Behaviors
Enter WCF
extensibility points.
What is
covered:
-
Service
description vs Runtime
-
Behavior
Interfaces
-
Runtime
Extensibility
o
Interceptors
o
Formatters
o
Instancing
o
Error
Handling
o
Some
Others
-
Metadata
Extensibility
-
Serialization
Extensibility
-
WCF
Channel Programming Model
What is
not covered:
-
Some
lesser-used interfaces
-
Security
Service description vs Runtime
-
Service (client) Description
o
All
the things needed to start the service (client)
o
Ednpoints
(Address/Binding/Contract)
o
Local
Behaviors
-
Before “Open”
o
Description
can be changes at will
o
Service
not “running”
-
After “Open”
o
Runtime
is initialized
o
Description
is immutable
o
Listeners
are started
o
The
Service is started
-
WCF
provides 4 interfaces to interact with the Service or Client descriptions
o
Service
o
Endpoint
o
Contract
o
operation
-
Each
Interface has 4 methods which follow the same pattern.
-
public
interface I[Service/Contract/Endpoint/Operation]Behavior
o
void
validate(Description) : Prevent host or client from opening if it finds
something invalid in the service description
o
void
AddBindingParameters(Description, BindingParameterCollection): This gives an
opportunity to the behavior to add more information to the Binding channels.
o
void
ApplyDispatchBehavior(Description, Runtime):
This is the place where the behavior gets hooked up to the runtime in the corresponding scope.
o
void
ApplyClientBehavior(Description, Runtime) * {This is only client side}
-
Called
during Open (Be it at the service side or the client side)
-
Ordering
o
Validate
à
AddBindingParameters à
Apply[Client/Dispatch]Behavior
o
Serviceà
Contract à Endpoint à Operation
-
Service Behavior
o
Service-wide
operations
§ Metadata : Validation of the
metadata exchange across the communication
§ Throttling
§ Debug
o
Public
interface IServiceBehavior
§ Validate
§ AddBindingParameters
§ ApplyDispatchBehavior
o
Added
via code, configuration, attributes
WCF Runtime
WCF is a
message stack with many message blocks from client calling the operation to the
service call getting executed on the server.
We will see
the most used blocks through which the messages pass.
·
WCF
Runtime
·
Message
Object
·
Message
Inspectors
·
Parameter
Inspector
·
Message
Formatters
Client Proxy Call à Parameter Inspector à Fomatter à Message Inspector à WCF stack à Message Inspector à Formatter à Parameter Inspector à Service Operation
First question is what is a Message, what is
the structure and Characteristics of the message.?
·
·
System.ServiceModel.Channel.Message
à
Abstract Class
·
SOAP/XML
·
Parts
o
Header
– Buffered
o
Body
o
Properties
: Dictionary not part of SOAP specification
·
Single-use
: Once the message is used and read then it cannot be used any more. One can manipulate
message headers at will.
·
Message
Versions: different versions of SOAP
protocol which are envelopes like SOAP 1.1, 1.2 or none (message is not SOAP
message but POX- Plain old XML)
·
XML
Message
Inspectors :
Most used
WCF extension from the WCF Runtime.
·
Usage:
inspect, modify, replace messages
·
Scenarios:
Logging, custom auth, tweaking messages, correlation between request and
response
·
Server Side
o
MessageInspector
is represented by the Interface: IDispatchMessageInspector
§ AfterReceiveRequest
§ BeforeSendReply
o
Dispatch
behaviors are typically added as endpoint behavior as a part of
ApplyDispatchBehavior to the DispatchRuntime object.
·
ClientSide
o
MessageInspector
is represented by the Interface: IClientMessageInspector
§ BeforeSendRequest
§ AfterReceiveReply
o
MessageInspectores
are added as a part of service endpoint to the clientRuntime object.
o
Correlation object Used as correlation so that
request can be set with something specific after the prior reply is received.
Parameter
Inspector
Parameter
inspectors are same as message inspectors but they are called on CLR objects not
the message objects. They are easier to use as they do not require any
knowledge about messages. Unlike Message inspector they are less powerful as
they have less access to message itself.
·
Usage:
Inspect and Modify operations inputs and outputs.
o
Return
value cannot be modified
·
Scenarios:
logging, parameter validation.
·
Same
Interface for Client and Server : IParameterInspector
o
IParameterInspector
§ BeforeCall
§ AfterCall
·
Adding
parameter inspectors often done in OperationBehavior
o
Server:
DispatchOperation
o
Client:
ClientOperation
·
Like
MessageInspector ParameterInspector has a Correlation object is returned by
BeforeCall and Passed to AfterCAll.
Message
Formatters
Message
formatters are the gateway between WCF messages and world of CLR objects.
·
Usage:
convert between CLR objects and Message
·
Unlike
Inspectors MessageFormatters are not optional but each operation has one and
only one instance MessageFormatter.
·
Scenarios:
supporting different formats, like passing some information as a part of
httpHeaders.
·
Server Side
o
MessageFormatter
is represented by the interface: IDispatchMessageFormatter
§ DeserializeRequest
§ SerializeReply
o
Message
formatters can be accessed using the DispatchOperation in the Endpoint and
operation behavior.
·
Client Side
o
MessageFormatter
is represented by the interface: IClientMessageFormatter
§ DeserializeRequest
§ SerializeReply
o
Message
formatters can be accessed using the ClientOperation in the Endpoint and
operation behavior.
·
One
difference between Inspectors and formatters is that it does not provide the Correlation object between request and
reply.
