I don't exactly know what RESTFUL is. Sure I know it's a mapping of a URL to a resource. But how's that different from an ajax call to a codeigniter URL which echos some JSON?
My application will have subscriptions with states/options, is there any reason I should be using a RESTful setup rather than just some ajax calls when a user switches some of the options for their subscriptions?
You should not necessarily use "pure" REST. If your requirements drive you towards an HTTP-based service returning JSON, then great. But that doesn't imply that you need other aspects of the REST architectural style. You may not need:
An architecture based on resources, in the sense they're defined by the HTTP protocol
A URL structure that maps to resources
You may not want the return result from one request to provide a set of URLs which indicate "where to go" for related requests.
REST is an architectural style, but it can also become a "religion". Be certain that whatever you do is driven by the requirements you need to fulfill, and not based on "ideology".
Related
Thanks for looking!
Background
I am building a strictly machine-to-machine web-service (restful) application. The application will listen for requests, retrieve data, construct objects, serialize to JSON and return the JSON object.
This application will ultimately be used by other web applications as well as iOS apps, Android apps, and even desktop apps.
The existing code that I have inherited makes a distinction based on how the service was called in terms of HTTP verbs (GET, POST, etc).
Question
In this day and age of machine-to-machine communication, is the HTTP verb even relevant any longer? Could it in fact be constraining for future adoption of the service API to base the code around HTTP verbs?
Update
fmgp provides a clear answer to "why" these verbs are used, but I feel should I clarify my concern:
Will other platforms such as iOS or Android (for example) be able to originate HTTP verb-based calls like GET and POST? If the answer is "no" then I assume that we should stay away from relying on these verbs and instead build the desired action into the request URL as a parameter.
In RestFul applications, you have a verb foreach CRUD operation:
Create: POST
Read: GET
Update: PUT
Delete: DELETE
Everything claimed "restful" will work the same way according to this philosophy.
There's nothing standard in that, just a clean, good designed, easy to understand programming style. Of course you may want to do all operation with only GET and some query parameters as soon as your client and server can handle it.
I was wondering what would be the best approach to make a Grails app offer a RESTful API (some CRUD actions mainly) that can be used by a web service, e.g. when you want to build a corresponding iOS app to your browser-based app or anything else.
I thought of building a separate part in my Grails application that takes calls from www.mywebapp.com/api/someAction so that I can reuse the Service layer. How would I do the URL mapping then? Only having one big ApiController does not sound very groovy.
Or is there any better approach I did not know of? This approach must support something like OAuth to authenticate the user who is calling the Web service.
Grails can definitely provide a REST api, but the level of difficulty in doing so varies depending on how mature (aka. how RESTful) you want the API to be.
Basic REST
Getting a basic level of RESTfullness, where you are manipulating json or xml representations of resources using the full span of HTTP verbs and leveraging the HTTP response codes, is pretty easy. There are 3 main pieces to getting that in place:
URL mapping
Here's an example of how I wrote my URL mappings on a recent project to allow for more RESTful URLs:
// RESTful list mapping
name restEntityList: "/$controller"(parseRequest: true) {
action = [GET: "list", POST: "save"]
}
// RESTful entity mapping
name restEntity: "/$controller/$id"(parseRequest: true) {
action = [GET: "show", PUT: "update", POST: "update", DELETE: "delete"]
constraints {
id matches: /\d+/
}
}
Content negotiation
The 3 different ways that Grails can handle content negotiation make the framework very flexible, allowing you to support a much broader range of clients who may not be able to set things like the Accept HTTP header.
You can use the content negotiation to respond to different requests in different ways using the withFormat block based on what the client has indicated they want. This powerful ability can also be used to version your API, much like how Github does.
Response status
HTTP already has a great response mechanism built into it that allows you to leverage innate abilities in the architecture, like cacheability and indemnipotent operations. While some web browsers don't handle certain response codes very gracefully, client applications using your API can use them to greatly simplify their internal code.
DRY REST
One of the best ways to make your application RESTful and keep it DRY at the same time is to leverage the controller scaffolding as much as possible, since CRUD is essentially the same for all domain objects. This article on making the default controller more RESTful, and this article on simplifying the default controller are both great resources for getting more power from the scaffolding.
Advanced REST
Once you get to that point, you have a pretty functional REST API for your grails application. You can do all basic CRUD operations and the resources are fairly easy to work with.
