@@ -47,7 +47,7 @@ github.com/sean-/seed e2103e2c35297fb7e17febb81e49b312087a2372

 github.com/hashicorp/go-sockaddr 6d291a969b86c4b633730bfc6b8b9d64c3aafed9

 github.com/hashicorp/go-multierror fcdddc395df1ddf4247c69bd436e84cfa0733f7e

 github.com/hashicorp/serf 598c54895cc5a7b1a24a398d635e8c0ea0959870

-github.com/docker/libkv 1d8431073ae03cdaedb198a89722f3aab6d418ef

+github.com/docker/libkv 458977154600b9f23984d9f4b82e79570b5ae12b

 github.com/vishvananda/netns 604eaf189ee867d8c147fafc28def2394e878d25

 github.com/vishvananda/netlink b2de5d10e38ecce8607e6b438b6d174f389a004e

@@ -63,6 +63,7 @@ github.com/hashicorp/consul v0.5.2

 github.com/boltdb/bolt fff57c100f4dea1905678da7e90d92429dff2904

 github.com/miekg/dns v1.0.7

 github.com/ishidawataru/sctp 07191f837fedd2f13d1ec7b5f885f0f3ec54b1cb

+go.etcd.io/bbolt v1.3.1-etcd.8

 # get graph and distribution packages

 github.com/docker/distribution 83389a148052d74ac602f5f1d62f86ff2f3c4aa5

@@ -90,7 +90,7 @@ Calls like `WatchTree` may return different events (or number of events) dependi

 Only `Consul` and `etcd` have support for TLS and you should build and provide your own `config.TLS` object to feed the client. Support is planned for `zookeeper`.

-##Roadmap

+## Roadmap

 - Make the API nicer to use (using `options`)

 - Provide more options (`consistency` for example)

@@ -98,10 +98,10 @@ Only `Consul` and `etcd` have support for TLS and you should build and provide y

 - Better key formatting

 - New backends?

-##Contributing

+## Contributing

 Want to hack on libkv? [Docker's contributions guidelines](https://github.com/docker/docker/blob/master/CONTRIBUTING.md) apply.

-##Copyright and license

+## Copyright and license

 Copyright © 2014-2016 Docker, Inc. All rights reserved, except as follows. Code is released under the Apache 2.0 license. The README.md file, and files in the "docs" folder are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file "LICENSE.docs". You may obtain a duplicate copy of the same license, titled CC-BY-SA-4.0, at http://creativecommons.org/licenses/by/4.0/.

@@ -10,9 +10,9 @@ import (

 	"sync/atomic"

 	"time"

-	"github.com/boltdb/bolt"

 	"github.com/docker/libkv"

 	"github.com/docker/libkv/store"

+	bolt "go.etcd.io/bbolt"

 )

 var (

@@ -1,6 +1,7 @@

 package etcd

 import (

+	"context"

 	"crypto/tls"

 	"errors"

 	"log"

@@ -9,8 +10,6 @@ import (

 	"strings"

 	"time"

-	"golang.org/x/net/context"

-

 	etcd "github.com/coreos/etcd/client"

 	"github.com/docker/libkv"

 	"github.com/docker/libkv/store"

@@ -30,13 +29,29 @@ type Etcd struct {

 }

 type etcdLock struct {

-	client    etcd.KeysAPI

-	stopLock  chan struct{}

+	client etcd.KeysAPI

+	key    string

+	value  string

+	ttl    time.Duration

+

+	// Closed when the caller wants to stop renewing the lock. I'm not sure

+	// why this is even used - you could just call the Unlock() method.

 	stopRenew chan struct{}

-	key       string

-	value     string

-	last      *etcd.Response

-	ttl       time.Duration

+	// When the lock is held, this is the last modified index of the key.

+	// Used for conditional updates when extending the lock TTL and when

+	// conditionall deleteing when Unlock() is called.

+	lastIndex uint64

+	// When the lock is held, this function will cancel the locked context.

+	// This is called both by the Unlock() method in order to stop the

+	// background holding goroutine and in a deferred call in that background

+	// holding goroutine in case the lock is lost due to an error or the

+	// stopRenew channel is closed. Calling this function also closes the chan

+	// returned by the Lock() method.

+	cancel context.CancelFunc

+	// Used to sync the Unlock() call with the background holding goroutine.

