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Facet Instance is a data structure associated with each incoming request to the TQLEngineA-Stack. Each facet instance is identified by its facet ID and represents a capability to perform certain actions on the TQLEngine. Incoming requests without valid facet IDs are rejected. Each facet instance is also associated with its Facet Type, which is a piece of executable code (a Java class) intended to actually process the request. Facet instances are deployed through packages. A package is a collection of related facet instances.defined by :
- User Specified Facet ID
- One of the A-Stack supported Facet Types
- Protocol Handler Name on which the requests will be listening.
Syntax
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<NewFacetInstance fidFid="helloworld" name="HelloWorld" type="SffMsgFacet"> <OnActivate/> <OnOpen ModifyPipeline="HttpServerExtensionArgs"/> <OnRequest> <DoResponse> <Process> <Message type="text"> <Value> Hello World from FacetScript! </Value> </Message> </Process> </DoResponse> </OnRequest> <OnResponse/> <OnCloseUser-specified unique identifier" Name="Name of the Facet Instance" Type="FacetType Name"> <!-- Blocks of Lifecycle stages --> <OnActivate/> <OnOpen ModifyPipeline="Server-side Name of the Protocol Handler"/> <OnRequest/> <OnResponse/> <OnClose/> <OnError/> </NewFacetInstance> |
Syntax Notes
- NewFacetInstances are defined within NewPackage definition. A package definition consists of a collection of FacetInstances.
- Examples of each of these variations will be provided in the next section.
- Incoming requests without valid facet IDs are rejected.
Facet Instance Lifecycle
Once a request legitimacy is established by successful resolution of its facet ID, a processing (Netty) pipeline is created for low level request processing.
Once request data is presented in a universal fashion (as an instance of ListMap data structure), TQLEngine A-Stack invokes appropriate facet type method using current connection context and facet instance information as arguments.
The facet lifecycle is the beginning-to-end stages of the facet pipeline that are marked by different facet events. Each facet event can be associated with invoking a method. The actual call arguments will be selected by the TQLEngine A-Stack by executing the event-specific piece of facet script found in the facet instance. That is, it is possible to specify a correspondent piece of facet script for each facet event. Such facet script may contain simple logic to check some request value or do template-based data transformation before actual java method invocation.
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For instance, upon facet instance activation (creation) the TQLEngine A-Stack will invoke the onActivate method; upon incoming request it will invoke onRequest method and so on.
| Event | Description |
|---|---|
| onActivate | Handler is called by the engine at the of activation of the facet |
| onDeactivate | Handler is called by the engine at the time of deactivation |
| onOpen | Handler is called, when facet pipeline is opened |
| onClose | Handler is called, when facet pipeline if closed |
| onRequest | Handler is called when the request is received on the pipeline |
| onResponse | Handler is called when the response is send on the pipeline |
| onError | If error in pipeline, this handler is called and pipeline gets closed |
Facet Instance
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Example
The “Hello, World” program is traditionally used to introduce a programming language. Here is an example of Hello, World in FacetScript:
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<NewPackage>
<NewFacetInstance fid="helloworld" name="HelloWorld" type="SffMsgFacet">
<OnActivate/>
<OnOpen ModifyPipeline="HttpServerExtensionArgs"/>
<OnRequest>
<DoResponse>
<Process>
<Message type="text">
<Value>
Hello World from FacetScript!
</Value>
</Message>
</Process>
</DoResponse>
</OnRequest>
<OnResponse/>
<OnClose/>
</NewFacetInstance>
</NewPackage> |
Once the NewFacetInstance is deployed on A-Stack following EndPoint will be generated:
http://localhost:8080/fid-helloworld
which produces HTTP Response as
Hello World from FacetScript!