validate object implements the corresponding interface (#3724)

Signed-off-by: zouyee <zounengren@cmss.chinamobile.com>

core/dnsserver/register.go

@@ -52,6 +52,9 @@ func (h *dnsContext) saveConfig(key string, cfg *Config) {
 	h.keysToConfigs[key] = cfg
 }
 
+// Compile-time check to ensure dnsContext implements the caddy.Context interface
+var _ caddy.Context = &dnsContext{}
+
 // InspectServerBlocks make sure that everything checks out before
 // executing directives and otherwise prepares the directives to
 // be parsed and executed.

core/dnsserver/server.go

@@ -20,6 +20,7 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/transport"
 	"github.com/coredns/coredns/request"
 
+	"github.com/caddyserver/caddy"
 	"github.com/miekg/dns"
 	ot "github.com/opentracing/opentracing-go"
 )
@@ -99,6 +100,9 @@ func NewServer(addr string, group []*Config) (*Server, error) {
 	return s, nil
 }
 
+// Compile-time check to ensure Server implements the caddy.GracefulServer interface
+var _ caddy.GracefulServer = &Server{}
+
 // Serve starts the server with an existing listener. It blocks until the server stops.
 // This implements caddy.TCPServer interface.
 func (s *Server) Serve(l net.Listener) error {

core/dnsserver/server_grpc.go

@@ -11,6 +11,7 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/reuseport"
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
+	"github.com/caddyserver/caddy"
 	"github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc"
 	"github.com/miekg/dns"
 	"github.com/opentracing/opentracing-go"
@@ -43,6 +44,9 @@ func NewServergRPC(addr string, group []*Config) (*ServergRPC, error) {
 	return &ServergRPC{Server: s, tlsConfig: tlsConfig}, nil
 }
 
+// Compile-time check to ensure Server implements the caddy.GracefulServer interface
+var _ caddy.GracefulServer = &Server{}
+
 // Serve implements caddy.TCPServer interface.
 func (s *ServergRPC) Serve(l net.Listener) error {
 	s.m.Lock()

core/dnsserver/server_https.go

@@ -14,6 +14,8 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/response"
 	"github.com/coredns/coredns/plugin/pkg/reuseport"
 	"github.com/coredns/coredns/plugin/pkg/transport"
+
+	"github.com/caddyserver/caddy"
 )
 
 // ServerHTTPS represents an instance of a DNS-over-HTTPS server.
@@ -44,6 +46,9 @@ func NewServerHTTPS(addr string, group []*Config) (*ServerHTTPS, error) {
 	return sh, nil
 }
 
+// Compile-time check to ensure Server implements the caddy.GracefulServer interface
+var _ caddy.GracefulServer = &Server{}
+
 // Serve implements caddy.TCPServer interface.
 func (s *ServerHTTPS) Serve(l net.Listener) error {
 	s.m.Lock()

core/dnsserver/server_tls.go

@@ -9,6 +9,7 @@ import (
 	"github.com/coredns/coredns/plugin/pkg/reuseport"
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
+	"github.com/caddyserver/caddy"
 	"github.com/miekg/dns"
 )
 
@@ -35,6 +36,9 @@ func NewServerTLS(addr string, group []*Config) (*ServerTLS, error) {
 	return &ServerTLS{Server: s, tlsConfig: tlsConfig}, nil
 }
 
+// Compile-time check to ensure Server implements the caddy.GracefulServer interface
+var _ caddy.GracefulServer = &Server{}
+
 // Serve implements caddy.TCPServer interface.
 func (s *ServerTLS) Serve(l net.Listener) error {
 	s.m.Lock()