validation.go

/*
Copyright 2014 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package errors

import (
	"fmt"
	"strings"

	"github.com/golang/glog"
)

// ValidationErrorType is a machine readable value providing more detail about why
// a field is invalid.  These values are expected to match 1-1 with
// CauseType in api/types.go.
type ValidationErrorType string

// TODO: These values are duplicated in api/types.go, but there's a circular dep.  Fix it.
const (
	// ValidationErrorTypeNotFound is used to report failure to find a requested value
	// (e.g. looking up an ID).
	ValidationErrorTypeNotFound ValidationErrorType = "FieldValueNotFound"
	// ValidationErrorTypeRequired is used to report required values that are not
	// provided (e.g. empty strings, null values, or empty arrays).
	ValidationErrorTypeRequired ValidationErrorType = "FieldValueRequired"
	// ValidationErrorTypeDuplicate is used to report collisions of values that must be
	// unique (e.g. unique IDs).
	ValidationErrorTypeDuplicate ValidationErrorType = "FieldValueDuplicate"
	// ValidationErrorTypeInvalid is used to report malformed values (e.g. failed regex
	// match).
	ValidationErrorTypeInvalid ValidationErrorType = "FieldValueInvalid"
	// ValidationErrorTypeNotSupported is used to report valid (as per formatting rules)
	// values that can not be handled (e.g. an enumerated string).
	ValidationErrorTypeNotSupported ValidationErrorType = "FieldValueNotSupported"
)

func ValueOf(t ValidationErrorType) string {
	switch t {
	case ValidationErrorTypeNotFound:
		return "not found"
	case ValidationErrorTypeRequired:
		return "required value"
	case ValidationErrorTypeDuplicate:
		return "duplicate value"
	case ValidationErrorTypeInvalid:
		return "invalid value"
	case ValidationErrorTypeNotSupported:
		return "unsupported value"
	default:
		glog.Errorf("unrecognized validation type: %#v", t)
		return ""
	}
}

// ValidationError is an implementation of the 'error' interface, which represents an error of validation.
type ValidationError struct {
	Type     ValidationErrorType
	Field    string
	BadValue interface{}
}

func (v ValidationError) Error() string {
	return fmt.Sprintf("%s: %v '%v'", v.Field, ValueOf(v.Type), v.BadValue)
}

// NewFieldRequired returns a ValidationError indicating "value required"
func NewFieldRequired(field string, value interface{}) ValidationError {
	return ValidationError{ValidationErrorTypeRequired, field, value}
}

// NewFieldInvalid returns a ValidationError indicating "invalid value"
func NewFieldInvalid(field string, value interface{}) ValidationError {
	return ValidationError{ValidationErrorTypeInvalid, field, value}
}

// NewFieldNotSupported returns a ValidationError indicating "unsupported value"
func NewFieldNotSupported(field string, value interface{}) ValidationError {
	return ValidationError{ValidationErrorTypeNotSupported, field, value}
}

// NewFieldDuplicate returns a ValidationError indicating "duplicate value"
func NewFieldDuplicate(field string, value interface{}) ValidationError {
	return ValidationError{ValidationErrorTypeDuplicate, field, value}
}

// NewFieldNotFound returns a ValidationError indicating "value not found"
func NewFieldNotFound(field string, value interface{}) ValidationError {
	return ValidationError{ValidationErrorTypeNotFound, field, value}
}

// ErrorList is a collection of errors.  This does not implement the error
// interface to avoid confusion where an empty ErrorList would still be an
// error (non-nil).  To produce a single error instance from an ErrorList, use
// the ToError() method, which will return nil for an empty ErrorList.
type ErrorList []error

// This helper implements the error interface for ErrorList, but prevents
// accidental conversion of ErrorList to error.
type errorListInternal ErrorList

// Error is part of the error interface.
func (list errorListInternal) Error() string {
	if len(list) == 0 {
		return ""
	}
	sl := make([]string, len(list))
	for i := range list {
		sl[i] = list[i].Error()
	}
	return strings.Join(sl, "; ")
}

// ToError converts an ErrorList into a "normal" error, or nil if the list is empty.
func (list ErrorList) ToError() error {
	if len(list) == 0 {
		return nil
	}
	return errorListInternal(list)
}

// Prefix adds a prefix to the Field of every ValidationError in the list. Returns
// the list for convenience.
func (list ErrorList) Prefix(prefix string) ErrorList {
	for i := range list {
		if err, ok := list[i].(ValidationError); ok {
			if strings.HasPrefix(err.Field, "[") {
				err.Field = prefix + err.Field
			} else if len(err.Field) != 0 {
				err.Field = prefix + "." + err.Field
			} else {
				err.Field = prefix
			}
			list[i] = err
		}
	}
	return list
}

// PrefixIndex adds an index to the Field of every ValidationError in the list. Returns
// the list for convenience.
func (list ErrorList) PrefixIndex(index int) ErrorList {
	return list.Prefix(fmt.Sprintf("[%d]", index))
}