Swift_Mime_SimpleMimeEntity

Complexity

Total Complexity

111

Size/Duplication

Total Lines	969
Duplicated Lines	0.31 %

Coupling/Cohesion

Components	2
Dependencies	9

Test Coverage

Coverage

97.91%

Importance

Changes	11
Bugs	4	Features	1

53 Methods

Rating	Name	Duplication	Size	Complexity
A	generateId()	0	6	1
A	getHeaders()	0	4	1
A	getNestingLevel()	0	4	1
A	getContentType()	0	4	1
A	setContentType()	0	9	1
A	getId()	0	6	2
A	getDescription()	0	4	1
A	getMaxLineLength()	0	4	1
A	setMaxLineLength()	0	6	1
A	getChildren()	0	4	1
A	getEncoder()	0	4	1
A	setBoundary()	0	7	1
A	charsetChanged()	0	4	1
A	encoderChanged()	0	4	1
A	toString()	0	7	1
A	setId()	0	9	2
A	setDescription()	0	8	2
A	setEncoder()	0	12	2
A	getBoundary()	0	8	2
B	_bodyToString()	0	28	6
A	__toString()	0	4	1
A	toByteStream()	0	7	1
D	_bodyToByteStream()	0	37	9
A	_getIdField()	0	4	1
A	_getHeaderFieldModel()	0	8	2
A	_setHeaderFieldModel()	0	10	2
C	setChildren()	0	58	11
A	getBody()	0	4	2
A	setBody()	0	14	3
A	_getHeaderParameter()	0	8	2
A	_setHeaderParameter()	0	10	2
A	_fixHeaders()	0	10	2
A	_getCache()	0	4	1
A	_clearCache()	0	4	1
A	getRandomId()	0	14	3
A	_generateNewCacheKey()	0	4	1
A	_readStream()	0	11	2
A	_setEncoding()	0	6	2
A	_assertValidBoundary()	0	6	2
A	_setContentTypeInHeaders()	0	6	2
A	_setNestingLevel()	0	4	1
A	_getCompoundLevel()	0	9	2
A	_getNeededChildLevel()	0	18	4
A	_createChild()	0	4	1
A	_notifyEncoderChanged()	0	6	2
A	_notifyCharsetChanged()	0	8	2
A	_sortChildren()	0	16	4
A	_childSortAlgorithm()	0	19	4
A	__destruct()	0	4	1
A	_assertValidId()	3	6	2
A	__clone()	0	19	4
B	__construct()	0	33	1
A	_getEmailValidator()	0	4	1

<?php

/*
 * This file is part of SwiftMailer.
 * (c) 2004-2009 Chris Corbyn
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

/**
 * A MIME entity, in a multipart message.
 *
 * @author Chris Corbyn
 */
class Swift_Mime_SimpleMimeEntity implements Swift_Mime_MimeEntity

PSR1 recommends that each class must be in a namespace of at least one level to avoid collisions.

{
    /**
     * A collection of Headers for this mime entity
     *
     * @var Swift_Mime_HeaderSet
     */
    private $_headers;

    /**
     * The body as a string, or a stream
     */
    private $_body;

    /**
     * The encoder that encodes the body into a streamable format
     *
     * @var Swift_Mime_ContentEncoder
     */
    private $_encoder;

    /**
     * The validator for email
     *
     * @var Swift_EmailValidatorBridge
     */
    private $_emailValidator;

    /**
     * A mime boundary, if any is used
     */
    private $_boundary;

    /**
     * Mime types to be used based on the nesting level
     *
     * @var array
     */
    private $_compositeRanges = array(
        'multipart/mixed' => array(self::LEVEL_TOP, self::LEVEL_MIXED),
        'multipart/alternative' => array(self::LEVEL_MIXED, self::LEVEL_ALTERNATIVE),
        'multipart/related' => array(self::LEVEL_ALTERNATIVE, self::LEVEL_RELATED),
    );

