<?php
namespace Aws\Glacier;
use Aws\HashInterface;
/**
* Encapsulates the creation of a tree hash from streamed data
*/
class TreeHash implements HashInterface
{
const MB = 1048576;
const EMPTY_HASH = 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';
/** @var string Algorithm used for hashing. */
private $algorithm;
/** @var string Buffered data that has not yet been hashed. */
private $buffer;
/** @var array Binary checksums from which the tree hash is derived. */
private $checksums = [];
/** @var string Resulting hash in binary form. */
private $hash;
public function __construct($algorithm = 'sha256')
{
$this->algorithm = $algorithm;
$this->reset();
}
/**
* {@inheritdoc}
* @throws \LogicException if the root tree hash is already calculated
*/
public function update($data)
{
// Error if hash is already calculated.
if ($this->hash) {
throw new \LogicException('You may not add more data to a '
. 'complete tree hash.');
}
// Buffer incoming data.
$this->buffer .= $data;
// When there is more than a MB of data, create a checksum.
while (strlen($this->buffer) >= self::MB) {
$data = substr($this->buffer, 0, self::MB);
$this->buffer = substr($this->buffer, self::MB) ?: '';
$this->checksums[] = hash($this->algorithm, $data, true);
}
return $this;
}
/**
* Add a checksum to the tree hash directly
*
* @param string $checksum The checksum to add
* @param bool $inBinaryForm TRUE if checksum is in binary form
*
* @return self
* @throws \LogicException if the root tree hash is already calculated
*/
public function addChecksum($checksum, $inBinaryForm = false)
{
// Error if hash is already calculated
if ($this->hash) {
throw new \LogicException('You may not add more checksums to a '
. 'complete tree hash.');
}
// Convert the checksum to binary form if necessary
$this->checksums[] = $inBinaryForm ? $checksum : hex2bin($checksum);
return $this;
}
public function complete()
{
if (!$this->hash) {
// Clear out the remaining buffer.
if ($this->buffer) {
$this->checksums[] = hash($this->algorithm, $this->buffer, true);
$this->buffer = '';
}
// If no hashes, add the EMPTY_HASH.
if (!$this->checksums) {
$this->checksums[] = hex2bin(self::EMPTY_HASH);
}
// Perform hashes up the tree to arrive at the root checksum.
$hashes = $this->checksums;
while (count($hashes) > 1) {
$sets = array_chunk($hashes, 2);
$hashes = array();
foreach ($sets as $set) {
$hashes[] = (count($set) === 1)
? $set[0]
: hash($this->algorithm, $set[0] . $set[1], true);
}
}
$this->hash = $hashes[0];
}
return $this->hash;
}
public function reset()
{
$this->hash = null;
$this->checksums = [];
$this->buffer = '';
}
}
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