Base64 and AJAX

[Bob Grossman]

I'm experimenting with updating images in a Web page by using AJAX to send new image display options to a Java method on the server. The server generates a Base64-encoded URI for a PNG image and writes it to a JSP Page. AJAX returns this page, I extract the URI from it using standard Javascript string methods, and I use innerHTML to replace the old image (the entire image, not just the src) with the new one.

Sometimes this procedure gives me a ? instead of the image. In fact, in one particular case, I have an image that displays just fine, but if I change an option, then change it back to what it was originally, I get a ?, even though the image (and presumably the URI) hasn't changed.

So here's my question. Is it possible that some, but not all, Base64-encoded strings could become corrupted by being written to a text document, then extracted into a Javascript variable, then parsed with standard Javascript string methods?

I'm using a class called Base64Coder from http://www.source-code.biz to do the encoding into Base64.

Here's the src for the image that displays just fine:

[Edit: ultra-wide Base64 string removed]

And here's what the Java method is returning upon the AJAX request to revert to the original image:

[Edit: ultra-wide Base64 string removed]

Here's the Javascript method I use to update the image:

    function updatePage() {
        if (xmlHttp.readyState == 4) { // ready to continue
            var responsePage = xmlHttp.responseText;
            var text = extractField(responsePage, 'imageURIValue');
            if (!isWhiteSpace(text)) {
                var imageBld = new String.builder();
                imageBld.append('<a onclick="showSource();">'<img src="');
                imageBld.append(text);
                imageBld.append('" \/>'<\/a>');
                setInnerHTML('fig', imageBld.toString());
            } // if there is text to display
        } // if ready to continue
    } // updatePage()

[Bear Bibeault]

That's a pretty odd way of doing things. Why don't you just change the src attribute of the image?

[Bob Grossman]

Because changing the src wasn't working either. Besides, I was originally using SVG to generate the image, so it was as little change as possible to drop in the entire tag in place of the SVG.

[Bear Bibeault]

Well, SVG is an entirely different beast. But with the normal image tag, changing the source should work without issues. Likely the URL you were using was wrong if it didn't work for you.

[Bob Grossman]

I agree. The question is, why is it wrong? Can the process of writing the base64 string to a text document cause information to be lost or corrupted?

[Bear Bibeault]

I don't know -- not something I'd ever try to do. If there are line terminators involved, then yeah, that's sometime a problem.