    /**
     * A set of filter rules to define what level an entity should be nested at
     *
     * @var array
     */
    private $_compoundLevelFilters = array();

    /**
     * The nesting level of this entity
     *
     * @var int
     */
    private $_nestingLevel = self::LEVEL_ALTERNATIVE;

    /**
     * A KeyCache instance used during encoding and streaming
     *
     * @var Swift_KeyCache
     */
    private $_cache;

    /**
     * Direct descendants of this entity
     *
     * @var Swift_Mime_MimeEntity[]|array
     */
    private $_immediateChildren = array();

    /**
     * All descendants of this entity
     *
     * @var Swift_Mime_MimeEntity[]
     */
    private $_children = array();

    /**
     * The maximum line length of the body of this entity
     *
     * @var int
     */
    private $_maxLineLength = 78;

    /**
     * The order in which alternative mime types should appear
     *
     * @var array
     */
    private $_alternativePartOrder = array(
        'text/plain' => 1,
        'text/html' => 2,
        'multipart/related' => 3,
    );

    /**
     * The CID of this entity
     *
     * @var string
     */
    private $_id;

    /**
     * The key used for accessing the cache
     *
     * @var string
     */
    private $_cacheKey;

    /**
     * @var string
     */
    protected $_userContentType;

    /**
     * Create a new SimpleMimeEntity with $headers, $encoder and $cache.
     *
     * @param Swift_Mime_HeaderSet       $headers
     * @param Swift_Mime_ContentEncoder  $encoder
     * @param Swift_KeyCache             $cache
     * @param Swift_EmailValidatorBridge $emailValidator
     */
    public function __construct(Swift_Mime_HeaderSet $headers, Swift_Mime_ContentEncoder $encoder, Swift_KeyCache $cache, Swift_EmailValidatorBridge $emailValidator)
    {
        $this->_cacheKey = $this->_generateNewCacheKey();
        $this->_cache = $cache;
        $this->_headers = $headers;
        $this->_emailValidator = $emailValidator;
        $this->setEncoder($encoder);
        $this->_headers->defineOrdering(array('Content-Type', 'Content-Transfer-Encoding'));

        // This array specifies that, when the entire MIME document contains
        // $compoundLevel, then for each child within $level, if its Content-Type
        // is $contentType then it should be treated as if it's level is
        // $neededLevel instead.  I tried to write that unambiguously! :-\
        // Data Structure:
        // array (
        //   $compoundLevel => array(

43% of this comment could be valid code. Did you maybe forget this after debugging?

        //     $level => array(

43% of this comment could be valid code. Did you maybe forget this after debugging?

        //       $contentType => $neededLevel

50% of this comment could be valid code. Did you maybe forget this after debugging?

        //     )
        //   )
        // )

        $this->_compoundLevelFilters = array(
            (self::LEVEL_ALTERNATIVE + self::LEVEL_RELATED) => array(
                self::LEVEL_ALTERNATIVE => array(
                    'text/plain' => self::LEVEL_ALTERNATIVE,
                    'text/html' => self::LEVEL_RELATED,
                ),
            ),
        );

        $this->_id = $this->getRandomId();
    }

    /**
     * Generate a new Content-ID or Message-ID for this MIME entity.
     *
     * @return string
     */
    public function generateId()
    {
        $this->setId($this->getRandomId());

        return $this->_id;
    }

    /**
     * Get the {@link Swift_Mime_HeaderSet} for this entity.
     *
     * @return Swift_Mime_HeaderSet
     */
    public function getHeaders()
    {
        return $this->_headers;
    }

    /**
     * Get the nesting level of this entity.
     *
     * @see LEVEL_TOP, LEVEL_MIXED, LEVEL_RELATED, LEVEL_ALTERNATIVE
     *
     * @return int
     */
    public function getNestingLevel()
    {
        return $this->_nestingLevel;
    }

    /**
     * Get the Content-type of this entity.
     *
     * @return string
     */
    public function getContentType()
    {
        return $this->_getHeaderFieldModel('Content-Type');
    }

