Merge pull request #10352 from starius/chainnotifier-unavallable

chainrpc: return Unavailable while notifier starts

docs/release-notes/release-notes-0.20.0.md

@@ -59,6 +59,11 @@
 - [Fixed a bug](https://github.com/lightningnetwork/lnd/pull/10330) to ensure that goroutine resources are properly freed in the case
   of a disconnection or other failure event.
 
+- Chain notifier RPCs now [return the gRPC `Unavailable`
+  status](https://github.com/lightningnetwork/lnd/pull/10352) while the
+  sub-server is still starting. This allows clients to reliably detect the
+  transient condition and retry without brittle string matching.
+
 # New Features
  
 * Use persisted [nodeannouncement](https://github.com/lightningnetwork/lnd/pull/8825) 
@@ -283,7 +288,7 @@ reader of a payment request.
 * [Require invoices to include a payment address or blinded paths](https://github.com/lightningnetwork/lnd/pull/9752) 
   to comply with updated BOLT 11 specifications before sending payments.
 
-* [LND can now recgonize DNS address type in node
+* [LND can now recognize DNS address type in node
   announcement msg](https://github.com/lightningnetwork/lnd/pull/9455). This
   allows users to forward node announcement with valid DNS address types. The
   validity aligns with Bolt 07 DNS constraints.

lnrpc/chainrpc/chain_server.go

@@ -18,6 +18,8 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 	"gopkg.in/macaroon-bakery.v2/bakery"
 )
 
@@ -84,8 +86,8 @@ var (
 
 	// ErrChainNotifierServerNotActive indicates that the chain notifier hasn't
 	// finished the startup process.
-	ErrChainNotifierServerNotActive = errors.New("chain notifier RPC is " +
-		"still in the process of starting")
+	ErrChainNotifierServerNotActive = status.Error(codes.Unavailable,
+		"chain notifier RPC is still in the process of starting")
 )
 
 // ServerShell is a shell struct holding a reference to the actual sub-server.