ulid

Package ulid provides code for generating variable length unique, lexigraphic identifiers (ULID) with programmable fills. Currently, there is a RandomGenerator that can be used to generate ULIDs with a randomized payload. To provide a custom payload, simply extend the BaseGenerator, and override the Generate method. It's important to call the BaseGenerator's Generate method, otherwise the skew and timestamp bits won't be set properly.

Unlike the canonical ULID, this version holds a placeholder byte for major clock skews which can often occur in distributed systems. The wire format is as follows: [ skew ][ millis ][ payload ]

- `skew` - 1 byte used to handle major clock skews (reserved, unused)
- `millis` - 6 bytes of a unix timestamp (should give us until the year 10k or so)
- `payload` - N bytes for the payload

import go.pitz.tech/lib/ulid

Usage

const (
	// SkewOffset is the starting byte position for the skew data.
	SkewOffset = 0
	// SkewLength is the number of bytes representing the skew.
	SkewLength = 1

	// UnixOffset is the starting byte position for the unix timestamp data.
	UnixOffset = 1
	// UnixLength is the number of bytes representing the unix timestamp data.
	UnixLength = 6

	// PayloadOffset is the starting byte position for the payload data.
	PayloadOffset = 7
)

var (
	// ErrInvalidBitCount is returned when an invalid number of bits is provided to the Generate method of a Generator.
	ErrInvalidBitCount = errors.New("bits must be divisible by 8")

	// ErrNotEnoughBits is returned when fewer than 64 bit ULIDs are requested to be generated.
	ErrNotEnoughBits = errors.New("must be at least 64 bits")

	// ErrInsufficientData is returned when the fill fails to return enough fata for the ULID.
	ErrInsufficientData = errors.New("failed to read sufficient payload data")
)

func RandomFill

func RandomFill(_ ULID, data []byte) (int, error)

RandomFill is a fill that populates the data payload with random data.

func ToContext

func ToContext(ctx context.Context, generator *Generator) context.Context

ToContext appends the provided generator to the provided context.

type Fill

type Fill func(ulid ULID, data []byte) (int, error)

Fill provides an abstraction for filling the data payload of a ULID.

type Generator

type Generator struct {
}

Generator is the base interface defines how to generate ULIDs of varying length.

func Extract

func Extract(ctx context.Context) *Generator

Extract is used to obtain the generator from a context. If none is present, the system generator is used.

func NewGenerator

func NewGenerator(skew byte, fill Fill) *Generator

NewGenerator constructs a generator using the provided skew and fill.

func (*Generator) Generate

func (g *Generator) Generate(ctx context.Context, bits int) (ULID, error)

Generate produces a new ULID unless an error occurs. A clock can be provided on the context to override how the Generator obtains a timestamp.

type ULID

type ULID []byte

ULID is a variable-length, generalized, unique lexographical identifier.

func Parse

func Parse(ulid string) (ULID, error)

Parse accepts a ULID string and attempts to extract a ULID from the provided string.

func (ULID) Bytes

func (ulid ULID) Bytes() []byte

Bytes returns a copy of the underlying byte array backing the ulid.

func (ULID) MarshalJSON

func (ulid ULID) MarshalJSON() ([]byte, error)

func (ULID) Payload

func (ulid ULID) Payload() []byte

Payload returns a copy of the payload bytes.

func (*ULID) Scan

func (ulid *ULID) Scan(src interface{}) (err error)

Scan attempts to parse the provided src value into the ULID.

func (ULID) Skew

func (ulid ULID) Skew() byte

Skew returns the current skew used to correct massive time skews.

func (ULID) String

func (ulid ULID) String() string

String returns a string representation of the payload. It's encoded using a crockford base32 encoding.

func (ULID) Timestamp

func (ulid ULID) Timestamp() time.Time

Timestamp returns the timestamp portion of the identifier.

func (*ULID) UnmarshalJSON

func (ulid *ULID) UnmarshalJSON(bytes []byte) error

func (ULID) Value

func (ulid ULID) Value() (driver.Value, error)

Value serializes the ULID so that it can be stored in SQL databases.