I have had a read on what's new in .NET4.6 and one of the things is ASP.NET 5 which I am quite excited about.
One of the new things is New modular HTTP request pipeline, however there is no more info on how exactly is it going to change.
The only reference in the article is
ASP.NET 5 introduces a new HTTP request pipeline that is lean and
fast. This pipeline is modular so you can add only the components that
you need. By reducing the overhead in the pipeline, your app will
experience better throughput. The new pipeline also supports OWIN.
What are major differences between ASP.NET4.5 and ASP.NET5 Http pipelines? How modularity will be controlled?
The biggest difference in my opinion is the modularity of the new request pipeline. In the past, the application lifecycle followed a relatively strict path that you could hook into via classes implementing IHttpModule. This would allow you to affect the request, but only at certain points along the way by subscribing to the different events that occur (e.g. BeginRequest, AuthenticateRequest, etc.).
The full descriptions of these can be found on MSDN: IIS 5 & 6 or IIS 7, and a walkthrough of creating such a module can be found here.
In the new ASP.NET 5 world, the request pipeline is decoupled from System.Web and IIS. Instead of a pre-defined path, it uses the concept of middleware. If you are familiar with OWIN, the idea is nearly identical, but the basic idea is that these Middleware Components are registered and then the request passes through them in the order that they are registered.
Each middleware component is provided a RequestDelegate (the next middleware component in the pipeline) and the current HttpContext per-request. On each request, the component is invoked, and then has the opportunity to pass the request along to the next in the chain if applicable. For example, an authentication component might opt not to pass the request along to the next component if authentication fails. Using this system, you can really handle a request any way you choose, and can be as light-weight or as feature-rich as you need it to be.
This example is a little bit dated now (e.g. IBuilder has been renamed to IApplicationBuilder), but it is still a great overview of how building and registering these components looks.
I'm reading the Spring Web Flow chapter in the book Pro Spring MVC. Unfortunately there's no explicit information, where the state during a flow execution is persisted. I assume it is saved in the JVM Heap and associated with the session.
Now HTTP is a stateless protocol (REST...) and I'd like to use Spring Web Flow without saving state on the server (besides the one and only state that a session might be authenticated).
One strategy is to send all parameters of the entire flow with every HTTP request of the flow (hidden input) and thus accumulating all necessary parameters until the flow has finished.
The overhead of re-validating parameters can be avoided with signatures over already validated parameters.
Do you know, whether it might be possible to use Spring Web Flow in this way? Has anybody already done this?
Update: Why?
Persisting state is not only a violation of the principles of HTTP as a stateless protocol but has practical problems too:
If the user browses with multiple browser tabs then this can lead to inconsistent state, race conditions or data loss.
Storing state on the server makes load balancing over several servers more complicate.
Testing and debugging becomes more complicate, because requests can not be tested or analyzed in isolation but only in the context of previous requests.
Cookies must be enabled to correlate servers sessions to requests.
The server needs to synchronize access to the server-side state.
The url of a request that also depends on server state does not contain all information necessary to bookmark the state inside a flow or to make sense of it in a bug report.
I've not yet looked at the details of Web Flow but I'm confident that one could have the same programming experience and still keep all information in the request parameters.
Update: I've now learned that my requested style of flow handling has a name: Continuations. The term continuation is more common in functional programming but it's apparently not uncommon to adapt the idea to HTTP interactions.
You might be interested in checking my bean flow FSM project (restflow):
https://github.com/alfonso-presa/restflow
Although it doesn't use Spring WebFlow, I think it may help answering the spirit of the question, as it allows the implementation of a stateless server orchestrated flow. I started this project because I wanted to make almost the same as you with spring WebFlow but I found it was not possible as state is stored in session (and also REST/json serialization is not built in).
It's main purpose is making an state-machine (just like WebFlow does) but with it's state stored in a bean, which you can persist in a distributed store, or easily sign or encrypt and send back to the client as continuation for next requests.
I hope you find it useful.
edit: I created a showcase project here: https://github.com/alfonso-presa/restflow-spring-web-sample
I'm looking into building an ASP.NET MVC application that exposes (other than the usual HTML pages) JSON and XML REST services, as well as Web Sockets.
In a perfect world, I would be able to use the same URLs for the Web Sockets interface as I do for the other services (and determine which data to return by what the user agent requests) but, knowing that IIS wasn't built for persistent connections, I need to know if there's a way that I can accept (and possibly even handshake) the Web Sockets connection and then pass the connection off to another service running on the server.
I do have a workaround in mind if this isn't possible that basically involves using ASP.NET to check for the Web Sockets connection upgrade headers, and responding with a HTTP/1.1 302 Found that points to a different host that has my Web Sockets service configured to directly listen to the appopriate endpoint(s).
If I completely understand your goal, I believe you can use the IIS7/7.5 Application Request Routing module to accomplish this.
