Yesterday was the release day of the Veronica Mars movie. As a Kickstarter backer, Ann got a digital copy of the movie. For reasons that I'm sure were not entirely technical, it was only available via Flixster/UltraViolet¹, so getting access to it involved registering for a new account and jumping through some hoops.

To actually download the movie for offline viewing, Flixster said it needed a “Flixster Desktop” client app. It was served as a ~29 MB .zip file, so it seemed like a straightforward download. I noticed that I was only getting ~ 30K/second download speeds, but I wasn't in a hurry, so I let it run. The download finished, but with only a ~21MB file that was malformed when I tried to expand it. I figured the WiFi of the hotel that we were staying at was somehow messing with the connection, so I tried again while tethered to my phone. I was still getting similarly slow download speeds, and the “completed” download was still too small. Since 30K/second was definitely under the expected tethered LTE throughput, I began to suspect Flixster's servers as the root cause. It certainly seemed plausible given that the file was served from desktop.flixster.com, which did not seem like a CDN domain². I guess ~60,000 fans were enough to DDoS it; from reading a Reddit thread, it seemed like I was not the only one.

The truncated downloads were of slightly different sizes, but it seemed like they finished in similar amounts of time, so I decided to be more scientific and timed the next attempt. It finished in exactly 10 minutes. My hypothesis was now that Flixster's server (or some intermediary) was terminating connections after 10 minutes, regardless of what was being transferred or what state it was in.

Chrome's download manager has a Pause/Resume link, so my next thought was to use it to break up the download into two smaller chunks. After getting the first 10 MB, I paused the download, disconnected the laptop from WiFi (to make sure the connection would not be reused) and then reconnected and tried resuming. Unfortunately, the download never restarted. I did a HEAD request on the file, and since the response headers did not include an Accept-Ranges header, I assumed that the server just didn't support resumable downloads, and that this path was a dead end.

After spending a few minutes trying to find a mirror of the app on sketchy download sites, a vague memory of Chrome's download manager not actually supporting HTTP range requests came to me. I did some quick tests with curl and saw that if I issued requests with --range parameters I got different results back. So it seemed like despite the lack of Accept-Ranges headers, the server (Apache fronted by Varnish) did in fact support range requests³.

I therefore downloaded the file in two chunks by using --range 0-10000000 and --range 10000000- and concatenated them with cat. Somewhat surprisingly, the resulting zip file was well-formed and expanded correctly. I put a copy of the file in my Dropbox account and shared it on the Reddit thread, it seemed to have helped a few others.

Of course, by the end of all this, I was more excited about having successfully downloaded the client app than getting or watching the movie itself⁴.

1. As opposed to say, iTunes or Amazon.
2. Now that I check the download page a day later, it seems to be served from static.flixstercdn.com, so I guess Flixster realized what was going on and fixed the problem.
3. A closer reading of section 14.5 of the HTTP 1.1 spec showed that servers MAY respond with Accept-Ranges: bytes, but are not required to.
4. Downloading the actual movie worked fine, I assume it was distributed over a CDN and thus wasn't quite so easily overwhelmed.