+	// This channel is closed when that background goroutine exits, signalling

+	// that it is okay to conditionally delete the key.

+	doneHolding chan struct{}

 }

 const (

@@ -472,112 +487,97 @@ func (s *Etcd) NewLock(key string, options *store.LockOptions) (lock store.Locke

 // doing so. It returns a channel that is closed if our

 // lock is lost or if an error occurs

 func (l *etcdLock) Lock(stopChan chan struct{}) (<-chan struct{}, error) {

-

-	// Lock holder channel

-	lockHeld := make(chan struct{})

-	stopLocking := l.stopRenew

-

+	// Conditional Set - only if the key does not exist.

 	setOpts := &etcd.SetOptions{

-		TTL: l.ttl,

+		TTL:       l.ttl,

+		PrevExist: etcd.PrevNoExist,

 	}

 	for {

-		setOpts.PrevExist = etcd.PrevNoExist

 		resp, err := l.client.Set(context.Background(), l.key, l.value, setOpts)

-		if err != nil {

-			if etcdError, ok := err.(etcd.Error); ok {

-				if etcdError.Code != etcd.ErrorCodeNodeExist {

-					return nil, err

-				}

-				setOpts.PrevIndex = ^uint64(0)

-			}

-		} else {

-			setOpts.PrevIndex = resp.Node.ModifiedIndex

-		}

-

-		setOpts.PrevExist = etcd.PrevExist

-		l.last, err = l.client.Set(context.Background(), l.key, l.value, setOpts)

-

 		if err == nil {

-			// Leader section

-			l.stopLock = stopLocking

-			go l.holdLock(l.key, lockHeld, stopLocking)

-			break

-		} else {

-			// If this is a legitimate error, return

-			if etcdError, ok := err.(etcd.Error); ok {

-				if etcdError.Code != etcd.ErrorCodeTestFailed {

-					return nil, err

-				}

-			}

+			// Acquired the lock!

+			l.lastIndex = resp.Node.ModifiedIndex

+			lockedCtx, cancel := context.WithCancel(context.Background())

+			l.cancel = cancel

+			l.doneHolding = make(chan struct{})

-			// Seeker section

-			errorCh := make(chan error)

-			chWStop := make(chan bool)

-			free := make(chan bool)

+			go l.holdLock(lockedCtx)

-			go l.waitLock(l.key, errorCh, chWStop, free)

+			return lockedCtx.Done(), nil

+		}

-			// Wait for the key to be available or for

-			// a signal to stop trying to lock the key

-			select {

-			case <-free:

-				break

-			case err := <-errorCh:

-				return nil, err

-			case <-stopChan:

-				return nil, ErrAbortTryLock

-			}

+		etcdErr, ok := err.(etcd.Error)

+		if !ok || etcdErr.Code != etcd.ErrorCodeNodeExist {

+			return nil, err // Unexpected error.

+		}

-			// Delete or Expire event occurred

-			// Retry

+		// Need to wait for the lock key to expire or be deleted.

+		if err := l.waitLock(stopChan, etcdErr.Index); err != nil {

+			return nil, err

 		}

-	}

-	return lockHeld, nil

+		// Delete or Expire event occurred.

+		// Retry

+	}

 }

-// Hold the lock as long as we can

+// Hold the lock as long as we can.

 // Updates the key ttl periodically until we receive

-// an explicit stop signal from the Unlock method

-func (l *etcdLock) holdLock(key string, lockHeld chan struct{}, stopLocking <-chan struct{}) {

-	defer close(lockHeld)

+// an explicit stop signal from the Unlock method OR

+// the stopRenew channel is closed.

+func (l *etcdLock) holdLock(ctx context.Context) {

+	defer close(l.doneHolding)

+	defer l.cancel()

 	update := time.NewTicker(l.ttl / 3)

 	defer update.Stop()

-	var err error

 	setOpts := &etcd.SetOptions{TTL: l.ttl}

 	for {

 		select {

 		case <-update.C:

-			setOpts.PrevIndex = l.last.Node.ModifiedIndex

-			l.last, err = l.client.Set(context.Background(), key, l.value, setOpts)

+			setOpts.PrevIndex = l.lastIndex

+			resp, err := l.client.Set(ctx, l.key, l.value, setOpts)

 			if err != nil {

 				return

 			}

-

-		case <-stopLocking:

+			l.lastIndex = resp.Node.ModifiedIndex

+		case <-l.stopRenew:

+			return

+		case <-ctx.Done():

 			return

 		}

 	}

 }

-// WaitLock simply waits for the key to be available for creation

-func (l *etcdLock) waitLock(key string, errorCh chan error, stopWatchCh chan bool, free chan<- bool) {

-	opts := &etcd.WatcherOptions{Recursive: false}

-	watcher := l.client.Watcher(key, opts)

+// WaitLock simply waits for the key to be available for creation.

