Understanding the structure of services makes up your main knowledge
in WCF programming. Here I want to talk about different concepts around
services.
Service Description
Each service is described by its description. Descriptions
show some information about the service. For example, what it can do and how can
you get access to it.
You can use four standards to describe the service:
·
WSDL
·
WS-Policy
·
WS-Metadata Exchange
·
XSD
You may be familiar with some of these standards from the
past and traditional web services.
Binding
Bindings define the way that a service can communicate with
other services and clients. As we talked in previous sections, each channel
has some characteristics and each binding uses a combination of various
available properties for a channel. There are some pre-defined bindings in
Windows Communication Foundation, but you can write a custom binding for your
own needs. If you want to be a success in development for WCF, it is essential
to have a good understanding about all pre-defined bindings and their
properties. This lets you to choose the correct binding which is an important part
of WCF development.
Here is a list of all built-in bindings in WCF. I strongly recommend
you to read this
article on MSDN to learn all properties for each binding type.
·
BasicHttpBinding
·
WSHttpBinding
·
WSDualHttpBinding
·
WSFederationHttpBinding
·
NetTcpBinding
·
NetNamedPipeBinding
·
NetMsmqBinding
·
NetPeerTcpBinding
·
MsmqIntergrationBinding
Some of these bindings are very common, like
BasicHttpBinding and WSHttpBinding. Some of these bindings support security
mechanisms and are secure. Some bindings support reliable sessions or duplex messaging.
Some of them support different encodings and contracts.
Contract
In WCF contracts define the structure of things. There are
three types of contracts:
·
Service Contract: A service contract defines what it does. A
service can have one or more service contracts. Service contracts are similar
to interfaces in Object Oriented Programming. You implement an interface for
your service logic. For example, a service that operates as a calculator may
have an ICalculator contract with four functions for add, subtract, multiply
and divide and implements this interface in Calculator class.
·
Data Contract: Data contracts let you to pass custom objects to
service operations. Using data contracts you define a structure for your
objects and pass them to methods. For example, you may have a Person class
that you the Person to be able to pass it to methods.
·
Message Contract: This is less common than previous contract
types, but you can use message contracts to change the structure of your
messages to use them in your application. For example, you can change the body
of a message.
Endpoint
Endpoints act like wharfs in ports. They are the access
points of a service. An endpoint associates a service contract and binding
with an address to let clients find the service and use it. Having at least
one endpoint is required for a service, but services can have more than one
endpoint.
An endpoint contains its elements: Address, Binding, and
Service Contract. A client sends a request to the address then it will be
passed to a service contract through a channel which is defined by binding.
There is a correlation between endpoints and addresses. An
address is created based on a few parameters:
·
The transport that is used for communication makes the prefix
that will be used (http://, https://, net.tcp:// or …).
·
The place where the service is hosted. As I said in the introduction
article, a service can be hosted in a virtual directory on IIS or can have its
own code for hosting. Format for an address that is hosted on IIS is a bit
different than the format for a service that is self-hosted.
·
The port that is used for communication.
