Re-vendor, primarily for https://github.com/containers/storage/pull/11

containers/storage got new dependencies, so we will need to re-vendor
eventually anyway, and having this separate from other major work is
cleaner.

But the primary goal of this commit is to see whether it makes skopeo
buildable on OS X.

vendor/github.com/containers/storage/pkg/truncindex/truncindex.go

@@ -0,0 +1,137 @@
+// Package truncindex provides a general 'index tree', used by Docker
+// in order to be able to reference containers by only a few unambiguous
+// characters of their id.
+package truncindex
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+
+	"github.com/tchap/go-patricia/patricia"
+)
+
+var (
+	// ErrEmptyPrefix is an error returned if the prefix was empty.
+	ErrEmptyPrefix = errors.New("Prefix can't be empty")
+
+	// ErrIllegalChar is returned when a space is in the ID
+	ErrIllegalChar = errors.New("illegal character: ' '")
+
+	// ErrNotExist is returned when ID or its prefix not found in index.
+	ErrNotExist = errors.New("ID does not exist")
+)
+
+// ErrAmbiguousPrefix is returned if the prefix was ambiguous
+// (multiple ids for the prefix).
+type ErrAmbiguousPrefix struct {
+	prefix string
+}
+
+func (e ErrAmbiguousPrefix) Error() string {
+	return fmt.Sprintf("Multiple IDs found with provided prefix: %s", e.prefix)
+}
+
+// TruncIndex allows the retrieval of string identifiers by any of their unique prefixes.
+// This is used to retrieve image and container IDs by more convenient shorthand prefixes.
+type TruncIndex struct {
+	sync.RWMutex
+	trie *patricia.Trie
+	ids  map[string]struct{}
+}
+
+// NewTruncIndex creates a new TruncIndex and initializes with a list of IDs.
+func NewTruncIndex(ids []string) (idx *TruncIndex) {
+	idx = &TruncIndex{
+		ids: make(map[string]struct{}),
+
+		// Change patricia max prefix per node length,
+		// because our len(ID) always 64
+		trie: patricia.NewTrie(patricia.MaxPrefixPerNode(64)),
+	}
+	for _, id := range ids {
+		idx.addID(id)
+	}
+	return
+}
+
+func (idx *TruncIndex) addID(id string) error {
+	if strings.Contains(id, " ") {
+		return ErrIllegalChar
+	}
+	if id == "" {
+		return ErrEmptyPrefix
+	}
+	if _, exists := idx.ids[id]; exists {
+		return fmt.Errorf("id already exists: '%s'", id)
+	}
+	idx.ids[id] = struct{}{}
+	if inserted := idx.trie.Insert(patricia.Prefix(id), struct{}{}); !inserted {
+		return fmt.Errorf("failed to insert id: %s", id)
+	}
+	return nil
+}
+
+// Add adds a new ID to the TruncIndex.
+func (idx *TruncIndex) Add(id string) error {
+	idx.Lock()
+	defer idx.Unlock()
+	if err := idx.addID(id); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Delete removes an ID from the TruncIndex. If there are multiple IDs
+// with the given prefix, an error is thrown.
+func (idx *TruncIndex) Delete(id string) error {
+	idx.Lock()
+	defer idx.Unlock()
+	if _, exists := idx.ids[id]; !exists || id == "" {
+		return fmt.Errorf("no such id: '%s'", id)
+	}
+	delete(idx.ids, id)
+	if deleted := idx.trie.Delete(patricia.Prefix(id)); !deleted {
+		return fmt.Errorf("no such id: '%s'", id)
+	}
+	return nil
+}
+
+// Get retrieves an ID from the TruncIndex. If there are multiple IDs
+// with the given prefix, an error is thrown.
+func (idx *TruncIndex) Get(s string) (string, error) {
+	if s == "" {
+		return "", ErrEmptyPrefix
+	}
+	var (
+		id string
+	)
+	subTreeVisitFunc := func(prefix patricia.Prefix, item patricia.Item) error {
+		if id != "" {
+			// we haven't found the ID if there are two or more IDs
+			id = ""
+			return ErrAmbiguousPrefix{prefix: string(prefix)}
+		}
+		id = string(prefix)
+		return nil
+	}
+
+	idx.RLock()
+	defer idx.RUnlock()
+	if err := idx.trie.VisitSubtree(patricia.Prefix(s), subTreeVisitFunc); err != nil {
+		return "", err
+	}
+	if id != "" {
+		return id, nil
+	}
+	return "", ErrNotExist
+}
+
+// Iterate iterates over all stored IDs, and passes each of them to the given handler.
+func (idx *TruncIndex) Iterate(handler func(id string)) {
+	idx.trie.Visit(func(prefix patricia.Prefix, item patricia.Item) error {
+		handler(string(prefix))
+		return nil
+	})
+}