PhutilRope.php
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	<?php

	/**
	* String-like object which reduces the cost of managing large strings. This
	* is particularly useful for buffering large amounts of data that is being
	* passed to `fwrite()`.
	*/
	final class PhutilRope extends Phobject {

	private $length = 0;
	private $buffers = array();

	// This is is arbitrary, it's just the maximum size I'm reliably able to
	// fwrite() to a pipe on OSX. In theory, we could tune this slightly based
	// on the pipe buffer size, but any value similar to this shouldn't affect
	// performance much.
	private $segmentSize = 16384;

	/**
	* Append a string to the rope.
	*
	* @param string $string String to append.
	* @return $this
	*/
	public function append($string) {
	if (!strlen($string)) {
	return $this;
	}

	$len = strlen($string);
	$this->length += $len;

	if ($len <= $this->segmentSize) {
	$this->buffers[] = $string;
	} else {
	for ($cursor = 0; $cursor < $len; $cursor += $this->segmentSize) {
	$this->buffers[] = substr($string, $cursor, $this->segmentSize);
	}
	}

	return $this;
	}


	/**
	* Get the length of the rope.
	*
	* @return int Length of the rope in bytes.
	*/
	public function getByteLength() {
	return $this->length;
	}


	/**
	* Get an arbitrary, nonempty prefix of the rope.
	*
	* @return string\|null Some rope prefix.
	*/
	public function getAnyPrefix() {
	$result = reset($this->buffers);
	if ($result === false) {
	return null;
	}

	return $result;
	}


	/**
	* Get prefix bytes of the rope, up to some maximum size.
	*
	* @param int $length Maximum number of bytes to read.
	* @return string Bytes.
	*/
	public function getPrefixBytes($length) {
	$result = array();

	$remaining_bytes = $length;
	foreach ($this->buffers as $buf) {
	$length = strlen($buf);
	if ($length <= $remaining_bytes) {
	$result[] = $buf;
	$remaining_bytes -= $length;
	} else {
	$result[] = substr($buf, 0, $remaining_bytes);
	$remaining_bytes = 0;
	}
	if (!$remaining_bytes) {
	break;
	}
	}

	return implode('', $result);
	}


	/**
	* Return the entire rope as a normal string.
	*
	* @return string Normal string.
	*/
	public function getAsString() {
	return implode('', $this->buffers);
	}


	/**
	* Remove a specified number of bytes from the head of the rope.
	*
	* @param int $remove Bytes to remove.
	* @return $this
	*/
	public function removeBytesFromHead($remove) {
	if ($remove <= 0) {
	throw new InvalidArgumentException(
	pht('Length must be larger than 0!'));
	}

	$remaining_bytes = $remove;
	foreach ($this->buffers as $key => $buf) {
	$len = strlen($buf);
	if ($len <= $remaining_bytes) {
	unset($this->buffers[$key]);
	$remaining_bytes -= $len;
	if (!$remaining_bytes) {
	break;
	}
	} else {
	$this->buffers[$key] = substr($buf, $remaining_bytes);
	break;
	}
	}

	if ($this->buffers) {
	$this->length -= $remove;
	} else {
	$this->length = 0;
	}

	return $this;
	}

	}

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