node/watchers/polygon: implement unsubscribe (TOB-WORMGUWA-7)

node/pkg/watchers/evm/connectors/common.go

@@ -37,9 +37,9 @@ type Connector interface {
 
 type PollSubscription struct {
 	errOnce   sync.Once
-	err       chan error
+	err       chan error    // subscription consumer reads, subscription fulfiller writes. used to propagate errors.
-	quit      chan error
+	quit      chan error    // subscription consumer writes, subscription fulfiller reads. used to signal that consumer wants to cancel the subscription.
-	unsubDone chan struct{}
+	unsubDone chan struct{} // subscription consumer reads, subscription fulfiller writes. used to signal that the subscription was successfully canceled
 }
 
 func NewPollSubscription() *PollSubscription {

node/pkg/watchers/evm/connectors/polygon.go

@@ -119,6 +119,8 @@ func (c *PolygonConnector) SubscribeForBlocks(ctx context.Context, errC chan err
 		for {
 			select {
 			case <-ctx.Done():
+				messageSub.Unsubscribe()
+				sub.unsubDone <- struct{}{}
 				return nil
 			case err := <-messageSub.Err():
 				sub.err <- err
@@ -126,6 +128,10 @@ func (c *PolygonConnector) SubscribeForBlocks(ctx context.Context, errC chan err
 				if err := c.processCheckpoint(ctx, sink, checkpoint); err != nil {
 					sub.err <- fmt.Errorf("failed to process checkpoint: %w", err)
 				}
+			case <-sub.quit:
+				messageSub.Unsubscribe()
+				sub.unsubDone <- struct{}{}
+				return nil
 			}
 		}
 	})