The next levels of the ladder to a true RESTful hypermedia API, however, are much harder to attain. Fixing this is on the road map for Grails, but currently it's rather painful. These pieces are:
Hypermedia resources
Content types
Versioning
Thankfully, there is a plugin that makes defining custom marshallers very easy, which allows us to fairly easily cover those three remaining pieces of the REST puzzle.
Finally, there is the aspect of securing the whole thing. In general, Spring Security will hold you in good stead as far as securing user-access to your api. Since most API access is from an application, and isn't user-visible, basic or digest authentication is usually the simplest way to go. There is an OAuth plugin that builds on Spring Security. I have not personally used it so I can't vouch for it's stability, but it looks pretty good to me.
In general, Grails is flexible and powerful enough to do REST very, very well, but the work has not been done yet to make it do REST cleanly out-of-the-box.
the grails documentation has a good walk though on setting up a RESTfull api
http://grails.org/doc/latest/guide/webServices.html#13.1
You can map it anyway, use any url structure. Grails UrlMapping is pretty flexible, it's only default behavior to map to /$controller/$action, but you can use your own mapping, you can event map each url manually, etc.
See UrlMapping docs - http://grails.org/doc/latest/guide/theWebLayer.html#urlmappings
url mapping:
"/api/element/$version/$master" {
controller = "element"
action = [GET:"show"]
}
This will map the http get to the show method of the controller element.
i.e. the show method:
DRY: The api is probably the same logic as the application. The difference is content negociation.
...
def show = {
def elements = elementService.findByMasterVersion(params.master, params.version)
withFormat {
xml {
render(status:200,text:elements as XML, contentType:"text/xml",encoding:"UTF-8")
}
json { ... }
html { ... }
}
}
Oauth is pretty damn complicated to implement and seems overkill for a lot of situation.
SO I am about to write a REST API with Django using django-piston but my employer just wanted to be able to retrieve and create data, so I was wondering what is the difference between:
just creating methods to set and retrieve data and making them
publicly available (of course with authentication and validation in
place)
creating a REST API for the purpose of creating and retrieving data
?
Thanks in advance!
Your second point is basically a sub set of your first point. REST is just a set of methods to create and retrieve data. It is however a fairly standardized set of methods using HTTP verbs instead of different urls to declare what you are trying to do.
So instead of /comments/new/, /comments/delete/, /comments/update/, you would just have /comments/ and POSTing to create, PUTing to update, and DELETEing to delete.
I also agree with Zach on TastyPie for what it's worth.
The two key alternatives to "RESTful" would be traditional html forms or a more formal RPC protocol thats implemented on top of HTTP, like XML-RPC or SOAP.
The main advantage of the former is that it can be invoked through a web-browser with no client code at all; but unless the application is designed in a thoughtful way, it's often quite difficult to drive such an interface from a custom client; which must often set cookies to do authentication and specify arguments that it isn't interested in. There's no notion of data types for this kind of API either, everything is text.
The latter has the advantage of getting you up and running in no time at all; You can just write normal functions in python, with a decorator, and they are available for clients that have the appropriate client libraries. The main disadvantage is also that this usually requires the client have such a library. Things like soap or xml-rpc are not typically an option for in-browser applications, or on resource-constrained devices.
RESTful is a sort of middle way that combines many advantages of both. Since the semantics are defined purely in terms of HTTP, any client capable of issuing HTTP can use a RESTful API. HTTP is much more flexible than plain old web forms, usually in terms of giving a Content-Type to the request or response that supports the needed structure. Unfortunately, there's not really a single standard defining how RESTful clients or services should represent their data, so there's necessarily a bit of customization on both ends to get things to work in the best way. Sometimes the flexibility means that you spend more time getting the api just right then you would have had to if you used a different interface, but it often leads to a thinner and yet less leaky abstraction.
There are a few standards or de-facto standards that are also good models of RESTful interfaces, such as json-rpc and the Atom Publishing Protocol.
I just finished reading Restful Web Services and Nobody Understands REST or HTTP and am trying to design an API with a RESTful design.
I've noticed a few patterns in API URI design:
http://api.example.com/users
http://example.com/api/users
http://example.com/users
Assume that these designs properly use Accept and Content-type headers for content negotiations between XHTML, JSON, or any format.