Here's a quick reference: http://learn.iis.net/page.aspx/489/using-the-application-request-routing-module/
Rather than 302 responses you could use ISAPI_rewrite to direct to an appropriate endpoint (and manipulate the HTTP header to get it there)
http://www.isapirewrite.com/docs/
Otherwise no, IIS cannot natively pass off an HTTP connection. The current MSFT method is to use a 302 or something else that is intercepting the raw socket and performing header manipulation prior to sending to IIS (or whatever other application)
It strikes me that this would be a better question to ask Microsoft than to ask us. Web Sockets is new technology, and rather than looking for a hack, you might want to ask Microsoft how they plan to support it. IIS is their software. Poke around on http://iis.net (maybe in http://forums.iis.net) and see what you learn.
The way to do this is to use a unique Session ID that is associated with the Http Session. From the description, it seems like you might want to scope this to a single HttpApplication instance, but this is not necessary (you may also persist a session across many application instances). Anyway, this session ID needs to be attached somehow to each Http Request (either with a cookie, querystring, static variable with the HttpApplication instance, form data). Then you persist the identifying information about the Http session somewhere with the ID.
This identifying information may vary depending on your needs but could entail the entire http request or just some stripped down representation that serves your particular purpose.
Using this SessionID somewhere in the Http request allows you to restore whatever information you need to call and interact with the appropriate services. The instances of the services may also need to be scoped to the session as well.
Basically, what I am suggesting is that you NOT directly pass the Http connection to an external process, but instead pass the necessary data to the external process, and allow create a mechanism for sending callback data. I think looking into the mediator pattern may be helpful for you in understanding what I mean here. http://en.wikipedia.org/wiki/Mediator_pattern . I hope this helps.
After reading a lot about the differences between REST and SOAP, I got the impression that REST is just another word for HTTP. Can someone explain what functionality REST adds to HTTP?
Note: I'm not looking for a comparison of REST versus SOAP.
No, REST is the way HTTP should be used.
Today we only use a tiny bit of the HTTP protocol's methods – namely GET and POST. The REST way to do it is to use all of the protocol's methods.
For example, REST dictates the usage of DELETE to erase a document (be it a file, state, etc.) behind a URI, whereas, with HTTP, you would misuse a GET or POST query like ...product/?delete_id=22.
HTTP is a protocol used for communication, usually used to communicate with internet resources or any application with a web browser client.
REST means that the main concept you are using while designing the application is the Resource: for each action you want to perform you need to define a resource on which you often do only CRUD operation, which is a simple task. For that it's very convenient to use four verbs used in HTTP protocol against the four CRUD operations (GET for Read, POST is for CREATE, PUT is for UPDATE and DELETE is for DELETE).
That's unlike the older concept of RPC (Remote Procedure Call), in which you have a set of actions you want to perform as a result of the user's call. if you think for example on how to describe a Facebook like on a post, with RPC you might create services called AddLikeToPost and RemoveLikeFromPost, and manage it along with all your other services related to FB posts, thus you won't need to create special object for Like.
With REST you will have a Like object which will be managed separately with Delete and Create functions. It also means it will describe a separate entity in your DB. That might look like a small difference, but working like that would usually yield a much simpler code and a much simpler application. With that design, most of the app's logic is obvious from the object's structure (model), unlike RPC with which you would usually have to explicitly add a lot more logic.
Designing a RESTful application is often a lot harder because it requires you to describe complicated things in a simple manner. Describing all functionalities using only CRUD functions is tricky, but after doing that your life would be a lot simpler, and you will find that you write a lot shorter methods.
One more restraint REST architecture presents is not to use a session context when communicating with a client (stateless), meaning all the information needed to understand who is the client and what he wants is passed with the web message. Each call to a function is self-descriptive, there is no previous conversation with the client which can be referenced in the message. Therefore, a client could not tell you "give me the next page" since you don't have a session to store what is the previous page and what kind of page you want, the client would have to say "my name is Yuval, get me page 2 of a specific post in a specific forum". This means a bit more data would have to transfer in the communication, but think of the difference between finding a bug reported from the "get me the next page" function in oppose to "get me page 2 of question ID 2190836 in stack overflow".
Of course there is a lot more to it, but to my humble opinion these are the main concepts in a teaspoon.
REST enforces the use of the available HTTP commands as they were meant to be used.
For example, I could do:
GET
http://example.com?method=delete&item=xxx
But with rest I would use the "DELETE" request method, removing the need for the "method" query param
DELETE
http://example.com?item=xxx
HTTP is an application protocol. REST is a set of rules, that when followed, enable you to build a distributed application that has a specific set of desirable constraints.
If you are looking for the most significant constraints of REST that distinguish a RESTful application from just any HTTP application, I would say the "self-description" constraint and the hypermedia constraint (aka Hypermedia as the Engine of Application State (HATEOAS)) are the most important.
