building server applications using objectivec and gnustep

GNUstep Presentation

Building Server Applications using Objective-C and GNUstepNicola Pero, Fosdem 2009

Server Applications

Server Applications = programs with no GUI

In GNUstep, server applications are based on GNUstep-base.

GNUstep-base is the most complete and extensively polished and tested part of GNUstep ...

but is little known to the public.People often identify GNUstep only with the GUI framework/development environment.

Objective-C

it is a programming language

it is a strict superset of C it is C with some new additional constructs

C code compiles as Objective-C code

C libraries can be linked and used natively from Objective-C

it adds Object-Oriented features to CDefining classes

Implementing methods

Instantiating classes and objects

Invoking class and object methods

Protocols, categories, selectors, forwarding

Why is Objective-C so special ?

It is compatible with C libraries

Is is a simple extension of C

It is a hybrid between C and SmalltalkIt can be as fast as raw C if you avoid the object-oriented extensions

It can be as high-level and flexible as Smalltalk if you use the object-oriented extensions

It allows experienced programmers to mix different programming styles in the same program

It is extremely flexible

Powerful Foundation class library

Why use Objective-C for Server Applications ?

Very fast. You can freely mix it with C and even assembler if you need.

High-level language. Organize your server code using high-level, object-orientated design patterns.

Powerful Foundation library (GNUstep-base). The API originates from OpenStep and the implementation has been polished for 13+ years.

OpenStep API - Foundation Kit (1994)

Foundation KitNon-graphical classesRoot classes: NSObject, NSProxy

Basic data classes: NSString, NSNumber, NSData, NSNull

Collection classes: NSArray, NSDictionary, NSSet

Execution control classes: NSRunLoop, NSTimer, NSThread, NSLock

I/O classes: NSTask, NSFileHandle

Notification classes: NSNotification, NSDistributedNotification

Serialization classes: NSArchiver, NSCoder

Resource management classes: NSBundle, NSUserDefaults

Distributed Objects Classes: NSConnection, NSPort

And many more...

ApplicationFoundation KitApplication KitOperating SystemOS Graphical SystemObjective-C Runtime

GNUstep-base

ApplicationGNUstep BaseGNUstep GUIOperating System (Any!)Graphical System (Any!)GNU Objective-C Runtime

GNUstep Back

Server Applications what do you need ?

gcc-objcObjective-C compiler

Objective-C runtime

gnustep-makeOfficial GNUstep Building System

Makefile library that automatically takes care of configuring and building on different platforms

gnustep-baseOpenStep Foundation Kit implementation

Provides core non-graphical Objective-C classes

Important dependencies

libffiRequired by gnustep-base

You may need to download it and install it from www.gnustep.org

libxmlRequired by gnustep-base

Install it from your GNU/Linux distribution

gnutls or opensslAllow gnustep-base to support https://

Install it from your GNU/Linux distribution

Typical Quick Installation (Ubuntu)

apt-get libgnustep-base-dev

Typical Manual Installation (RedHat)

yum install gcc-objc libxml-devel openssl-devel

wget ftp://sourceware.org/pub/libffi/libffi-3.0.1.tar.gztar xfvz libffi-3.0.1.tar.gzcd libffi-3.0.1./configuremakesu -c 'make install'

wget ftp://ftp.gnustep.org/pub/gnustep/core/gnustep-make-2.0.8.tar.gztar xfvz gnustep-make-2.0.8.tar.gzcd gnustep-make-2.0.8.tar.gz./configuremakesu -c 'make install'

. /usr/GNUstep/System/Library/Makefiles/GNUstep.sh

wget ftp://ftp.gnustep.org/pub/gnustep/core/gnustep-base-1.18.0.tar.gztar xfvz gnustep-base-1.18.0.tar.gzcd gnustep-base-1.18.0./configure enable-opensslmakesu -c 'make install'

Hello World! Program

Hello World using Objective-C / GNUstep-base

hello.m

#import

int main (void){ NSLog (@Hello world!); return 0;
}



GNUmakefile

include $(GNUSTEP_MAKEFILES)/common.make

TOOL_NAME = hellohello_OBJC_FILES = hello.m

include $(GNUSTEP_MAKEFILES)/tool.make



Usual compilation commands

make

make clean

make distclean

make install

make messages=yes

make install messages=yes



Compilation results are in ./obj

Let's try it out: Tutorial Compilation Session

GNUstep-base coding: where to start

GNUstep Mini Tutorials (Introduction):

http://www.gnustep.it/nicola/Tutorials/index.html

GNUstep Base Documentation (API Reference):

http://www.gnustep.org/resources/documentation/Developer/Base/Reference/index.html

