EventManager: add "on-demand" trigger

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

internal/util/errors.go

@@ -24,6 +24,14 @@ const (
 		"sftpgo serve -c \"<path to dir containing the default config file and templates directory>\""
 )
 
+// errors definitions
+var (
+	ErrValidation     = NewValidationError("")
+	ErrNotFound       = NewRecordNotFoundError("")
+	ErrMethodDisabled = NewMethodDisabledError("")
+	ErrGeneric        = NewGenericError("")
+)
+
 // ValidationError raised if input data is not valid
 type ValidationError struct {
 	err string
@@ -39,6 +47,12 @@ func (e *ValidationError) GetErrorString() string {
 	return e.err
 }
 
+// Is reports if target matches
+func (e *ValidationError) Is(target error) bool {
+	_, ok := target.(*ValidationError)
+	return ok
+}
+
 // NewValidationError returns a validation errors
 func NewValidationError(error string) *ValidationError {
 	return &ValidationError{
@@ -55,6 +69,12 @@ func (e *RecordNotFoundError) Error() string {
 	return fmt.Sprintf("not found: %s", e.err)
 }
 
+// Is reports if target matches
+func (e *RecordNotFoundError) Is(target error) bool {
+	_, ok := target.(*RecordNotFoundError)
+	return ok
+}
+
 // NewRecordNotFoundError returns a not found error
 func NewRecordNotFoundError(error string) *RecordNotFoundError {
 	return &RecordNotFoundError{
@@ -74,6 +94,12 @@ func (e *MethodDisabledError) Error() string {
 	return fmt.Sprintf("Method disabled error: %s", e.err)
 }
 
+// Is reports if target matches
+func (e *MethodDisabledError) Is(target error) bool {
+	_, ok := target.(*MethodDisabledError)
+	return ok
+}
+
 // NewMethodDisabledError returns a method disabled error
 func NewMethodDisabledError(error string) *MethodDisabledError {
 	return &MethodDisabledError{
@@ -90,6 +116,12 @@ func (e *GenericError) Error() string {
 	return e.err
 }
 
+// Is reports if target matches
+func (e *GenericError) Is(target error) bool {
+	_, ok := target.(*GenericError)
+	return ok
+}
+
 // NewGenericError returns a generic error
 func NewGenericError(error string) *GenericError {
 	return &GenericError{