rescan: add IsCurrent to the ChainSource interface

This is required for the follow up commit where access to the IsCurrent
method is required in the rescanState.rescan method which only has
access to the ChainSource interface.

rescan.go

@@ -74,6 +74,10 @@ type ChainSource interface {
 	//
 	// TODO(wilmer): extend with best hash as well.
 	Subscribe(bestHeight uint32) (*blockntfns.Subscription, error)
+
+	// IsCurrent returns true if the backend chain thinks that its view of
+	// the network is current.
+	IsCurrent() bool
 }
 
 // ScanProgressHandler is used in rescanOptions to update the caller with the

rescan_test.go

@@ -272,6 +272,12 @@ func (c *mockChainSource) setFailGetFilter(b bool) {
 	c.failGetFilter = b
 }
 
+// IsCurrent returns true if the backend chain thinks that its view of
+// the network is current.
+func (c *mockChainSource) IsCurrent() bool {
+	return true
+}
+
 // GetCFilter returns the filter of the given type for the block with the given
 // hash.
 func (c *mockChainSource) GetCFilter(hash chainhash.Hash,