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