cephfs admin: add support for returning not-implemented errors

Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/admin/response.go

@@ -20,8 +20,26 @@ var (
 
 const (
 	deprecatedSuffix = "call is deprecated and will be removed in a future release"
+	missingPrefix    = "No handler found"
+	einval           = -22
 )
 
+type cephError interface {
+	ErrorCode() int
+}
+
+// NotImplementedError error values will be returned in the case that an API
+// call is not available in the version of Ceph that is running in the target
+// cluster.
+type NotImplementedError struct {
+	response
+}
+
+// Error implements the error interface.
+func (e NotImplementedError) Error() string {
+	return fmt.Sprintf("API call not implemented server-side: %s", e.status)
+}
+
 // response encapsulates the data returned by ceph and supports easy processing
 // pipelines.
 type response struct {
@@ -57,6 +75,11 @@ func (r response) Status() string {
 // that response is no longer needed for processing.
 func (r response) End() error {
 	if !r.Ok() {
+		if ce, ok := r.err.(cephError); ok {
+			if ce.ErrorCode() == einval && strings.HasPrefix(r.status, missingPrefix) {
+				return NotImplementedError{response: r}
+			}
+		}
 		return r
 	}
 	return nil

cephfs/admin/response_test.go

@@ -125,4 +125,28 @@ func TestResponse(t *testing.T) {
 		assert.False(t, rtemp.Ok())
 		assert.Equal(t, "x", rtemp.Status())
 	})
+
+	t.Run("notImplemented", func(t *testing.T) {
+		rtemp := response{
+			status: "No handler found for this function",
+			err:    myCephError(-22),
+		}
+		if assert.False(t, rtemp.Ok()) {
+			err := rtemp.End()
+			assert.Error(t, err)
+			var n NotImplementedError
+			assert.True(t, errors.As(err, &n))
+			assert.Contains(t, err.Error(), "not implemented")
+		}
+	})
+}
+
+type myCephError int
+
+func (myCephError) Error() string {
+	return "oops"
+}
+
+func (e myCephError) ErrorCode() int {
+	return int(e)
 }