    /**
     * Set the Content-type of this entity.
     *
     * @param string $type
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setContentType($type)
    {
        $this->_setContentTypeInHeaders($type);
        // Keep track of the value so that if the content-type changes automatically
        // due to added child entities, it can be restored if they are later removed
        $this->_userContentType = $type;

        return $this;
    }

    /**
     * Get the CID of this entity.
     *
     * The CID will only be present in headers if a Content-ID header is present.
     *
     * @return string
     */
    public function getId()
    {
        $tmp = (array) $this->_getHeaderFieldModel($this->_getIdField());

        return $this->_headers->has($this->_getIdField()) ? current($tmp) : $this->_id;
    }

    /**
     * Set the CID of this entity.
     *
     * @param string $id
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setId($id)
    {
        if (!$this->_setHeaderFieldModel($this->_getIdField(), $id)) {
            $this->_headers->addIdHeader($this->_getIdField(), $id);
        }
        $this->_id = $id;

        return $this;
    }

    /**
     * Get the description of this entity.
     *
     * This value comes from the Content-Description header if set.
     *
     * @return string
     */
    public function getDescription()
    {
        return $this->_getHeaderFieldModel('Content-Description');
    }

    /**
     * Set the description of this entity.
     *
     * This method sets a value in the Content-ID header.
     *
     * @param string $description
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setDescription($description)
    {
        if (!$this->_setHeaderFieldModel('Content-Description', $description)) {
            $this->_headers->addTextHeader('Content-Description', $description);
        }

        return $this;
    }

    /**
     * Get the maximum line length of the body of this entity.
     *
     * @return int
     */
    public function getMaxLineLength()
    {
        return $this->_maxLineLength;
    }

    /**
     * Set the maximum line length of lines in this body.
     *
     * Though not enforced by the library, lines should not exceed 1000 chars.
     *
     * @param int $length
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setMaxLineLength($length)
    {
        $this->_maxLineLength = $length;

        return $this;
    }

    /**
     * Get all children added to this entity.
     *
     * @return Swift_Mime_MimeEntity[]
     */
    public function getChildren()
    {
        return $this->_children;
    }

    /**
     * Set all children of this entity.
     *
     * @param Swift_Mime_MimeEntity[] $children
     * @param int                     $compoundLevel For internal use only
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setChildren(array $children, $compoundLevel = null)
    {
        // TODO: Try to refactor this logic

        $compoundLevel = isset($compoundLevel) ? $compoundLevel : $this->_getCompoundLevel($children);
        $immediateChildren = array();
        $grandchildren = array();
        $newContentType = $this->_userContentType;

        foreach ($children as $child) {
            $level = $this->_getNeededChildLevel($child, $compoundLevel);
            if (empty($immediateChildren)) {
                // first iteration
                $immediateChildren = array($child);
            } else {
                $nextLevel = $this->_getNeededChildLevel($immediateChildren[0], $compoundLevel);
                if ($nextLevel === $level) {
                    $immediateChildren[] = $child;
                } elseif ($level < $nextLevel) {
                    // re-assign immediateChildren to grandchildren
                    $grandchildren = array_merge($grandchildren, $immediateChildren);
                    // set new children
                    $immediateChildren = array($child);
                } else {
                    $grandchildren[] = $child;
                }
            }
        }

        if ($immediateChildren) {

The expression $immediateChildren of type array is implicitly converted to a boolean; are you sure this is intended? If so, consider using ! empty($expr) instead to make it clear that you intend to check for an array without elements.

