# ulid
Universally Unique Lexicographically Sortable Identifier implementation for Elixir
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[](https://rubygems.org/gems/ulid)
[](https://github.com/rafaelsales/ulid)
# Universally Unique Lexicographically Sortable Identifier
UUID can be suboptimal for many uses-cases because:
- It isn't the most character efficient way of encoding 128 bits of randomness
- The string format itself is apparently based on the original MAC & time version (UUIDv1 from Wikipedia)
- It provides no other information than randomness
Instead, herein is proposed ULID:
- 128-bit compatibility with UUID
- 1.21e+24 unique ULIDs per millisecond
- 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)
### Installation
If [available in Hex](https://hex.pm/docs/publish), the package can be installed as:
1. Add `ulid` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[{:ulid, "~> 0.1.0"}]
end
```
2. Ensure `ulid` is started before your application:
```elixir
def application do
[applications: [:ulid]]
end
```
### Usage
```elixir
Ulid.generate # 01ARZ3NDEKTSV4RRFFQ69G5FAV
```
## Specification
Below is the current specification of ULID as implemented in this repository. *Note: the binary format has not been implemented.*
```
01AN4Z07BY 79KA1307SR9X4MV3
|----------| |----------------|
Timestamp Randomness
10 chars 16 chars
48bits 80bits
base32 base32
```
### Components
**Timestamp**
- 48 bit integer
- UNIX-time in milliseconds
- Won't run out of space till the year 10895 AD.
**Randomness**
- 80 bits
- Cryptographically secure source of randomness, if possible
### Sorting
The left-most character must be sorted first, and the right-most character sorted last. The default ASCII order is used for sorting.
### 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_low |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16_bit_uint_time_high | 16_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32_bit_uint_random |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
```
### String Representation
```
ttttttttttrrrrrrrrrrrrrrrr
where
t is Timestamp
r is Randomness
```
## Test Suite
```
mix test
```
### Credits and references:
* https://github.com/alizain/ulid
* https://github.com/ulid-org/spec
