Parsing sensor frames from a serial port with struct
Serial devices do not respect your read boundaries. A parser has to cope with half frames, garbage and bad checksums, and resynchronise on its own.
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memoryview: slicing a large buffer without copying it
Slicing bytes copies the data. When you parse a big buffer piece by piece, that adds up. memoryview slices share the memory instead.
Rolling out a Content-Security-Policy without breakage
Start in report-only mode, read the reports for a while, then enforce. The order matters more than the policy you write first.
Service worker updates: why users keep the old version
A new service worker installs, then waits. Until you understand why, deployments seem to have no effect on some users for days.
CORS preflights: what triggers them and what you can cache
Every OPTIONS request in your logs is a preflight the browser decided it needed. Knowing the rules lets you remove half of them.
JWT mistakes that keep showing up in code review
The token is signed, not encrypted. Pin the algorithm, check the claims, and think twice about where you store it and how you will ever revoke it.
Password hashing parameters you can defend in an audit
Choosing Argon2id, scrypt, bcrypt or PBKDF2 is the easy part. Setting the cost, upgrading old hashes and avoiding bcrypt truncation is where audits find problems.
You committed a secret. Rotate first, rewrite later
Removing a key from the latest commit does nothing for the copies that already exist. The order of the response matters more than the cleanup tool.
OPcache in production: the settings that actually matter
OPcache is on by default in most builds, but the defaults check files on every request and quietly evict scripts when memory runs out. Two settings and one deploy step fix that.
