pgwire: allow Flush message during portal exeuction

Release note (bug fix): A Flush message sent during portal execution in
the pgwire extended protocol no longer results in an error.

pkg/sql/pgwire/command_result.go

@@ -507,6 +507,13 @@ func (r *limitedCommandResult) moreResultsNeeded(ctx context.Context) error {
 			if err := r.conn.Flush(r.pos); err != nil {
 				return err
 			}
+		case sql.Flush:
+			// Flush has no client response, so just advance the position and flush
+			// any  existing results.
+			r.conn.stmtBuf.AdvanceOne()
+			if err := r.conn.Flush(r.pos); err != nil {
+				return err
+			}
 		default:
 			// If the portal is immediately followed by a COMMIT, we can proceed and
 			// let the portal be destroyed at the end of the transaction.

pkg/sql/pgwire/testdata/pgtest/portals

@@ -114,12 +114,14 @@ ReadyForQuery
 {"Type":"ReadyForQuery","TxStatus":"I"}
 
 # Execute a portal with limited rows inside a transaction.
+# This also tests that we can handle Flush during the portal execution.
 
 send
 Query {"String": "BEGIN"}
 Parse {"Query": "SELECT * FROM generate_series(1, 2)"}
 Bind
 Execute {"MaxRows": 1}
+Flush
 Sync
 ----
 
@@ -140,6 +142,7 @@ ReadyForQuery
 
 send
 Execute {"MaxRows": 1}
+Flush
 Sync
 ----
 
@@ -155,6 +158,7 @@ ReadyForQuery
 
 send
 Execute {"MaxRows": 1}
+Flush
 Sync
 ----
 
@@ -354,7 +358,7 @@ Execute {"MaxRows": 2}
 Sync
 ----
 
-until
+until ignore=NoticeResponse
 ReadyForQuery
 ReadyForQuery
 ReadyForQuery

pkg/testutils/pgtest/datadriven.go

@@ -288,6 +288,8 @@ func toMessage(typ string) interface{} {
 		return &pgproto3.ErrorResponse{}
 	case "Execute":
 		return &pgproto3.Execute{}
+	case "Flush":
+		return &pgproto3.Flush{}
 	case "Parse":
 		return &pgproto3.Parse{}
 	case "PortalSuspended":