Wyyme Software: WCF Fundamentals

Introducing WCF

Difference between WCF and Web service

Sample SOAP message

Introducing WCF

WCF Architecture

Contracts

Contracts layer are next to that of Application layer. Developer will directly use this contract to develop the service. We are also going to do the same now. Let us see briefly what these contracts will do for us and we will also know that WCF is working on message system.

Service contracts

- Describe about the operation that service can provide. Example, Service provided to know the temperature of the city based on the zip code, this service we call as Service contract. It will be created using Service and Operational Contract attribute.

Data contract

- It describes the custom data type which is exposed to the client. This defines the data types, are passed to and from service. Data types like int, string are identified by the client because it is already mention in XML schema definition language document, but custom created class or datatype cannot be identified by the client e.g. Employee data type. By using DataContract we can make client aware that we are using Employee data type for returning or passing parameter to the method.

Message Contract

- Default SOAP message format is provided by the WCF runtime for communication between Client and service. If it is not meeting your requirements then we can create our own message format. This can be achieved by using Message Contract attribute.

Policies and Binding

- Specify conditions required to communicate with a service e.g security requirement to communicate with service, protocol and encoding used for binding.

Service Runtime

- It contains the behaviors that occur during runtime of service.

Throttling Behavior- Controls how many messages are processed.
Error Behavior - Specifies what occurs, when internal error occurs on the service.
Metadata Behavior - Tells how and whether metadata is available to outside world.
Instance Behavior - Specifies how many instance of the service has to be created while running.
Transaction Behavior - Enables the rollback of transacted operations if a failure occurs.
Dispatch Behavior - Controls how a message is processed by the WCF Infrastructure.

Messaging

- Messaging layer is composed of channels. A channel is a component that processes a message in some way, for example, by authenticating a message. A set of channels is also known as a channel stack. Channels are the core abstraction for sending message to and receiving message from an Endpoint. Broadly we can categories channels as

Transport Channels

Handles sending and receiving message from network. Protocols like HTTP, TCP, name pipes and MSMQ.
Protocol Channels

Implements SOAP based protocol by processing and possibly modifying message. E.g. WS-Security and WS-Reliability.

Activation and Hosting

- Services can be hosted or executed, so that it will be available to everyone accessing from the client. WCF service can be hosted by following mechanism

IIS

Internet information Service provides number of advantages if a Service uses Http as protocol. It does not require Host code to activate the service, it automatically activates service code.
Windows Activation Service

(WAS) is the new process activation mechanism that ships with IIS 7.0. In addition to HTTP based communication, WCF can also use WAS to provide message-based activation over other protocols, such as TCP and named pipes.
Self-Hosting

WCF service can be self hosted as console application, Win Forms or WPF application with graphical UI.
Windows Service

WCF can also be hosted as a Windows Service, so that it is under control of the Service Control Manager (SCM).

WCF Experience

Demo of Simple WCF services Host

Services and End Points

Some Build in Bindings

Demo of Simple WCF Client application

Programming Services

WCF Service Model Architecture

Contracts

Define Data Contract

Define Service Contracts

Message Contract

MessageHeaderArray Attribute

Message Contract Properties

Fault Contract

Instancing and Threading

Instance Deactivation

Durable Service

Throttling

Programming Model

Operation Services on WCF

WCF Hosting Services

Address and Bindings

WCF Address

WCF Bindings

Types of Bindings

Metadata Exchange

Service Exceptions

Transfer mode

Events

Transaction

Two-phase committed protocol

Consider the scenario where I am having single client which use single service for communication and interacting with single database. In which service starts and manage the transaction, now it will be easy for the service to manage the transaction.

Consider for example client calling multiple service or service itself calling another service, this type of system are called as Distributed Service-oriented application. Now the questions arise that which service will begin the transaction? Which service will take responsibility of committing the transaction? How would one service know what the rest of the service feels about the transaction? Service could also be deployed in different machine and site. Any network failure or machine crash also increases the complexity for managing the transaction.