with
> code-samples or scenario/use-case descriptions to illustrate?
>
>
> On Fri, Apr 21, 2017 at 7:07 PM, Rivera, John <rive...@buffalo.edu> wrote:
>
>> This is exactly how I handle most of my middleware as well — I have a
>> project that uses the CQRS architectural pattern, and I decorate each
>> command handler using this exact pattern.
>>
>> I build the dependency graph in my dependency injection container, and
>> use a mediator to dispatch commands to their (decorated) handlers.
>>
>> This is excellent for fine-tuned control over specific command handlers
>> and their aspects.
>>
>> However, I can see a use for the PSR-15 style middleware — I see two
>> different kinds of middleware: fine-grained middleware (some requests needs
>> to be authenticated, some needs to be within a database transaction, maybe
>> one or two requests result in an event that you need to fire off, etc), and
>> the general middleware (you want to log all requests, you want to catch any
>> exceptions and handle them appropriately, etc).
>>
>> I think the approach we are discussing here is ideal for fine-grained
>> middleware — it makes the dependency graph explicit and easy to configure
>> and maintain separately. PSR-15 is ideal for general middleware, which you
>> can take a more functional approach to — there would (or should) only be a
>> few layers, and they would apply to the application as a whole.
>>
>> Just my two cents.
>> John
>>
>> On Apr 21, 2017, at 12:40 PM, Beau Simensen <simen...@gmail.com> wrote:
>>
>>
>>
>> On Friday, April 21, 2017 at 10:42:11 AM UTC-5, Rasmus Schultz wrote:
>>>
>>>
>>> $kernel = new NotFoundMiddleware();
>>> $kernel = new RouterMiddleware(new Router(...), $kernel);
>>> $kernel = new CacheMiddleware($kernel);
>>> $kernel = new ErrorHandlerMiddleware();
>>>
>>>
>> Off the top of my head, it feels like this would be difficult to
>> automatically wire with a DI container since each middleware will need to
>> be constructed with the previous middleware already instantiated.
>> Especially given you cannot have consistent known arguments, this will be
>> difficult to automate.
>>
>> return $this->container->get($id)->process($request);
>>
>>
>> I think you tried to address this with the ContainerProxyMiddleware but
>> it skips the construction part. How would the container know which $kernel
>> to use in the constructor for the object at $id? This looks nice, API-wise,
>> but it is ignoring how this object would actually be constructed.
>>
>> One of the things we did with Stack was required the first argument to
>> always be the kernel and any additional arguments (if any at all) would
>> have to follow after that. We used Stack Builder to help try and solve
>> those problems. It still seemed messy and I was never very happy with it.
>>
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