CapabilityClient

The CapabilityClient class in Fabric is responsible for all interactions with the capabilities2 server. It manages service clients for querying available capabilities, establishing bonds, allocating and freeing capabilities, connecting them according to the plan, and triggering execution.

Responsibilities

• Discover available interfaces and providers from the capabilities2 server
• Establish a bond for plan execution
• Allocate (use) and free capabilities as required by the plan
• Connect capabilities according to the parsed plan's connections
• Trigger the first node to start execution

Main Methods

Main Methods and Related Services

Method	Purpose	Related Capability Service
initialize(node)	Set up service clients, read service names from capability_client.services.*, and wait for each service to become available	(all services below)
getInterfaces(capabilities)	Query all available interfaces and populate the list	/capabilities/get_interfaces
getSemanticInterfaces(capabilities)	Query and append semantic interfaces for each capability	/capabilities/get_semantic_interfaces
getProviders(capabilities)	Query and set providers and alternatives for each capability	/capabilities/get_providers
request_bond()	Establish a bond with the server and return the bond ID	/capabilities/establish_bond
use_capabilities(plan)	Request allocation of all capabilities in the plan	/capabilities/use_capability
free_capabilities(plan)	Free all started capabilities in the plan	/capabilities/free_capability
connect_capabilities(plan)	Configure connections between capabilities as per the plan	/capabilities/connect_capability
trigger_first_node(plan)	Trigger the first capability in the plan to start execution	/capabilities/trigger_capability

Usage in Fabric

• The Fabric server creates and initializes a CapabilityClient at startup.
• When a plan is processed, the client:
  1. Queries interfaces and providers for all required capabilities.
  2. Establishes a bond for the plan.
  3. Allocates (uses) all required capabilities.
  4. Configures connections between capabilities as specified in the plan's connections.
  5. Triggers the first node to start execution.
  6. Frees capabilities when the plan is complete or on error.

Example Flow

1. Initialization: initialize(node) sets up all service clients and waits for them to become available.
2. Discovery: getInterfaces() and getProviders() populate the list of capabilities and their providers.
3. Bonding: request_bond() establishes a bond for the plan.
4. Allocation: use_capabilities(plan) allocates all required capabilities.
5. Connection: connect_capabilities(plan) configures the event-driven connections between capabilities.
6. Execution: trigger_first_node(plan) starts the plan execution.
7. Cleanup: free_capabilities(plan) releases all used capabilities.

Error Handling

• All service calls are checked for validity and throw fabric::fabric_exception on failure.
• The client waits for each service to become available before proceeding. The wait timeout is controlled by capability_client.service_wait_timeout_sec.
• If any step fails, capabilities are freed and errors are logged.

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The CapabilityClient is a central component for orchestrating the dynamic allocation, connection, and management of capabilities in Fabric, ensuring robust and flexible plan execution.