http-multipart-19689166.php

<?php
/**
 * Create zip from inline binary attachment to multi-part message
 *
 * @link http://stackoverflow.com/a/19746863/367456
 */

/**
 * Class HttpFiledValue
 *
 * Hands On Parameter Parsing and Extraction via http_parse_params()
 */
class HttpFieldValue implements ArrayAccess
{
    private $value;

    public function __construct($value)
    {
        $this->value = $value;
    }

    public function getParameterByName($name)
    {
        $params = http_parse_params($this);
        foreach ($params->params as $index => $param) {

            if (!is_array($param)) {
                if ($name === NULL) {
                    return $param;
                }
                continue;
            }

            foreach ($param as $paramName => $value) {
                if ($name === $paramName) {
                    return $value;
                }
            }
        }
    }

    public function __toString()
    {
        return $this->value;
    }

    public function offsetExists($offset)
    {
        return NULL !== $this->getParameterByName($offset);
    }

    public function offsetGet($offset)
    {
        return $this->getParameterByName($offset);
    }

    public function offsetSet($offset, $value)
    {
        throw new BadMethodCallException('Read only.');
    }

    public function offsetUnset($offset)
    {
        throw new BadMethodCallException('Read only.');
    }
}

/**
 * Class MultipartRelatedHttpMessage
 */
class MultipartHttpMessage extends HttpMessage
{
    /**
     * @param null $message
     * @param null $class_name
     * @return MultipartHttpMessage
     */
    public static function fromString($message = NULL, $class_name = NULL)
    {
        if (NULL === $class_name) {
            $class_name = __CLASS__;
        }
        return parent::fromString($message, $class_name);
    }

    /**
     * @return array|HttpMessage[]
     * @throws UnexpectedValueException
     */
    public function getParts()
    {
        $boundary = $this->getBoundary();
        if (!$boundary) {
            return [];
        }

        $needle    = "--$boundary";
        $needleLen = strlen($needle);
        $counter   = 0;
        $offset    = 0;
        $parts     = [];
        $foundLast = FALSE;

        while (false !== $pos = strpos($this->body, $needle, $offset)) {
            $nextTwo = substr($this->body, $pos + $needleLen, 2);
            if ($nextTwo === "--") {
                $message   = substr($this->body, $offset, $pos - $offset);
                $parts[]   = self::fromString("HTTP/1.1 206 Partial Content\r\n$message");
                $foundLast = TRUE;
                $counter++;
                break;
            }

            if ($nextTwo === "\r\n") {
                if (!$counter) {
                } else {
                    $message = substr($this->body, $offset, $pos - $offset);
                    $parts[] = self::fromString("HTTP/1.1 206 Partial Content\r\n$message");
                }
                $offset = $pos + $needleLen + 2;
                $counter++;
                continue;
            }
            throw new UnexpectedValueException($nextTwo);
        }

        // add last one on good luck if it didn't found the last-marker so far
        if (!$foundLast) {
            $message = substr($this->body, $offset);
            $parts[] = self::fromString("HTTP/1.1 206 Partial Content\r\n$message");
        }

        return $parts;
    }


    /**
     * @param string $header
     * @return HttpFieldValue|string
     */
    public function getHeader($header)
    {
        return new HttpFieldValue(parent::getHeader($header));
    }

    public function getHeaders()
    {
        $headers = parent::getHeaders(); #
        foreach ($headers as &$header) {
            $header = new HttpFieldValue("$header");
        }
        return $headers;
    }

    public function getBoundary()
    {
        return $this->getHeader('content-type')['boundary'];
    }
}

$url = 'http://developer.ebay.com/DevZone/file-transfer/CallRef/Samples/downloadFile_basic_out_xml.txt';
$raw = file_get_contents('downloadFile_basic_out_xml.txt');

$message = MultipartHttpMessage::fromString($raw);

echo 'Boundary: ', $message->getBoundary(), "\n";

foreach ($message->getParts() as $index => $part) {
    printf("Part #%d:\n", $index);
    foreach ($part->getHeaders() as $name => $value) {
        printf("  %s: %s (%s)\n", $name, $value[NULL], $value);
    }
}