            $lowestLevel = $this->_getNeededChildLevel($immediateChildren[0], $compoundLevel);

            // Determine which composite media type is needed to accommodate the immediate children.
            foreach ($this->_compositeRanges as $mediaType => $range) {
                if ($lowestLevel > $range[0] && $lowestLevel <= $range[1]) {
                    $newContentType = $mediaType;

                    break;
                }
            }

            // Put any grandchildren in a sub-part.
            if (!empty($grandchildren)) {
                $subentity = $this->_createChild();
                $subentity->_setNestingLevel($lowestLevel);
                $subentity->setChildren($grandchildren, $compoundLevel);
                array_unshift($immediateChildren, $subentity);
            }
        }

        $this->_immediateChildren = $immediateChildren;
        $this->_children = $children;
        $this->_setContentTypeInHeaders($newContentType);
        $this->_fixHeaders();
        $this->_sortChildren();

        return $this;
    }

    /**
     * Get the body of this entity as a string.
     *
     * @return string
     */
    public function getBody()
    {
        return $this->_body instanceof Swift_OutputByteStream ? $this->_readStream($this->_body) : $this->_body;
    }

    /**
     * Set the body of this entity, either as a string, or as an instance of
     * {@link Swift_OutputByteStream}.
     *
     * @param mixed       $body
     * @param string|null $contentType optional
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setBody($body, $contentType = null)
    {
        if ($body !== $this->_body) {
            $this->_clearCache();
        }

        $this->_body = $body;

        if ($contentType) {

The expression $contentType of type string|null is loosely compared to true; this is ambiguous if the string can be empty. You might want to explicitly use !== null instead.

            $this->setContentType($contentType);
        }

        return $this;
    }

    /**
     * Get the encoder used for the body of this entity.
     *
     * @return Swift_Mime_ContentEncoder
     */
    public function getEncoder()
    {
        return $this->_encoder;
    }

    /**
     * Set the encoder used for the body of this entity.
     *
     * @param Swift_Mime_ContentEncoder $encoder
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setEncoder(Swift_Mime_ContentEncoder $encoder)
    {
        if ($encoder !== $this->_encoder) {
            $this->_clearCache();
        }

        $this->_encoder = $encoder;
        $this->_setEncoding($encoder->getName());
        $this->_notifyEncoderChanged($encoder);

        return $this;
    }

    /**
     * Get the boundary used to separate children in this entity.
     *
     * @return string
     */
    public function getBoundary()
    {
        if (!isset($this->_boundary)) {
            $this->_boundary = '_=_swift_v5_' . time() . '_' . md5(getmypid() . mt_rand() . uniqid('', true)) . '_=_';
        }

        return $this->_boundary;
    }

    /**
     * Set the boundary used to separate children in this entity.
     *
     * @param string $boundary
     *
     * @throws Swift_RfcComplianceException
     *
     * @return Swift_Mime_SimpleMimeEntity
     */
    public function setBoundary($boundary)
    {
        $this->_assertValidBoundary($boundary);
        $this->_boundary = $boundary;

        return $this;
    }

    /**
     * Receive notification that the charset of this entity, or a parent entity
     * has changed.
     *
     * @param string $charset
     */
    public function charsetChanged($charset)
    {
        $this->_notifyCharsetChanged($charset);
    }

    /**
     * Receive notification that the encoder of this entity or a parent entity
     * has changed.
     *
     * @param Swift_Mime_ContentEncoder $encoder
     */
    public function encoderChanged(Swift_Mime_ContentEncoder $encoder)
    {
        $this->_notifyEncoderChanged($encoder);
    }

    /**
     * Get this entire entity as a string.
     *
     * @return string
     */
    public function toString()
    {
        $string = $this->_headers->toString();
        $string .= $this->_bodyToString();

        return $string;
    }

    /**
     * Get this entire entity as a string.
     *
     * @return string
     */
    protected function _bodyToString()
    {
        $string = '';

        if (
            isset($this->_body)
            &&
            empty($this->_immediateChildren)
        ) {
            if ($this->_cache->hasKey($this->_cacheKey, 'body')) {
                $body = $this->_cache->getString($this->_cacheKey, 'body');
            } else {
                $body = "\r\n" . $this->_encoder->encodeString($this->getBody(), 0, $this->getMaxLineLength());
                $this->_cache->setString($this->_cacheKey, 'body', $body, Swift_KeyCache::MODE_WRITE);
            }
            $string .= $body;
        }

