runtime/v2: manager supports server interceptor

Currently, the runc shimv2 commandline manager doesn't support ttrpc
server's customized option, for example, the ttrpc server interceptor.
This commit is to allow the task plugin can return the
`UnaryServerInterceptor` option to the manager so that the task plugin
can do enhancement before handling the incoming request, like API-level
failpoint control.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

runtime/v2/shim/util.go

@@ -30,6 +30,7 @@ import (
 	"github.com/containerd/containerd/namespaces"
 	"github.com/containerd/containerd/protobuf/proto"
 	"github.com/containerd/containerd/protobuf/types"
+	"github.com/containerd/ttrpc"
 	exec "golang.org/x/sys/execabs"
 )
 
@@ -167,3 +168,28 @@ func ReadAddress(path string) (string, error) {
 	}
 	return string(data), nil
 }
+
+// chainUnaryServerInterceptors creates a single ttrpc server interceptor from
+// a chain of many interceptors executed from first to last.
+func chainUnaryServerInterceptors(interceptors ...ttrpc.UnaryServerInterceptor) ttrpc.UnaryServerInterceptor {
+	n := len(interceptors)
+
+	// force to use default interceptor in ttrpc
+	if n == 0 {
+		return nil
+	}
+
+	return func(ctx context.Context, unmarshal ttrpc.Unmarshaler, info *ttrpc.UnaryServerInfo, method ttrpc.Method) (interface{}, error) {
+		currentMethod := method
+
+		for i := n - 1; i > 0; i-- {
+			interceptor := interceptors[i]
+			innerMethod := currentMethod
+
+			currentMethod = func(currentCtx context.Context, currentUnmarshal func(interface{}) error) (interface{}, error) {
+				return interceptor(currentCtx, currentUnmarshal, info, innerMethod)
+			}
+		}
+		return interceptors[0](ctx, unmarshal, info, currentMethod)
+	}
+}