The self-description constraint requires a RESTful request to be completely self descriptive in the users intent. This allows intermediaries (proxies and caches) to act on the message safely.
The HATEOAS constraint is about turning your application into a web of links where the client's current state is based on its place in that web. It is a tricky concept and requires more time to explain than I have right now.
HTTP is a contract, a communication protocol and REST is a concept, an architectural style which may use HTTP, FTP or other communication protocols but is widely used with HTTP.
REST implies a series of constraints about how Server and Client should interact. HTTP is a communication protocol with a given mechanism for server-client data transfer, it's most commonly used in REST API just because REST was inspired by WWW (world wide web) which largely used HTTP before REST was defined, so it's easier to implement REST API style with HTTP.
There are three major constraints in REST (but there are more):
Interaction between server and client should be described via hypertext only.
Server and client should be loosely coupled and make no assumptions about each other. Client should only know resource entry point. Interaction data should be provided by the server in the response.
Server shouldn't store any information about request context. Requests must be independent and idempotent (means if same request is repeated infinitely, exactly same result is retrieved)
And HTTP is just a communication protocol (a tool) that can help to achieve this.
For more info check these links:
https://martinfowler.com/articles/richardsonMaturityModel.html
http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hypertext-driven
REST = Representational State Transfer
REST is a set of rules, that when followed, enable you to build a distributed application that has a specific set of desirable constraints.
REST is a protocol to exchange any(XML, JSON etc ) messages that can use HTTP to transport those messages.
Features:
It is stateless which means that ideally no connection should be maintained between the client and server.
It is the responsibility of the client to pass its context to the server and then the server can store this context to process the client's further request. For example, session maintained by server is identified by session identifier passed by the client.
Advantages of Statelessness:
Web Services can treat each method calls separately.
Web Services need not maintain the client's previous interaction.
This in turn simplifies application design.
HTTP is itself a stateless protocol unlike TCP and thus RESTful Web Services work seamlessly with the HTTP protocols.
Disadvantages of Statelessness:
One extra layer in the form of heading needs to be added to every request to preserve the client's state.
For security we need to add a header info to every request.
HTTP Methods supported by REST:
GET: /string/someotherstring
It is idempotent and should ideally return the same results every time a call is made
PUT:
Same like GET. Idempotent and is used to update resources.
POST: should contain a url and body
Used for creating resources. Multiple calls should ideally return different results and should create multiple products.
DELETE:
Used to delete resources on the server.
HEAD:
The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The meta information contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request.
OPTIONS:
This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
HTTP Responses
Go here for all the responses.
Here are a few important ones:
200 - OK
3XX - Additional information needed from the client and url redirection
400 - Bad request
401 - Unauthorized to access
403 - Forbidden
The request was valid, but the server is refusing action. The user might not have the necessary permissions for a resource, or may need an account of some sort.
404 - Not Found
The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.
405 - Method Not Allowed
A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.
404 - Request not found
500 - Internal Server Failure
502 - Bad Gateway Error
Not quite...
http://en.wikipedia.org/wiki/Representational_State_Transfer
REST was initially described in the
context of HTTP, but is not limited to
that protocol. RESTful architectures
can be based on other Application
Layer protocols if they already
provide a rich and uniform vocabulary
for applications based on the transfer
of meaningful representational state.
RESTful applications maximise the use
of the pre-existing, well-defined
interface and other built-in
capabilities provided by the chosen
network protocol, and minimise the
addition of new application-specific
features on top of it.
http://www.looselycoupled.com/glossary/SOAP
(Simple Object Access Protocol) The
standard for web services messages.
Based on XML, SOAP defines an envelope
format and various rules for
describing its contents. Seen (with
WSDL and UDDI) as one of the three
foundation standards of web services,
it is the preferred protocol for
exchanging web services, but by no
means the only one; proponents of REST
say that it adds unnecessary
complexity.
REST is a specific way of approaching the design of big systems (like the web).
It's a set of 'rules' (or 'constraints').
HTTP is a protocol that tries to obey those rules.
From You don't know the difference between HTTP and REST
So REST architecture and HTTP 1.1 protocol are independent from each
other, but the HTTP 1.1 protocol was built to be the ideal protocol to
follow the principles and constraints of REST. One way to look at the
relationship between HTTP and REST is, that REST is the design, and
HTTP 1.1 is an implementation of that design.
HTTP is a communications protocol that transports messages over a network.
SOAP is a protocol to exchange XML-based messages that can use HTTP to transport those messages.
Rest is a protocol to exchange any(XML or JSON) messages that can use HTTP to transport those messages.
REST is not necessarily tied to HTTP. RESTful web services are just web services that follow a RESTful architecture.