        if (!empty($this->_immediateChildren)) {
            foreach ($this->_immediateChildren as $child) {
                $string .= "\r\n\r\n--" . $this->getBoundary() . "\r\n";
                $string .= $child->toString();
            }
            $string .= "\r\n\r\n--" . $this->getBoundary() . "--\r\n";
        }

        return $string;
    }

    /**
     * Returns a string representation of this object.
     *
     * @see toString()
     *
     * @return string
     */
    public function __toString()
    {
        return $this->toString();
    }

    /**
     * Write this entire entity to a {@see Swift_InputByteStream}.
     *
     * @param Swift_InputByteStream
     */
    public function toByteStream(Swift_InputByteStream $is)
    {
        $is->write($this->_headers->toString());
        $is->commit();

        $this->_bodyToByteStream($is);
    }

    /**
     * Write this entire entity to a {@link Swift_InputByteStream}.
     *
     * @param Swift_InputByteStream
     */
    protected function _bodyToByteStream(Swift_InputByteStream $is)
    {
        if (empty($this->_immediateChildren)) {
            if (isset($this->_body)) {
                if ($this->_cache->hasKey($this->_cacheKey, 'body')) {
                    $this->_cache->exportToByteStream($this->_cacheKey, 'body', $is);
                } else {
                    $cacheIs = $this->_cache->getInputByteStream($this->_cacheKey, 'body');
                    if ($cacheIs) {
                        $is->bind($cacheIs);
                    }

                    $is->write("\r\n");

                    if ($this->_body instanceof Swift_OutputByteStream) {
                        $this->_body->setReadPointer(0);

                        $this->_encoder->encodeByteStream($this->_body, $is, 0, $this->getMaxLineLength());
                    } else {
                        $is->write($this->_encoder->encodeString($this->getBody(), 0, $this->getMaxLineLength()));
                    }

                    if ($cacheIs) {
                        $is->unbind($cacheIs);
                    }
                }
            }
        }

        if (!empty($this->_immediateChildren)) {
            foreach ($this->_immediateChildren as $child) {
                $is->write("\r\n\r\n--" . $this->getBoundary() . "\r\n");
                $child->toByteStream($is);
            }
            $is->write("\r\n\r\n--" . $this->getBoundary() . "--\r\n");
        }
    }

    /**
     * Get the name of the header that provides the ID of this entity.
     */
    protected function _getIdField()
    {
        return 'Content-ID';
    }

    /**
     * Get the model data (usually an array or a string) for $field.
     *
     * @param string $field
     *
     * @return string
     */
    protected function _getHeaderFieldModel($field)
    {
        if ($this->_headers->has($field)) {
            return $this->_headers->get($field)->getFieldBodyModel();
        } else {
            return null;
        }
    }

    /**
     * Set the model data for $field.
     *
     * @param string $field
     * @param $model
     *
     * @return bool
     */
    protected function _setHeaderFieldModel($field, $model)
    {
        if ($this->_headers->has($field)) {
            $this->_headers->get($field)->setFieldBodyModel($model);

            return true;
        }

        return false;
    }

    /**
     * Get the parameter value of $parameter on $field header.
     * @param string $field
     * @param string $parameter
     *
     * @return string|false
     */
    protected function _getHeaderParameter($field, $parameter)
    {
        if ($this->_headers->has($field)) {
            return $this->_headers->get($field)->getParameter($parameter);

The method getParameter does only exist in Swift_Mime_ParameterizedHeader, but not in Swift_Mime_Headers_MailboxHeader.

