Building Server Applications Using ObjectiveC And GNUstep

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 C
Defining 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 Smalltalk
It 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 Kit Non-graphical classes
Root 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...
Application Foundation Kit Application Kit Operating System OS Graphical System Objective-C Runtime

GNUstep-base Application GNUstep Base GNUstep GUI Operating System (Any!) Graphical System (Any!) GNU Objective-C Runtime GNUstep Back

Server Applications – what do you need ?
gcc-objc
Objective-C compiler
Objective-C runtime
gnustep-make
Official GNUstep Building System
Makefile library that automatically takes care of configuring and building on different platforms
gnustep-base
OpenStep Foundation Kit implementation
Provides “core” non-graphical Objective-C classes

Important dependencies
libffi
Required by gnustep-base
You may need to download it and install it from www.gnustep.org
libxml
Required by gnustep-base
Install it from your GNU/Linux distribution
gnutls or openssl
Allow 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.gz tar xfvz libffi-3.0.1.tar.gz cd libffi-3.0.1 ./configure make su -c 'make install' <edit /etc/ld.so.conf adding /usr/local/lib, then run ldconfig as root> wget ftp://ftp.gnustep.org/pub/gnustep/core/gnustep-make-2.0.8.tar.gz tar xfvz gnustep-make-2.0.8.tar.gz cd gnustep-make-2.0.8.tar.gz ./configure make su -c 'make install' . /usr/GNUstep/System/Library/Makefiles/GNUstep.sh wget ftp://ftp.gnustep.org/pub/gnustep/core/gnustep-base-1.18.0.tar.gz tar xfvz gnustep-base-1.18.0.tar.gz cd gnustep-base-1.18.0 ./configure –enable-openssl make su -c 'make install'

“Hello World!” Program
“Hello World” using Objective-C / GNUstep-base hello.m
#import <Foundation/Foundation.h> int main (void) { NSLog (@“Hello world!”); return 0; }

“Hello World” using Objective-C / GNUstep-base GNUmakefile
include $(GNUSTEP_MAKEFILES)/common.make TOOL_NAME = hello hello_OBJC_FILES = hello.m include $(GNUSTEP_MAKEFILES)/tool.make

“Hello World” using Objective-C / GNUstep-base Usual compilation commands
make make clean make distclean make install make messages=yes make install messages=yes

“Hello World” using Objective-C / GNUstep-base 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 Design
Transparent 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 Classes
NSString 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, NSMutableString
String class
Full Unicode support
Class cluster implementation means ASCII strings are still extremely fast
Static strings
NSString *string = @”This is a test string”;

NSArray, NSMutableArray
Array class
NSMutableArray provides arrays that grow dynamically
NSDictionary, NSMutableDictionary
Hashtable/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
NSRunLoop
NSRunLoop
Event-based model
NSFileHandle
NSTimer
Threads
NSThread
NSLock

GNUstep-base: Notifications
GNUstep-base supports notifications and observers
Flexible way to connect objects
NSNotificationCenter
Objects can “observe” a notification and specify which method
they 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 to
an 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 methods
of 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 parties
SOPE (opengroupware.org)
Apple Cocoa non-GUI frameworks can sometime be used

GNUstep Database Libraries
You can use your own preferite C library
SQLClient
GDL2
SOPE
The 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 features
Connection pooling
Advanced transaction support
Query caching
Update Batching

GDL2
(GNUstep Database Library v2)
High-level features
SQL 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 support
EOInterface
DBModeler (GUI program)

SQLClient
SQL 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
GDL2
High-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 Library
A 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 it
Allows 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 and
classes in Java and vice versa
Pros
Is very cool
Cons
Can 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

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Building Server Applications Using ObjectiveC And GNUstep

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