Move external backend key logic to receiver methods of backend.Key (#…

…45985) (#46196)

There are a number of places that the backend.Key is assumed to
be a []byte and is passed to various functions from the `bytes`
package. This creates equivalent functionality on the backend.Key
type so that all assumptions about the backend key type can be
removed.

lib/backend/backend.go

@@ -18,12 +18,10 @@ limitations under the License.
 package backend
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"io"
 	"sort"
-	"strings"
 	"time"
 
 	"github.com/gravitational/trace"
@@ -198,7 +196,7 @@ type Watch struct {
 // String returns a user-friendly description
 // of the watcher
 func (w *Watch) String() string {
-	return fmt.Sprintf("Watcher(name=%v, prefixes=%v)", w.Name, string(bytes.Join(w.Prefixes, []byte(", "))))
+	return fmt.Sprintf("Watcher(name=%v, prefixes=%v)", w.Name, w.Prefixes)
 }
 
 // Watcher returns watcher
@@ -365,7 +363,7 @@ func (it Items) Swap(i, j int) {
 
 // Less is part of sort.Interface.
 func (it Items) Less(i, j int) bool {
-	return bytes.Compare(it[i].Key, it[j].Key) < 0
+	return it[i].Key.Compare(it[j].Key) < 0
 }
 
 // TTL returns TTL in duration units, rounds up to one second
@@ -415,24 +413,3 @@ func (p earliest) Less(i, j int) bool {
 func (p earliest) Swap(i, j int) {
 	p[i], p[j] = p[j], p[i]
 }
-
-// Separator is used as a separator between key parts
-const Separator = '/'
-
-// NewKey joins parts into path separated by Separator,
-// makes sure path always starts with Separator ("/")
-func NewKey(parts ...string) Key {
-	return internalKey("", parts...)
-}
-
-// ExactKey is like Key, except a Separator is appended to the result
-// path of Key. This is to ensure range matching of a path will only
-// math child paths and not other paths that have the resulting path
-// as a prefix.
-func ExactKey(parts ...string) Key {
-	return append(NewKey(parts...), Separator)
-}
-
-func internalKey(internalPrefix string, parts ...string) Key {
-	return Key(strings.Join(append([]string{internalPrefix}, parts...), string(Separator)))
-}

lib/backend/buffer.go

@@ -319,7 +319,7 @@ type BufferWatcher struct {
 // String returns user-friendly representation
 // of the buffer watcher
 func (w *BufferWatcher) String() string {
-	return fmt.Sprintf("Watcher(name=%v, prefixes=%v, capacity=%v, size=%v)", w.Name, string(bytes.Join(w.Prefixes, []byte(", "))), w.capacity, len(w.eventsC))
+	return fmt.Sprintf("Watcher(name=%v, prefixes=%v, capacity=%v, size=%v)", w.Name, w.Prefixes, w.capacity, len(w.eventsC))
 }
 
 // Events returns events channel.  This method performs internal work and should be re-called after each event

lib/backend/dynamo/dynamodbbk.go

@@ -17,7 +17,6 @@ limitations under the License.
 package dynamo
 
 import (
-	"bytes"
 	"context"
 	"net/http"
 	"sort"
@@ -517,7 +516,7 @@ func (b *Backend) CompareAndSwap(ctx context.Context, expected backend.Item, rep
 	if len(replaceWith.Key) == 0 {
 		return nil, trace.BadParameter("missing parameter Key")
 	}
-	if !bytes.Equal(expected.Key, replaceWith.Key) {
+	if expected.Key.Compare(replaceWith.Key) != 0 {
 		return nil, trace.BadParameter("expected and replaceWith keys should match")
 	}
 	r := record{

lib/backend/etcdbk/etcd.go

@@ -18,9 +18,7 @@ limitations under the License.
 package etcdbk
 
 import (
-	"bytes"
 	"context"
-	"crypto/subtle"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/base64"
@@ -736,7 +734,7 @@ func (b *EtcdBackend) CompareAndSwap(ctx context.Context, expected backend.Item,
 	if len(replaceWith.Key) == 0 {
 		return nil, trace.BadParameter("missing parameter Key")
 	}
-	if subtle.ConstantTimeCompare(expected.Key, replaceWith.Key) != 1 {
+	if expected.Key.Compare(replaceWith.Key) != 0 {
 		return nil, trace.BadParameter("expected and replaceWith keys should match")
 	}
 	var opts []clientv3.OpOption
@@ -1019,7 +1017,7 @@ func fromType(eventType mvccpb.Event_EventType) types.OpType {
 }
 
