Currently we're developing a RESTful service that has a requirement to return (echo) the newly created/updated resource entity in certain scenarios and alternatively echo nothing back in others; therefore saving network load.
Two solutions have been presented.
Query Variable
POST http://service/resource?echo=false
Accept Header
if ( request.has_header( "Accept" ) )
echo back newly created resource
else
ignore
Is the second scenario improper use of HTTP Headers?
As you've already surmised, the second usage is an improper use of that header. The principle of a "correct" RESTful interface is one that adheres to HTTP standards. Adhering to the standard means using the grammar of HTTP the way it's prescribed. The second proposal would qualify as as not using it as prescribed. Don't take it from me (what do I know), take it from the HTTP spec itself
The Accept request-header field can be used to specify certain media types which are acceptable for the response. Accept headers can be used to indicate that the request is specifically limited to a small set of desired types
That's it. It's meant to be used for Content Negotiation (AKA Conneg); repurposing it, while possible, is frowned upon
I have a web service that triggers some long operations on the server via asynchronous methods. Each operation has 3 methods:
One of them start the operation and immediately returns a ticket number.
One of them is called continuously from the client; it receives the ticket number and returns a boolean value, saying whether the operation is done.
The last one of them is called only after the operation is finished; it receives the ticket number and returns the result of the operation.
I'm not sure how to call this methods. I think about calling the methods something like this:
OperationName_Start
OperationName_IsReady
OperationName_GetResult
but I'm afraid I could be reinventing the wheel. Is there any well known naming convention for this usage pattern?
Its a shame you couldn't get an answer the first time around. I would strongly suggest reading this SOA Principles Link to gain a better understanding of the principals and importance of web service naming.
It's key to remember to name from the perspective of the consumer and maximise consumability and re-useability. Its also useful to remember that when you invoke a service, your are performing and action on an object i.e. you should have a verb and a noun. Also remember that web services are very very similar to functions in an object oriented language, so its helpful to think of what the code of the function of the web service would look like.
It's helpful to consider scenarios like:
What would happen if i changed the system the web service was calling?
Is there another scenario that could call this service?
How granular should the service be? What are the performance impacts of these decisions?
Without knowing the business context of what you are trying to achieve, we'll assume a basic example of submitting and electronic payment.
In this scenario, you may have:
ElectronicPayment_SendPayment (Note: the use of 'Send' keeping the business context, not the technical context; send could be via email, post, webservice. From your 'Start' example, what are you starting; here, the intent of the service is apparent)
ElectronicPayment_CheckStatus (Note: this is from the consumer's perspective. It's likely that checking processing status is a generic service, that could be seperated into something along the lines of CheckProcessingStatus (TicketNumber tN)
ElectronicPayment_RetrieveReciept (Note: Request/Response pattern with semantic link. Business Context of receipt and payment maintained)
Naming is highly contextual, and the above is not perfect, but hopefully it helps yourself and others who stumble upon this.
From the lack of answers, I assume that apparently there isn't a widely used standard on this issue, so it's OK to roll my own.
I chose to stick with:
OperationName_Start
OperationName_IsReady
OperationName_GetResult
I want to provide different answers to the same question for different users, based on the access rights. I read this question:
Excluding private data in RESTful response
But I don't agree with the accepted answer, which states that you should provide both /people.xml and /unauthenticated/people.xml, since my understanding of REST is that a particular resource should live in a particular location, not several depending on how much of its information you're interested in.
The system I'm designing is even more complicated than that one. Let's say that a user has created a number of circles of friends, and assigned different access rights to them. For example, my "acquaintances" circle might have access to my birthday, and my "professional" circle might have access to my employment history, but not the other way around. In order to apply the answer from the question I mentioned, I need to have a way of getting all of the user's circles (which I might want to keep secret for security reasons), and then go through /circles/a/users/42, /circles/b/users/42, /circles/c/users/42 and so on, and then merge the results to display the maximum amount of information available. Obviously there's not necessarily a single circle that gets all the information that any of the other circles get. I believe this is tricky enough (note that I probably need to do this with several kinds of objects and that future versions might require a different procedure), but what if I want to impose security restrictions on a particular user despite the fact that he's also in some of my circles? Can that problem even be solved? Even if I refuse to respond to any of the above-mentioned queries and come up with a new one that could give me an answer, it'd still reveal the fact that this specific user is treated differently due to individual access restrictions.
