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Hyperbee

Hyperbee is an append only B-tree based on Hypercore. It provides a key/value-store API, with methods for inserting and getting key-value pairs, atomic batch insertions, and creating sorted iterators. It uses a single Hypercore for storage, using a technique called embedded indexing. It provides features like cache warmup extension, efficient diffing, version control, sorted iteration, and sparse downloading.

As with the Hypercore, a Hyperbee can only have a single writer on a single machine; the creator of the Hyperdrive is the only person who can modify it as they're the only one with the private key. That said, the writer can replicate to many readers, in a manner similar to BitTorrent.

GitHub (Hyperbee)

Installation

Install with npm:

npm install hyperbee

API

const db = new Hyperbee(core, [options])

Make a new Hyperbee instance. core should be a Hypercore.

options include:

Property Description Type Default
valueEncoding Encoding type for the values. Takes values of 'json', 'utf-8', or 'binary'. String 'binary'
keyEncoding Encoding type for the keys. Takes values of 'ascii', 'utf-8', or 'binary'. String 'binary'

Currently read/diff streams sort based on the encoded value of the keys.

Properties

db.core {#db.core}

The underlying Hypercore backing this bee.

db.version {#db.version}

A number that indicates how many modifications were made, is useful as a version identifier.

db.id {#db.id}

String containing the ID (z-base-32 of the public key) identifying this bee.

db.key {#db.key}

Buffer containing the public key identifying this bee.

db.discoveryKey {#db.discoverykey}

Buffer containing a key derived from db.key.

This discovery key is not for verifying the data, it's only to announce or look for peers that are sharing the same bee, without leaking the bee key.

db.writable {#db.writable}

Boolean indicating to put or delete data in this bee.

db.readable {#db.readable}

Boolean indicating if we can read from this bee. After closing the bee this will be false.

Methods

await db.ready() {#db.ready}

Waits until the internal state is loaded.

Use it once before reading synchronous properties like db.version, unless any of the other APIs have been called first.

await db.close() {#db.close}

Fully close this bee, including its core.

await db.put(key, [value], [options]) {#db.put}

Inserts a new key. Value can be optional.

If inserting a series of data atomically or high performance is needed then check the db.batch API.

options includes:

{
  cas (prev, next) { return true }
}

Compare And Swap (cas)

cas option is a function comparator to control whether the put succeeds.

By returning true it will insert the value, otherwise, it won't.

It receives two args: prev is the current node entry, and next is the potential new node.

await db.put('number', '123', { cas })
console.log(await db.get('number')) // => { seq: 1, key: 'number', value: '123' }

await db.put('number', '123', { cas })
console.log(await db.get('number')) // => { seq: 1, key: 'number', value: '123' }
// Without cas this would have been { seq: 2, ... }, and the next { seq: 3 }

await db.put('number', '456', { cas })
console.log(await db.get('number')) // => { seq: 2, key: 'number', value: '456' }

function cas (prev, next) {
  // can use same-data or same-object lib, depending on the value complexity
  return prev.value !== next.value
}

const { seq, key, value } = await db.get(key, [options]) {#db.get}

Gets a key's value. Returns null if the key doesn't exist.

seq is the Hypercore index at which this key was inserted.

options include:

Property Description Type Default
wait Wait for the meta-data of hypercore to be updated Boolean true
update Determine if the core has to be updated before any operation Boolean true
keyEncoding Encoding type for the keys. Takes values of 'json', 'utf-8', or 'binary'. String binary
valueEncoding Encoding type for the values. Takes values of 'json', 'utf-8', or 'binary'. String binary

db.get(key, [options]) uses the state at the time of initiating the read, so the write operations that complete after get is initiated and before it is resolved are ignored.

await db.del(key, [options]) {#db.del}

Delete a key.

options include:

{
  cas (prev) { return true }
}

Compare And Swap (cas)

cas option is a function comparator to control whether the del succeeds.

By returning true it will delete the value, otherwise, it won't.

It only receives one arg: prev which is the current node entry.

// This won't get deleted
await db.del('number', { cas })
console.log(await db.get('number')) // => { seq: 1, key: 'number', value: 'value' }

// Change the value so the next time we try to delete it then "cas" will return true
await db.put('number', 'can-be-deleted')

await db.del('number', { cas })
console.log(await db.get('number')) // => null

function cas (prev) {
  return prev.value === 'can-be-deleted'
}

const { key, value } = await db.getBySeq(seq, [options]) {#db.getbyseq}

Gets the key and value from a block number.

seq is the Hypercore index. Returns null if block doesn't exists.

const stream = db.replicate(isInitiatorOrStream) {#db.replicate}

See more about how replicate works at core.replicate.

const batch = db.batch() {#db.batch}

Makes a new atomic batch that is either fully processed or not processed at all.

If there are several inserts and deletions then a batch can be much faster.

await batch.put(key, [value], [options]) {#db.put}

Inserts a key into a batch.

options are the same as db.put method.

const { seq, key, value } = await batch.get(key, [options]) {#batch.get}

Gets a key, and value out of a batch.

options are the same as db.get method.

await batch.del(key, [options]) {#batch.del}

Deletes a key into the batch.

options are the same as db.del method.

await batch.flush() {#batch.flush}

Commits the batch to the database, and releases any locks it has acquired.

await batch.close() {#batch.close}

Destroys a batch, and releases any locks it has acquired on the db.

Call this to abort a batch without flushing it.

Learn more about db.batch()

A batch is atomic: it is either processed fully or not at all.

A Hyperbee has a single write lock. A batch acquires this write lock with its first modifying operation (put, del), and releases it when it flushes. We can also explicitly acquire the lock with await batch.lock(). If using the batch only for read operations, the write lock is never acquired. Once the write lock is acquired, the batch must flush before any other writes to the Hyperbee can be processed.

A batch's state snaps at creation time, so write operations applied outside of the batch are not taken into account when reading. Write operations within the batch do get taken into account, as is to be expected — if we first run await batch.put('myKey', 'newValue') and later run await batch.get('myKey'), then 'newValue' should be observed.

const stream = db.createReadStream([range], [options]) {#db.createreadstream}

Make a read stream. Sort order is based on the binary value of the keys. All entries in the stream are similar to the ones returned from db.get.

range should specify the range to read and looks like this:

{
  gt: 'only return keys > than this',
  gte: 'only return keys >= than this',
  lt: 'only return keys < than this',
  lte: 'only return keys <= than this'
}

options include:

Property Description Type Default
reverse determine order of the keys Boolean false
limit maximum number of entries needed Integer -1

const { seq, key, value } = await db.peek([range], [options]) {#db.peek}

Similar to doing a read stream and returning the first value, but a bit faster than that.

const stream = db.createHistoryStream([options]) {#db.createhistorystream}

Create a stream of all entries ever inserted or deleted from the db. Each entry has an additional type property indicating if it was a put or del operation.

options include:

Property Description Type Default
live determine whether the stream will wait for new data and never end or not Boolean false
reverse determine the order in which data is received Boolean false
gt start after this index Integer null
gte start with this seq (inclusive) Integer null
lt stop before this index Integer null
lte stop after this index Integer null
limit maximum number of entries needed Integer -1

If any of the gte, gt, lte, lt arguments are < 0 then they'll implicitly be added with the version before starting so doing { gte: -1 } makes a stream starting at the last index.

const stream = db.createDiffStream(otherVersion, [options]) {#db.creatediffstream}

Creates a stream of shallow changes between two versions of the db.

options are the same as db.createReadStream, except for reverse.

Each entry is sorted by key and looks like this:

{
  left: <the entry in the db>,
  right: <the entry in the other version>
}

If an entry exists in db but not in the other version, then left is set and right will be null, and vice versa.

If the entries are causally equal (i.e., they have the identical seq), they are not returned, only the diff.

const entryWatcher = await db.getAndWatch(key, [options]) {#db.getandwatch}

Returns a watcher which listens to changes on the given key.

entryWatcher.node contains the current entry in the same format as the result of bee.get(key), and will be updated as it changes.

By default, the node will have the bee's key encoding and value encoding, but it can be overwritten by setting the keyEncoding and valueEncoding options.

Listen to entryWatcher.on('update') to be notified when the value of node has changed.

Call await watcher.close() to stop the watcher.

const watcher = db.watch([range]) {#db.watch}

Listens to changes that are on the optional range.

range options are the same as createReadStream except they are reversed.

By default, the yielded snapshots will have the bee's key encoding and value encoding, but can be overwritten by setting the keyEncoding and valueEncoding options.

Usage example:

for await (const [current, previous] of watcher) {
  console.log(current.version)
  console.log(previous.version)
}

Returns a new value after a change, current and previous are snapshots that are auto-closed before the next value.

Methods:

await watcher.ready()

Waits until the watcher is loaded and detects changes.

await watcher.destroy()

Stops the watcher. Using break inside the for await loop will also destroy the watcher.

Do not attempt to manually close the snapshots. Since they're used internally, let them be auto-closed.

Watchers are not supported on subs and checkouts. Instead, use the range option to limit the scope.

const snapshot = db.checkout(version) {#db.checkout}

Get a read-only snapshot of a previous version.

const snapshot = db.snapshot() {#db.snapshot}

Shorthand for getting a checkout for the current version.

const sub = db.sub('sub-prefix', options = {}) {#db.sub}

Create a sub-database where a given value will prefix all entries.

This makes it easy to create namespaces within a single Hyperbee.

options include:

Property Description Type Default
sep A namespace separator Buffer Buffer.alloc(1)
valueEncoding Encoding type for the values. Takes values of 'json', 'utf-8', or 'binary'. String defaults to the parents
keyEncoding Encoding type for the keys. Takes values of 'ascii', 'utf-8', or 'binary'. String defaults to the parents

For example:

const root = new Hyperbee(core)
const sub = root.sub('a')

// In root, this will have the key ('a' + separator + 'b')
await sub.put('b', 'hello')

// Returns => { key: 'b', value: 'hello')
await sub.get('b')

const header = await db.getHeader([options]) {#db.getheader}

Returns the header contained in the first block. Throws an error if undecodable.

options are the same as the core.get method.

const isHyperbee = await Hyperbee.isHyperbee(core, [options]) {#db.ishyperbee}

Returns true if the core contains a Hyperbee, false otherwise.

This requests the first block on the core, so it can throw depending on the options.

options are the same as the core.get method.