Building Medium Size Projects'

1
Building Medium Size Projects.

• Some Fundamentals and Principles.
• By
• Abdelilah Essiari

2
Conventions

• Must agree on a set of conventions.
• consistent gt professional gt good first
  impression
• consistent gt predictability gt saving time
• Examples
• void addElementAt(Object element, int index)
• Class names start with upper case
• Function names start with lower case
• Use of the this operator (this.arg arg) in a
  set method.

3
Languages

• Choose a language. (Java/C/C/Python)
• Prefer Object Oriented Language
• Inheritance, Encapsulation, Polymorphism
• Prefer safe languages.
• Buffer overflows.
• Automatic initialization.
• Prefer static-typed languages
• Help from the compiler

4
Languages

• Objectives are the same.
• Robustness
• Small code size
• Efficiency
• Elegance
• Easy to maintain/extend
• Portability
• It is the how that changes.

5
Languages

• Know the weaknesses.
• Know the strengths.
• Dont push it.
• Do unnatural things.
• Not all features are good.

6
Walk before you run

• Quote from Knuth.
• Early optimization is the root of all evil.
• Quote from Henessy and Patterson.
• A program executes 90 percent of its
  instructions in 10 percent of its code.

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WE DO NOT LIKE

• Global variables/functions
• Long methods and large classes.
• Long parameter lists.
• Code duplication.
• Side effects.
• Dependencies.

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Global Variables/functions

• Hard to find.
• Polluting the global name space.
• Rigid.
• Use the Singleton pattern or a utility class.

9
How Java deals with system wide constants

• void foo() Properties props
  System.getProperties()
• String ssl props.getProperty(SSL,
  OFF)
• 
  
• if (ssl.equals(ON))
• else

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Long Parameter Lists

• Do not pass in every thing the method needs.
• Try passing enough so that the method can get to
  everything it needs.
• As a last resort, use a Parameter Object.

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Side effects

• Avoid modifying global variables after they have
  been initialized. (READ ONLY)
• Reduce number of functions that modify member
  variables inside a class, ideally to constructors
  and set methods.
• Helper functions that do not modify member
  variables can be moved and tested more easily.

12
Dependencies

• Design by Interfaces.
• Construction Patterns. (Virtual Constructors,
  Factories)
• Opaque pointers and forward declarations.
• // The header file below has no need to
  include anything
• class A // Forward declaration
• class B // Forward declaration
• class X
• public
• void f(const A a)
• void g(B b) doIt(b) //
  Interesting
• private
• class Ximpl // Forward
  declaration
• Ximpl impl

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Do Not Remember What You Can Compute

• Calling a simple getMethod()
• I have an object x, its brother, and its cousin.
• Calling a more involved function
• I need x, y, xy, xy, x x,
• This tends to make your classes have too many
  member variables. If your intent is
• caching for efficiencys case, remember
• the evils of early optimization.

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Understand Exceptions

• All modern languages have exception handling
  mechanisms.
• Why Exceptions?
• Programmers tend to ignore error codes.
• Voluminous error handling code obscures the
  functional code
• Constructors do not have return values

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Understand Exceptions

• Exceptions vs. Errors
• Errors indicate bugs in the code.
• Exceptions indicate errors by events external to
• the code.
• In java
• Checked Exceptions. (External events)
• Runtime Exceptions. (Programming bugs)
• Errors (virtual machine bugs)
• Java forces programmers to catch checked
  exceptions.

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When to Catch Exceptions

• Catch at the point closest to the occurrence of
  the exception that allows execution to proceed in
  a stable way.
• You can catch and rethrow in order to
• convert exceptions.
• log major events in the system.

