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package digestset
import (
"errors"
"sort"
"strings"
"sync"
digest "github.com/opencontainers/go-digest"
)
var (
// ErrDigestNotFound is used when a matching digest
// could not be found in a set.
ErrDigestNotFound = errors.New("digest not found")
// ErrDigestAmbiguous is used when multiple digests
// are found in a set. None of the matching digests
// should be considered valid matches.
ErrDigestAmbiguous = errors.New("ambiguous digest string")
)
// Set is used to hold a unique set of digests which
// may be easily referenced by easily referenced by a string
// representation of the digest as well as short representation.
// The uniqueness of the short representation is based on other
// digests in the set. If digests are omitted from this set,
// collisions in a larger set may not be detected, therefore it
// is important to always do short representation lookups on
// the complete set of digests. To mitigate collisions, an
// appropriately long short code should be used.
type Set struct {
mutex sync.RWMutex
entries digestEntries
}
// NewSet creates an empty set of digests
// which may have digests added.
func NewSet() *Set {
return &Set{
entries: digestEntries{},
}
}
// checkShortMatch checks whether two digests match as either whole
// values or short values. This function does not test equality,
// rather whether the second value could match against the first
// value.
func checkShortMatch(alg digest.Algorithm, hex, shortAlg, shortHex string) bool {
if len(hex) == len(shortHex) {
if hex != shortHex {
return false
}
if len(shortAlg) > 0 && string(alg) != shortAlg {
return false
}
} else if !strings.HasPrefix(hex, shortHex) {
return false
} else if len(shortAlg) > 0 && string(alg) != shortAlg {
return false
}
return true
}
// Lookup looks for a digest matching the given string representation.
// If no digests could be found ErrDigestNotFound will be returned
// with an empty digest value. If multiple matches are found
// ErrDigestAmbiguous will be returned with an empty digest value.
func (dst *Set) Lookup(d string) (digest.Digest, error) {
dst.mutex.RLock()
defer dst.mutex.RUnlock()
if len(dst.entries) == 0 {
return "", ErrDigestNotFound
}
var (
searchFunc func(int) bool
alg digest.Algorithm
hex string
)
dgst, err := digest.Parse(d)
if err == digest.ErrDigestInvalidFormat {
hex = d
searchFunc = func(i int) bool {
return dst.entries[i].val >= d
}
} else {
hex = dgst.Hex()
alg = dgst.Algorithm()
searchFunc = func(i int) bool {
if dst.entries[i].val == hex {
return dst.entries[i].alg >= alg
}
return dst.entries[i].val >= hex
}
}
idx := sort.Search(len(dst.entries), searchFunc)
if idx == len(dst.entries) || !checkShortMatch(dst.entries[idx].alg, dst.entries[idx].val, string(alg), hex) {
return "", ErrDigestNotFound
}
if dst.entries[idx].alg == alg && dst.entries[idx].val == hex {
return dst.entries[idx].digest, nil
}
if idx+1 < len(dst.entries) && checkShortMatch(dst.entries[idx+1].alg, dst.entries[idx+1].val, string(alg), hex) {
return "", ErrDigestAmbiguous
}
return dst.entries[idx].digest, nil
}
// Add adds the given digest to the set. An error will be returned
// if the given digest is invalid. If the digest already exists in the
// set, this operation will be a no-op.
func (dst *Set) Add(d digest.Digest) error {
if err := d.Validate(); err != nil {
return err
}
dst.mutex.Lock()
defer dst.mutex.Unlock()
entry := &digestEntry{alg: d.Algorithm(), val: d.Hex(), digest: d}
searchFunc := func(i int) bool {
if dst.entries[i].val == entry.val {
return dst.entries[i].alg >= entry.alg
}
return dst.entries[i].val >= entry.val
}
idx := sort.Search(len(dst.entries), searchFunc)
if idx == len(dst.entries) {
dst.entries = append(dst.entries, entry)
return nil
} else if dst.entries[idx].digest == d {
return nil
}
entries := append(dst.entries, nil)
copy(entries[idx+1:], entries[idx:len(entries)-1])
entries[idx] = entry
dst.entries = entries
return nil
}
// Remove removes the given digest from the set. An err will be
// returned if the given digest is invalid. If the digest does
// not exist in the set, this operation will be a no-op.
func (dst *Set) Remove(d digest.Digest) error {
if err := d.Validate(); err != nil {
return err
}
dst.mutex.Lock()
defer dst.mutex.Unlock()
entry := &digestEntry{alg: d.Algorithm(), val: d.Hex(), digest: d}
searchFunc := func(i int) bool {
if dst.entries[i].val == entry.val {
return dst.entries[i].alg >= entry.alg
}
return dst.entries[i].val >= entry.val
}
idx := sort.Search(len(dst.entries), searchFunc)
// Not found if idx is after or value at idx is not digest
if idx == len(dst.entries) || dst.entries[idx].digest != d {
return nil
}
entries := dst.entries
copy(entries[idx:], entries[idx+1:])
entries = entries[:len(entries)-1]
dst.entries = entries
return nil
}
// All returns all the digests in the set
func (dst *Set) All() []digest.Digest {
dst.mutex.RLock()
defer dst.mutex.RUnlock()
retValues := make([]digest.Digest, len(dst.entries))
for i := range dst.entries {
retValues[i] = dst.entries[i].digest
}
return retValues
}
// ShortCodeTable returns a map of Digest to unique short codes. The
// length represents the minimum value, the maximum length may be the
// entire value of digest if uniqueness cannot be achieved without the
// full value. This function will attempt to make short codes as short
// as possible to be unique.
func ShortCodeTable(dst *Set, length int) map[digest.Digest]string {
dst.mutex.RLock()
defer dst.mutex.RUnlock()
m := make(map[digest.Digest]string, len(dst.entries))
l := length
resetIdx := 0
for i := 0; i < len(dst.entries); i++ {
var short string
extended := true
for extended {
extended = false
if len(dst.entries[i].val) <= l {
short = dst.entries[i].digest.String()
} else {
short = dst.entries[i].val[:l]
for j := i + 1; j < len(dst.entries); j++ {
if checkShortMatch(dst.entries[j].alg, dst.entries[j].val, "", short) {
if j > resetIdx {
resetIdx = j
}
extended = true
} else {
break
}
}
if extended {
l++
}
}
}
m[dst.entries[i].digest] = short
if i >= resetIdx {
l = length
}
}
return m
}
type digestEntry struct {
alg digest.Algorithm
val string
digest digest.Digest
}
type digestEntries []*digestEntry
func (d digestEntries) Len() int {
return len(d)
}
func (d digestEntries) Less(i, j int) bool {
if d[i].val != d[j].val {
return d[i].val < d[j].val
}
return d[i].alg < d[j].alg
}
func (d digestEntries) Swap(i, j int) {
d[i], d[j] = d[j], d[i]
}
|
