When One Door Closes

by Gregory Porter

Pop culture portrays hacking as super intense programmers cracking into the FBI database or reverse engineering a virus (or writing one if the hacker is a villain).  It's all very glamorous.  But that, reader of 2600, as I'm sure you know, isn't really what hacking is about.  It's about problem-solving with creativity and ingenuity.  Today, I'm writing about one such experience.

I recently saw a tweet advertising a free virtual conference.  I registered and looked at the schedule.  Alas, a doctor's appointment overlapped with the presentation I wanted to see.

Nevertheless, I logged in that morning, found a page for that presentation, and bookmarked it.  Maybe I'd be able to come back that afternoon and watch it, I thought.

I got sidetracked and forgot about my bookmark and the presentation for a couple of days.  When I saw a "thank you for attending" email, I thought, oh yeah, let's give watching it a try.  Unfortunately, the conference website didn't allow me to re-login.  It had closed the door, so to speak, because the show was over.  I went about my day, checking the conference's YouTube channel, regretting not scheduling my appointment for another time.  I logged into my computer and, lo-and-behold, I see my forgotten bookmark.  I click it.  Huzzah, it works!

They may have closed the door but they didn't seem to be kicking me out now that I was already there.  That said, I felt as if I was on borrowed time.  If the cookie expires or I refresh the page, surely they would kick me out.  So as the presentation is playing, I am looking through the site to see if there is a "Download" button.  Unfortunately, and not surprisingly, no such button; they'd want you to stay on their platform for the conference.

All right, now if they are going to potentially cut me off, let's find another way to download it.  I open up the browser's "Developer Tools" and switch to the "Network" tab.  Naturally, there are network calls going out, but there was a series that piqued my interest.  Every couple of seconds, a request was made to the following URLs in what seemed to be a pattern (note that this has been changed slightly for brevity and privacy):

https://conference.net/896aaae5d1e4ac3f_960x540p-1.2Mbps-1200000_00010.ts
https://conference.net/896aaae5d1e4ac3f_960x540p-1.2Mbps-1200000_00011.ts
https://conference.net/896aaae5d1e4ac3f_960x540p-1.2Mbps-1200000_00012.ts

Let's start out by seeing if I can get something if I Curl-ed one of those URLs:

$ curl https://conference.net/896aaae5d1e4ac3f_960x540p-1.2Mbps-1200000_00010.ts > test.ts

MPEG TS is a video file geared towards streaming and opening test.ts with VLC revealed a five-second video!  Now, we're cookin' with gas.

The next step was to make a Bash script to cycle from zero to the ending video number and Curl the URLs.

#!/bin/bash
for i in {0..600}
  do
    curl 'https://conference.net/896aaae5d1e4ac3f_960x540p-1.2Mbps-1200000_0000${i}.ts' > $i.ts
  done
exit 0

I then hit a snag.  It seems the last five characters in the URL were a fixed length.  Meaning, for the first file, the URL is 00001.ts while the six-hundredth would be 00600.ts.

Now, this felt very much like a problem out of my computer science education.  But I don't have a clue about how to do that in Bash.  I let out a sigh.  Would this be where my quest would end?  No!  There must be another way.

So let's take a step back and think about the data that we are going to be using.  We know the string is going to have four zeroes when i is less than ten, three zeros when i is between ten and 100, and two zeros when i is between 100 and 1000.

Let's adapt our script to account for just those scenarios:

#!/bin/bash
for i in {0..600}
  do
  if [ $i -lt 10 ]; then
	curl 'https://conference.net/896a-aae5d1e4ac3f_960x540p-1.2Mbps-1200000_0000${i}' > $i.ts
  elif [ $i -lt 100 ]; then
	curl 'https://conference.net/896a-aae5d1e4ac3f_960x540p-1.2Mbps-1200000_000${i}' > $i.ts
  elif [ $i -lt 1000 ]; then
	curl 'https://conference.net/896a-aae5d1e4ac3f_960x540p-1.2Mbps-1200000_00${i}' > $i.ts
  else
	echo "Something is a miss"
  fi
  done
exit 0

# Concatenate the files with: ls -v | xargs cat > video.ts

Is it the fanciest approach?  No, but it does work.  Upon running the script, I had about 550 short video files.  The last step is to concatenate them with:

$ ls -v | xargs cat > video.ts

Note, ls -v is needed because a simple:

$ cat *.ts > video.ts

will result in an ordering of:

1.ts
10.ts 
100.ts 
101.ts 
102.ts
103.ts
...

And so, my quest to download the conference presentation was successful!  The moral of the story, don't let a closed-door be the be-all and end-all (unless you'd be infringing on someone's privacy, then it's probably best to let them be).

As a reader of 2600, I'm sure you've seen all sorts of really complicated technical solutions to problems; don't feel intimidated!  After all, a very simple solution to a problem is still a solution.

Thanks for reading, happy hacking, and stay safe.

Code: WhenOneDoor.sh

#!/bin/bash
#
# From 2600 Magazine - Volume 39, No. 1
# Letter from David Mooter
#
PLAYLIST_FILE=`mktemp`
TEMP_FILE=`mktemp`

curl -s -L --compressed --retry 3 "${1}" -o "${PLAYLIST_FILE}"

BASE_PATH=`echo "$1" | sed 's|\(.*\)/.*|\1|'`/

while IFS= read -r INPUT_LINE
do
	if [ "${INPUT_LIN:0:1}" != "#" ]
	then
		curl -s -L --compressed --retry 3 "${BASE_PATH}${INPUT_LINE}" -o "${TEMP_FILE}"
		cat "{TEMP_FILE}" >> "{$2}"
		rm "${TEMP_FILE}"
	fi
done < "${PLAYLIST_FILE}"
rm "${PLAYLIST_FILE}"

Alternate: M3U.sh
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