What am I missing here? Is it even possible for me to develop a RESTful web service?
If the conclusion is that the behavior is not RESTful, would this still constitute as a situation where it'd be morally okay to break the REST contract? If so, what are the negative implications? Do I risk proxy caching issues for example?
According to Fielding's dissertation (it really is a great writing):
A resource is a conceptual mapping to a set of entities, not the entity that corresponds to the mapping at any particular point in time.
In other words, if you have a resource that is defined as "the requesting user's assigned projects" and representations thereof accessible by a URI of /projects, you do not violate any constraints of REST by returning one list of projects (i.e., representation) for user A and another (representation) for user B when they GET that same URI. In this way, the interface is uniform/consistent.
In addition to this, REST only prescribes that an explicit caching instruction be included with the response, whether that is 'cache for this long' or 'do not cache at all':
Cache constraints require that the data within a response to a request be implicitly or explicitly labeled as cacheable or non-cacheable.
How you choose to manage that is up to you.
Keeping that in mind,
You should feel comfortable returning a representation of a resource that varies depending on the user requesting a representation of a particular resource, as long as you are not violating the constraints of a uniform interface -- don't use a single resource identifier to return representations of different resources.
If it helps, consider that the server responds with varying representations of a resource as well -- XML or JSON, French or English, etc. The credentials sent with the request are just another factor the server is able to use in determining which representation to to send in response. That's what the header section is there for.
I agree that the other solution doesn't seem right. It makes the URL structure complicated and more difficult to find the resource. However, if you did REST properly, it shouldn't matter what the URL for the resource is as the server controls it (and is free to relocate it as it sees fit). If your client is really "REST", it would discover the resources it needed through prior negotiation with the server. So the path truly would not matter on the client. I don't like it because its confusing to use - not because of some violation of REST principles.
But that probably doesn't answer your question -
What you didn't mention is your security setup - presumably you are a passing a session token with the request as part of the request header. So your back-end processing should have the ability to tie it to particular set of security constraints. From there, you form the list with whatever business logic you need and return a limited resource based on the user's security tied to the session.
For the algorithm itself, one usually implements a least or most restrictive type algorithm that merges the allowable data into a response (very similar to java realms or Microsoft's user security model).
If the data is structured differently for the restricted/non-restricted case, you could create two different representations of the data and return which ever one the user was authorized to see. The client should be asking for the accepted mime response types anyway, and it would just provide different answers based on the session security in the request header. Alternatively, you could provide optional elements with the representations and fill out the appropriate one base on authorization (although this is a little hack-ee in my opinion).
Related:
Why would one use REST instead of Web services?
When deciding whether to implement a web service using SOAP or REST (by which I mean HTTP/XML in a RESTful manner) what should I be aware of and what should I be thinking of? I presume that this isn't a one size fits all thing so how do I choose which to use.
The two protocols have very different uses in the real world.
SOAP(using WSDL) is a heavy-weight XML standard that is centered around document passing. The advantage with this is that your requests and responses can be very well structured, and can even use a DTD. The downside is it is XML, and is very verbose. However, this is good if two parties need to have a strict contract(say for inter-bank communication). SOAP also lets you layer things like WS-Security on your documents. SOAP is generally transport-agnostic, meaning you don't necessarily need to use HTTP.
REST is very lightweight, and relies upon the HTTP standard to do it's work. It is great to get a useful web service up and running quickly. If you don't need a strict
API definition, this is the way to go. Most web services fall into this category. You can version your API so that updates to the API do not break it for people using old versions(as long as they specify a version). REST essentially requires HTTP, and is format-agnostic(meaning you can use XML, JSON, HTML, whatever).
