Crate rusty_ulid
source ·Expand description
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
- UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
- UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
- UUID v4 provides no other information than randomness which can cause fragmentation in many data structures
Instead, herein is proposed ULID:
01ARZ3NDEKTSV4RRFFQ69G5FAV
- 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)
- Monotonic sort order (correctly detects and handles the same millisecond)
Specification
Below is the current specification of ULID as implemented in this crate.
01AN4Z07BY 79KA1307SR9X4MV3
|----------| |----------------|
Timestamp Randomness
48bits 80bits
Components
Timestamp
- 48 bit integer
- UNIX-time in milliseconds
- Won’t run out of space until
+10889-08-02T05:31:50.655Z
.
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 (lexical order). The default ASCII character set must be used. Within the same millisecond, sort order is not guaranteed
Canonical String Representation
ttttttttttrrrrrrrrrrrrrrrr
where
t is Timestamp (10 characters)
r is Randomness (16 characters)
Encoding
Crockford’s Base32 is used as shown. This alphabet excludes the letters I, L, O, and U to avoid confusion and abuse.
0123456789ABCDEFGHJKMNPQRSTVWXYZ
Monotonicity
When generating a ULID within the same millisecond, we can provide some
guarantees regarding sort order. Namely, if the same millisecond is detected,
the random
component is incremented by 1 bit in the least significant bit position
(with carrying).
If, in the extremely unlikely event that, you manage to generate more than 280 ULIDs within the same millisecond, or cause the random component to overflow with less, the generation will fail.
Overflow Errors when Parsing Base32 Strings
Technically, a 26-character Base32 encoded string can contain 130 bits of
information, whereas a ULID must only contain 128 bits. Therefore, the largest
valid ULID encoded in Base32 is 7ZZZZZZZZZZZZZZZZZZZZZZZZZ
, which corresponds to
an epoch time of 281474976710655
or 2 ^ 48 - 1
.
Any attempt to decode or encode a ULID larger than this should be rejected by all implementations, to prevent overflow bugs.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Re-exports
pub use crate::crockford::DecodingError;