Are these URI's a matter of a pure RESTful implementation vs implicit content negotiation?
My thoughts are that by explicitly using API in the URI is so that a client will expect a data format that is not inherently human pleasing hypermedia and can be more easily consumed without explicitly setting an Accept header. In other words, the API is implying that you expect JSON or XML rather than XHTML.
Is this a matter of separating resource representations
logically on the server side?
The only justification I can come up with for why someone would design their URI's with an API subdomain is because, based off my assumption that this is a scaling technique, it should make routing request load easier in a multi-tiered server infrastructure. Maybe situations exist where reverse proxies are stripping the headers? I don't know. Different servers handling different representations?
Maybe a subdomain is used for external consumers only so that the server avoids the overhead from internal usage. Rate limiting?
Am I missing a point?
My proposed design would attempt to follow RESTful practices by setting appropriate headers, using HTTP verbs appropriately and representing resources in a fashion that I feel including 'API' in the URI would be redundant.
Why would someone design a RESTful API with 'API' in the URI?
Or could they? Maybe my problem with not understanding this design is that it doesn't matter as long as it follows some combination of specification which may not lead to a RESTful API implementation but close? There is more than one way to skin a keyboard cat.
HATEOAS related?
Update: While researching this topic I have come to the conclusion that it's important to consider ideas from REST but not to treat it as a religion. Thus, whether or not to have 'api' in the URI is more of a design decision than a steadfast rule. If you plan to expose your website's API publicly it would be a good idea to use an api subdomain to help deal with the application's logic. I hope that someone will contribute their insight for others to learn from.
I would (and have) done it to separate it from the 'website' infrastructure because it's probably going to have a higher load and require more infrastructure - it's a lot easier to do millions of API calls a day than get that in page views because you have the full load of n sites/companies and their efforts and traction, collectively and even in some cases individually they're going to attract more traffic than you yourself.
This is my understanding and point of view about your question :
Are these URI's a matter of a pure RESTful implementation vs implicit
content negotiation?
No, they are not part of any official documentation (that I know of), and are usually at the developper/team standards discretion. For example, Zend Framework uses some utility classes to detect XHR requests and how responses should be returned. Granted, ZF is not pure RESTful design (or most PHP application as a matter of fact), but it is still possible to write such designs even in PHP.
I have often seen api being used in urls when the returned data expected is indeed not meant to be used as is for display to the end user. However it is usually a design decision and not necessarily an implied standard.
Is this a matter of separating resource representations logically on
the server side?
More or less. For example, when performing a PUT request, for example, the interface does not necessarily need to be entirely refreshed, and often a simple response message is good enough. While this response message is part of the view, it is not the view. So, for example, http://domay.com/users/ would return the interface to manage users (or whatever), http://domain.com/users/api would perform operations and return interface updates (without a page reload).
Am I missing a point?
Weell, no. Since it is a design decision to use or not api in the URL, you're not missing anything here. With the proper headers,
http://domain.com/users/api/get
http://domain.com/users/get
http://domain.com/users/
can all be valid RESTful requests.
Why would someone design a RESTful API with 'API' in the URI?
Simply put, to have an URL naming convention. So that, when looking at a request in logs, documentation, etc. One will understand it's purpose.
Also keep in mind, that most frameworks (django, RoR,...) provide URL-based routing out of the box. You probably need different views for API vs. HTML responses to manage things like authentication, trotting, limits-check and other specific stuff differently.
Putting in place an additional HTTP-Header based routing system to allow, as you say, implicit content negotiation is often not worth the effort.
User-visible webpage URLs are subject to the whims of webmasters, designers, corporate organization, marketing, fashion, technology, etc.
An API, on the other hand, is supposed to remain stable. By using a subdomain you isolate your API from the rest of the website and the changes it is likely to undergo in time.
I see APIs such as PayPal, etc. offering to call their services using NVP or SOAP/WSDL. When using a .NET environment (3.5) using traditional web services (no WCF) which is better and why? I know WSDL lets you drop in the API URL and it generates the wrappers for you. So then why do companies even offer NVP?
There seems to be never-ending confusion in this industry about the different types of web services.
SOAP is a messaging protocol. It has as much in common with REST as an apple has with a lawn tractor. Some of the things you want in a messaging protocol are:
Headers and other non-content "attributes."