+func (l *etcdLock) waitLock(stopWait <-chan struct{}, afterIndex uint64) error {

+	waitCtx, waitCancel := context.WithCancel(context.Background())

+	defer waitCancel()

+	go func() {

+		select {

+		case <-stopWait:

+			// If the caller closes the stopWait, cancel the wait context.

+			waitCancel()

+		case <-waitCtx.Done():

+			// No longer waiting.

+		}

+	}()

+	watcher := l.client.Watcher(l.key, &etcd.WatcherOptions{AfterIndex: afterIndex})

 	for {

-		event, err := watcher.Next(context.Background())

+		event, err := watcher.Next(waitCtx)

 		if err != nil {

-			errorCh <- err

-			return

+			if err == context.Canceled {

+				return ErrAbortTryLock

+			}

+			return err

 		}

-		if event.Action == "delete" || event.Action == "expire" {

-			free <- true

-			return

+		switch event.Action {

+		case "delete", "compareAndDelete", "expire":

+			return nil // The key has been deleted or expired.

 		}

 	}

 }

@@ -585,19 +585,17 @@ func (l *etcdLock) waitLock(key string, errorCh chan error, stopWatchCh chan boo

 // Unlock the "key". Calling unlock while

 // not holding the lock will throw an error

 func (l *etcdLock) Unlock() error {

-	if l.stopLock != nil {

-		l.stopLock <- struct{}{}

-	}

-	if l.last != nil {

+	l.cancel()      // Will signal the holdLock goroutine to exit.

+	<-l.doneHolding // Wait for the holdLock goroutine to exit.

+

+	var err error

+	if l.lastIndex != 0 {

 		delOpts := &etcd.DeleteOptions{

-			PrevIndex: l.last.Node.ModifiedIndex,

-		}

-		_, err := l.client.Delete(context.Background(), l.key, delOpts)

-		if err != nil {

-			return err

+			PrevIndex: l.lastIndex,

 		}

+		_, err = l.client.Delete(context.Background(), l.key, delOpts)

 	}

-	return nil

+	return err

 }

 // Close closes the client connection

new file mode 100644

@@ -0,0 +1,20 @@

+The MIT License (MIT)

+

+Copyright (c) 2013 Ben Johnson

+

+Permission is hereby granted, free of charge, to any person obtaining a copy of

+this software and associated documentation files (the "Software"), to deal in

+the Software without restriction, including without limitation the rights to

+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of

+the Software, and to permit persons to whom the Software is furnished to do so,

+subject to the following conditions:

+

+The above copyright notice and this permission notice shall be included in all

+copies or substantial portions of the Software.

+

+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS

+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR

+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER

+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN

+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

new file mode 100644

@@ -0,0 +1,953 @@

+bbolt

+=====

+

+[![Go Report Card](https://goreportcard.com/badge/github.com/etcd-io/bbolt?style=flat-square)](https://goreportcard.com/report/github.com/etcd-io/bbolt)

+[![Coverage](https://codecov.io/gh/etcd-io/bbolt/branch/master/graph/badge.svg)](https://codecov.io/gh/etcd-io/bbolt)

+[![Build Status Travis](https://img.shields.io/travis/etcd-io/bboltlabs.svg?style=flat-square&&branch=master)](https://travis-ci.com/etcd-io/bbolt)

+[![Godoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](https://godoc.org/github.com/etcd-io/bbolt)

+[![Releases](https://img.shields.io/github/release/etcd-io/bbolt/all.svg?style=flat-square)](https://github.com/etcd-io/bbolt/releases)

+[![LICENSE](https://img.shields.io/github/license/etcd-io/bbolt.svg?style=flat-square)](https://github.com/etcd-io/bbolt/blob/master/LICENSE)

+

+bbolt is a fork of [Ben Johnson's][gh_ben] [Bolt][bolt] key/value

+store. The purpose of this fork is to provide the Go community with an active

+maintenance and development target for Bolt; the goal is improved reliability

+and stability. bbolt includes bug fixes, performance enhancements, and features

+not found in Bolt while preserving backwards compatibility with the Bolt API.

