My talk at NSConf was about cross-platform Objective-C. Those people who I talked to after the session will know that my goal is clear. There are plenty of people out there who have learned Objective-C to get onto the iOS or Mac app stores. Those people need some server-side smarts in their apps, and want to benefit from the skills they’ve already acquired. In other words: they want Objective-C on the server.
I’m now in a position to offer that :). I took a look at the GNUstepWeb project, a reimplementation of WebObjects 4.5. It was in a fairly parlous state, and wouldn’t even build on my Mac. I’ve fixed that. It’s still a bit of a faff, but we’re in a position to start playing with server-side ObjC and see whether there’s any value in having a better product.
Building GSW on the Mac
GNUstep-make
First, you need to grab GNUstep from SVN. Now you need to compile GNUstep-make, the build system. On Mac OS X you do the following:
cd modules/core/make
./configure --with-library-combo=apple-apple-apple
make
make install
The weird configure invocation tells GNUstep you’re going to use the Apple Objective-C runtime, and the Foundation (and AppKit) libraries instead of GNU replacements.
GNUstep-make includes a shell script that defines the locations of various folders. You should import that into your shell environment:
. /Library/GNUstep/Makefiles/GNUstep.sh
Consider adding that line to your .bash_profile.
GNUstep-base
Then you build the GNUstep-base extensions, some additional classes and macros for working with Foundation code.
cd modules/core/base
./configure
make
make install
GDL2
GDL2 is the GNUstep Database Library; an EOF-like framework for interacting with databases. If you’re going to use a DBMS like MySQL for your web apps, you should install that and its developer headers before doing:
cd modules/dev-libs/gdl2
./configure --disable-gorm-palette
make
make install
(Aside: GORM is the GNUstep version of Interface Builder. You don’t need the plugin for working with entities in GORM, and you can’t build it on Mac OS X so that’s why it’s disabled in the configure invocation.)
GNUstepWeb
Now here’s the good stuff. Build and install GSW. At time of writing, there’s an open bug that stops it building on Mac OS X, so you’ll need to grab the patch from this bug report. Apply that patch, then:
cd modules/dev-libs/gsweb
./configure
make
make install
A sample app
You probably want to see a sample GSW app, so it’s a good job I wrote one :-). Clone the HelloGSW project on GitHub. I’ll show you how to build and run that before we get into how it works.
Building HelloGSW
cd HelloGSW
make
Running HelloGSW
HelloGSW.gswa/Contents/MacOS/HelloGSW
this will spit a load of output to the console, including a URL that looks like http://localhost:9001/WebObjects/HelloGSW.woa/0/. Open that URL in your browser. You should see this:
HelloGSW code walkthrough
The interesting code is in the Main class, which is a subclass of GSWComponent (and conventionally the default component to show for a new visitor). Each “page” in a GSW app is a component, though of course you could arrange to return XML, JSON or any other format rather than HTML. HTML is the default and the easiest to work with, and indeed we’ll start by looking at a section of the HTML file, Main.wo/Main.html.
<p>The time is <webobject name=now_string></webobject>.</p>
This is clearly the paragraph that puts the date onto the screen, but you can see that there’s this weird <webobject> tag in there. That’s going to be substituted with our date object at runtime, but how? To answer this question, look at the Main.wo/Main.wod file.
now_string:WOString {value = now}
This file contains bindings, which if you’re familiar with Cocoa work pretty similar to Cocoa Bindings. This tells us that there’s a web object called now_string, that it’s an instance of WOString, and that its value binding is bound to something called now.
That now binding is actually a key on the component object. We might expect to see a method called -(NSString *)now defined on Main to fill in the value of this string. Indeed, if we look at Main.m:
- (NSString *)now {
NSDate *theDate = [NSDate date];
return [theDate description];
}
Where to go from here?
The start is to build more GSW apps, and of more complexity. However there are things that need to be done along the way: all of the rest of the code and files in this project are meaningless boilerplate. This stuff needs to be hidden, automated or removed. Then we can also automate the process: compare how much of a faff setting up this app was with running a Rails app in Heroku (and I haven’t even set up an adaptor to a real web server!). It’d be really useful to simplify common tasks in modern web applications, such as exposing REST interfaces and non-HTML document formats.
Conclusions
Objective-C is not just a client app language. It’s got a long heritage as a server technology, but unfortunately the tools for doing that are quite out of date. They’re still useful though, so people who have come into the Objective-C fold recently can expand the use of their newly-found skills. Hopefully people will adopt—and contribute to—GNUstepWeb and help everyone to make it a useful modern server technology.
