WCF Communication Patterns: More than RequestReply

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WCF Communication PatternsMore than
Request-Reply

• Christian Weyer
• thinktecture
• Co-Founder Solution Architect
• http//www.thinktecture.com/staff/christian
• christian.weyer_at_thinktecture.com

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WCF Communication PatternsMore than
Request-Reply

• Christian Weyer
• thinktecture
• Co-Founder Solution Architect
• http//www.thinktecture.com/staff/christian
• christian.weyer_at_thinktecture.com

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What To Expect

• ABC 101
• Internals 101
• MEPs 101
• Contracts and MEPs
• Bindings and MEPs
• Real-World Check

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ABC 101
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WCF Birds Eye View
Client
Service
Endpoint
Endpoint
Endpoint
Endpoint
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WCF Address, Binding, Contract
Service
Client
C
B
A
C
B
A
A
B
C
C
B
A
Address Where?
Contract What?
Binding How?
Endpoint
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Internals 101
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WSDL Importer
Service Model Layer
Contract
Contract
WSDL Exporter
Client Code parameters
Service Type parameters
Operation Invoker
Dispatcher Runtime
Parameter Inspector
Parameter Inspector
Client Runtime
Message Formatter
Message Formatter
Operation Selector
Message Inspector
Message Inspector
Channel
Channel Layer
Custom Channel
Channel
Custom Channel
Channel
Custom Channel
Channel
Custom Channel
Transport Channel byte
Transport Channel byte
Encoder
Encoder
Custom Encoder
Custom Encoder
Custom Transport
Custom Transport
Added by configuring the runtime with behaviors
Added by adding binding elements to the binding
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Layered Extensibility
Service Model Extensibility (local only)
Channel Extensibility (affects the wire)
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MEPs 101
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Telephone or answering machine

• Synchronous vs. asynchronous execution
• Orthogonal to communication pattern
• Developers typically choose the way of least
  resistance
• Synchronous programming is what they are used to
• Threading, synchronization, callbacks et. al. are
  too cumbersome
• Real power is in decoupling systems
• Asynchronous communication in distributed
  solutions can solve a lot of issues but can
  also introduce new ones

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Message-based Communication

• Messages travel between communication parties
• Messages can be grouped into different message
  exchange patterns (MEPs)
• MEPs can be implemented synchronously or
  asynchronously
• WCF supports different MEPs
• One-way
• Request-reply
• Duplex
• WCF MEPs implemented by different kinds of
  channels

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Channel Shapes
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Channel Shaping

• Possible mismatch
• Physical transport
• Logical message exchange patterns
• Channel shapes implemented in transport bindings
• Express support for MEPs
• WCF ServiceModel analyzes contract
• Which channel shapes will be supported?
• ServiceChannelFactory.BuildChannelFactory and
  DispatcherBuilder.GetSupportedChannelTypes have
  the details

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Contracts MEPs
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Contracts Request-Reply

• Most commonly used MEP
• It is easy to use and looks natural
• R/R can be implemented in WCF by several
  approaches
• Parameter list
• DataContract
• MessageContract
• Message
• Mind the public face of contracts, i.e. the
  metadata

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Contracts One-Way

• O/W operations smell more feasible when
  decoupling is goal
• No return values, rather void
• Use IsOneWay property of OperationContract
• O/W operations can still block
• Not really fire-and-forget semantics

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Contracts Duplex

• Having peer communication parties
• Blurring the line between client and server
• Use CallbackContract property of ServiceContract
• Operations in contracts can be one-way, but need
  no to be
• If using non-one-way beware of threading issues

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Contracts Streaming

• Buffered communication can be very expensive with
  large data
• WCF offers streamed transfer
• Contract parameters must have certain shape
• Use Message, IXmlSerializable or System.IO.Stream
  or derivate as type
• Use MessageContract
• Headers will be buffered
• Body as System.IO.Stream will be streamed
• Only works with appropriate binding

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Bindings MEPs
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WCFs Hidden Power
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Bindings Request-Reply

• Almost all out-of-the-box bindings support
  request-reply
• MSMQ-based bindings do not
• For all bindings and MEPs
• Beware of default min/max values on binding
  elements for e.g. message sizes and buffers and
  timeouts
• Beware of possible throttles on service behavior

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Bindings One-Way

• All bindings support one-way operations
• Use OneWayBindingElement for custom bindings to
  shape channel
• Performs a message-level shape change
• Can take a IDuplexSessionChannel or a
  IRequestChannel and expose it as a
  IOutputChannel, or conversely it can take a
  IDuplexSessionChannel or a IReplyChannel and
  expose it as a IInputChannel

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Bindings Duplex

• Duplex out-of-the-box
• netTcp
• wsDualHttp
• netNamedPipe
• netPeerTcp
• Manual duplex session-less, e.g.

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Bindings Streaming

• Enable streaming on the baked-in bindings
• All standard bindings besides MSMQ-based
• Enable streaming on the transport binding
  element, e.g.
• Possible transferMode values
• Buffered
• Streamed
• StreamedRequest
• StreamedResponse
• Only transport security and no reliable sessions
  allowed

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MSMQ transport

• MSMQ is different always has been
• Duplex MEP over MSMQ-based binding can be
  achieved by e.g. doing it manually
• Leverage message headers
• Access headers through OperationContext in user
  code
• Access headers through message inspectors in
  ServiceModel extensions
• Use GUID to correlate messages

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Real-World Check

• Common gotchas
• Nice features, but do I really need them?
• What about interop, e.g. with Java?
• Firewalls NATs
• Deployment of MSMQ
• Support for mobile devices
• Not always is WCF the hammer, as not always
  everything is a nail

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Sample Application YAPOS ?

• Yet Another Purchase Order Scenario?No, dont
  fear.
• Lets bring some coolness into our dev life
  talk about developer videos and media
• Every good developer these days needs to deal
  with online resources and multimedia content
• MSDN.TV
• Channel 9
• Dotnetpro.tv (German)

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Sample Application Scenario
Reviewer
Media Service
Web Server
User
New Media Service
Message Queue
Message Queue
Upload Service
Web Server
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Resources

• Email Christian Weyer
• christian.weyer_at_thinktecture.com
• Weblog Christian Weyer
• http//blogs.thinktecture.com/cweyer
• thinktecture
• http//www.thinktecture.com

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