        } else {
            return false;
        }
    }

    /**
     * Set the parameter value of $parameter on $field header.
     * @param string $field
     * @param string $parameter
     * @param mixed  $value
     *
     * @return bool
     */
    protected function _setHeaderParameter($field, $parameter, $value)
    {
        if ($this->_headers->has($field)) {
            $this->_headers->get($field)->setParameter($parameter, $value);

The method setParameter does only exist in Swift_Mime_ParameterizedHeader, but not in Swift_Mime_Headers_MailboxHeader.

            return true;
        }

        return false;
    }

    /**
     * Re-evaluate what content type and encoding should be used on this entity.
     */
    protected function _fixHeaders()
    {
        if (count($this->_immediateChildren)) {
            $this->_setHeaderParameter('Content-Type', 'boundary', $this->getBoundary());
            $this->_headers->remove('Content-Transfer-Encoding');
        } else {
            $this->_setHeaderParameter('Content-Type', 'boundary', null);
            $this->_setEncoding($this->_encoder->getName());
        }
    }

    /**
     * Get the KeyCache used in this entity.
     *
     * @return Swift_KeyCache
     */
    protected function _getCache()
    {
        return $this->_cache;
    }

    /**
     * Get the email-validator.
     *
     * @return Swift_EmailValidatorBridge
     */
    protected function _getEmailValidator()
    {
        return $this->_emailValidator;
    }

    /**
     * Empty the KeyCache for this entity.
     */
    protected function _clearCache()
    {
        $this->_cache->clearKey($this->_cacheKey, 'body');
    }

    /**
     * Returns a random Content-ID or Message-ID.
     *
     * @return string
     */
    protected function getRandomId()

getRandomId uses the super-global variable $_SERVER which is generally not recommended.

    {
        $idLeft = $this->_generateNewCacheKey();
        $idRight = !empty($_SERVER['SERVER_NAME']) ? $_SERVER['SERVER_NAME'] : 'swift.generated';
        $id = $idLeft . '@' . $idRight;

        try {
            $this->_assertValidId($id);
        } catch (Swift_RfcComplianceException $e) {
            $id = $idLeft . '@swift.generated';
        }

        return $id;
    }

    /**
     * generate a new cache-key
     *
     * @return string
     */
    private function _generateNewCacheKey()
    {
        return md5(getmypid() . '.' . time() . '.' . uniqid(mt_rand(), true));
    }

    private function _readStream(Swift_OutputByteStream $os)
    {
        $string = '';
        while (false !== $bytes = $os->read(8192)) {
            $string .= $bytes;
        }

        $os->setReadPointer(0);

        return $string;
    }

    /**
     * @param string $encoding
     */
    private function _setEncoding($encoding)
    {
        if (!$this->_setHeaderFieldModel('Content-Transfer-Encoding', $encoding)) {
            $this->_headers->addTextHeader('Content-Transfer-Encoding', $encoding);
        }
    }

    /**
     * @param string $boundary
     *
     * @throws Swift_RfcComplianceException
     */
    private function _assertValidBoundary($boundary)
    {
        if (!preg_match('/^[a-z0-9\'\(\)\+_\-,\.\/:=\?\ ]{0,69}[a-z0-9\'\(\)\+_\-,\.\/:=\?]$/Di', $boundary)) {
            throw new Swift_RfcComplianceException('Mime boundary set is not RFC 2046 compliant.');
        }
    }

    private function _setContentTypeInHeaders($type)
    {
        if (!$this->_setHeaderFieldModel('Content-Type', $type)) {
            $this->_headers->addParameterizedHeader('Content-Type', $type);
        }
    }

    private function _setNestingLevel($level)
    {
        $this->_nestingLevel = $level;
    }

    /**
     * @param Swift_Mime_MimeEntity[] $children
     *
     * @return int
     */
    private function _getCompoundLevel($children)
    {
        $level = 0;
        foreach ($children as $child) {
            $level |= $child->getNestingLevel();
        }

        return $level;
    }

    /**
     * @param Swift_Mime_MimeEntity $child
     * @param integer $compoundLevel
     *
     * @return int
     */
    private function _getNeededChildLevel($child, $compoundLevel)
    {
        $filter = array();
        foreach ($this->_compoundLevelFilters as $bitmask => $rules) {
            if (($compoundLevel & $bitmask) === $bitmask) {
                $filter = $rules + $filter;
            }
        }

