Bandwidth test files — and why mine are filled with Celine Dion
I needed two files of known size — 100KB and exactly 1MB — to test mobile-data throughput on Android phones. Filling them with random bytes is boring. Filling them with the Titanic theme song, repeated until the byte count is right, is much more on-brand for what we are actually testing.
Routine bit of test infrastructure I’m putting up today, mostly so I can find it later when I need it.
I keep two files at:
http://intrepidkarthi.com/files/android/titanic.checker ▸ 100 KB
http://intrepidkarthi.com/files/android/titanicmb.checker ▸ 1 MBThey are bandwidth-test files. You point an Android device’s data connection at one of them, request it, and time how long the download takes. From that you back-calculate the effective throughput. Standard mobile-engineering plumbing. We use these all the time on the Norton Mobile team — when a customer says “the Norton update was slow on 3G in Bangalore”, the first question is what was their actual line speed?, and the cleanest way to answer it is two files of known size on a host the device can reach without authentication.
why “titanic”
The naming is functional, not poetic. Titanic because the file is full of Celine Dion’s My Heart Will Go On lyrics, repeated until the byte count is exactly the size I want. titanicmb for the megabyte version.
EverynightinmydreamsIseeyou,IfeelyouThatishowIknowyougoon.
FaracrossthedistanceandspacesbetweenusYouhavecometoshow
yougoon.Near,Far,whereveryouare,Ibelievethattheheartdoesgoon.
… [repeat until 102,400 bytes / 1,048,576 bytes] …Spaces stripped. Punctuation kept. Repeated to fill. The 100KB file is exactly 102,400 bytes; the 1MB file is exactly 1,048,576 bytes. Open them in any text editor and stare at the void.
why not random bytes
Two reasons:
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Compression. Some HTTP middleboxes between you and the server (carrier proxies in particular) will gzip text on the fly. Random bytes do not compress; English text does. If you serve random test files, you measure the cleartext throughput. If you serve English-text test files, you measure the carrier’s actual delivered throughput including any compression, which is often what the user feels. Both are useful, depending on what you are debugging.
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Verifiability. A file full of random bytes can be silently corrupted by a buggy proxy and you will never notice. A file that is supposed to start with Every night in my dreams I see you and ends mid-lyric, you can eyeball the response and immediately tell whether the device received what the server sent. Diagnosability for free.
reality.txt
I also dropped a third file in the same directory called reality.txt. It contains, in full:
Hey, Idiot. Nothing is real in this world!!!
This is for anyone who finds the URL via random crawling and clicks reality.txt expecting an answer. It’s also a placeholder I use to verify that the directory itself is reachable — curl http://intrepidkarthi.com/files/android/reality.txt is the smallest possible reachability check, and the response is short enough to grep for.
Engineering sense of humour. Boring tools. Use them.
— Karthikeyan Norton Mobile · Symantec