56 lines
1.5 KiB
Go
56 lines
1.5 KiB
Go
package ksuid
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import (
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"encoding/binary"
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"errors"
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"math"
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)
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// Sequence is a KSUID generator which produces a sequence of ordered KSUIDs
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// from a seed.
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//
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// Up to 65536 KSUIDs can be generated by for a single seed.
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//
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// A typical usage of a Sequence looks like this:
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//
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// seq := ksuid.Sequence{
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// Seed: ksuid.New(),
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// }
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// id, err := seq.Next()
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//
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// Sequence values are not safe to use concurrently from multiple goroutines.
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type Sequence struct {
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// The seed is used as base for the KSUID generator, all generated KSUIDs
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// share the same leading 18 bytes of the seed.
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Seed KSUID
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count uint32 // uint32 for overflow, only 2 bytes are used
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}
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// Next produces the next KSUID in the sequence, or returns an error if the
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// sequence has been exhausted.
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func (seq *Sequence) Next() (KSUID, error) {
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id := seq.Seed // copy
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count := seq.count
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if count > math.MaxUint16 {
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return Nil, errors.New("too many IDs were generated")
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}
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seq.count++
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return withSequenceNumber(id, uint16(count)), nil
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}
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// Bounds returns the inclusive min and max bounds of the KSUIDs that may be
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// generated by the sequence. If all ids have been generated already then the
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// returned min value is equal to the max.
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func (seq *Sequence) Bounds() (min KSUID, max KSUID) {
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count := seq.count
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if count > math.MaxUint16 {
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count = math.MaxUint16
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}
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return withSequenceNumber(seq.Seed, uint16(count)), withSequenceNumber(seq.Seed, math.MaxUint16)
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}
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func withSequenceNumber(id KSUID, n uint16) KSUID {
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binary.BigEndian.PutUint16(id[len(id)-2:], n)
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return id
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}
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