Zend\Diactoros\MessageTrait::hasHeader PHP Method

Checks if a header exists by the given case-insensitive name.

public hasHeader ( string $header ) : boolean
$header	string	Case-insensitive header name.
return	boolean	Returns true if any header names match the given header name using a case-insensitive string comparison. Returns false if no matching header name is found in the message.

    public function hasHeader($header)
    {
        return array_key_exists(strtolower($header), $this->headerNames);
    }

MessageTrait