route/vendor/github.com/oklog/ulid/README.md

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2017-10-06 15:29:20 +00:00
# Universally Unique Lexicographically Sortable Identifier
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A Go port of [alizain/ulid](https://github.com/alizain/ulid) with binary format implemented.
## Background
A GUID/UUID can be suboptimal for many use-cases because:
- It isn't the most character efficient way of encoding 128 bits
- It provides no other information than randomness
A ULID however:
- Is compatible with UUID/GUID's
- 1.21e+24 unique ULIDs per millisecond (1,208,925,819,614,629,174,706,176 to be exact)
- Lexicographically sortable
- Canonically encoded as a 26 character string, as opposed to the 36 character UUID
- Uses Crockford's base32 for better efficiency and readability (5 bits per character)
- Case insensitive
- No special characters (URL safe)
## Install
```shell
go get github.com/oklog/ulid
```
## Usage
An ULID is constructed with a `time.Time` and an `io.Reader` entropy source.
This design allows for greater flexibility in choosing your trade-offs.
Please note that `rand.Rand` from the `math` package is *not* safe for concurrent use.
Instantiate one per long living go-routine or use a `sync.Pool` if you want to avoid the potential contention of a locked `rand.Source` as its been frequently observed in the package level functions.
```go
func ExampleULID() {
t := time.Unix(1000000, 0)
entropy := rand.New(rand.NewSource(t.UnixNano()))
fmt.Println(ulid.MustNew(ulid.Timestamp(t), entropy))
// Output: 0000XSNJG0MQJHBF4QX1EFD6Y3
}
```
## Specification
Below is the current specification of ULID as implemented in this repository.
### Components
**Timestamp**
- 48 bits
- UNIX-time in milliseconds
- Won't run out of space till the year 10895 AD
**Entropy**
- 80 bits
- User defined entropy source.
### Encoding
[Crockford's Base32](http://www.crockford.com/wrmg/base32.html) is used as shown.
This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.
```
0123456789ABCDEFGHJKMNPQRSTVWXYZ
```
### Binary Layout and Byte Order
The components are encoded as 16 octets. Each component is encoded with the Most Significant Byte first (network byte order).
```
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32_bit_uint_time_high |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16_bit_uint_time_low | 16_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```
### String Representation
```
01AN4Z07BY 79KA1307SR9X4MV3
|----------| |----------------|
Timestamp Entropy
10 chars 16 chars
48bits 80bits
base32 base32
```
## Test
```shell
go test ./...
```
## Benchmarks
On a Intel Core i7 Ivy Bridge 2.7 GHz, MacOS 10.12.1 and Go 1.8.0beta1
```
BenchmarkNew/WithCryptoEntropy-8 2000000 747 ns/op 16 B/op 1 allocs/op
BenchmarkNew/WithEntropy-8 20000000 63.9 ns/op 16 B/op 1 allocs/op
BenchmarkNew/WithoutEntropy-8 50000000 29.4 ns/op 16 B/op 1 allocs/op
BenchmarkMustNew/WithCryptoEntropy-8 2000000 744 ns/op 16 B/op 1 allocs/op
BenchmarkMustNew/WithEntropy-8 20000000 68.0 ns/op 16 B/op 1 allocs/op
BenchmarkMustNew/WithoutEntropy-8 50000000 34.0 ns/op 16 B/op 1 allocs/op
BenchmarkParse-8 50000000 30.6 ns/op 0 B/op 0 allocs/op
BenchmarkMustParse-8 50000000 36.2 ns/op 0 B/op 0 allocs/op
BenchmarkString-8 20000000 61.6 ns/op 32 B/op 1 allocs/op
BenchmarkMarshal/Text-8 30000000 53.3 ns/op 32 B/op 1 allocs/op
BenchmarkMarshal/TextTo-8 100000000 22.8 ns/op 0 B/op 0 allocs/op
BenchmarkMarshal/Binary-8 300000000 4.40 ns/op 0 B/op 0 allocs/op
BenchmarkMarshal/BinaryTo-8 2000000000 1.16 ns/op 0 B/op 0 allocs/op
BenchmarkUnmarshal/Text-8 100000000 20.0 ns/op 0 B/op 0 allocs/op
BenchmarkUnmarshal/Binary-8 300000000 5.25 ns/op 0 B/op 0 allocs/op
BenchmarkNow-8 100000000 14.3 ns/op 0 B/op 0 allocs/op
BenchmarkTimestamp-8 2000000000 0.29 ns/op 0 B/op 0 allocs/op
BenchmarkTime-8 2000000000 0.58 ns/op 0 B/op 0 allocs/op
BenchmarkSetTime-8 2000000000 0.85 ns/op 0 B/op 0 allocs/op
BenchmarkEntropy-8 200000000 7.17 ns/op 0 B/op 0 allocs/op
BenchmarkSetEntropy-8 2000000000 0.83 ns/op 0 B/op 0 allocs/op
```
## Prior Art
- [alizain/ulid](https://github.com/alizain/ulid)
- [RobThree/NUlid](https://github.com/RobThree/NUlid)
- [imdario/go-ulid](https://github.com/imdario/go-ulid)