Source: idempotency.go in package github.com/aws/aws-sdk-go/private/protocol

package protocol

import (
	"crypto/rand"
	"fmt"
	"reflect"
)

RandReader is the random reader the protocol package will use to read random bytes from. This is exported for testing, and should not be used.

var RandReader = rand.Reader

const idempotencyTokenFillTag = `idempotencyToken`

CanSetIdempotencyToken returns true if the struct field should be automatically populated with a Idempotency token. Only *string and string type fields that are tagged with idempotencyToken which are not already set can be auto filled.

func CanSetIdempotencyToken(v reflect.Value, f reflect.StructField) bool {

To auto fill an Idempotency token the field must be a string, tagged for auto fill, and have a zero value.

	case *string:
		return u == nil && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
	case string:
		return len(u) == 0 && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
	}

	return false
}

GetIdempotencyToken returns a randomly generated idempotency token.

func GetIdempotencyToken() string {
	b := make([]byte, 16)
	RandReader.Read(b)

	return UUIDVersion4(b)
}

SetIdempotencyToken will set the value provided with a Idempotency Token. Given that the value can be set. Will panic if value is not setable.

func SetIdempotencyToken(v reflect.Value) {
	if v.Kind() == reflect.Ptr {
		if v.IsNil() && v.CanSet() {
			v.Set(reflect.New(v.Type().Elem()))
		}
		v = v.Elem()
	}
	v = reflect.Indirect(v)

	if !v.CanSet() {
		panic(fmt.Sprintf("unable to set idempotnecy token %v", v))
	}

	b := make([]byte, 16)
	_, err := rand.Read(b)

TODO handle error

		return
	}

	v.Set(reflect.ValueOf(UUIDVersion4(b)))
}

UUIDVersion4 returns a Version 4 random UUID from the byte slice provided

https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29 13th character is "4"

17th character is "8", "9", "a", or "b"

	u[8] = (u[8] | 0x80) & 0xBF

	return fmt.Sprintf(`%X-%X-%X-%X-%X`, u[0:4], u[4:6], u[6:8], u[8:10], u[10:])