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A function that makes debugging hard

• X createX(int arg1, A arg2, C arg3)
• // This function does not throw
• X x createX(arg1, arg2, arg3)
• if (x NULL)
• // Dont have a clue what happened

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A very suspicious function

• void doSomething() try
• catch(Exception ex)
• System.out.print( Is anyone
  watching the screen?)
• return

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Plan ahead

• void doSomething(SomeObject obj) try
• .
• catch(SomeCheckedException ex)
• // should never happen, I have
  analyzed the situation blah blah
• What if the programmer miscalculated? Or
  maybe things have
• changed. I know print something. NO!
• How about throwing IllegalStateException(S
  URPRISE SUPRISE)

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Planning for the future

• A good Java Function.
• void doSomething(SomeObject obj)
  switch(obj.getState()) case RUNNING
• break case SUSPENDED
• break
• default
• throw new IllegalStateException()
  

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Try HARD not to do the following

• Throw a checked exception when it is a runtime
  exception.
• Throw a runtime exception when it is a checked
  exception.
• Catch an exception and sit quietly on it.

22
Report Errors Immediately

• void setHandler(Handler handler)
  this.handler handler
• // bad unless handler is optional.
• void setHandler(Handler handler)
  if (handler null) throw new
  IllegalArgumentException()

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Signal intent/Prevent abuse

• access modifiers (public/private/protected)
• const
• enumerations
• passing by reference (C)
• final in Java and virtual destructors in C
• namespaces in C
• packages in Java
• friend in C

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Signal intent/Prevent abuse

• Class X // Pointers
• public
• constY foo(const A a, const B b) const //
  b can be null
• Class X // References
• public
• const Y foo(const Aa) const
• const Y foo(const A a, const B b) const

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Signal intent/Prevent abuse

• NEVER make member variables public.
• Do not pollute the public interface of an object
  with helper functions. Hide them.
• Protected member variables break encapsulation.
• Try Factory methods.
• Try protected get methods.

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Prevent abuse

• Encapsulation in C.
• Hide the structures and provide clients
• with the interface.
• Header file (.h) contains forward
  declarations
• and prototypes.
• Source file (.c) contains structure and
  function definitions.
• Forced to write init, free, getters, setters,
  copy.

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Prevent abuse

• Immutable objects (Java)
• You do this by not providing public modifying
  methods such as set methods.
• You can do this dynamically by using the Proxy
  pattern.
• Collection getWidgets()
• return Collections.unmodifiabl
  eCollection(myPreciousCollection)
• Cool if one tries to modify my precious
  collection, he will get an UnsupportedOperation
  Exception.

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Prevent abuse

• Smart pointers in C
• A proxy that holds a raw pointer.
• Used for memory management.
• They can make the difference between a
  successful project and a failure
• Essential ingredient of successful, robust
  applications

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Smart Pointers

• void foo() A a new A()
• a-gtf()
• a-gtg()
• delete(a) // Hope this line is
  executed. (Optimistic)
• void foo() // a will always be
  deleted.
• SmartPtrltAgt a new A()
• a-gtf()
• a-gtg()

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Smart Objects behave like ints

• // internal class
• class Ximpl
• public
• void f()
• private
• // member variables

• // Exposed to clients.
• class X
• public
• void f() impl-gtf()
• private
• SmartPtrltXimplgt impl
• Usage X x // x is a smart
• x.f() // object

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Summary

• Classes exposed to clients should be immune to
  abuse.
• Good error reporting.
• Give reasonable default values.
• Provide a builder for complex objects

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Summary

• Avoid the not to do list.
• Consistency
• Remember that the complexity of a piece of code
  should not be greater than the complexity of the
  problem that it is solving.

