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// Copyright 2019-present Facebook
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Package pulid implements the pulid type.
// A pulid is an identifier that is a two-byte prefixed ULIDs, with the first two bytes encoding the type of the entity.
package pulid
import (
// ID implements a PULID - a prefixed ULID.
type ID string
// The default entropy source.
var defaultEntropySource *ulid.MonotonicEntropy
func init() {
// Seed the default entropy source.
// TODO: To improve testability, this package should allow control of entropy sources and the time.Now implementation.
defaultEntropySource = ulid.Monotonic(rand.Reader, 0)
// newULID returns a new ULID for time.Now() using the default entropy source.
func newULID() ulid.ULID {
return ulid.MustNew(ulid.Timestamp(time.Now()), defaultEntropySource)
// MustNew returns a new PULID for time.Now() given a prefix. This uses the default entropy source.
func MustNew(prefix string) ID { return ID(prefix + fmt.Sprint(newULID())) }
// UnmarshalGQL implements the graphql.Unmarshaler interface
func (u *ID) UnmarshalGQL(v interface{}) error {
return u.Scan(v)
// MarshalGQL implements the graphql.Marshaler interface
func (u ID) MarshalGQL(w io.Writer) {
_, _ = io.WriteString(w, strconv.Quote(string(u)))
// Scan implements the Scanner interface.
func (u *ID) Scan(src interface{}) error {
if src == nil {
return fmt.Errorf("pulid: expected a value")
s, ok := src.(string)
if !ok {
return fmt.Errorf("pulid: expected a string")
*u = ID(s)
return nil
// Value implements the driver Valuer interface.
func (u ID) Value() (driver.Value, error) {
return string(u), nil