 func (b *EtcdBackend) trimPrefix(in backend.Key) backend.Key {
-	return bytes.TrimPrefix(in, backend.Key(b.cfg.Key))
+	return in.TrimPrefix(backend.Key(b.cfg.Key))
 }
 
 func (b *EtcdBackend) prependPrefix(in backend.Key) string {

lib/backend/firestore/firestorebk.go

@@ -516,7 +516,7 @@ func (b *Backend) CompareAndSwap(ctx context.Context, expected backend.Item, rep
 	if len(replaceWith.Key) == 0 {
 		return nil, trace.BadParameter("missing parameter Key")
 	}
-	if !bytes.Equal(expected.Key, replaceWith.Key) {
+	if expected.Key.Compare(replaceWith.Key) != 0 {
 		return nil, trace.BadParameter("expected and replaceWith keys should match")
 	}
 

lib/backend/key.go

@@ -16,5 +16,93 @@
 
 package backend
 
+import (
+	"bytes"
+	"fmt"
+	"strings"
+)
+
 // Key is the unique identifier for an [Item].
-type Key = []byte
+type Key []byte
+
+// Separator is used as a separator between key parts
+const Separator = '/'
+
+// NewKey joins parts into path separated by Separator,
+// makes sure path always starts with Separator ("/")
+func NewKey(parts ...string) Key {
+	return internalKey("", parts...)
+}
+
+// ExactKey is like Key, except a Separator is appended to the result
+// path of Key. This is to ensure range matching of a path will only
+// math child paths and not other paths that have the resulting path
+// as a prefix.
+func ExactKey(parts ...string) Key {
+	return append(NewKey(parts...), Separator)
+}
+
+func internalKey(internalPrefix string, parts ...string) Key {
+	return Key(strings.Join(append([]string{internalPrefix}, parts...), string(Separator)))
+}
+
+// String returns the textual representation of the key with
+// each component concatenated together via the [Separator].
+func (k Key) String() string {
+	return string(k)
+}
+
+// HasPrefix reports whether the key begins with prefix.
+func (k Key) HasPrefix(prefix Key) bool {
+	return bytes.HasPrefix(k, prefix)
+}
+
+// TrimPrefix returns the key without the provided leading prefix string.
+// If the key doesn't start with prefix, it is returned unchanged.
+func (k Key) TrimPrefix(prefix Key) Key {
+	return bytes.TrimPrefix(k, prefix)
+}
+
+func (k Key) PrependPrefix(p Key) Key {
+	return append(p, k...)
+}
+
+// HasSuffix reports whether the key ends with suffix.
+func (k Key) HasSuffix(suffix Key) bool {
+	return bytes.HasSuffix(k, suffix)
+}
+
+// TrimSuffix returns the key without the provided trailing suffix string.
+// If the key doesn't end with suffix, it is returned unchanged.
+func (k Key) TrimSuffix(suffix Key) Key {
+	return bytes.TrimSuffix(k, suffix)
+}
+
+func (k Key) Components() [][]byte {
+	if len(k) == 0 {
+		return nil
+	}
+
+	sep := []byte{Separator}
+	return bytes.Split(bytes.TrimPrefix(k, sep), sep)
+}
+
+func (k Key) Compare(o Key) int {
+	return bytes.Compare(k, o)
+}
+
+// Scan implement sql.Scanner, allowing a [Key] to
+// be directly retrieved from sql backends without
+// an intermediary object.
+func (k *Key) Scan(scan any) error {
+	switch key := scan.(type) {
+	case []byte:
+		*k = bytes.Clone(key)
+	case string:
+		*k = []byte(strings.Clone(key))
+	default:
+		return fmt.Errorf("invalid Key type %T", scan)
+	}
+
+	return nil
+}