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scan.go
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scan.go
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package sensitive
import (
"errors"
"fmt"
"reflect"
"sync"
)
var (
ErrInvalidTagConfiguration = errors.New("invalid 'sensitive' tag configuration")
ErrUnsupportedType = errors.New("unsupported 'sensitive' type")
ErrUnsupportedFieldType = errors.New("'sensitive' field type must be convertible to string")
ErrMultipleNestedSubjectID = errors.New("potential multiple nested subject IDs")
ErrSubjectIDNotFound = errors.New("subject ID is not found")
)
// Struct provides an accessor for sensitive struct fields and subject identifiers.
type Struct interface {
// Replace accepts a replacement function and applies it to each sensitive data field.
Replace(fn ReplaceFunc) error
// SubjectID returns the resolved SubjectID of the sensitive struct.
// It panics if the SubjectID is not resolved.
SubjectID() string
// HasSensitive indicates whether the struct contains sensitive data fields.
HasSensitive() bool
private()
}
// FieldReplace contains metadata for sensitive fields.
type FieldReplace struct {
// SubjectID is the identifier for the sensitive data subject, resolved at the struct level.
// This field may be empty if it is not required by the calling function.
SubjectID string
// Name is the name of the sensitive field.
Name string
// RType is the original type of the sensitive field.
// Note that this type must be convertible to a string.
RType reflect.Type
// Kind is the user-defined type of sensitive data, defined as an option in the 'sensitive' tag.
Kind string
// Options are the options specified in the 'sensitive' tag.
Options TagOptions
}
// ReplaceFunc is a callback function executed by the [Struct.Replace] method.
// It receives the original value of the sensitive field, converted to a string,
// and returns the new value as a string along with any error that may occur.
type ReplaceFunc func(fr FieldReplace, val string) (string, error)
// Scan inspects the given value and returns an accessor for the sensitive struct.
// It returns an error if the value is not a pointer to a struct or if the 'sensitive' tag is misconfigured.
//
// The [Struct] accessor and the [Scan] function are low-level components.
// In most cases, you should consider using the [Redact] or [Mask] functions instead.
func Scan(v any, requireSubject bool) (accessor Struct, err error) {
defer func() {
// normalize error
if err != nil && !errors.Is(err, ErrUnsupportedType) {
err = errors.Join(ErrInvalidTagConfiguration, err)
}
}()
if v == nil {
err = fmt.Errorf("%w '%v'", ErrUnsupportedType, nil)
return
}
tt := reflect.TypeOf(v)
if tt.Kind() != reflect.Pointer {
err = fmt.Errorf("%w '%v'", ErrUnsupportedType, tt)
return
}
if tt.Kind() == reflect.Pointer {
tt = tt.Elem()
}
if tt.Kind() != reflect.Struct {
err = fmt.Errorf("%w '%v'", ErrUnsupportedType, tt)
return
}
var ssType sensitiveStructType
ssType, err = scanStructType(tt)
if err != nil {
return
}
if !ssType.hasSensitive {
// The struct does not contain sensitive data, so there is no need to resolve the subject ID value.
// Therefore, calling 'reflect.ValueOf' is unnecessary due to its associated cost.
accessor = sensitiveStruct{
typ: ssType,
}
return
}
structValue := sensitiveStruct{
typ: ssType,
val: reflect.ValueOf(v).Elem(),
}
if requireSubject {
if _, err = structValue.resolveSubject(); err != nil {
return
}
}
accessor = structValue
return
}
var (
stringType = reflect.TypeFor[string]()
)
var (
cache map[reflect.Type]*sensitiveStructType = make(map[reflect.Type]*sensitiveStructType)
cacheMu sync.RWMutex
)
type sensitiveStructContext struct {
seen map[reflect.Type]*sensitiveStructType
}
type sensitiveField struct {
sf reflect.StructField
isSub, isData, isNested bool
prefix string
isSlice, isMap bool
nestedStructType *sensitiveStructType
nestedStructTypeRef reflect.Type
kind string
options TagOptions
}
func (f sensitiveField) getType(cache map[reflect.Type]*sensitiveStructType) *sensitiveStructType {
if f.nestedStructTypeRef != nil {
return cache[f.nestedStructTypeRef]
}
return f.nestedStructType
}
func (f sensitiveField) IsZero() bool {
// TBD find a better condition??