GNUstep-base coding: basic classes

Class cluster DesignTransparent way of optimizing classes without changing the public API

When you create a NSString or NSArray you actually get an instance of a subclass optimized to perform best in your situation

Method dispatch is dynamic, so that works

You can implement your own subclasses for performance

Mutable and non-mutable ClassesNSString vs NSMutableString

NSString is for constant strings that never change

NSMutableString is for strings that might change

Allows a lot of optimizations inside the library


NSString, NSMutableStringString class

Full Unicode support

Class cluster implementation means ASCII strings are still extremely fast

Static strings

NSString *string = @This is a test string;


NSArray, NSMutableArrayArray class

NSMutableArray provides arrays that grow dynamically

NSDictionary, NSMutableDictionaryHashtable/associative array class

NSMutableDictionary provides associative arrays that grow dynamically

{Name = Gorm.app;Description = GNUstep GUI Builder Application;}

(one, two, three);

GNUstep-base: Runloops and threads

NSRunLoopNSRunLoop

Event-based model

NSFileHandle

NSTimer

ThreadsNSThread

NSLock

GNUstep-base: Notifications

GNUstep-base supports notifications and observersFlexible way to connect objects

NSNotificationCenter

Objects can observe a notification and specify which methodthey want invoked when that notification is posted

Anything can post a notification

The notification is delivered to all observer

See NSNotificationCenter documentation for more information

GNUstep-base: Delegates

Objective-C and GNUstep-base encourage using delegates

A delegate allows you to extend a class without subclassing it

Subclassing can be heavy, and not that flexible

Delegates are more flexible you can delegate part of the code toan object of any class

-setDelegate: (NSObject *)delegate;-delegate;

GNUstep-base: Distributed Objects

Remote method invocation

High-level

You can expose objects in one process to other processes

Other processes can then contact the object and invoke methodsof the objects, as if they were local objects

Very natural to use

Excellent for building networks of processes that work cooperatively

See http://www.gnustep.it/nicola/Tutorials/ for a tutorial on Distributed Objects.

A look at some useful libraries

You can use any C library you want

Objective-C libraries provided by GNUstep check the dev-libs module in subversion

Objective-C libraries provided by other partiesSOPE (opengroupware.org)

Apple Cocoa non-GUI frameworks can sometime be used

GNUstep Database Libraries

You can use your own preferite C library

GNUstep Database LibrariesSQLClient

GDL2

SOPEThe best choice if you use the SOPE application server

Not so interesting if you're not


SQLClient

SQL Layer (low-level)Standard SQL layer to execute SQL queries/commands

Backend bundles (plugins) for the different databases (standard bundles: PostgreSQL, MySQL, SQLite, Oracle)

High-performance featuresConnection pooling

Advanced transaction support

Query caching

Update Batching


GDL2 (GNUstep Database Library v2)

High-level featuresSQL layer with EOAdaptors (plugins) for different database (standard bundles: PostgreSQL, SQLite)

Object-to-relationship mapping

Extensive use of KVC

Supports and encourages MVC patterns

Rapid development/integration supportEOInterface

DBModeler (GUI program)


SQLClientSQL only

You have to write your SQL code

Performance-oriented

Excellent for very high-performance servers where you write and tune each and every single SQL command

GDL2High-level framework

You works with models and objects you do not need to write SQL

Can be a bit hard to get into, but people love it once they get used to it

Excellent for large and properly structured OO projects

Performance is generally good

GNUstep WebServer Library

WebServer LibraryA library to implement quickly http/https server applications

Appropriate to develop efficient APIs for your system

Could be used for web pages but that is not the focus

Provides a full web server

Usually used with Apache in front as a reverse-proxy

Jigs: GNUstep Java Interface

What is itAllows you to use Objective-C libraries or objects from Java

And allows you to use Java libraries or objects from Objective-C

Objects and classes in Objective-C are mapped to objects andclasses in Java and vice versa

ProsIs very cool

ConsCan be slow, use it with moderation

Problems can be hard to debug

Limited support for cross-language subclassing

Not easy to port to other platforms

SOPE

An extensive set of frameworks

A complete Web application server environment

Apple WebObjects compatible app server extended with Zope concepts

XML processing (SAX2, DOM, XML-RPC)

MIME/IMAP4 processing

LDAP connectivity

RDBMS connectivity

iCalendar parsing

http://sope.opengroupware.org

Questions ?

Thank you

For more information

www.gnustep.org

building server applications using objectivec and gnustep

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