Defensive Programming
What shouldn't happen will happen.
Slide 4
Slide 4 text
“Defensive programming is …
intended to ensure the continuing
function of a piece of software under
unforeseen circumstances.
en.wikipedia.org/wiki/Defensive_programming
Slide 5
Slide 5 text
1. You want robust software
2. You want easy debugging
3. You want to re-use code
4. You have an unpredictable environment
5. You have user generated data
Slide 6
Slide 6 text
1. How I became paranoid
2. Frank Underwood’s greatest compliment
3. Why I respect types
4. How you can be more defensive
5. Takeaways for the sceptics
Slide 7
Slide 7 text
1
How I became paranoid
Slide 8
Slide 8 text
No content
Slide 9
Slide 9 text
No content
Slide 10
Slide 10 text
No content
Slide 11
Slide 11 text
10:00 10:02 10:04
Slide 12
Slide 12 text
10:00 12:00 14:00
Slide 13
Slide 13 text
No content
Slide 14
Slide 14 text
No content
Slide 15
Slide 15 text
No content
Slide 16
Slide 16 text
Tip 1
Don’t dismiss “small” problems
Slide 17
Slide 17 text
No content
Slide 18
Slide 18 text
Tip 2
Define the absolutes
Slide 19
Slide 19 text
No content
Slide 20
Slide 20 text
Tip 3
Unit test your defence
Slide 21
Slide 21 text
2
Frank Underwood’s
Greatest Compliment
Slide 22
Slide 22 text
Defensive Programming
Tip 4
Be ruthlessly pragmatic
Slide 23
Slide 23 text
1. That Can’t Happen!
Slide 24
Slide 24 text
2. How did that happen?
Slide 25
Slide 25 text
3. How did that ever work?
Slide 26
Slide 26 text
1. It happened
2. Here’s how
3. I can fix that
Slide 27
Slide 27 text
getsentry.com/welcome/
Slide 28
Slide 28 text
No content
Slide 29
Slide 29 text
No content
Slide 30
Slide 30 text
No content
Slide 31
Slide 31 text
Defensive Programming
Tip 5
Monitor & log everything
Slide 32
Slide 32 text
7% Requests
Production Errors
Slide 33
Slide 33 text
11% Defense
Production Errors
Slide 34
Slide 34 text
36% Ungraphable data
Production Errors
Slide 35
Slide 35 text
46% Type Errors
Production Errors
Slide 36
Slide 36 text
3
Why I respect types
Slide 37
Slide 37 text
W
AT!!
Slide 38
Slide 38 text
No content
Slide 39
Slide 39 text
No content
Slide 40
Slide 40 text
bit.ly/monitoring-plants
Slide 41
Slide 41 text
Defensive Programming
Tip 6
Don’t trust user data
Slide 42
Slide 42 text
No content
Slide 43
Slide 43 text
No content
Slide 44
Slide 44 text
Defensive Programming
Tip 7
…will be race conditions. There…
Slide 45
Slide 45 text
4
How you can
be more defensive
Slide 46
Slide 46 text
No content
Slide 47
Slide 47 text
Oh no! That request failed. Try again?
Slide 48
Slide 48 text
No content
Slide 49
Slide 49 text
Loading…
Slide 50
Slide 50 text
No content
Slide 51
Slide 51 text
No content
Slide 52
Slide 52 text
No content
Slide 53
Slide 53 text
Defensive Programming
Tip 8
Don’t forget defensive design
Slide 54
Slide 54 text
5
Takeaways for the skeptics
Slide 55
Slide 55 text
No content
Slide 56
Slide 56 text
Tip 9
Make debugging easier
Slide 57
Slide 57 text
Portal
Slide 58
Slide 58 text
A B
Slide 59
Slide 59 text
A B
Slide 60
Slide 60 text
Tip 10
Write defensive code
but don’t be defensive