+

+Bolt is a pure Go key/value store inspired by [Howard Chu's][hyc_symas]

+[LMDB project][lmdb]. The goal of the project is to provide a simple,

+fast, and reliable database for projects that don't require a full database

+server such as Postgres or MySQL.

+

+Since Bolt is meant to be used as such a low-level piece of functionality,

+simplicity is key. The API will be small and only focus on getting values

+and setting values. That's it.

+

+[gh_ben]: https://github.com/benbjohnson

+[bolt]: https://github.com/boltdb/bolt

+[hyc_symas]: https://twitter.com/hyc_symas

+[lmdb]: http://symas.com/mdb/

+

+## Project Status

+

+Bolt is stable, the API is fixed, and the file format is fixed. Full unit

+test coverage and randomized black box testing are used to ensure database

+consistency and thread safety. Bolt is currently used in high-load production

+environments serving databases as large as 1TB. Many companies such as

+Shopify and Heroku use Bolt-backed services every day.

+

+## Project versioning

+

+bbolt uses [semantic versioning](http://semver.org).

+API should not change between patch and minor releases.

+New minor versions may add additional features to the API.

+

+## Table of Contents

+

+  - [Getting Started](#getting-started)

+    - [Installing](#installing)

+    - [Opening a database](#opening-a-database)

+    - [Transactions](#transactions)

+      - [Read-write transactions](#read-write-transactions)

+      - [Read-only transactions](#read-only-transactions)

+      - [Batch read-write transactions](#batch-read-write-transactions)

+      - [Managing transactions manually](#managing-transactions-manually)

+    - [Using buckets](#using-buckets)

+    - [Using key/value pairs](#using-keyvalue-pairs)

+    - [Autoincrementing integer for the bucket](#autoincrementing-integer-for-the-bucket)

+    - [Iterating over keys](#iterating-over-keys)

+      - [Prefix scans](#prefix-scans)

+      - [Range scans](#range-scans)

+      - [ForEach()](#foreach)

+    - [Nested buckets](#nested-buckets)

+    - [Database backups](#database-backups)

+    - [Statistics](#statistics)

+    - [Read-Only Mode](#read-only-mode)

+    - [Mobile Use (iOS/Android)](#mobile-use-iosandroid)

+  - [Resources](#resources)

+  - [Comparison with other databases](#comparison-with-other-databases)

+    - [Postgres, MySQL, & other relational databases](#postgres-mysql--other-relational-databases)

+    - [LevelDB, RocksDB](#leveldb-rocksdb)

+    - [LMDB](#lmdb)

+  - [Caveats & Limitations](#caveats--limitations)

+  - [Reading the Source](#reading-the-source)

+  - [Other Projects Using Bolt](#other-projects-using-bolt)

+

+## Getting Started

+

+### Installing

+

+To start using Bolt, install Go and run `go get`:

+

+```sh

+$ go get go.etcd.io/bbolt/...

+```

+

+This will retrieve the library and install the `bolt` command line utility into

+your `$GOBIN` path.

+

+

+### Importing bbolt

+

+To use bbolt as an embedded key-value store, import as:

+

+```go

+import bolt "go.etcd.io/bbolt"

+

+db, err := bolt.Open(path, 0666, nil)

+if err != nil {

+  return err

+}

+defer db.Close()

+```

+

+

+### Opening a database

+

+The top-level object in Bolt is a `DB`. It is represented as a single file on

+your disk and represents a consistent snapshot of your data.

+

+To open your database, simply use the `bolt.Open()` function:

+

+```go

+package main

+

+import (

+	"log"

+

+	bolt "go.etcd.io/bbolt"

+)

+

+func main() {

+	// Open the my.db data file in your current directory.

+	// It will be created if it doesn't exist.

+	db, err := bolt.Open("my.db", 0600, nil)

+	if err != nil {

+		log.Fatal(err)

+	}

+	defer db.Close()

+

+	...

