REST - Representational State Transfer

REST

REST strictly refers to a collection of network architecture principles which outline how resources are defined and addressed. The term is often used in a looser sense to describe any simple interface which transmits domain-specific data over HTTP without an additional messaging layer such as SOAP or session tracking via HTTP cookies.

REST Principles:

• Application state and functionality are divided into resources
• Every resource is uniquely addressable using a universal syntax for use in hypermedia links
• All resources share a uniform interface for the transfer of state between client and resource, consisting of
  • A constrained set of well-defined operations
  • A constrained set of content types, optionally supporting code on demand
• A protocol which is:
  • Client-server
  • Stateless
  • Cacheable
  • Layered

REST:

• Provides improved response times and server loading characteristics due to support for caching
• Improves server scalability by reducing the need to maintain communication state. This means that different servers can be used to handle initial and subsequent requests
• Requires less client-side software to be written than other approaches, because a single browser can access any application and any resource
• Depends less on vendor software than mechanisms which layer additional messaging frameworks on top of HTTP
• Provides equivalent functionality when compared to alternative approaches to communication
• Does not require a separate resource discovery mechanism, due to the use of hyperlinks in content
• Provides better long-term compatibility and evolvability characteristics than RPC. This is due to:
  • The capability of document types such as HTML to evolve without breaking backwards- or forwards-compatibility, and
  • The ability of resources to add support for new content types as they are defined without dropping or reducing support for older content types.
  
  Various websites and web applications offer REST-like developer interfaces to data (e.g. Flickr or Amazon S3).

Difference between POX/HTTP, SOAP, and REST....

• REST is an architectural style that is independent, but compatible, with XML. It’s about identifiable resources, resource representations, a fixed (uniform) interface, and linking. HTTP is REST’s most popular instantiation.

• POX/HTTP means exchanging plain old XML documents over HTTP. RESTful POX, i.e. using XML in a RESTful manner, would mean POX is a subset of REST. Many, if not most POX applications don’t care about REST very much, though — they’d thus be part of a distinct set of applications.

• SOAP is a standard document format for building high-level protocols. Anything that uses SOAP is (by definition) not just using plain old XML, and thus not POX; it may be RESTful, unless it violates REST principles.

For best explanations visit http://tomayko.com/writings/rest-to-my-wife.

Blogged with the Flock Browser

YaHoo messenger smilies. :)

:-??       confused
%-(        not listening
:o3        dog
~:>        Chiken
:(|)         Monkey
>:/        bring it on
;))          giggle
[-o<     pray
3:-o     cow
:-@      chatter

Blogged with the Flock Browser

Silverlight HTTP Pipeline

In Silverlight 2, by default, only able to talk back to the site of origin server is allowed.
To acheive that the HTTP request is going back to site of origin look at the deployment URI of the XAP and the request URI.
Comparing these two URIs, 3 things must match:

1. Same domain. http://foo.com  is different than http://bar.foo.com or http://www.foo.com
2. Same protocol. http://foo.com is different than https://foo.com
3. Same port. http://foo.com is different than http://foo.com:8080

HTTP requests themselves are:

• Asynchronous only
• Can only be initiated on the UI thread

There are two APIs in Silverlight for HTTP communication.  The first is WebClient and the second is HttpWebRequest.

WebClient

WebClient is a great API with a simple, events-based paradigm.  Used to easily download a string or a Stream.

WebClient, behind the scenes, does a GET request and then gives back the result in the form required.  It also automatically resolves relative URIs against the deployment URI of the XAP.

   1: private void DownloadString()

   2: {

   3:     WebClient webClient = new WebClient();

   4:  

   5:     // Hook up events

   6:     webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(webClient_DownloadProgressChanged);

   7:     webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webClient_DownloadStringCompleted);

   8:  

   9:     // Initiate download

  10:     webClient.DownloadStringAsync(new Uri("myfeed.xml", UriKind.Relative));

  11: }

  12:  

  13: void webClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)

  14: {

  15:     // Update progress UI

  16:     progressTextBox.Text = e.ProgressPercentage;

  17: }

  18:  

  19: void webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)

  20: {

  21:     if (e.Error == null)

  22:     {

  23:         // Clear progress UI and show downloaded string

  24:         progressTextBox.Text = "";

  25:         feedTextBox.Text = e.Result;

  26:     }

  27: }

  28:  

HttpWebRequest & HttpWebResponse

HttpWebRequest and HttpWebResponse are the standard .NET HTTP apis.  They are much more powerful than WebClient but also more complex to use. Used to set headers or to issue a POST request.