Generally I use REST, because I don't need fancy WS-* features. SOAP is good though if you want computers to understand your webservice using a WSDL. REST specifications are generally human-readable only.
The following links provide useful information about WSDL vs REST including Pros and Cons
A couple of key points are that
1) SOAP was designed for a distributed computing environment where as REST was designed for a point to point environment.
2) WADL can be used to define the interface for REST services.
http://www.ajaxonomy.com/2008/xml/web-services-part-1-soap-vs-rest
http://ajaxonomy.com/2008/xml/web-services-part-2-wsdl-and-wadl
Regarding WSDL (meaning "SOAP") as being "heavy-weight". Heavy matters how? If the toolset is doing all the "heavy lifting" for you, then why does it matter?
I have never yet needed to consume a complicated REST API. When I do, I expect I'll wish for a WSDL, which my tools will gladly convert into a set of proxy classes, so I can just call what appear to be methods. Instead, I suspect that in order to consume a non-trivial REST-based API, it will be necessary to write by hand a substantial amount of "light-weight" code.
Even when that's all done, you still will have translated human-readable documentation into code, with all the attendant risk that the humans read it wrong. Since WSDL is a machine-readable description of the service, it's much harder to "read it wrong".
Just a note: since this post, I have had the opportunity to work with a moderately complicated REST service. I did, indeed, wish for a WSDL or the equivalent, and I did, indeed, have to write a lot of code by hand. In fact, a substantial part of the development time was spent removing the code duplication of all the code that called different service operations "by hand".
This probably really belongs as comments in several of the above posts, but I don't yet have the rep to do that, so here goes.
I think it is interesting that a lot of the pros and cons often cited for SOAP and REST have (IMO) very little to do with the actual values or limits of the two technologies. Probably the most cited pro for REST is that it is "light-weight" or tends to be more "human readable". At one level this is certainly true, REST does have a lower barrier to entry - there is less required structure than SOAP (though I agree with those who have said that good tooling is largely the answer here - too bad much of the SOAP tooling is pretty dreadful).
Beyond that initial entry cost however, I think the REST impression comes from a combination of the form of the request URLs and the complexity of the data exchanged by most REST services. REST tends to encourage simpler, more human readable request URLs and the data tends to be more digestable as well. To what extent however are these inherent to REST and to what extent are they merely accidental. The simpler URL structure is a direct result of the architecture - but it could be equally well applied to SOAP based services. The more digestable data is more likely to be a result of the lack of any defined structure. This means you'd better keep your data formats simple or you are going to be in for a lot of work. So here SOAP's additional structure, which should be a benefit is actually enabling sloppy design and that sloppy design then gets used as a dig against the technology.
So for use in the exchange of structured data between computer systems I'm not sure that REST is inherently better than SOAP (or visa-versa), they are just different. I think the comparison above of REST vs SOAP to dynamic vs. static typing is a good one. Where dyanmic languages tend to run in to trouble is in long term maintenance and upkeep of a system (and by long term I'm not talking a year or 2, I'm talking 5 or 10). It will be interesting to see if REST runs into the same challenges over time. I tend to think it will so if I were building a distributed, information processing system I would gravitate to SOAP as the communication mechanism (also because of the tranmission and application protocol layering and flexibility that it affords as has been mentioned above).
In other places though REST seems more appropriate. AJAX between the client and its server (regardless of payload) is one major example. I don't have much care for the longevity of this type of connection and ease of use and flexibility are at a premimum. Similarly if I needed quick access to some external service and I didn't think I was going to care about the maintainability of the interaction over time (again I'm assuming this is where REST is going to end up costing me more, one way or another), then I might choose REST just so I could get in and out quickly.
Anyway, they are both viable technologies and depending on what tradeoffs you want to make for a given application they can serve you well (or poorly).