        $realLevel = $child->getNestingLevel();
        $lowercaseType = Swift::strtolowerWithStaticCache($child->getContentType());

        if (isset($filter[$realLevel], $filter[$realLevel][$lowercaseType])) {
            return (int)$filter[$realLevel][$lowercaseType];
        }

        return (int)$realLevel;
    }

    /**
     * @return Swift_Mime_SimpleMimeEntity
     */
    private function _createChild()
    {
        return new self($this->_headers->newInstance(), $this->_encoder, $this->_cache, $this->_emailValidator);
    }

    /**
     * @param Swift_Mime_ContentEncoder $encoder
     */
    private function _notifyEncoderChanged(Swift_Mime_ContentEncoder $encoder)
    {
        foreach ($this->_immediateChildren as $child) {
            $child->encoderChanged($encoder);
        }
    }

    /**
     * @param string $charset
     */
    private function _notifyCharsetChanged($charset)
    {
        $this->_encoder->charsetChanged($charset);
        $this->_headers->charsetChanged($charset);
        foreach ($this->_immediateChildren as $child) {
            $child->charsetChanged($charset);
        }
    }

    private function _sortChildren()
    {
        $shouldSort = false;
        foreach ($this->_immediateChildren as $child) {
            // NOTE: This include alternative parts moved into a related part
            if ($child->getNestingLevel() === self::LEVEL_ALTERNATIVE) {
                $shouldSort = true;
                break;
            }
        }

        // Sort in order of preference, if there is one
        if ($shouldSort) {
            usort($this->_immediateChildren, array($this, '_childSortAlgorithm'));
        }
    }

    /**
     * @param Swift_Mime_MimeEntity $a
     * @param Swift_Mime_MimeEntity $b
     *
     * @return int
     */
    private function _childSortAlgorithm($a, $b)
    {
        $typePrefs = array();

        $types = array(
            Swift::strtolowerWithStaticCache($a->getContentType()),
            Swift::strtolowerWithStaticCache($b->getContentType())
        );

        foreach ($types as $type) {
            if (isset($this->_alternativePartOrder[$type])) {
                $typePrefs[] = $this->_alternativePartOrder[$type];
            } else {
                $typePrefs[] = max($this->_alternativePartOrder) + 1;
            }
        }

        return $typePrefs[0] >= $typePrefs[1] ? 1 : -1;
    }

    /**
     * Empties it's own contents from the cache.
     */
    public function __destruct()
    {
        $this->_cache->clearAll($this->_cacheKey);
    }

    /**
     * Throws an Exception if the id passed does not comply with RFC 2822.
     *
     * @param string $id
     *
     * @throws Swift_RfcComplianceException
     */
    private function _assertValidId($id)
    {
        if ($this->_emailValidator->isValidWrapper($id) === false) {

This code seems to be duplicated across your project.

            throw new Swift_RfcComplianceException('Invalid ID given <' . $id . '>');
        }
    }

    /**
     * Make a deep copy of object.
     */
    public function __clone()
    {
        $this->_headers = clone $this->_headers;
        $this->_encoder = clone $this->_encoder;

        // TODO? do we need this ? -> https://github.com/bmurashin/swiftmailer/commit/ef5c5134e6e02afc2e8ff3287bfa74be1b33dcaf
        //$this->_cacheKey = $this->_generateNewCacheKey();

59% of this comment could be valid code. Did you maybe forget this after debugging?

        //$this->generateId();

84% of this comment could be valid code. Did you maybe forget this after debugging?

        $children = array();
        foreach ($this->_children as $pos => $child) {
            if ($child instanceof Swift_Mime_Attachment || $child instanceof Swift_Mime_EmbeddedFile) {
                $children[$pos] = $child;
            } else {
                $children[$pos] = clone $child;
            }
        }
        $this->setChildren($children);
    }
}