204 No Content
Sometimes you want to send an HTTP request and you don't care about the response. This is often used for logging stuff on the server. Usually you request a 1x1 pixel GIF file and send a bunch of query parameters. E.g.
htp://example.org/blank.gif?user=stoyan&browser=msie&creditcard=123JUSTKIDDING567
Such 1x1 gifs are often called "web bugs" or "beacons" and sometimes used for sneaky purposes such as checking whether-you-opened-that-email-I-sent-you-that-you-didn't-reply-to-although-I-told-you-it-was-urgent-dammit-now-I'm-gonna-tell-the-boss-yes-this-time-I'm-telling-the-boss!
Now (after we relax a bit)... instead of having your server send a blank GIF, however small, can you just send.. nothing? Yep, you can. Your server can respond with a "204 No content" header. Cool, eh, especially when you want to squeeze every bit of network traffic?
So the example above can look like:
htp://example.org/nope.php?user=stoyan&browser=msie&creditcard=123JUSTKIDDING567
And nope.php could be like:
// .... log whatever you need to log, then reply: header("HTTP/1.0 204 No Content");
Here's what this looks like in Net Panel.
And an example in the wild (Google search beacon)
Another application of 204s I was thinking could be favicons. If you don't want to deal with favicons, but you don't want to respond with a 404 Not Found either, you can just configure Apache to send 204 to favicon requests. Could be useful when your application generates subdomains for your users, since the browser will request the favicon from each subdomian (unless you have a link-ed favicon).
This entry was posted on Sunday, March 8th, 2009 and is filed under performance. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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March 8th, 2009 at 4:45 pm
It’s better to send the header, and flush the output first, and then do your logging. That way the client isn’t waiting for you to do your back end work.
April 13th, 2009 at 12:06 pm
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April 13th, 2009 at 5:12 pm
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April 30th, 2009 at 9:24 am
Your URL examples are missing a ‘t’ in h-t-t-p.
April 30th, 2009 at 10:17 am
heh, true, thanks Steve.
March 30th, 2010 at 11:07 am
Actually, it’s not so good for favicons as favicons served as 200 with cache headers can be cached by browser and never requested again. They can probably fit into the same TCP packet anyway being quite small. While 204s are probably not cached as there is nothing to cache (although I couldn’t find any specifics in HTTP spec).
August 25th, 2010 at 10:56 am
Can’t you just change the method of your ajax request from GET or POST to HEAD?
Head doesn’t return any content, just 200 and the headers. It’s essentially a 204, but not a 204. =)
November 30th, 2010 at 2:34 pm
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November 30th, 2010 at 2:46 pm
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December 25th, 2010 at 2:56 am
lol! nice…?
HattieInABox
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September 23rd, 2011 at 10:01 am
I was wondering what your opinion on below would be:
imagine a large scale website that does analytics using yetanotherblank.gif
would it be faster to have .htaccess rewrite rule yetanotherblank.gif -> nope.php
where script.php would contain your code from nope.php.
In my tests image is served much faster (you could even serve it from image host that does no script processing)..
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June 2nd, 2012 at 3:40 am
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