1 files changed, 127 insertions, 0 deletions
diff --git a/pkg/registrar/registrar.go b/pkg/registrar/registrar.go
new file mode 100644
index 000000000..1e75ee995
--- /dev/null
+++ b/pkg/registrar/registrar.go
@@ -0,0 +1,127 @@
+// Package registrar provides name registration. It reserves a name to a given key.
+package registrar
+
+import (
+	"errors"
+	"sync"
+)
+
+var (
+	// ErrNameReserved is an error which is returned when a name is requested to be reserved that already is reserved
+	ErrNameReserved = errors.New("name is reserved")
+	// ErrNameNotReserved is an error which is returned when trying to find a name that is not reserved
+	ErrNameNotReserved = errors.New("name is not reserved")
+	// ErrNoSuchKey is returned when trying to find the names for a key which is not known
+	ErrNoSuchKey = errors.New("provided key does not exist")
+)
+
+// Registrar stores indexes a list of keys and their registered names as well as indexes names and the key that they are registered to
+// Names must be unique.
+// Registrar is safe for concurrent access.
+type Registrar struct {
+	idx   map[string][]string
+	names map[string]string
+	mu    sync.Mutex
+}
+
+// NewRegistrar creates a new Registrar with the an empty index
+func NewRegistrar() *Registrar {
+	return &Registrar{
+		idx:   make(map[string][]string),
+		names: make(map[string]string),
+	}
+}
+
+// Reserve registers a key to a name
+// Reserve is idempotent
+// Attempting to reserve a key to a name that already exists results in an `ErrNameReserved`
+// A name reservation is globally unique
+func (r *Registrar) Reserve(name, key string) error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if k, exists := r.names[name]; exists {
+		if k != key {
+			return ErrNameReserved
+		}
+		return nil
+	}
+
+	r.idx[key] = append(r.idx[key], name)
+	r.names[name] = key
+	return nil
+}
+
+// Release releases the reserved name
+// Once released, a name can be reserved again
+func (r *Registrar) Release(name string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	key, exists := r.names[name]
+	if !exists {
+		return
+	}
+
+	for i, n := range r.idx[key] {
+		if n != name {
+			continue
+		}
+		r.idx[key] = append(r.idx[key][:i], r.idx[key][i+1:]...)
+		break
+	}
+
+	delete(r.names, name)
+
+	if len(r.idx[key]) == 0 {
+		delete(r.idx, key)
+	}
+}
+
+// Delete removes all reservations for the passed in key.
+// All names reserved to this key are released.
+func (r *Registrar) Delete(key string) {
+	r.mu.Lock()
+	for _, name := range r.idx[key] {
+		delete(r.names, name)
+	}
+	delete(r.idx, key)
+	r.mu.Unlock()
+}
+
+// GetNames lists all the reserved names for the given key
+func (r *Registrar) GetNames(key string) ([]string, error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	names, exists := r.idx[key]
+	if !exists {
+		return nil, ErrNoSuchKey
+	}
+	return names, nil
+}
+
+// Get returns the key that the passed in name is reserved to
+func (r *Registrar) Get(name string) (string, error) {
+	r.mu.Lock()
+	key, exists := r.names[name]
+	r.mu.Unlock()
+
+	if !exists {
+		return "", ErrNameNotReserved
+	}
+	return key, nil
+}
+
+// GetAll returns all registered names
+func (r *Registrar) GetAll() map[string][]string {
+	out := make(map[string][]string)
+
+	r.mu.Lock()
+	// copy index into out
+	for id, names := range r.idx {
+		out[id] = names
+	}
+	r.mu.Unlock()
+	return out
+}