   1: private void SendPostRequest()

   2: {

   3:     HttpWebRequest request = WebRequest.Create(new Uri("http://foo.com/upload")) as HttpWebRequest;

   4:     request.Method = "POST";

   5:  

   6:     //  Set ContentType through property 

   7:     request.ContentType = "application/xml";

   8:  

   9:     //  Set other headers through Headers property

  10:     request.Headers["x-custom-header"] = "value";

  11:  

  12:     //  Initiate getting request stream

  13:     IAsyncResult asyncResult =

  14:     request.BeginGetRequestStream(new AsyncCallback(RequestStreamCallback), request);

  15: }

  16:  

  17: private void RequestStreamCallback(IAsyncResult ar)

  18: {

  19:     HttpWebRequest request = ar.AsyncState as HttpWebRequest;

  20:  

  21:     // populate request stream

  22:     request.ContentType = "text/xml";

  23:     Stream requestStream = request.EndGetRequestStream(ar);

  24:     StreamWriter streamWriter = new StreamWriter(requestStream, Encoding.UTF8);

  25:     streamWriter.Write("<?xml version="1.0"?>"

  26:                        + "<entry xmlns="http://www.w3.org/2005/Atom">"

  27:                        + "<author>"

  28:                        + "<name>Elizabeth Bennet</name>"

  29:                        + "<email>liz@gmail.com</email>"

  30:                        + "</author>"

  31:                        + "<title type="text">Entry 1</title>"

  32:                        + "<content type="text">This is my entry</content>"

  33:                        + "</entry>");

  34:     streamWriter.Close();

  35:  

  36:     // Make async call for response

  37:     request.BeginGetResponse(new AsyncCallback(ResponseCallback), request);

  38: }

  39:  

  40: private void ResponseCallback(IAsyncResult ar)

  41: {

  42:     HttpWebRequest request = ar.AsyncState as HttpWebRequest;

  43:     WebResponse response = request.EndGetResponse(ar);

  44:  

  45:     // use response.  

  46: }

Thanks to Scorbs for such a in depth explanation, for more please visit http://scorbs.com/.

Blogged with the Flock Browser

The 23 Gang of Four Design Patterns .. Revisited

The Gang of Four (GoF)(from Design Patterns: Elements of  Reusable Object-Oriented Software, Addison-Wesley Professional Computing Series, by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides).

These 23 GoF patterns are generally considered the foundation for all other patterns. They are categorized in three groups: Creational, Structural, and Behavioral.

Creational Patterns

1. Abstract Factory:  Creates an instance of several families of classes. Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
2. Builder: Separates object construction from its representation. Separate the construction of a complex object from its representation so that the same construction processes can create different representations.
3. Factory Method: Creates an instance of several derived classes. Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.
4. Prototype: A fully initialized instance to be copied or cloned. Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
5. Singleton: A class of which only a single instance can exist. Ensure a class only has one instance, and provide a global point of access to it.

Structural Patterns

1. Adapter: Match interfaces of different classes.Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.
2. Bridge: Separates an object’s interface from its implementation. Decouple an abstraction from its implementation so that the two can vary independently.
3. Composite: A tree structure of simple and composite objects. Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
4. Decorator: Add responsibilities to objects dynamically.  Attach additional responsibilities to an object dynamically. Decorators provide a             flexible alternative to subclassing for extending functionality.
5. Facade: A single class that represents an entire subsystem. Provide a unified interface to a set of interfaces in a system. Facade defines a higher-level interface that makes the subsystem easier to use.
6. Flyweight: A fine-grained instance used for efficient sharing. Use sharing to support large numbers of fine-grained objects efficiently. A flyweight is a shared object that can be used in multiple contexts simultaneously. The flyweight acts as an independent object in each context — it’s indistinguishable from an instance of the object that’s not shared.
7. Proxy: An object representing another object. Provide a surrogate or placeholder for another object to control access to it.

Behavioral Patterns

1. Chain of Resp. : A way of passing a request between a chain of objects. Avoid coupling the sender of a request to its receiver by giving more than one object a  chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.
2. Command: Encapsulate a command request as an object. Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
3. Interpreter: A way to include language elements in a program. Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
4. Iterator: Sequentially access the elements of a collection. Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
5. Mediator: Defines simplified communication between classes. Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.
6. Memento: Capture and restore an object's internal state. Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later.
7. Observer: A way of notifying change to a number of classes. Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
8. State: Alter an object's behavior when its state changes. Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
9. Strategy: Encapsulates an algorithm inside a class. Define a family of algorithms, encapsulate each one, and make them interchangeable.            Strategy lets the algorithm vary independently from clients that use it.
10. Template: Defer the exact steps of an algorithm to a subclass. Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure.
11. Visitor: Defines a new operation to a class without change. Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.

I must also mention and credit goes to http://www.dofactory.com/Patterns/Patterns.aspx for the most of the above information.

Blogged with the Flock Browser