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DSDS SHARED C LIBRARY

• Support for linux, solaris, FreeBsd, andWindows
• Threads/Synchronization
• Sockets/ServerSockets
• URL/URLConnections (file, http, https)
• Security Wrappers around openssl C library
• Properties, StringTokenizer, File,, etc

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DSDS SHARED C LIBRARY

• Use the Standard C library.
• Emphasis on Design and Robustness.
• Provide clients with easy to use smart objects.
• No pointers
• No need to use the or the -gt
• Good Error reporting
• No need for memory management/resource
• management

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Threads

• Thread.start()
• Thread.join()
• Thread.getId()
• Thread cur ThreadgetCurrentThread()
• Thread objects are smart Objects

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Threads

• class MyCommand public Runnable
• public
• void run()
• cur ThreadgetCurrentThread()
• private
• Thread cur
• void foo()
• Thread t new Thread(new MyCommand)
• t-gtstart()
• delete(t)
• void foo()
• Command command(new MyCommand)
• Thread t(command)
• t.start()

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Socket/ServerSocket

• SocketImpl connect, getInputStream,
  getOutputStream,
• bind, listen, accept
• Socket connect. getInputStream,
  getOutputStream
• ServerSocket bind, listen, accept)
• SSLSocket extends Socket
• SSLSocketImpl extends SocketImpl
• Socket s
• SSLSocket secureSocket (SSLSocket) s
• We will not be denied. ?

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Mutexes.

• Mutexes and Recursive mutexes.
• class MyObject
  
• public
• void f()
• mutex.lock()
• mutex.unlock()
• void g() SmartMutex
  sm(mutex)
• private
• Mutex mutex

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Conditions

• Condition cond
• cond.lock()
• cond.wait()
• cond.notify()
• cond.notifyAll()

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Provider

• // INSTALL PROVIDER AT START-UP
• Provider provider new OpenSSLProvider()
  
• po.loadDigestAlgorithms()
• po.loadSignatureAlgorithms()
• po.seedRandomGenerator(seed)
• ProvidersetProvider(po)
• Provides Base64, MessageDigest, Signature,
  Hmac,
• PublicKey/PrivateKey
  generation, encoding, and decoding
• X509Certificate generation,
  encoding, decoding
• SecretKey generation,
  encoding, and decoding.
• SSLContext, SSLSocket,
  SSLServerSocket,
• KeyStore. (PKCS12)

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Private Keys/Public Keys

• KeyFactory fac KeyFactorygetInstance()
• KeyPair pair generateRSAKeyPair(1024, 3)
• KeyPair pair generateDSAKeyPair(512)
• // DECODING
• privateKey fac.initPrivateKeyFromFile(PEM,
  fileName)
• // ENCODING
• fac.writePrivateKeyToFile(PEM, privateKey,
  fileName)

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Message Digest Engine

• MessageDigest eng MessageDigestgetInstance
  (MD5)
• eng.update(data)
• eng.update(moreData)
• string digest eng.digest()
• // Convenient
• string digest MessageDigestdigest(MD5,
  data)

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Base64 Engine

• // ENCODING
• Base64 eng Base64getInstance()
• eng.encodeUpdate(data)
• eng.encodeUpdate(moreData)
• string enc eng.encode()
• // Convenient
• string enc Base64encode(data)

• // DECODING
• Base64 eng Base64getInstance()
• eng.decodeUpdate(enc)
• string data eng.decode()
• // Convenient
• string data Base64decode(enc)

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Signature Engine

• // Signing
• Signature eng SignaturegetInstance(RSA/
  MD5)
• eng.initSign(privateKey)
• eng.update(data)
• string signature eng.sign()
• // Verifying
• Signature eng SignaturegetInstance(RSA/
  MD5)
• eng.initVerify(publicKey())
• eng.update(data)
• bool verified eng.verify(signature)

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X509 Certificates

• CertificateFactory fac CertificateFactorygetIn
  stance()
• X509Certificate cert fac.initCertFromFile(PEM
  , fileName)
• bool verified cert.verify(caPublicKey)
• bool valid cert.checkValidity()

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HMAC Engine

• Hmac eng HmacgetInstance(DES/MD5)
• eng.init(secretKey)
• eng.update(data)
• string keyedDigest eng.digest()

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Conclusion

• Have a nice weekend.