+}

+```

+

+Please note that Bolt obtains a file lock on the data file so multiple processes

+cannot open the same database at the same time. Opening an already open Bolt

+database will cause it to hang until the other process closes it. To prevent

+an indefinite wait you can pass a timeout option to the `Open()` function:

+

+```go

+db, err := bolt.Open("my.db", 0600, &bolt.Options{Timeout: 1 * time.Second})

+```

+

+

+### Transactions

+

+Bolt allows only one read-write transaction at a time but allows as many

+read-only transactions as you want at a time. Each transaction has a consistent

+view of the data as it existed when the transaction started.

+

+Individual transactions and all objects created from them (e.g. buckets, keys)

+are not thread safe. To work with data in multiple goroutines you must start

+a transaction for each one or use locking to ensure only one goroutine accesses

+a transaction at a time. Creating transaction from the `DB` is thread safe.

+

+Read-only transactions and read-write transactions should not depend on one

+another and generally shouldn't be opened simultaneously in the same goroutine.

+This can cause a deadlock as the read-write transaction needs to periodically

+re-map the data file but it cannot do so while a read-only transaction is open.

+

+

+#### Read-write transactions

+

+To start a read-write transaction, you can use the `DB.Update()` function:

+

+```go

+err := db.Update(func(tx *bolt.Tx) error {

+	...

+	return nil

+})

+```

+

+Inside the closure, you have a consistent view of the database. You commit the

+transaction by returning `nil` at the end. You can also rollback the transaction

+at any point by returning an error. All database operations are allowed inside

+a read-write transaction.

+

+Always check the return error as it will report any disk failures that can cause

+your transaction to not complete. If you return an error within your closure

+it will be passed through.

+

+

+#### Read-only transactions

+

+To start a read-only transaction, you can use the `DB.View()` function:

+

+```go

+err := db.View(func(tx *bolt.Tx) error {

+	...

+	return nil

+})

+```

+

+You also get a consistent view of the database within this closure, however,

+no mutating operations are allowed within a read-only transaction. You can only

+retrieve buckets, retrieve values, and copy the database within a read-only

+transaction.

+

+

+#### Batch read-write transactions

+

+Each `DB.Update()` waits for disk to commit the writes. This overhead

+can be minimized by combining multiple updates with the `DB.Batch()`

+function:

+

+```go

+err := db.Batch(func(tx *bolt.Tx) error {

+	...

+	return nil

+})

+```

+

+Concurrent Batch calls are opportunistically combined into larger

+transactions. Batch is only useful when there are multiple goroutines

+calling it.

+

+The trade-off is that `Batch` can call the given

+function multiple times, if parts of the transaction fail. The

+function must be idempotent and side effects must take effect only

+after a successful return from `DB.Batch()`.

+

+For example: don't display messages from inside the function, instead

+set variables in the enclosing scope:

+

+```go

+var id uint64

+err := db.Batch(func(tx *bolt.Tx) error {

+	// Find last key in bucket, decode as bigendian uint64, increment

+	// by one, encode back to []byte, and add new key.

+	...

+	id = newValue

+	return nil

+})

+if err != nil {

+	return ...

+}

+fmt.Println("Allocated ID %d", id)

+```

+

+

+#### Managing transactions manually

+

+The `DB.View()` and `DB.Update()` functions are wrappers around the `DB.Begin()`

+function. These helper functions will start the transaction, execute a function,

+and then safely close your transaction if an error is returned. This is the

+recommended way to use Bolt transactions.

+

+However, sometimes you may want to manually start and end your transactions.

+You can use the `DB.Begin()` function directly but **please** be sure to close

+the transaction.

+

+```go

+// Start a writable transaction.

+tx, err := db.Begin(true)

+if err != nil {

+    return err

+}

+defer tx.Rollback()

+

+// Use the transaction...

+_, err := tx.CreateBucket([]byte("MyBucket"))

+if err != nil {

+    return err

+}

+

+// Commit the transaction and check for error.

+if err := tx.Commit(); err != nil {

+    return err

+}

+```

+

+The first argument to `DB.Begin()` is a boolean stating if the transaction

+should be writable.

