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// Copyright 2018 Canonical Ltd.
// Licensed under the LGPL, see LICENCE file for details.
package simplekv
import (
"context"
"time"
errgo "gopkg.in/errgo.v1"
)
var (
// ErrNotFound is the error cause used when an identity cannot be
// found in storage.
ErrNotFound = errgo.New("not found")
// ErrDuplicateKey is the error cause used when SetKeyOnce
// tries to set a duplicate key.
ErrDuplicateKey = errgo.New("duplicate key")
)
// KeyNotFoundError creates a new error with a cause of ErrNotFound and
// an appropriate message.
func KeyNotFoundError(key string) error {
err := errgo.WithCausef(nil, ErrNotFound, "key %s not found", key)
err.(*errgo.Err).SetLocation(1)
return err
}
// Store holds the interface implemented by the various backend implementations.
type Store interface {
// Context returns a context that is suitable for passing to the
// other Store methods. Store methods called with
// such a context will be sequentially consistent; for example, a
// value that is set in Set will immediately be available from
// Get.
//
// The returned close function must be called when the returned
// context will no longer be used, to allow for any required
// cleanup.
Context(ctx context.Context) (_ context.Context, close func())
// Get retrieves the value associated with the given key. If
// there is no such key an error with a cause of ErrNotFound will
// be returned.
Get(ctx context.Context, key string) ([]byte, error)
// Set updates the given key to have the specified value.
//
// If the expire time is non-zero then the entry may be garbage
// collected at some point after that time. Clients should not
// rely on the value being removed at the given time.
Set(ctx context.Context, key string, value []byte, expire time.Time) error
// Update updates the value for the given key. The getVal
// function is called with the old value of the key and should
// return the new value, which will be updated atomically;
// getVal may be called several times, so should not have
// side-effects.
//
// If an entry for the given key did not previously exist, old
// will be nil.
//
// If getVal returns an error, it will be returned by Update with
// its cause unchanged.
//
// If the expire time is non-zero then the entry may be garbage
// collected at some point after that time. Clients should not
// rely on the value being removed at the given time.
Update(ctx context.Context, key string, expire time.Time, getVal func(old []byte) ([]byte, error)) error
}
// KeyLister holds the interface used to list keys store in the Store.
type KeyLister interface {
Store
// Keys returns a distinct list of stored keys.
Keys(ctx context.Context) ([]string, error)
}
// SetKeyOnce is like Store.Set except that if the key already
// has a value associated with it it returns an error with a cause of
// ErrDuplicateKey.
func SetKeyOnce(ctx context.Context, kv Store, key string, value []byte, expire time.Time) error {
err := kv.Update(ctx, key, expire, func(old []byte) ([]byte, error) {
if old != nil {
return nil, errgo.WithCausef(nil, ErrDuplicateKey, "key %s already exists", key)
}
return value, nil
})
return errgo.Mask(err, errgo.Is(ErrDuplicateKey))
}
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