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1 efrain 1 
<?php
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namespace Aws;
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use GuzzleHttp\Psr7\StreamDecoratorTrait;
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use Psr\Http\Message\StreamInterface;
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/**
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 * Stream decorator that calculates a rolling hash of the stream as it is read.
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 */
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class HashingStream implements StreamInterface
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{
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    use StreamDecoratorTrait;
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    /** @var StreamInterface */
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    private $stream;
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    /** @var HashInterface */
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    private $hash;
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    /** @var callable|null */
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    private $callback;
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    /**
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     * @param StreamInterface $stream     Stream that is being read.
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     * @param HashInterface   $hash       Hash used to calculate checksum.
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     * @param callable        $onComplete Optional function invoked when the
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     *                                    hash calculation is completed.
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     */
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    public function __construct(
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        StreamInterface $stream,
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        HashInterface $hash,
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        callable $onComplete = null
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    ) {
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        $this->stream = $stream;
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        $this->hash = $hash;
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        $this->callback = $onComplete;
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    }
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    public function read($length)
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    {
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        $data = $this->stream->read($length);
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        $this->hash->update($data);
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        if ($this->eof()) {
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            $result = $this->hash->complete();
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            if ($this->callback) {
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                call_user_func($this->callback, $result);
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            }
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        }
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        return $data;
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    }
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    public function seek($offset, $whence = SEEK_SET)
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    {
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        if ($offset === 0) {
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            $this->hash->reset();
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            return $this->stream->seek($offset);
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        }
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        // Seeking arbitrarily is not supported.
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        return false;
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    }
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}