Merge pull request #55 from dmcgowan/add-digestset

Add digestset subpackage

digestset/set.go

@@ -0,0 +1,262 @@
+// Copyright 2020, 2020 OCI Contributors
+// Copyright 2017 Docker, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+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]
+}