may I have some example/typical use case of HATEOAS? I agree it can be a very powerful concept provide great flexibility but I am not sure how to properly get benefit from HATEOAS. would be great if you can share your experience/use case.
A good answer from #dreamer above, but HATEOAS is not present in most REST-based services. It is a constraint on the REST architecture style that allows clients to interact with a service entirely via the hypermedia contained in the resources.
If you look at the Twitter or Facebook REST APIs, you won't find hypermedia. Look at the Facebook friendlist resource. There are no hypertext links in that resource that you can use to transition the state of the resource - to delete, update, etc. Instead, you need to read the out-of-band documentation to understand what you need to do to delete that resource.
One of the claimed advantages of using hypermedia in your APIs is that you can manage change within the resources themselves. For example, what if Facebook wanted to add additional functionality to the frendlist? If it were built with HATEOAS in mind, the resource would be updated to add the hyperlinks provides those additional state transitions.
If this sounds difficult, you're right. But as a developer of client applications, however, once you understand how the hypermedia is presented, you can build applications that will evolve along with the API itself.
So how do you build APIs using HATEOAS? A number of options are out there, but I like the Hypertext Application Language (HAL) the best.
UPDATE: Since you asked for an example, here's a link to a demo using HAL.
Good public HATEOAS use cases are hard to find, because there are a lot of misconceptions around REST, and HATEOAS can be hard to implement. You really need to have a good understanding of its benefits, before you're willing to put yourself through the trouble of getting it to work, and if the clients don't follow it correctly, all work will be in vain.
From my experience, implementing proper REST in a company is a culture change as important as moving to version control systems or agile development. Unless everyone adopts it and understands it, it causes more trouble than it solves.
Having that in mind, I think the best example one will find is the foxycart.com HAL API, on the link below:
https://api-sandbox.foxycart.com/hal-browser/hal_browser.html#/
It's very powerful concept used in RESTful presentation of the application to the client. There are many many projects which are adopting this interface now. A typical use case for this is Web Services APIs using RESTful APIs. A RESTful APIs typically consists of the following elements:
base URI, such as http://example.com/resources/
an Internet media type for the data. This is often JSON but can be any other valid Internet media type (e.g. XML, Atom, microformats, images, etc.)
standard HTTP methods (e.g., GET, PUT, POST, or DELETE)
hypertext links to reference state
hypertext links to reference related resources
The application state can be modified using above HTTP methods for example, to get a particular resource, A client can issue a REST query using curl like:
curl -X GET --url "http://example.com/resource/" -X "Content-Type:application/json"
you could go through the man pages for curl and its usage. More on RESTful interface concepts can be looked upon at wiki
Related
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 thought to practice SOAP API. I know it is a time for REST but I thought to give a try to SOAP. I somehow got Flickr.com API supporting SOAP but it has very difficult documentation. No, working examples are available.
Q1. So, do anyone know where I can learn SOAP. Do anyone has SOAP working example for Flickr API
Q2. Any service other than Flickr providing SOAP interface. I saw Google search api has closed new request for SOAP.
regards
SOAP has been largely superseded by REST on the public Internet - as you have noted in your question and has been alluded to in comments.
There are still large users in the Intranet context, companies with an installed base of SOAP, Service Bus, and other concepts that you may well come across if you end up working at one of them. (There are still CORBA users out there also!) When you control both ends of the application, you may have less reason to be flexible using REST.
So if you are looking for useful public implementations you are mostly out of luck.
That said: do create your own services and try them out on your own. Define a service and implement it. Create a client in a different language. Create another client in a third language.
If you are looking for an educational experience, this will lead you down some of the same paths that has lead to REST use in wide-scale disparate systems (and may also shed light on why the public/private has split the way it has)
Good Luck
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
Does anybody know a wiki engine that can be built on top of a RESTful application?
I have a restful application, that exposes a document resource,
I want the wiki engine to use the REST API to persist the documents, instead of saving them to a DB.
I am also open for suggestions of an open-source wiki engines that can be easily modified to support such functionality.
As Wikis were originally designed to work in a standard browser, and most browsers did not support anything except GET and POST, REST is not a concept used a lot on the wiki world. However, nowadays, some wikis (foswiki - the community fork of TWiki for instance) provide you a REST API to it http://foswiki.org/System/CommandAndCGIScripts#rest ).
But you need the opposite: a wiki with a customizable backend (storage) that could be plugged on top of a REST storage service. As wikis with a pluggable backend, I know only of pmwiki http://www.pmwiki.org/wiki/PmWiki/PmWiki and foswiki (the open fork of TWiki) http://foswiki.org.
Okay, this is a puzzler. Wikis in general are more or less the canonical example of a RESTful approach. The page name names a resource. What do you want that isn't in, eg, Twiki?
While you could try to find a wiki that can use a REST backend, it may be better to write a small wiki yourself. Because even though a your backend has REST interface, that doesn't mean you can put some other application in front of it.
dokuwiki does not use a database. It is a filesystem based wiki. I don't know its internal code structure but you might be able to use it as your base.