magento_duplicate_header.php

// @overright = app/code/core/Mage/Core/Controller/Response/Http.php

public function sendHeaders()
    {
        if (!$this->canSendHeaders()) {
            Mage::log('HEADERS ALREADY SENT: '.mageDebugBacktrace(true, true, true));
            return $this;
        }
        if (in_array(substr(php_sapi_name(), 0, 3), array('cgi', 'fpm')))
        {
            // remove duplicate headers
            $remove = array('status', 'content-type');
 
            // already sent headers
            $sent = array();
            foreach (headers_list() as $header)
            {
                // parse name
                if (!$pos = strpos($header, ':'))
                        continue;
                $sent[strtolower(substr($header, 0, $pos))] = true;
            }
 
            // raw headers
            $headersRaw = array();
            foreach ($this->_headersRaw as $i=>$header)
            {
                // parse name
                if (!$pos = strpos($header, ':'))
                        continue;
                $name = strtolower(substr($header, 0, $pos));
 
                if (in_array($name, $remove))
                {
                        // check sent headers
                        if ($sent[$name])
                        {
                            unset($this->_headersRaw[$i]);
                            continue;
                        }
 
                        // check header
                        if (!is_null($existing = $headers[$name]))
                        {
                            $this->_headersRaw[$existing] = $header;
                            unset($this->_headersRaw[$i]);
                        }
                        else
                            $headersRaw[$name] = $i;
                }
            }
 
            // object headers
            $headers = array();
            foreach ($this->_headers as $i=>$header)
            {
                $name = strtolower($header['name']);
                if (in_array($name, $remove))
                {
                        // check sent headers
                        if ($sent[$name])
                        {
                            unset($this->_headers[$i]);
                            continue;
                        }
 
                        // check header
                        if (!is_null($existing = $headers[$name]))
                        {
                            $this->_headers[$existing] = $header;
                            unset($this->_headers[$i]);
                        }
                        else
                            $headers[$name] = $i;
 
                        // check raw headers
                        if (!is_null($existing = $headersRaw[$name]))
                            unset($this->_headersRaw[$existing]);
                }
            }
        }
 
        parent::sendHeaders();
    }