One year ago it became clear that Infovark had outgrown the Windows Communication Foundation (WCF).
We’d decided to use WCF because we wanted Infovark to provide web services, and we liked the fact that we could deploy WCF to client machines. Since WCF is built directly on top of HttpListener, a core part of the Microsoft .NET Framework, we wouldn’t need to use System.Net or Microsoft IIS.
But we’ve struggled with WCF for a variety of reasons. First, we wanted to use a REST model for our web services, and WCF’s support for REST architectures lags behind its SOAP support.
Second, there’s no easy way to return HTML from WCF. We tried transforming our XML with XSLT and returning the XHTML results as a Stream. This works, but the programming experience is frustrating.
Last, because of the previous two reasons, we were left with a website that was way too rigid and programmer-like. It didn’t feel like an organic website. The tool we’d picked was forcing us to compromise on our website design goals.
Infovark’s primary mission is to help human beings, not other computers. That means that the look and feel of the web interface should be our number one priority. Awesome web services are nice to have, but happy users are more important.
So for the past few months, we’ve been hunting for an alternative web server. We can’t use IIS because its footprint is too heavy. Most IT departments won’t allow us to install IIS on client machines.
We could use Apache. It has a nice embeddable version, but interacting with it via C# is tricky. We’d prefer something a little more Microsoft-native.
That basically leaves us with one commercial option and two open source options.
(If you know of other web servers worth investigating, please let us know in the comments!)
More important than picking an alternative web hosting framework for Infovark is the timing of the switch. We don’t want to impede future development.
As a stopgap, we might try plugging in the Spark View Engine to replace our current XML-XSLT-XHTML rendering path. Who knows? If it improves our web development flow, we might be able to keep our WCF base after all.
I ran into a problem yesterday. I’d sent a HTTP POST request to a collection of resources on our RESTful web service. Our server responded with an
HTTP 201: Created status code and the URI of the new resource in the
And then… nothing happened.
This was not what I was expecting. I expected my web browser to follow up with a GET request to the URI I’d provided. But Firefox 3 wasn’t biting. A problem with Firefox? I checked in IE8 and Google Chrome and got the same behavior.
Had I misread the HTTP spec? Did I misunderstand the REST pattern? I grabbed for my worn copy of RESTful Web Services. Nope.
HTTP 201 seemed to be the right status for this situation.
Had I blundered into some common error? I checked Stefan Tilkov’s useful list of REST Antipatterns. But I couldn’t find anything that quite matched my situation.
I started Googling, but couldn’t find much apart from this question about HTTP Post on Stack Overflow. There were some cryptic responses (to which I’ve added my own answer now).
The answer is that while web service clients will often “take the hint” provided by a
HTTP 201: Created response, web browsers won’t. If you actually want a web browser to go somewhere else, you need to send a status code in the 3xx series. In this situation, the status code you want is
HTTP 303: See Other.
Once I changed the status code returned by the server, all the web browsers followed up the response with a GET to the new URI.
I know it’s possible to transmit Internet Protocol by carrier pigeon, but I’m not sure I could recommend it to our customers with a straight face. By the same token, I’m continually surprised to hear vendors and consultants insist that Web Services can be done without the web.
Yet I’ve seen that claim repeated all over the Internet. Sure, it’s true in the academic sense. Technically, there’s nothing wrong with “webless” web services, just like IP by avian carrier will eventually get the job done (though latency and packet loss are a challenge). But practically speaking, why would you use anything other than HTTP?
The “webless web services” meme has infected a number of good ideas. The SOAP standard is a case in point. At first, SOAP was a simple XML wrapper around an XML payload. (Remember when the S in SOAP stood for Simple?) Then a variety of industry heavyweights jumped on the bandwagon, and soon SOAP could be used with any protocol.
Nicholas Allen recently shared a great presentation on REST and SOA given by Stefan Tilkov at QCon. Stefan makes some great points about how RESTful web service design aligns well with the goals of Service Oriented Architecture (SOA).
Sure, you could use the WS-* stack if you like, but RESTful web architecture is a proven, scalable and truly simple approach, as long as you don’t mind having to use HTTP.
Much of the added plumbing in the WS-* stack is there to help transition older computer-to-computer network communication technologies. It allows applications that depend on CORBA or DCOM to tunnel through firewalls. But unless you’re trying to retrofit a system built before, say, 1998, you can skip all that stuff.
Wasn’t using web protocol the whole point of web services anyway? As Stefan said in his closing comments: “Protocol independence is a bug, not a feature.”
Use a RESTful architecture for new development. Put the web back in web services.
I finally figured out the source of my HTTP 400 problem. Apparently the Windows Communication Foundation deals with exceptions differently depending on your InstanceContextMode settings. I had been using the
Single setting but I should have used the
PerCall setting. In PerCall mode, the try/catch block works as expected.
I think it has something to do with the way that WCF distinguishes between channel exceptions and message faults.
Anyway, if you’re building a REST web service, you’ll want to make sure your class is decorated with the following ServiceBehavior attribute.
In part one of this series, I listed several websites and blogs that had useful information on the Windows Communication Foundation (WCF) and REST. I also mentioned that if I was stating again, I’d probably use something other than WCF. Perhaps deriving my own REST server from System.Net.HTTPListener, for example.
Vish asked for some additional details in his comment to that post. He works on the Microsoft WCF development team and was curious about our experience.
I had just begun putting together my response when I noticed Scott Guthrie’s post about Service Pack 1 for the .NET Framework 3.5 beta release. Steve Maine also posted specifics about the ADO.Net Data Services and WCF changes.
So, Vish, it seems your team’s beaten me to the punch on some of these issues! Many of the difficulties I was having with WCF and REST were addressed by the service pack. Here’s an overview of our key stumbling blocks:
I’ll talk about all five of these areas in more detail in upcoming posts in this series. And I’ll be sure check out the SP1 beta once we get our Infovark Alpha release out the door.