Phly\Http\MessageTrait::getHeaderLine PHP Method

getHeaderLine() public method

This method returns all of the header values of the given case-insensitive header name as a string concatenated together using a comma. NOTE: Not all header values may be appropriately represented using comma concatenation. For such headers, use getHeader() instead and supply your own delimiter when concatenating. If the header does not appear in the message, this method MUST return a null value.
public getHeaderLine ( $header ) : string | null
return string | null A string of values as provided for the given header concatenated together using a comma. If the header does not appear in the message, this method MUST return a null value.
    public function getHeaderLine($header)
    {
        $value = $this->getHeader($header);
        if (empty($value)) {
            return null;
        }
        return implode(',', $value);
    }