client/setec: sketch of keyring

Not complete, needs work.

Author: creachadair

client/setec/keyring.go

@@ -0,0 +1,62 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package setec
+
+import (
+	"sync"
+
+	"github.com/tailscale/setec/types/api"
+)
+
+/*
+   TODO:
+   - Cache needs to be able to hold multiple values.
+   - Keep track of single- vs keyring-valued secrets.
+   - Update polling logic to use GetAll for keyrings.
+   - Add settings.
+*/
+
+// A Keyring represents a a collection of one or more available versions of a
+// named secret.
+type Keyring struct {
+	name string
+
+	mu     sync.Mutex
+	active int                // index into values
+	values []*api.SecretValue // in increasing order by version
+}
+
+// Get returns the key at index i of the keyring. Index 0 always refers to the
+// current active version, and further indexes refer to other versions in order
+// from newest to oldest.
+//
+// If i >= r.Len(), Get returns nil. If i < 0, Get panics.
+//
+// The Keyring retains ownership of the bytes returned, but the store will
+// never modify the contents of the secret, so it is safe to share the slice
+// without copying as long as the caller does not modify them.
+func (r *Keyring) Get(i int) []byte {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	switch {
+	case i < 0:
+		panic("index is negative")
+	case i < len(r.values):
+		return r.values[i].Value
+	default:
+		return nil
+	}
+}
+
+// GetString returns a copy of the key at index i of the keyring as a string.
+// If i >= r.Len(), GetString returns "". Otherwise, GetString behaves as Get.
+func (r *Keyring) GetString(i int) string { return string(r.Get(i)) }
+
+// Len reports the number of keys stored in r. The length is always positive,
+// counting the active version.
+func (r *Keyring) Len() int {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return len(r.values)
+}