What is Rest -
1- Client-server
2- Stateless
3- Cacheable
4- Layered system
5- Code on demand
6- Uniform interface
REST APIs must be hypertext-driven
From Roy Fielding's blog here's a set of ways to check if you're building a HTTP API or a REST API:
API designers, please note the following rules before calling your creation a REST API:
A REST API should not be dependent on any single communication protocol, though its successful mapping to a given protocol may be dependent on the availability of metadata, choice of methods, etc. In general, any protocol element that uses a URI for identification must allow any URI scheme to be used for the sake of that identification. [Failure here implies that identification is not separated from interaction.]
A REST API should not contain any changes to the communication protocols aside from filling-out or fixing the details of underspecified bits of standard protocols, such as HTTP’s PATCH method or Link header field. Workarounds for broken implementations (such as those browsers stupid enough to believe that HTML defines HTTP’s method set) should be defined separately, or at least in appendices, with an expectation that the workaround will eventually be obsolete. [Failure here implies that the resource interfaces are object-specific, not generic.]
A REST API should spend almost all of its descriptive effort in defining the media type(s) used for representing resources and driving application state, or in defining extended relation names and/or hypertext-enabled mark-up for existing standard media types. Any effort spent describing what methods to use on what URIs of interest should be entirely defined within the scope of the processing rules for a media type (and, in most cases, already defined by existing media types). [Failure here implies that out-of-band information is driving interaction instead of hypertext.]
A REST API must not define fixed resource names or hierarchies (an obvious coupling of client and server). Servers must have the freedom to control their own namespace. Instead, allow servers to instruct clients on how to construct appropriate URIs, such as is done in HTML forms and URI templates, by defining those instructions within media types and link relations. [Failure here implies that clients are assuming a resource structure due to out-of band information, such as a domain-specific standard, which is the data-oriented equivalent to RPC’s functional coupling].
A REST API should never have “typed” resources that are significant to the client. Specification authors may use resource types for describing server implementation behind the interface, but those types must be irrelevant and invisible to the client. The only types that are significant to a client are the current representation’s media type and standardized relation names. [ditto]
A REST API should be entered with no prior knowledge beyond the initial URI (bookmark) and set of standardized media types that are appropriate for the intended audience (i.e., expected to be understood by any client that might use the API). From that point on, all application state transitions must be driven by client selection of server-provided choices that are present in the received representations or implied by the user’s manipulation of those representations. The transitions may be determined (or limited by) the client’s knowledge of media types and resource communication mechanisms, both of which may be improved on-the-fly (e.g., code-on-demand). [Failure here implies that out-of-band information is driving interaction instead of hypertext.]
REST is a light version of SOAP, with no sugars or colors agents added.
The goal of both SOAP and REST is to allow the communication between Information Systems that may be written in different languages and use different communiation protocols.
While SOAP uses API contracts to expose it's services and define the way a client can call a service, what Parameters should be sent and what results are to be expected, REST on the other hand has uses no API contracts, for a client to know what services exist and how to call them it should look into the Rest API documentation (this can be defined in a yml file with a OpenAPI or Swagger).
Second SOAP is verbose, it reyes on XML to send a request and describe the services, parameteres and the results returned. On the other hand REST relyed on simple JSON Objects to send requests and receive results. JSON is simple to undersand, lightweight and does not use too much bandwith when sending requests or receiving results.
Our web services are distributed across different servers for various reasons (such as decreasing latency to the client), and they're not always all up-to-date. Rather than throwing an exception when a method doesn't exist because the particular web service is too old, it would be nicer if we could have the client check if the service responds to a given method before calling it, and otherwise disable the feature (or work around it).
Is there a way to do that?
Get the WSDL (append ?wsdl to the URL) - you can parse that any way you like.
Unit test the web service to ensure its signatures don't break. When you write code that breaks the method signature, you'll know and can adjust the other applications accordingly.
Or just don't break the web services and publish them in a way that enable syou to version them. As in http://services.domain.com/MyService/V1.1/Service.asmx (for .NET) so that way your applications that use v1.1 won't break when you publish v1.2 and make breaking changes.
I would also check out using an internal UDDI server if it's really that big of a hasle to manage your web services. Using the Green Pages of UDDI will tell you what you want to know about the service.
When you are making a SOAP request you are just sending an HTTP request to a server. If the server understands it, it will respond with an HTTP 200 and some XML back, if it doesn't it will send you some error HTTP code (404, 500, ...)
There is no general way to ask for the existance of a "method" exposed by a web service. Try to use the WSDL exposed if it is automatic, or just try to use the "method" and check for an error in the response (you don't have to send an exception to the user...)
Also, I don't know if I understood you well, but you are thinking of quering the server twice, once to check if the method exists, and second to make the actual call it if it does? I would just check for the error if it doesn't, and proceed normally if it does.