return f.sf.Name == ""
}
type sensitiveStructType struct {
hasSensitive bool
subField sensitiveField
sensitiveFields []sensitiveField
rt reflect.Type
}
type sensitiveStruct struct {
typ sensitiveStructType
val reflect.Value
subjectID string
}
func (ps sensitiveStruct) private() {}
var _ Struct = &sensitiveStruct{}
// resolveSubject resolves the sensitive struct subject ID value by walking through
// the struct and its nested sensitive structs.
//
// It returns an error if the subject ID is missing or duplicated.
func resolveSubject(pt sensitiveStructType, pv reflect.Value) (string, error) {
subject := ""
if !pt.subField.IsZero() {
subject = pt.subField.prefix + reflect.Indirect(pv.FieldByIndex(pt.subField.sf.Index)).String()
}
for _, ssField := range pt.sensitiveFields {
if !ssField.isNested {
continue
}
sensitiveFieldV := pv.FieldByIndex(ssField.sf.Index)
if sensitiveFieldV.IsZero() {
continue
}
cacheMu.Lock()
ssT := ssField.getType(cache)
cacheMu.Unlock()
// I believe ssT can't be nil
ssTv := *ssT
sensitiveFieldV = reflect.Indirect(sensitiveFieldV)
nestedSubject := ""
switch {
case ssField.isSlice:
for i := 0; i < sensitiveFieldV.Len(); i++ {
nestedSubject, _ = resolveSubject(ssTv, sensitiveFieldV.Index(i))
if nestedSubject != "" {
break
}
}
case ssField.isMap:
for _, k := range sensitiveFieldV.MapKeys() {
nestedSubject, _ = resolveSubject(ssTv, sensitiveFieldV.MapIndex(k))
if nestedSubject != "" {
break
}
}
default:
nestedSubject, _ = resolveSubject(ssTv, sensitiveFieldV)
}
if nestedSubject != "" {
if subject != "" && subject != nestedSubject {
return "", ErrMultipleNestedSubjectID
}
subject = nestedSubject
}
}
if subject == "" {
return "", fmt.Errorf("%w in '%v'", ErrSubjectIDNotFound, pt.rt)
}
return subject, nil
}
func (ps *sensitiveStruct) resolveSubject() (string, error) {
if ps.subjectID == "" {
var err error
ps.subjectID, err = resolveSubject(ps.typ, ps.val)
if err != nil {
return "", err
}
}
return ps.subjectID, nil
}
func (ss sensitiveStruct) SubjectID() string {
s, err := ss.resolveSubject()
if err != nil {
panic(err)
}
return s
}
func (ss sensitiveStruct) HasSensitive() bool {
return ss.typ.hasSensitive
}
func (s sensitiveStruct) Replace(fn ReplaceFunc) error {
var (
newVal string
err error
)
for _, ssField := range s.typ.sensitiveFields {
v := s.val.FieldByIndex(ssField.sf.Index)
if v.IsZero() {
continue
}
if !v.CanSet() {
continue
}
elem := reflect.Indirect(v)
if ssField.isData {
val := elem.String()
newVal, err = fn(FieldReplace{
SubjectID: s.subjectID,
RType: ssField.sf.Type,
Kind: ssField.kind,
Options: ssField.options,
}, val)
if err != nil {
return err
}
if newVal != val {
elem.SetString(newVal)
}
continue
}
if ssField.isNested {
var ssT sensitiveStructType
cacheMu.Lock()
ssTPtr := ssField.getType(cache)
cacheMu.Unlock()
// I believe ssTPtr can't be nil
ssT = *ssTPtr
if !ssT.hasSensitive {
continue
}
switch {
case ssField.isSlice:
for i := 0; i < elem.Len(); i++ {
if err := (&sensitiveStruct{
