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<?php |
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namespace Violet\StreamingJsonEncoder; |
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use Psr\Http\Message\StreamInterface; |
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/** |
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* Provides a http stream interface for encoding JSON. |
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* |
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* @author Riikka Kalliomäki <[email protected]> |
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* @copyright Copyright (c) 2016-2020 Riikka Kalliomäki |
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* @license http://opensource.org/licenses/mit-license.php MIT License |
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*/ |
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class JsonStream implements StreamInterface |
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{ |
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/** @var BufferJsonEncoder|null The encoder used to produce the JSON stream or null once closed */ |
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private $encoder; |
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/** @var int The current position of the cursor in the JSON stream */ |
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private $cursor; |
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/** @var string|null Buffered output from encoding the value as JSON or null when at EOF */ |
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private $buffer; |
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/** |
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* JsonStream constructor. |
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* @param BufferJsonEncoder|mixed $value A JSON encoder to use or a value to encode |
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*/ |
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public function __construct($value) |
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{ |
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if (!$value instanceof BufferJsonEncoder) { |
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$value = (new BufferJsonEncoder($value)) |
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->setOptions(JSON_PARTIAL_OUTPUT_ON_ERROR) |
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->setIndent(0); |
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} |
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$this->encoder = $value; |
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$this->rewind(); |
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} |
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/** |
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* Returns the JSON encoder used for the JSON stream. |
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* @return BufferJsonEncoder The currently used JSON encoder |
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* @throws \RuntimeException If the stream has been closed |
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*/ |
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private function getEncoder() |
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{ |
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if (!$this->encoder instanceof BufferJsonEncoder) { |
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throw new \RuntimeException('Cannot operate on a closed JSON stream'); |
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} |
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return $this->encoder; |
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} |
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/** |
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* Returns the entire JSON stream as a string. |
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* |
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* Note that this operation performs rewind operation on the JSON encoder. Whether |
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* this works or not is dependant on the underlying value being encoded. An empty |
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* string is returned if the value cannot be encoded. |
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* |
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* @return string The entire JSON stream as a string |
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*/ |
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public function __toString() |
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{ |
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try { |
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$this->rewind(); |
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return $this->getContents(); |
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} catch (\Exception $exception) { |
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return ''; |
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} |
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} |
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/** |
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* Frees the JSON encoder from memory and prevents further reading from the JSON stream. |
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*/ |
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public function close() |
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{ |
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$this->encoder = null; |
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} |
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/** |
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* Detaches the underlying PHP resource from the stream and returns it. |
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* @return null Always returns null as no underlying PHP resource exists |
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*/ |
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public function detach() |
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{ |
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return null; |
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} |
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/** |
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* Returns the total size of the JSON stream. |
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* @return null Always returns null as the total size cannot be determined |
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*/ |
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public function getSize() |
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{ |
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return null; |
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} |
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/** |
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* Returns the current position of the cursor in the JSON stream. |
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* @return int Current position of the cursor |
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*/ |
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public function tell() |
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{ |
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$this->getEncoder(); |
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return $this->cursor; |
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} |
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/** |
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* Tells if there are no more bytes to read from the JSON stream. |
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* @return bool True if there are no more bytes to read, false if there are |
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*/ |
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public function eof() |
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{ |
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return $this->buffer === null; |
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} |
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/** |
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* Tells if the JSON stream is seekable or not. |
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* @return bool Always returns true as JSON streams as always seekable |
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*/ |
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public function isSeekable() |
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{ |
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return true; |
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} |
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/** |
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* Seeks the given cursor position in the JSON stream. |
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* |
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* If the provided seek position is less than the current cursor position, a rewind |
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* operation is performed on the underlying JSON encoder. Whether this works or not |
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* depends on whether the encoded value supports rewinding. |
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* |
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* Note that since it's not possible to determine the end of the JSON stream without |
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* encoding the entire value, it's not possible to set the cursor using SEEK_END |
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* constant and doing so will result in an exception. |
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* |
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* @param int $offset The offset for the cursor |
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* @param int $whence Either SEEK_CUR or SEEK_SET to determine new cursor position |
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* @throws \RuntimeException If SEEK_END is used to determine the cursor position |
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*/ |
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public function seek($offset, $whence = SEEK_SET) |
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{ |
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$position = $this->calculatePosition($offset, $whence); |
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if (!isset($this->cursor) || $position < $this->cursor) { |
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$this->getEncoder()->rewind(); |
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$this->buffer = ''; |
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$this->cursor = 0; |
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} |
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$this->forward($position); |
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} |
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/** |
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* Calculates new position for the cursor based on offset and whence. |
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* @param int $offset The cursor offset |
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* @param int $whence One of the SEEK_* constants |
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* @return int The new cursor position |
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* @throws \RuntimeException If SEEK_END is used to determine the cursor position |
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*/ |
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private function calculatePosition($offset, $whence) |
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{ |
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if ($whence === SEEK_CUR) { |
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return max(0, $this->cursor + (int) $offset); |
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} elseif ($whence === SEEK_SET) { |