+

+

+### Using buckets

+

+Buckets are collections of key/value pairs within the database. All keys in a

+bucket must be unique. You can create a bucket using the `DB.CreateBucket()`

+function:

+

+```go

+db.Update(func(tx *bolt.Tx) error {

+	b, err := tx.CreateBucket([]byte("MyBucket"))

+	if err != nil {

+		return fmt.Errorf("create bucket: %s", err)

+	}

+	return nil

+})

+```

+

+You can also create a bucket only if it doesn't exist by using the

+`Tx.CreateBucketIfNotExists()` function. It's a common pattern to call this

+function for all your top-level buckets after you open your database so you can

+guarantee that they exist for future transactions.

+

+To delete a bucket, simply call the `Tx.DeleteBucket()` function.

+

+

+### Using key/value pairs

+

+To save a key/value pair to a bucket, use the `Bucket.Put()` function:

+

+```go

+db.Update(func(tx *bolt.Tx) error {

+	b := tx.Bucket([]byte("MyBucket"))

+	err := b.Put([]byte("answer"), []byte("42"))

+	return err

+})

+```

+

+This will set the value of the `"answer"` key to `"42"` in the `MyBucket`

+bucket. To retrieve this value, we can use the `Bucket.Get()` function:

+

+```go

+db.View(func(tx *bolt.Tx) error {

+	b := tx.Bucket([]byte("MyBucket"))

+	v := b.Get([]byte("answer"))

+	fmt.Printf("The answer is: %s\n", v)

+	return nil

+})

+```

+

+The `Get()` function does not return an error because its operation is

+guaranteed to work (unless there is some kind of system failure). If the key

+exists then it will return its byte slice value. If it doesn't exist then it

+will return `nil`. It's important to note that you can have a zero-length value

+set to a key which is different than the key not existing.

+

+Use the `Bucket.Delete()` function to delete a key from the bucket.

+

+Please note that values returned from `Get()` are only valid while the

+transaction is open. If you need to use a value outside of the transaction

+then you must use `copy()` to copy it to another byte slice.

+

+

+### Autoincrementing integer for the bucket

+By using the `NextSequence()` function, you can let Bolt determine a sequence

+which can be used as the unique identifier for your key/value pairs. See the

+example below.

+

+```go

+// CreateUser saves u to the store. The new user ID is set on u once the data is persisted.

+func (s *Store) CreateUser(u *User) error {

+    return s.db.Update(func(tx *bolt.Tx) error {

+        // Retrieve the users bucket.

+        // This should be created when the DB is first opened.

+        b := tx.Bucket([]byte("users"))

+

+        // Generate ID for the user.

+        // This returns an error only if the Tx is closed or not writeable.

+        // That can't happen in an Update() call so I ignore the error check.

+        id, _ := b.NextSequence()

+        u.ID = int(id)

+

+        // Marshal user data into bytes.

+        buf, err := json.Marshal(u)

+        if err != nil {

+            return err

+        }

+

+        // Persist bytes to users bucket.

+        return b.Put(itob(u.ID), buf)

+    })

+}

+

+// itob returns an 8-byte big endian representation of v.

+func itob(v int) []byte {

+    b := make([]byte, 8)

+    binary.BigEndian.PutUint64(b, uint64(v))

+    return b

+}

+

+type User struct {

+    ID int

+    ...

+}

+```

+

+### Iterating over keys

+

+Bolt stores its keys in byte-sorted order within a bucket. This makes sequential

+iteration over these keys extremely fast. To iterate over keys we'll use a

+`Cursor`:

+

+```go

+db.View(func(tx *bolt.Tx) error {

+	// Assume bucket exists and has keys

+	b := tx.Bucket([]byte("MyBucket"))

+

+	c := b.Cursor()

+

+	for k, v := c.First(); k != nil; k, v = c.Next() {

+		fmt.Printf("key=%s, value=%s\n", k, v)

+	}

+

+	return nil

+})

+```

+

+The cursor allows you to move to a specific point in the list of keys and move

+forward or backward through the keys one at a time.

+

+The following functions are available on the cursor:

+

+```

+First()  Move to the first key.

+Last()   Move to the last key.

+Seek()   Move to a specific key.

+Next()   Move to the next key.

+Prev()   Move to the previous key.

+```

+

+Each of those functions has a return signature of `(key []byte, value []byte)`.

+When you have iterated to the end of the cursor then `Next()` will return a

+`nil` key.  You must seek to a position using `First()`, `Last()`, or `Seek()`

+before calling `Next()` or `Prev()`. If you do not seek to a position then

+these functions will return a `nil` key.