subjectID: s.subjectID, // inherit parent subject ID
val: reflect.Indirect(elem.Index(i)),
typ: ssT,
}).Replace(fn); err != nil {
return err
}
}
case ssField.isMap:
for _, k := range elem.MapKeys() {
mapElem := elem.MapIndex(k)
if mapElem.IsZero() {
continue
}
mapElem = reflect.Indirect(elem.MapIndex(k))
if !mapElem.CanAddr() {
newElem := reflect.New(mapElem.Type()).Elem()
newElem.Set(mapElem)
if err := (&sensitiveStruct{
subjectID: s.subjectID, // inherit parent subject ID
val: newElem,
typ: ssT,
}).Replace(fn); err != nil {
return err
}
elem.SetMapIndex(k, newElem)
continue
}
if err := (&sensitiveStruct{
subjectID: s.subjectID,
val: reflect.Indirect(elem.MapIndex(k)),
typ: ssT,
}).Replace(fn); err != nil {
return err
}
}
default:
if err := (&sensitiveStruct{
subjectID: s.subjectID,
val: elem,
typ: ssT,
}).Replace(fn); err != nil {
return err
}
}
}
}
return nil
}
func scanStructType(rt reflect.Type) (sensitiveStructType, error) {
cacheMu.Lock()
defer cacheMu.Unlock()
if _, ok := cache[rt]; !ok {
c := sensitiveStructContext{seen: cache}
ssT, err := scanStructTypeWithContext(c, rt)
if err != nil {
return sensitiveStructType{}, err
}
cache[rt] = &ssT
}
return *cache[rt], nil
}
func scanStructTypeWithContext(c sensitiveStructContext, rt reflect.Type) (sensitiveStructType, error) {
sensitiveFields := make([]sensitiveField, 0)
var subjectField sensitiveField
for i := 0; i < rt.NumField(); i++ {
field := rt.Field(i)
if !field.IsExported() {
continue
}
tag, _ := extractTag(field.Tag)
if tag == "" {
continue
}
name, opts := parseTag(tag)
ssField := sensitiveField{
sf: field,
isSub: name == tagSubjectID,
isData: name == tagData,
isNested: name == tagDive,
prefix: opts["prefix"],
kind: opts["kind"],
options: opts,
}
switch {
case ssField.isSub:
if !field.Type.ConvertibleTo(stringType) {
return sensitiveStructType{}, ErrUnsupportedFieldType
}
if !subjectField.IsZero() {
return sensitiveStructType{}, ErrMultipleNestedSubjectID
}
subjectField = ssField
case ssField.isData:
tt := field.Type
if tt.Kind() == reflect.Ptr {
tt = tt.Elem()
}
if tt.Kind() != reflect.String {
continue
}
sensitiveFields = append(sensitiveFields, ssField)
case ssField.isNested:
tt := field.Type
if tt.Kind() == reflect.Ptr {
tt = tt.Elem()
}
if tt.Kind() == reflect.Slice {
ssField.isSlice = true
tt = tt.Elem()
}
if tt.Kind() == reflect.Map {
ssField.isMap = true
tt = tt.Elem()
}
if tt.Kind() == reflect.Ptr {
tt = tt.Elem()
}
_, seen := c.seen[tt]
if !seen {
var ssType sensitiveStructType
var err error
c.seen[tt] = &ssType
ssType, err = scanStructTypeWithContext(c, tt)
if err != nil {
return sensitiveStructType{}, err
}
ssField.nestedStructType = &ssType
} else {
ssField.nestedStructTypeRef = tt
}
sensitiveFields = append(sensitiveFields, ssField)
default:
return sensitiveStructType{}, fmt.Errorf("invalid tag name '%s'", name)
}
}
return sensitiveStructType{
hasSensitive: len(sensitiveFields) > 0,
subField: subjectField,
sensitiveFields: sensitiveFields,
rt: rt,
}, nil
}