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return max(0, (int) $offset); |
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} elseif ($whence === SEEK_END) { |
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throw new \RuntimeException('Cannot set cursor position from the end of a JSON stream'); |
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} |
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throw new \InvalidArgumentException("Invalid cursor relative position '$whence'"); |
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} |
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/** |
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* Forwards the JSON stream reading cursor to the given position or to the end of stream. |
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* @param int $position The new position of the cursor |
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*/ |
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private function forward($position) |
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{ |
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$encoder = $this->getEncoder(); |
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while ($this->cursor < $position) { |
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$length = strlen($this->buffer); |
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if ($this->cursor + $length > $position) { |
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$this->buffer = substr($this->buffer, $position - $this->cursor); |
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$this->cursor = $position; |
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break; |
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} |
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$this->cursor += $length; |
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$this->buffer = ''; |
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if (!$encoder->valid()) { |
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$this->buffer = null; |
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break; |
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} |
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$this->buffer = $encoder->current(); |
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$encoder->next(); |
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} |
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} |
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/** |
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* Seeks the beginning of the JSON stream. |
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* |
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* If the encoding has already been started, rewinding the encoder may not work, |
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* if the underlying value being encoded does not support rewinding. |
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*/ |
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public function rewind() |
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{ |
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$this->seek(0); |
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} |
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/** |
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* Tells if the JSON stream is writable or not. |
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* @return bool Always returns false as JSON streams are never writable |
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*/ |
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public function isWritable() |
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{ |
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return false; |
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} |
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/** |
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* Writes the given bytes to the JSON stream. |
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* |
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* As the JSON stream does not represent a writable stream, this method will |
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* always throw a runtime exception. |
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* |
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* @param string $string The bytes to write |
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* @return int The number of bytes written |
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* @throws \RuntimeException Always throws a runtime exception |
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*/ |
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public function write($string) |
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{ |
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throw new \RuntimeException('Cannot write to a JSON stream'); |
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} |
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/** |
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* Tells if the JSON stream is readable or not. |
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* @return bool Always returns true as JSON streams are always readable |
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*/ |
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public function isReadable() |
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{ |
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return true; |
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} |
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/** |
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* Returns the given number of bytes from the JSON stream. |
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* |
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* The underlying value is encoded into JSON until enough bytes have been |
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* generated to fulfill the requested number of bytes. The extraneous bytes are |
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* then buffered for the next read from the JSON stream. The stream may return |
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* fewer number of bytes if the entire value has been encoded and there are no |
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* more bytes to return. |
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* |
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* @param int $length The number of bytes to return |
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* @return string The bytes read from the JSON stream |
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*/ |
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public function read($length) |
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{ |
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if ($this->eof()) { |
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return ''; |
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} |
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$length = max(0, (int) $length); |
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$encoder = $this->getEncoder(); |
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while (strlen($this->buffer) < $length && $encoder->valid()) { |
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$this->buffer .= $encoder->current(); |
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$encoder->next(); |
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} |
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if (strlen($this->buffer) > $length || $encoder->valid()) { |
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$output = substr($this->buffer, 0, $length); |
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$this->buffer = substr($this->buffer, $length); |
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} else { |
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$output = (string) $this->buffer; |
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$this->buffer = null; |
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} |
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$this->cursor += strlen($output); |
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return $output; |
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} |
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/** |
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* Returns the remaining bytes from the JSON stream. |
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* @return string The remaining bytes from JSON stream |
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*/ |
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public function getContents() |
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{ |
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if ($this->eof()) { |
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return ''; |
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} |
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$encoder = $this->getEncoder(); |
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$output = $this->buffer; |
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while ($encoder->valid()) { |
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$output .= $encoder->current(); |
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$encoder->next(); |
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} |
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$this->cursor += strlen($output); |
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$this->buffer = null; |
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return $output; |
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} |
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/** |
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* Returns the metadata related to the JSON stream. |
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* |
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* No underlying PHP resource exists for the stream, but this method will |
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* still return relevant information regarding the stream that is similar |
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* to PHP stream meta data. |
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* |
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* @param string|null $key The key of the value to return |
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* @return array|mixed|null The meta data array, a specific value or null if not defined |
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*/ |
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public function getMetadata($key = null) |
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{ |
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$meta = [ |
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'timed_out' => false, |
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'blocked' => true, |
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'eof' => $this->eof(), |
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'unread_bytes' => strlen($this->buffer), |
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'stream_type' => get_class($this->encoder), |
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'wrapper_type' => 'OBJECT', |
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'wrapper_data' => [ |
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'step' => $this->encoder->key(), |
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'errors' => $this->encoder->getErrors(), |
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], |
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'mode' => 'r', |
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'seekable' => true, |
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'uri' => '', |
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]; |
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return $key === null ? $meta : (isset($meta[$key]) ? $meta[$key] : null); |
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} |
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} |
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