PHP: Grab an image from a stream (in an img tag) but if it's not there, i don't want the img tag written. How?

Question

I currently have code like this in a web based file called 'view_file.php' to grab an image from an internal network.

<img src="put_file.php?type=<?=$TN_TYPE;?>&path=<?=$TN_PATH;?>&filename=<?=$TN_FILENAME;?>" />

The 'put_file.php' script allows access to an internal server that we don't want to expose to the internet. This script checks to see if an image is available and if it is, sends an image header and then uses readfile() to stream the image to the 'view_file.php' page.

The problem is if there isn't an image available, instead of streaming a temporary 'spacer.gif' i want to not have the img tag written at all.

Any Ideas how to do this? I'm thinking maybe move the img tag into the 'put_file.php' script, but how to mix strings and steams?

Answer 1

You can use base64 to do what you want.

http://www.sweeting.org/mark/blog/2005/07/12/base64-encoded-images-embedded-in-html

Answer 2

Can't be done simply I think.

• You could make a call to put_file.php in PHP, see what it returns, and if it returns an empty value (or a 404 header or whatever) refrain from writing the img tag. Obvious con: The request is made twice, and it complicates the script.

• You could create the image element in JavaScript depending on the result of an Ajax call to put_file.php. Obvious con: Doesn't show up straight after loading, and needs JavaScript.

Both these options could be reduced to making one request by piping the results of the testing request into base64-encoded data: URI's, but that is highly incompatible (no IE support) and bloats the page on browser side (the image data plus 33% overhead would be present straight in the source code, or the JavaScript memory, respectively). I wouldn't recommend it.

If at all possible, I personally would stick with the spacer.gif solution.

Update: One other idea, if it's just that you don't want the images to appear, would be sending a 404 header when the image isn't there, and utilizing the onerror event of the img tag to, say, do a <img onerror='this.style.display = "none"'>. Requires Javascript, of course. The error event seems to be fully supported in all browsers (reference here, german only sorry, but you'll see the icons :).

Answer 3

It seemd like you write the IMG tag before checking its presence. Your server can send a 1x1 transparent image or return 404 error. 404 will cause a "broken image" icon in various browsers.

Best way is to check for presence of image inside your container php script, somehting along these lines:

<?php
    if (is_present($TN_PATH, $TN_FILENAME))
    {
        ?>
        <img src="put_file.php?type=<?=$TN_TYPE;?>&path=<?=$TN_PATH;?>&filename=<?=$TN_FILENAME;?>" />
        <?php
    }
?>

An alternate and ugly way is to use JavaScript/Ajax to query image status and/or display them.