1.10.08. Giddy-up 401, File Uploads, and Safari

I've recently been doing some work to support ZODB 3.8 BlobFiles in our Zope 3 based sites and applications. Doing this brought me back around to seeing some behavior I've seen in the past and probably learned to ignore: uploading a large file from Safari using a basic HTML form (with proper encoding type, POST, etc) seems to take inexplicably long. Even worse - once behind Apache, you might not get an expected response, if any. You might get a 'timed out' response, unsure if the app server has everything and will finish the request/response cycle on its own.

It turns out that Safari does not eagerly send along authentication information along with each request when logged in with Basic Auth. When it does, it seems to have a very short time window.

So say you're logged in to your application with basic auth (for better or worse). The normal pattern is that when encountering an unauthenticated situation, Zope will challenge with a 401 status code and the WWW-Authenticate header (or something like that - I'm away from all specs right now). If you're not logged in, then you get the basic auth dialog box and send along the credentials. If you are "logged in", then the browser doesn't ask for credentials again, but just sends them along.

The downside is that this causes a request to be repeated. And if you just tried uploading a 5 MB file, then that whole file has to be re-submitted to make the full request.

It's the right thing to do with the basic (ha!) information at hand - trying to post all of that data in a single request. But Safarishould recognize that it's submitting to the same server (if not the same URL!) and should automatically include the auth headers. Safari seems to do this, but only on requests in very short windows.

Firefox, on the other hand, seems to have a much longer window in which it will send the credentials along automatically on the first request, instead of waiting for the challenge.

I don't know how other browsers do it. I'm not sure what the spec says, if anything. Glancing at O'Reilly's "HTTP - The Definitive Guide" didn't seem to give any indication of whether it's better for the client to assume that it should send the authentication tokens along with each request back to the same server, or if it's better for the client to hold off on constantly sending that info along unless challenged.

Most of the time this doesn't really seem to matter - it's not something end users typically see as it goes by fast enough to rarely be noticed. Of course there are other ways of getting credentials (cookies, sessions, subdomain/remote ip mapping, etc) which we often use on the main public-facing side of our sites. But for content management and admin, Basic Auth is such an easy fallback, especially in a framework like Zope (1, 2, or 3) which has long had a strong security story and would automatically handle this crap for you way back in the days of Bobo (1996, if not earlier).

It's just an annoyance. Glad I nailed it down to this: uploading large files with Safari (I think IE is, or was, similar) to basic-auth protected sites often can time out because the browser posts once, gets the 401-Unauthorized challenge, and does the post again - this time with the auth info.


  • don't use basic auth for sites that expect moderate to heavy uploading via forms.
  • recommend and/or use browsers that send the auth token along more often in the first request.
  • provide better interfaces for uploading files; providing better communication with the uploader about status, and perhaps having a better interface into the destination web app. Fortunately there are appear to be some free and open solutions out there already.


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