Add agent business logic

Signed-off-by: Chris Doherty <[email protected]>

internal/agent/agent.go

@@ -0,0 +1,85 @@
+package agent
+
+import (
+	"context"
+	"errors"
+
+	"github.com/go-logr/logr"
+	"github.com/tinkerbell/tink/internal/agent/event"
+	"github.com/tinkerbell/tink/internal/agent/workflow"
+)
+
+// Agent is the core data structure for handling workflow execution on target nodes. It leverages
+// a Transport and a ContainerRuntime to retrieve workflows and execute actions.
+//
+// The agent runs a single workflow at a time. Concurrent requests to run workflows will have the
+// second workflow rejected with an event.WorkflowRejected event.
+type Agent struct {
+	Log logr.Logger
+
+	// ID is the unique identifier for the agent. It is used by the transport to identify workflows
+	// scheduled for this agent.
+	ID string
+
+	// Transport is the transport used by the agent for communicating workflows and events.
+	Transport Transport
+
+	// Runtime is the container runtime used to execute workflow actions.
+	Runtime ContainerRuntime
+
+	sem chan struct{}
+}
+
+// Start finalizes the Agent configuration and starts the configured Transport so it is ready
+// to receive workflows. On receiving a workflow, it will leverage the configured Runtime to
+// execute workflow actions.
+func (agent *Agent) Start(ctx context.Context) error {
+	if agent.ID == "" {
+		return errors.New("ID field must be set before calling Start()")
+	}
+
+	if agent.Transport == nil {
+		return errors.New("Transport field must be set before calling Start()")
+	}
+
+	if agent.Runtime == nil {
+		//nolint:stylecheck // Specifying field on data structure
+		return errors.New("Runtime field must be set before calling Start()")
+	}
+
+	agent.Log = agent.Log.WithValues("agent_id", agent.ID)
+
+	// Initialize the semaphore and add a resource to it ensuring we can run 1 workflow at a time.
+	agent.sem = make(chan struct{}, 1)
+	agent.sem <- struct{}{}
+
+	agent.Log.Info("Starting agent")
+	return agent.Transport.Start(ctx, agent.ID, agent)
+}
+
+// HandleWorkflow satisfies transport.
+func (agent *Agent) HandleWorkflow(ctx context.Context, wflw workflow.Workflow, events event.Recorder) error {
+	// sem isn't protected by a synchronization data structure so this is technically invoking
+	// undefined behavior. Its also a misuse of the data structure so we're making a best effort
+	// without adding complexity.
+	if agent.sem == nil {
+		return errors.New("Agent must have Start() called before calling HandleWorkflow()")
+	}
+
+	select {
+	case <-agent.sem:
+		// Replenish the semaphore on exit so we can pick up another workflow.
+		defer func() { agent.sem <- struct{}{} }()
+		return agent.run(ctx, wflw, events)
+
+	default:
+		reject := event.WorkflowRejected{
+			ID:      wflw.ID,
+			Message: "workflow already in progress",
+		}
+		if err := events.RecordEvent(ctx, reject); err != nil {
+			agent.Log.Info("Failed to record event", logEventKey, reject)
+		}
+		return nil
+	}
+}