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fields.go
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fields.go
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package validate
import (
"fmt"
"reflect"
"slices"
"strings"
"unsafe"
)
const (
jsonTag = "json"
yamlTag = "yaml"
xmlTag = "xml"
uriTag = "uri"
queryTag = "query"
headerTag = "header"
formTag = "form"
fileTag = "file"
nonStructTypeParameter = "T must be a struct type"
)
type notFieldPointerError struct {
structValue reflect.Value
target int
}
func (e notFieldPointerError) Error() string {
return fmt.Sprintf("argument %d should be a pointer to a field of %s", e.target,
e.structValue.Type().String())
}
// Fields validates the fields of a struct of type T.
//
// It uses the tags of the binding functions (such as "uri", "query" or "json") from the fields to build a message for
// the user in case the validation fails.
// If none of these tags are set or are set as the empty string, Fields uses the field's name instead.
//
// If T is not a struct type, Fields panics.
func Fields[T any](target *T, validations ...Field) error {
violations := slices.DeleteFunc(validations, func(f Field) bool { return f.Valid })
if len(violations) == 0 {
return nil
}
structValue := reflect.ValueOf(target).Elem()
if structValue.Kind() != reflect.Struct {
panic(nonStructTypeParameter)
}
var (
fields = reflect.VisibleFields(structValue.Type())
fieldsPerAddress = getFieldsPerAddress(fields, structValue)
argumentAddresses = make(map[any]unsafe.Pointer)
)
for vi, validation := range violations {
for ai, argument := range validation.Fields {
argumentAddress, ok := getArgumentAddress(argumentAddresses, argument)
if !ok {
panic(notFieldPointerError{structValue, ai}.Error())
}
field, ok := fieldsPerAddress[argumentAddress]
if !ok {
panic(notFieldPointerError{structValue, ai}.Error())
}
violations[vi].Message = strings.ReplaceAll(
violations[vi].Message,
fmt.Sprintf("{%d}", ai),
getReplacement(field, jsonTag, uriTag, queryTag, headerTag, formTag, yamlTag, xmlTag, fileTag),
)
}
}
return Error{Violations: violations}
}
func getReplacement(field reflect.StructField, tags ...string) string {
for _, tag := range tags {
value, ok := field.Tag.Lookup(tag)
if ok && value != "" {
return value
}
}
return field.Name
}
func getArgumentAddress(addresses map[any]unsafe.Pointer, argument any) (unsafe.Pointer, bool) {
address, ok := addresses[argument]
if ok {
return address, true
}
argumentValue := reflect.ValueOf(argument)
if argumentValue.Kind() != reflect.Pointer {
return nil, false
}
address, ok = argumentValue.UnsafePointer(), true
addresses[argument] = address
return address, ok
}
func getFieldsPerAddress(
fields []reflect.StructField,
structValue reflect.Value,
) map[unsafe.Pointer]reflect.StructField {
fieldsPerAddress := make(map[unsafe.Pointer]reflect.StructField, len(fields))
for _, field := range fields {
fieldValue := structValue.FieldByIndex(field.Index)
if fieldValue.Kind() == reflect.Pointer {
fieldsPerAddress[fieldValue.UnsafePointer()] = field
} else {
fieldsPerAddress[fieldValue.Addr().UnsafePointer()] = field
}
}
return fieldsPerAddress
}