forked from TrueCloudLab/distribution
75 lines
2.1 KiB
Go
75 lines
2.1 KiB
Go
package protocol
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import (
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"crypto/rand"
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"fmt"
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"reflect"
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)
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// RandReader is the random reader the protocol package will use to read
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// random bytes from. This is exported for testing, and should not be used.
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var RandReader = rand.Reader
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const idempotencyTokenFillTag = `idempotencyToken`
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// CanSetIdempotencyToken returns true if the struct field should be
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// automatically populated with a Idempotency token.
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//
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// Only *string and string type fields that are tagged with idempotencyToken
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// which are not already set can be auto filled.
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func CanSetIdempotencyToken(v reflect.Value, f reflect.StructField) bool {
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switch u := v.Interface().(type) {
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// To auto fill an Idempotency token the field must be a string,
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// tagged for auto fill, and have a zero value.
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case *string:
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return u == nil && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
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case string:
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return len(u) == 0 && len(f.Tag.Get(idempotencyTokenFillTag)) != 0
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}
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return false
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}
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// GetIdempotencyToken returns a randomly generated idempotency token.
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func GetIdempotencyToken() string {
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b := make([]byte, 16)
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RandReader.Read(b)
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return UUIDVersion4(b)
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}
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// SetIdempotencyToken will set the value provided with a Idempotency Token.
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// Given that the value can be set. Will panic if value is not setable.
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func SetIdempotencyToken(v reflect.Value) {
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if v.Kind() == reflect.Ptr {
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if v.IsNil() && v.CanSet() {
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v.Set(reflect.New(v.Type().Elem()))
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}
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v = v.Elem()
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}
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v = reflect.Indirect(v)
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if !v.CanSet() {
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panic(fmt.Sprintf("unable to set idempotnecy token %v", v))
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}
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b := make([]byte, 16)
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_, err := rand.Read(b)
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if err != nil {
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// TODO handle error
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return
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}
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v.Set(reflect.ValueOf(UUIDVersion4(b)))
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}
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// UUIDVersion4 returns a Version 4 random UUID from the byte slice provided
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func UUIDVersion4(u []byte) string {
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// https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_.28random.29
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// 13th character is "4"
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u[6] = (u[6] | 0x40) & 0x4F
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// 17th character is "8", "9", "a", or "b"
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u[8] = (u[8] | 0x80) & 0xBF
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return fmt.Sprintf(`%X-%X-%X-%X-%X`, u[0:4], u[4:6], u[6:8], u[8:10], u[10:])
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}
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