vendor/github.com/aws/aws-sdk-go/private/protocol/idempotency.go

   1 package protocol
   2
   3 import (
   4         "crypto/rand"
   5         "fmt"
   6         "reflect"
   7 )
   8
   9 // RandReader is the random reader the protocol package will use to read
  10 // random bytes from. This is exported for testing, and should not be used.
  11 var RandReader = rand.Reader
  12
  13 const idempotencyTokenFillTag = `idempotencyToken`
  14
  15 // CanSetIdempotencyToken returns true if the struct field should be
  16 // automatically populated with a Idempotency token.
  17 //
  18 // Only *string and string type fields that are tagged with idempotencyToken
  19 // which are not already set can be auto filled.
  20 func CanSetIdempotencyToken(v reflect.Value, f reflect.StructField) bool {
  21         switch u := v.Interface().(type) {
  22         // To auto fill an Idempotency token the field must be a string,
  23         // tagged for auto fill, and have a zero value.
  24         case *string:
  25                 return u == nil && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
  26         case string:
  27                 return len(u) == 0 && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
  28         }
  29
  30         return false
  31 }
  32
  33 // GetIdempotencyToken returns a randomly generated idempotency token.
  34 func GetIdempotencyToken() string {
  35         b := make([]byte, 16)
  36         RandReader.Read(b)
  37
  38         return UUIDVersion4(b)
  39 }
  40
  41 // SetIdempotencyToken will set the value provided with a Idempotency Token.
  42 // Given that the value can be set. Will panic if value is not setable.
  43 func SetIdempotencyToken(v reflect.Value) {
  44         if v.Kind() == reflect.Ptr {
  45                 if v.IsNil() && v.CanSet() {
  46                         v.Set(reflect.New(v.Type().Elem()))
  47                 }
  48                 v = v.Elem()
  49         }
  50         v = reflect.Indirect(v)
  51
  52         if !v.CanSet() {
  53                 panic(fmt.Sprintf("unable to set idempotnecy token %v", v))
  54         }
  55
  56         b := make([]byte, 16)
  57         _, err := rand.Read(b)
  58         if err != nil {
  59                 // TODO handle error
  60                 return
  61         }
  62
  63         v.Set(reflect.ValueOf(UUIDVersion4(b)))
  64 }
  65
  66 // UUIDVersion4 returns a Version 4 random UUID from the byte slice provided
  67 func UUIDVersion4(u []byte) string {
  68         // https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
  69         // 13th character is "4"
  70         u[6] = (u[6] | 0x40) & 0x4F
  71         // 17th character is "8", "9", "a", or "b"
  72         u[8] = (u[8] | 0x80) & 0xBF
  73
  74         return fmt.Sprintf(`%X-%X-%X-%X-%X`, u[0:4], u[4:6], u[6:8], u[8:10], u[10:])
  75 }