1. WCF WCF as a
programming platform that is used to build Service-Oriented applications.
Microsoft has unified all its existing distributed application technologies
(e.g. MS Enterprise Services, ASMX web services, MSMQ, .NET Remoting etc) at
one platform
2. Difference between WCF and
ASMX Web Services
1.
ASP.NET web service is designed to send and receive
messages using SOAP over HTTP only.
While WCF can exchange messages
using any format (SOAP is default) over any transport protocol (HTTP, TCP/IP,
MSMQ, Named Pipes etc)
2. Web services is hosted in IIS only. WCF
can be hosted in IIS, WAS, Console, Windows NT Service
3. Web service has only Limited security , WCF is consistency security programming
model.
4. Web services uses Xml serializer and WCF
uses Data contract serializer.
2. WCF Endpoints
1.
Client uses endpoint to communicate with WCF Service.
A WCF service
endpoint has three basic elements i.e. Address, Binding and Contract.
Address: It defines
“WHERE”. Address is the URL that identifies the location of the service.
Binding: It defines
“HOW”. Binding defines how the service can be accessed.
Contract: It defines
“WHAT”. Contract identifies what is exposed by the service.
3. Operation Overloading
while exposing WCF Services?
By default, WSDL doesn’t support operation overloading.
Overloading behavior can be achieved by using “Name” property of
OperationContract attribute.
[ServiceContract]
interface IMyCalculator
{
[OperationContract(Name = “SumInt”)]
int Sum(int arg1,int arg2);
[OperationContract(Name = “SumDouble”)]
double Sum(double arg1,double arg2);
}
4.Message Exchange Patterns (MEPs) supported by WCF
1.Request/Response
2.One
Way
3.Duplex
Request/Response
It’s the default pattern. In this pattern, a response message
will always be generated to consumer when the operation is called, even with
the void return type. In this scenario, response will have empty SOAP body.
One Way
In some cases, we are interested to send a message to service
in order to execute certain business functionality but not interested in
receiving anything back. One way MEP will work in such scenarios.
If we want queued message delivery, One way is the only
available option.
Duplex
The Duplex MEP is basically a two-way message channel. In
some cases, we want to send a message to service to initiate some
longer-running processing and require a notification back from service in order
to confirm that the requested process has been completed.
5.Standard Bindings in WCF
1. BasicHttpBinding is standard binding is designed to expose a
service as if it is an ASMX/ASP.NET web service.
2. NetTcpBinding provides transport level security,
Transport Level security means providing security at the transport layer
itself.
3. wsHttpBinding provides following security None,Transport,Message and Transport with
message credentials
other bindings are WebHttpBinding - Wcf Restful service,
netNamedPipeBinding,netTcpBinding,netPeerTcpBinding and netmsmqBinding
6. Core components of WCF
Service
Service Class: A service class implementing in any CLR-based
language and expose at least one method.
Hosting Environment: a managed
process for running service.
Endpoint: a client
uses it to communicate with service.
7.Multiple endpoints for
different binding types
Yes, we can have multiple endpoints for different binding
types. For example, an endpoint with wsHttpBinding and another one with
netTcpBinding.
8. Contracts in WCF?
A Contract is basically an agreement between the two parties
i.e. Service and Client.
1. Behavioral Contracts define that what operations
client can perform on a service.
ServiceContract [Interface] attribute is used to mark a
type as Service contract that contains operations. OperationContract
[Method in Interface]attributes is
used to mark the operations that will be exposed. Fault Contract
defines what errors are raised by the service being exposed.
2.
Structural Contracts
DataContract
[Class] attribute define types that
will be moved between the parties.
MessageContract
attribute define the structure of SOAP message.
9. Different WCF Instance
Activation Methods available
Per Call: A new
instance is created against each incoming request from client and later
disposed off as response generated.
Per Session: an instance
for each session.
Singleton: All incoming
requests are served by only one instance.
10.Different ways to handle
concurrency in WCF?
Single: means at a
given time, only a single request can be processed by WCF service instance.
Other requests will be waiting until the first one is fully served.
Multiple: means
multiple requests can be served by multiple threads of a single WCF service
instance.
Reentrant: means a
single WCF service instance can process one request at a given time but the
thread can exit the service to call another service.
[ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple]
public class MyService : IMyService
{
}
11.WCF throttling
WCF throttling enables us to regulate the maximum number of
WCF instances, concurrent calls and concurrent sessions.
maxConcurrentInstances=”2147483647”
maxConcurrentCalls=”16″
maxConcurrentSessions=”10″
12.Fault contract
when some exception occurs at a WCF service level, it will
not expose as it is to client. Reason is that WCF exception is a CLR exception
and it doesn’t make sense to expose it outside CLR because it contains internal
details of service code like stack trace. So, WCF handles and returns error
details to client using Fault Contract.“So,
fault contract is a contract that contains the details of possible exception(s)
that might occur in a service code.”
[ServiceContract]
public interface
IService1
{
[OperationContract]
[FaultContract(typeof(MyFaultDetails))]
int MyOperation1();
}
[DataContract]
public class
MyFaultDetails
{
[DataMember]
public string ErrorDetails { get;
set; }
}
public int MyOperation1()
{
Try{ //Do something…… }catch()
{
MyFaultDetails ex = new
MyFaultDetails();
ex.ErrorDetails = “Specific
error details here.“;
throw new FaultException(ex,“Reason:
Testing…..“);
}
}
13.Transfer Security Modes
None – No security
at all. Very risky to choose.
Transport – Securing
message transfer with transport protocol like TCP, IPs, HTTPs, MSMQ. It’s Ideal for Intranet scenarios having
point to point communication.
Message – Securing
message by encrypting it. Good for scenarios even when multiple intermediaries
involved.
Mixed – TransportWithMessageCredential
uses transport for message privacy and service authentication with client
authentication handled at message level.
Both -Using both
Message as well as transport security. In this case a secured encrypted message
travel over a secure transport (pipe) only supported by MSMQ Binding.
14.Reliable Messaging in WCF?
We know that networks are not perfect enough and those might
drop signals or in some scenarios there can be a possibility of wrong order of
messages during message exchange.
WCF allows us to ensure the reliability of messaging by
implementing WS-ReliableMessaging protocol.
enabled=”true”
ordered=”true”
inactivityTimeout=”00:02:00″
/>
15.Reliable Sessions in WCF?
Reliable sessions actually ensure that the caller for
messages will know about the lost message(s) but it can’t guarantee about the
delivery of message(s).
There is a misconception about reliable sessions that it
ensures the session will never expire or stays for a very long time. This we
can achieve by using timeout for sessions.