REST is not a protocol; It's an architectural style. Or a paradigm if you want. That means that it's a lot looser defined that SOAP is. For basic CRUD, you can lean on standard protocols such as Atompub, but for most services you'll have more commands than just that.
As a consumer, SOAP can be a blessing or a curse, depending on the language support. Since SOAP is very much modelled on a strictly typed system, it works best with statically typed languages. For a dynamic language it can easily become crufty and superfluous. In addition, the client-library support isn't that good outside the world of Java and .NET
To me we should be careful when we use the word web service. We should all the time specify if we are speaking of SOAP web service, REST web service or other kind of web services because we are speaking about different things here and people don't understand anymore if we named all of them web services.
Basically SOAP web services are very well established for years and they follow a strict specification that describe how to communicate with them based on the SOAP specification.
Now REST web services are a bit newer and basically looks like simpler because they are not using any communication protocol. Basically what you send and receive when you use a REST web service is plain XML. People like it because they can parse the xml the way they want without having to deal with a more sophisticated communication protocol like SOAP.
To me REST services are almost like if you would create a servlet instead of a SOAP web service. The servlet get data in and return data out. The format of the data are xml based. We can also imagine to use something else than xml if we want. For instance tags could be used instead of xml and that would be not REST anymore but something else (Could be even lighter in term of weight because xml is not light by nature). Would we call that still a web service? Yes we could but that will not follow any current standard and this is the main issue here if we start to call everything web services but we can do it the way we want then we are loosing on the interoperability side of the things. That means that the format of the data that is exchanged with the web service is not standardized anymore. That requires then that server and client agree on the format of the data whereas with SOAP this is all predefined already and server and client can interoperate without to know each other because they follow the same standard.
What people don't like with SOAP is that they have hard time to understand it and they cannot generate the queries manually. Computers can do that very well however so this is where we need to be clear: are web services queries and response supposed to be used directly by the end users or do we agree that web services are underneath API called by computer systems based on some normalized standards?
SOAP: It can be transported via SMTP also, means we can invoke the service using Email simple text format also
It needs additional framework/engine should be in web service consumer machine to convert SOAP message to respective objects structure in various languages.
REST: Now WSDL2.0 supports to describe REST web service also
We can use when you want to make your service as lightweight, example calling from mobile devices like cell phone, pda etc...
for enterprise systems in which your system is confined within your corporations, its easier and proper to use soap because you are almost in control of clients. it's easier since there a variety of tools which creates classes (proxies) and looks like you are doing your regular OOP which matches your java or .net environment (in which most corporates use).
I would use REST for internet facing applications for exposing interfaces (like twitter api) since clients can be using javascripts or html or others in which typing is not strict. REST being more liberal makes more sense.
Also for internet facing clients (world wide web), its easier to parse json or xml coming out of a rest interface rather than a purely xml coming from a soap interface. it's hard to use proxies on javascript and javascript does not naturally support objects. If you are using REST with javascript, you would just usually parse the json string and you're off. internet facing interfaces are usually very simple (so most of the time its simple parsing) and does not usually demand consistency that is why REST is adequate enough.
For enterprise applications I don't think REST is adequate because transactions, security, strict typing, schemas play a very important in enterprise applications development that is why SOAP is more suited for them.
My conclusion is that SOAP is for Enterprise systems, REST is for the Internet or WWW.
You can use it interchangeably but you may find yourself having a difficult time eventually not using the correct tool for the job.
sorry for my bad english.
In defence of REST it closely follows the principles of HTTP and addressability e.g. read operations use GET, update operations use POST etc. I find this to be a far cleaner approach. The Oreilly book RESTful Web Services explains this far better than I can, if you read it I think you would prefer the REST approach
The toolset on the client side would be one. And the familiarity with SOAP services the other. More and more services are going the RESTful route these days, and testing such services can be done with simple cURL examples.
Although, it's not all that difficult to implement both methods and allow for the widest utilization from clients.
