SOAP or REST for Web Services? [closed]

I built one of the first SOAP servers, including code generation and WSDL generation, from the original spec as it was being developed, when I was working at Hewlett-Packard. I do NOT recommend using SOAP for anything.

The acronym "SOAP" is a lie. It is not Simple, it is not Object-oriented, it defines no Access rules. It is, arguably, a Protocol. It is Don Box's worst spec ever, and that's quite a feat, as he's the man who perpetrated "COM".

There is nothing useful in SOAP that can't be done with REST for transport, and JSON, XML, or even plain text for data representation. For transport security, you can use https. For authentication, basic auth. For sessions, there's cookies. The REST version will be simpler, clearer, run faster, and use less bandwidth.

XML-RPC clearly defines the request, response, and error protocols, and there are good libraries for most languages. However, XML is heavier than you need for many tasks.

REST is an architecture, SOAP is a protocol.

That's the first problem.

You can send SOAP envelopes in a REST application.

SOAP itself is actually pretty basic and simple, it's the WSS-* standards on top of it that make it very complex.

If your consumers are other applications and other servers, there's a lot of support for the SOAP protocol today, and the basics of moving data is essentially a mouse-click in modern IDEs.

If your consumers are more likely to be RIAs or Ajax clients, you will probably want something simpler than SOAP, and more native to the client (notably JSON).

JSON packets sent over HTTP is not necessarily a REST architecture, it's just messages to URLs. All perfectly workable, but there are key components to the REST idiom. It is easy to confuse the two however. But just because you're talking HTTP requests does not necessarily mean you have a REST architecture. You can have a REST application with no HTTP at all (mind, this is rare).

So, if you have servers and consumers that are "comfortable" with SOAP, SOAP and WSS stack can serve you well. If you're doing more ad hoc things and want to better interface with web browsers, then some lighter protocol over HTTP can work well also.

REST is a fundamentally different paradigm from SOAP. A good read on REST can be found here: How I explained REST to my wife.

If you don't have time to read it, here's the short version: REST is a bit of a paradigm shift by focusing on "nouns", and restraining the number of "verbs" you can apply to those nouns. The only allowed verbs are "get", "put", "post" and "delete". This differs from SOAP where many different verbs can be applied to many different nouns (i.e. many different functions).

For REST, the four verbs map to the corresponding HTTP requests, while the nouns are identified by URLs. This makes state management much more transparent than in SOAP, where its often unclear what state is on the server and what is on the client.

In practice though most of this falls away, and REST usually just refers to simple HTTP requests that return results in JSON, while SOAP is a more complex API that communicates by passing XML around. Both have their advantages and disadvantages, but I've found that in my experience REST is usually the better choice because you rarely if ever need the full functionality you get from SOAP.