Vendor continuity

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

vendor/github.com/stevvooe/continuity/digests.go

@@ -0,0 +1,88 @@
+package continuity
+
+import (
+	"fmt"
+	"io"
+	"sort"
+
+	"github.com/opencontainers/go-digest"
+)
+
+// Digester produces a digest for a given read stream
+type Digester interface {
+	Digest(io.Reader) (digest.Digest, error)
+}
+
+// ContentProvider produces a read stream for a given digest
+type ContentProvider interface {
+	Reader(digest.Digest) (io.ReadCloser, error)
+}
+
+type simpleDigester struct {
+	algorithm digest.Algorithm
+}
+
+func (sd simpleDigester) Digest(r io.Reader) (digest.Digest, error) {
+	digester := sd.algorithm.Digester()
+
+	if _, err := io.Copy(digester.Hash(), r); err != nil {
+		return "", err
+	}
+
+	return digester.Digest(), nil
+}
+
+// uniqifyDigests sorts and uniqifies the provided digest, ensuring that the
+// digests are not repeated and no two digests with the same algorithm have
+// different values. Because a stable sort is used, this has the effect of
+// "zipping" digest collections from multiple resources.
+func uniqifyDigests(digests ...digest.Digest) ([]digest.Digest, error) {
+	sort.Stable(digestSlice(digests)) // stable sort is important for the behavior here.
+	seen := map[digest.Digest]struct{}{}
+	algs := map[digest.Algorithm][]digest.Digest{} // detect different digests.
+
+	var out []digest.Digest
+	// uniqify the digests
+	for _, d := range digests {
+		if _, ok := seen[d]; ok {
+			continue
+		}
+
+		seen[d] = struct{}{}
+		algs[d.Algorithm()] = append(algs[d.Algorithm()], d)
+
+		if len(algs[d.Algorithm()]) > 1 {
+			return nil, fmt.Errorf("conflicting digests for %v found", d.Algorithm())
+		}
+
+		out = append(out, d)
+	}
+
+	return out, nil
+}
+
+// digestsMatch compares the two sets of digests to see if they match.
+func digestsMatch(as, bs []digest.Digest) bool {
+	all := append(as, bs...)
+
+	uniqified, err := uniqifyDigests(all...)
+	if err != nil {
+		// the only error uniqifyDigests returns is when the digests disagree.
+		return false
+	}
+
+	disjoint := len(as) + len(bs)
+	if len(uniqified) == disjoint {
+		// if these two sets have the same cardinality, we know both sides
+		// didn't share any digests.
+		return false
+	}
+
+	return true
+}
+
+type digestSlice []digest.Digest
+
+func (p digestSlice) Len() int           { return len(p) }
+func (p digestSlice) Less(i, j int) bool { return p[i] < p[j] }
+func (p digestSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }