Block API

The Block API is the single endpoint for authoring IPLD data structures. Unless you're
implementing a new codec you can get everything you need from the Block API: encoding,
decoding, cid creation w/ hashing.

``javascript
import Block from '@ipld/block/defaults'

const b1 = Block.encoder({ hello: 'world' }, 'dag-cbor')

// link between blocks
const b2 = Block.encoder({ head: await b1.cid() }, 'dag-cbor')

// write to a standard key value store
for (const block of [b1, b2]) {
const cid = await block.cid()
await put(cid.toString('base64'), block.encode())
}

// write to a store that understands the Block interface
await Promise.all([put(b1), put(b2)])
`

Block.encoder(object, codec, algorithm = 'sha2-256')

Create a Block instance from a native object.

The cid as well as encoding will not happen until requested
and then will be cached when appropriate.

`javascript
let block = Block.encoder({hello: 'world'}, 'dag-cbor')
`

Returns a Block instance.

Block.decoder(binary, codec, algorithm = 'sha2-256')

Create a Block instance from an existing binary encoded block

The cid as well as decoding will not happen until requested
and then will be cached when appropriate.

`javascript
let block = Block.decoder(someBuffer, 'dag-cbor')
`

Returns a Block instance.

Block.create(binary, cid)

Create a new block from the raw binary data and cid.

cid can be an instance of CID or a base encoded string of a cid.

Returns a Block instance.

Block(opts)

Once a block instance is created the information represented in the block is considered
immutable.

$3

Returns decoded block data.

A new object is returned on every call that is copied from a cached version of
the decoded block. This means you are free to mutate the return value and
that we'll never do more than one actual block decode in the codec.

$3

Returns the cached block data directly.

Waring: If you mutate the return value bad things will happen.

This operation is very fast and useful as long as you can ensure the return value
will not be mutated.

$3

Promise that resolves to a cid instance. Cached after creation.

$3

Returns a Buffer instance encoded from the source input.

The first time the block is encoded it is cached indefinitely. This method returns
a new copied buffer that you are free to mutate.

$3

Returns a Buffer instance encoded from the source input.

Warning: If you mutate the return value bad things will happen.

This returns the internal cached versoin of the block encode. It's very fast
and useful if you are certain the buffer won't be mutated.

$3

Returns an instance of Reader()` from the codec implementation.

$3

Returns true/false if the CID's multihash matches the given block.

If a CID hasn't been created yet it will return true since we know the hash will
match in our eventually created CID.