如何使用Javascript从URL获取HTTP标头（内容类型）

Question

Good afternoon! Here is what I am trying to achieve.

I have an input which allow the user to enter an URL (mostly for images) but it can also be a different type of file. I am searching for a way to verify that the url exists and also get the mime type.

Here is a jsfiddle of my javascript tests.

I found a way to do it using a PHP and AJAX with a function like that:

PHP:

function get_url_content_type( $url ) {

    $header = get_headers( $url, 1 );

    if ( isset( $header['Content-Type'] ) ) {

        return $header['Content-Type'];
    }
}

I am not sure that is the right way to do it, does anyone have better ideas?

Many thanks!

Answer 1

jQuery will already convert the response based on the content type (check this url for details) if you dont specify a type on the $.ajax() call.

So all you can do is check the type of the generated response, to deduce the Content-Type that was sent:

$.get("myPage.html", { }, function(data) {
  if(typeof(data) === "string") {
    //html
  } else {
    //JSON
  }
});

In this case, it doesn't work because google explicitly disables Cross-Origin Request on its hosted images. If you run your tests with Firebug enabled, you will get the message:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.google.com/images/srpr/logo11w.png . This can be fixed by moving the resource to the same domain or enabling CORS.

However, enabling CORS will need some work at server side that I don't think google is willing to do.

EDIT:

If you want to generate a client-side preview of some files, try using something like:

• https://github.com/markserbol/urlive