If you need to pick one, I'd suggest REST, it's easier.
The previous answers contain a lot of information, but I think there is a philosophical difference that hasn't been pointed out. SOAP was the answer to "how to we create a modern, object-oriented, platform and protocol independent successor to RPC?". REST developed from the question, "how to we take the insights that made HTTP so successful for the web, and use them for distributed computing?"
SOAP is a about giving you tools to make distributed programming look like ... programming. REST tries to impose a style to simplify distributed interfaces, so that distributed resources can refer to each other like distributed html pages can refer to each other. One way it does that is attempt to (mostly) restrict operations to "CRUD" on resources (create, read, update, delete).
REST is still young -- although it is oriented towards "human readable" services, it doesn't rule out introspection services, etc. or automatic creation of proxies. However, these have not been standardized (as I write). SOAP gives you these things, but (IMHO) gives you "only" these things, whereas the style imposed by REST is already encouraging the spread of web services because of its simplicity. I would myself encourage newbie service providers to choose REST unless there are specific SOAP-provided features they need to use.
In my opinion, then, if you are implementing a "greenfield" API, and don't know that much about possible clients, I would choose REST as the style it encourages tends to help make interfaces comprehensible, and easy to develop to. If you know a lot about client and server, and there are specific SOAP tools that will make life easy for both, then I wouldn't be religious about REST, though.
You can easily transition your WSDL-spewing WCF web components to other uses just by changing your configuration settings. You can go across HTTP and then also named pipes, tcp, custom protocols, etc without having to change your code. I believe WCF components may also be easier to set up for stuff like security, two-way calling, transactions, concurrency, etc.
REST pretty much limits you to HTTP (which is fine in many cases).
I know that this discussion is an old one, but after reading all the answers and commented, I believe that everyone missed the most important point about the difference between the 2 systems: SOAP uses complex types to not only give you the data, but validate it and keep it in the strict type designation it was defined for. A WSDL tells you what the data format is, what the data type is, allows you to add reg-ex pattern-style rules, and defines how many times a piece of data must be, and may be, allowed in a request/response.
Rest on the other-hand has none of these mechanisms.
SOAP is complex and heavy because it allows you to send complex heavy hierarchical data. REST is plain text, with the origin and endpoint sorting out the rules.
SOAP is business independent, because it has all the data rules embedded in the document.
The difference between SOAP and REST is that SOAP is a self-contained business oriented schema. REST is a text document.
What is the minimum set of HTTP verbs that a server should allow for a web service to be classed as RESTful?
What if my hoster doesn't permit PUT and DELETE?
Is this actually important, can I live happily ever after with just GET and POST ?
Update: Thanks for the answers folks, Roger's answer was probably best because of the link to the Bill Venners and Elliotte Rusty Harold interview. I now get it.
Yes, you can live without PUT and DELETE.
This article tells you why:
http://www.artima.com/lejava/articles/why_put_and_delete.html
While to true RESTafrians this may be heresy, in the real world you do what you can, with what you have. Be as rational as you can and as consistent with your own convention as you can, but you can definitely build a good RESTful system without P and D.
rp
You can also use X-Http-Verb-Override:DELETE inst. of HTTP DELETE. This is also usefull for Silverlight clients who cant change the HTTP verbs and only support GET and POST...
If you just use GET and POST, it's still RESTful. Your web service may only do things which only required GET or POST, so that's fine.
REST allows for breaking protocol convention if the implementations of the protocol are broken (so that the only non-standard things you do are to get around the broken parts of the implementation). So it is allowable within REST to use some other method to represent generally unsupported verbs like DELETE or PUT.
edit: Here is a quote from Fielding, who is the one that created and defined REST:
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.]
Today's web browsers only handle GETS + POSTS. In Rails, for example, PUTS + DELETES are "faked" through hidden form fields.
Unless your framework has some workaround to "support" PUTS + DELETES, don't worry about them for now.