Alternative to building a proper web service for iPhone app to consume

Question

I am in the process of scoping the development of an iPhone app for a client. Among other things, the app will allow users to browse through and place orders on specific (tangible) products.

The client has a website that currently does a similar thing and due to their limited budget and the fact that the website runs on a third-party proprietary platform which they have no control over, we are investigating possible alternatives to building a web service.

On the website, user registration and authentication, as well as order placing is done through POST requests via secure HTTP. The response is always a formatted HTML page which will contain strings indicating whether the request was successful or not, and if there was an error, what the error is etc.

So provided I can replicate the POST requests on the phone, and parse the HTML responses to read the results of each request, do you think this is an acceptable alternative to building a web service to handle this?

Apart from the possibility of pages changing (which we can manage) and the fact that I will probably have to download and parse a relatively large HTML response, are there any other drawbacks to this solution and is there anything else that I might be missing?

Many thanks in advance for your thoughts. Cheers, Rog

Answer 1

Don't go for a parsing solution on the iPhone for 4 reasons:

• Server can change their design and break your application (AppStore submition is long) + They can also detect that the request are sent from an application based on user agent which you have to update the application to change it.
• Some of the requests might be made thru Javascript so you not only have to parse (X)HTML but also Javascript request (which can be in the form of XMLHttpRequest, but don't have to)
• Long term evolution of the mobile market : maybe your client want (or will want) an application for android, Blackberry, Bada OS (Samsung), Symbian (Nokia/ OVIStore), Java Mobile or Windows Phone 7?
• Of course network traffic, Memory and CPU needed to parse HTML (look the time it takes to the browser to do it?)

Regarding the traffic, if the application will not have a huge traffic you can home-host your proxy. Or you can find some provider to host it for you. I guess you won't need more than a couple of Megabytes of storage but maybe traffic. For less than 100€/year you can find some with unlimited traffic (like OVH Pro plan or Infomaniak). But if you want to go Java have a look at Google App Engine : you pay only if your traffic is important and if your application generate many CPU Cycles. If not : you don't have to pay. And it's hosted on Google server : reliable.

Answer 2

If the client is open, you could consider the paypal API.

Answer 3

So, you're going to parse HTML and formulate POSTs off a third-party server, and pray that they don't even so much as rename a form field.

Your question is in two parts:

1. Do I think that a miracle is an acceptable solution? I don't.
2. Do I think that aside from the fact a miracle is required, are there any other drawbacks? None that I can think of.

You didn't ask, but this is a terrible course of action. Two suggestions.

1. I spy an assumption that the providers of the third-party platform aren't interested in enabling third-party applications by providing an API. They have a very good business reason for this, which is that it promotes platform lock-in. Reach out to their support department and have a talk with them.

2. You have to sell the client on building an intermediary web service. To at least try to mitigate the damage that changes on this third-party platform can do to your app, I recommend that you build and operate a proxy that receives requests from your applications, and proxies them over to the third-party platform. You should build into this client-server protocol a means for returning "we are in maintenance mode, go away" messages to apps, for that inevitable day when the third-party server changes something that breaks your app (they swapped the billing and shipping address pages, for instance) and you have to rush through an update through Apple to deal with it.

The proxy could be written in something more flexible and easy to bash stuff out in, such as PHP, Python, Perl, or Ruby. It could be hosted at Amazon in a micro instance.

p.s. This question is inappropriately tagged objective C.

Answer 4

I think utilising the web language of JSON would contribute to the diminishing of the parsing time. By building a REST service that, when sent a GET request, returns the correct information for easy sorting, you could then display the output a lot faster than that of parsing straight HTML.

I prefer JSON over XML, but everyone has their personal preference. You should look at a few very good libraries that are built specifically for parsing purposes of both XML and JSON.

For XML I recommend using the inbuilt libxml parser. Albeit, this can sometimes deem very difficult to use. A simple Google search will bring up a heap of results that relate specifically to what parser should be used depending on what task is to be completed.

As for a JSON parser, I recommend SBJSON. I am currently using it one of the biggest projects I have undertaken and it is definitely working perfectly for my use.

If you need a good way to connect to a RESTful web service, you should try LRResty.

Answer 5

HTML is the worst because of parsing (1-2secs per page), memory, and changes, but you already know that. Check in advance that ALL the data you need is exposed on the HTML.

If you use an intermediary server you are moving work elsewhere and you have another server to maintain. I would only do that if memory is an issue. Check How To Choose The Best XML Parser for Your iPhone Project for memory/performance/xpath support. libxml2 is a good option, but it depends on your needs. And maybe you'll want to check ASIHTTPRequest features before using the SDK.

Answer 6

You could create an intermediary server that will communicate with the client server, and on it expose some REST web services with json (small overhead and easy to handle) responses that will be consumed by the iPhone app.