+

+During iteration, if the key is non-`nil` but the value is `nil`, that means

+the key refers to a bucket rather than a value.  Use `Bucket.Bucket()` to

+access the sub-bucket.

+

+

+#### Prefix scans

+

+To iterate over a key prefix, you can combine `Seek()` and `bytes.HasPrefix()`:

+

+```go

+db.View(func(tx *bolt.Tx) error {

+	// Assume bucket exists and has keys

+	c := tx.Bucket([]byte("MyBucket")).Cursor()

+

+	prefix := []byte("1234")

+	for k, v := c.Seek(prefix); k != nil && bytes.HasPrefix(k, prefix); k, v = c.Next() {

+		fmt.Printf("key=%s, value=%s\n", k, v)

+	}

+

+	return nil

+})

+```

+

+#### Range scans

+

+Another common use case is scanning over a range such as a time range. If you

+use a sortable time encoding such as RFC3339 then you can query a specific

+date range like this:

+

+```go

+db.View(func(tx *bolt.Tx) error {

+	// Assume our events bucket exists and has RFC3339 encoded time keys.

+	c := tx.Bucket([]byte("Events")).Cursor()

+

+	// Our time range spans the 90's decade.

+	min := []byte("1990-01-01T00:00:00Z")

+	max := []byte("2000-01-01T00:00:00Z")

+

+	// Iterate over the 90's.

+	for k, v := c.Seek(min); k != nil && bytes.Compare(k, max) <= 0; k, v = c.Next() {

+		fmt.Printf("%s: %s\n", k, v)

+	}

+

+	return nil

+})

+```

+

+Note that, while RFC3339 is sortable, the Golang implementation of RFC3339Nano does not use a fixed number of digits after the decimal point and is therefore not sortable.

+

+

+#### ForEach()

+

+You can also use the function `ForEach()` if you know you'll be iterating over

+all the keys in a bucket:

+

+```go

+db.View(func(tx *bolt.Tx) error {

+	// Assume bucket exists and has keys

+	b := tx.Bucket([]byte("MyBucket"))

+

+	b.ForEach(func(k, v []byte) error {

+		fmt.Printf("key=%s, value=%s\n", k, v)

+		return nil

+	})

+	return nil

+})

+```

+

+Please note that keys and values in `ForEach()` are only valid while

+the transaction is open. If you need to use a key or value outside of

+the transaction, you must use `copy()` to copy it to another byte

+slice.

+

+### Nested buckets

+

+You can also store a bucket in a key to create nested buckets. The API is the

+same as the bucket management API on the `DB` object:

+

+```go

+func (*Bucket) CreateBucket(key []byte) (*Bucket, error)

+func (*Bucket) CreateBucketIfNotExists(key []byte) (*Bucket, error)

+func (*Bucket) DeleteBucket(key []byte) error

+```

+

+Say you had a multi-tenant application where the root level bucket was the account bucket. Inside of this bucket was a sequence of accounts which themselves are buckets. And inside the sequence bucket you could have many buckets pertaining to the Account itself (Users, Notes, etc) isolating the information into logical groupings.

+

+```go

+

+// createUser creates a new user in the given account.

+func createUser(accountID int, u *User) error {

+    // Start the transaction.

+    tx, err := db.Begin(true)

+    if err != nil {

+        return err

+    }

+    defer tx.Rollback()

+

+    // Retrieve the root bucket for the account.

+    // Assume this has already been created when the account was set up.

+    root := tx.Bucket([]byte(strconv.FormatUint(accountID, 10)))

+

+    // Setup the users bucket.

+    bkt, err := root.CreateBucketIfNotExists([]byte("USERS"))

+    if err != nil {

+        return err

+    }

+

+    // Generate an ID for the new user.

+    userID, err := bkt.NextSequence()

+    if err != nil {

+        return err

+    }

+    u.ID = userID

+

+    // Marshal and save the encoded user.

+    if buf, err := json.Marshal(u); err != nil {

+        return err

+    } else if err := bkt.Put([]byte(strconv.FormatUint(u.ID, 10)), buf); err != nil {

+        return err

+    }

+

+    // Commit the transaction.

+    if err := tx.Commit(); err != nil {

+        return err

+    }