Addressing - routing of a message to different servers/recipients based on the headers;
Guaranteed delivery via queuing and other methods;
Encryption, signing, and other security features;
Transactions and orchestrations;
Accurate representation of complex structured data in a single message;
...and so on. This is not an exhaustive list. What WSDL adds to SOAP, primarily, is:
Discoverability via a contract, a form of machine-readable "documentation" that tells consumers exactly what is required in order to send a message and allows proxies to be auto-generated;
Strict, automated schema validation of messages, the same way XSD works for XML.
REST is not a messaging protocol. REST is a system of resources and actions. It is a solid choice for many architectures for several important reasons as outlined by other answers. It also has little to no relevance to "NVP" services like PayPal and flickr.
PayPal's NVP API is not REST. It is an alternative, RPC-like messaging protocol over HTTP POST for clients that don't support or have difficulty supporting SOAP. This isn't my opinion, it's a statement of fact. One of the fields in the NVP is actually METHOD. This is clearly RPC verbiage. Take a look at their API for UpdateRecurringPaymentsProfile and try to tell me that this makes a lick of sense to describe as a "resource". It's not a resource, it's an operation.
In the case of PayPal specifically, the "NVP" (HTTP POST) API is inferior to the SOAP API in almost every way. It is there for consumers who can't use SOAP. If you can use it, you definitely should.
And I'm not necessarily bashing PayPal for this, either. I know a lot of folks have bashed them for not putting together a "proper" RESTful API but that is not what I am getting at. Not every service in the world can be accurately described with REST. PayPal isn't really a resource-based system, it's a transactional system, so I can forgive their architects and developers for not having a perfectly elegant REST architecture. It's debatable perhaps, but it's not black-and-white. It's fine; I'll just use the SOAP system if I need to.
Compare this to, say, the Twitter API. This is a true REST service. Every "operation" you can perform on this API is accurately described as either the retrieval or submission of a particular kind of resource. A resource is a tweet, a status, a user. In this case it literally makes no sense to use a complex SOAP API because you're not really sending messages, you're not performing transactions, you're just asking for specific things, and these things can be described with a single URL. The only difference is that instead of getting an HTML web page back, you're getting some XML or JSON data; the way you request it is exactly the same.
A REST Web Service usually (always?) uses HTTP GET for the retrieval of some resource. And Twitter does exactly this. GET still uses "Name-Value Pairs" - that's the query string, ?q=twitterapi&show_user=true. Those bits after the ? are name-value pairs. And here's a great example of why you would want to use REST over SOAP; you can hook this up to an RSS feed and get streaming updates. I can turn it into a Live Bookmark in Firefox. Or I can download it in JSON format and bind it to something like a jqGrid. The interesting thing is not that the request uses "Name-Value Pairs"; the interesting thing is that it's a simple URL and can be consumed by anything that knows how to request a web page.
So to try and summarize all of what I've said, think of it this way:
Use a REST API (if available) when you want to expose data, or consume or publish it, as a permanent resource.
Use a SOAP API when the system is transactional in nature and/or when you need the advanced features that a complex messaging protocol can offer, such as RM and addressing.
Use an RPC API (which includes just about any API that's modeled entirely around HTTP POST) when there is no SOAP API or when you are unable to use the SOAP API.
Hope that clears up some of the confusion.
I assume that by Name Value Pairs, you mean REST services.
The benefits to REST are primarily ease of development, simplicity and elegance, and lower overhead (which is very important if you are sending and receiving a lot of small messages).
Here are some of the advantages of REST:
REST is more lightweight
Human readable results
Everything is a URI addressable resource
REST services are more easily cached
REST is easier to build (no toolkits are required)
REST is easier to call (HTTP - GET, POST, PUT, DELETE)
NVP is HTTP POST
name=fred
amount=100
code=403
etc
This is the default format from any HTML browser so it's simple to implement for sending data to a web service
I don't think it's a good format for receiving data from web service? JSON or XML would be more suitable
No everyone uses VisualStudio, or has access to automatic wrapper generators, or wants to use such a beast
Many web mashups are coded in Javascript, so using HTTP POST to send data is the simplest way. The return result is a standard HTML response code (200, 403, 500, etc) and/or some JSON
Many service providers offer multiple API's to cater for all customers