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