I recently came across a question: how do you read extended file attributes in Racket. Not being actually that familiar with extended file attributes, I searched online. Nothing seems to currently exist (other than in the FUSE module, but that’s specific to FUSE), but there is a system level exectuable that one could wrap to do this. I haven’t done much1 with Racket’s system
or system*
function before, so let’s give it a whirl.
cyu’s Rack::Cors middleware is rather handy if want to control your CORS (Cross-Origin Resource Sharing) settings in a Ruby-on-Rails project. Previously, there was a fairly major issue where :credentials => true was the default (which you generally do not want), but there were also some more complicated tweaks that I wanted to make.
One problem I recently had to deal with was wanting to:
Access-Control-Allow-Credentials) to be sent for sibling subdomainsI work on a lot of projects.
$ ls ~/Projects/ | wc -l
29
$ ls ~/Projects/work/ | wc -l
67And that’s just what I have checked out at the moment. 😇
If you have a website that allows users to submit URLs, one of the (many many) things people will try to do to break your site is to submit URLs that use the javascript: protocol (rather than the more expected http: or https:). This is almost never something that you want, since it allows users to submit essentially arbitrary code that other users will run on click in the context of your domain (same origin policy).
So how do you fix it?
First thought would be to try to check the protocol:
> safe_url = (url) => !url.match(/^javascript:/)
[Function: safe_url]
> safe_url('http://www.example.com')
true
> safe_url('javascript:alert(1)')
false
As part of general security good practices, you should always (whenever possible):
secure and http_onlyHSTS)Quite often, I’ll find myself wanting to query and manipulate MySQL data entirely on the command line. I could be building up a pipeline or working on a task that I’m going to eventually automate but haven’t quite gotten to yet. Whenver I have to do something like that, I have a small pile of scripts I’ve written over time that help out:
skiphead: Skip the first line of output, used to skip over headers in a query responseskipuntil: Skip all lines until we see one matching a pattern, used to resume partial taskscommaify: Take a list of single values on the command line and turn them into a comma separated list (for use in IN clauses)csv2json: a previously posted script for converting csv/tab delimited output to jsonjq: not my script, but used to take the output of csv2json and query it further in ways that would be complicated to do with SQLAdmitedly, the first two of those are one liners and I could easily remember them, but the advantage of a single command that does it is tab completion. sk<tab>, arrow to select which one I want, and off we go. I could put them as an alias, but I don’t always use the same shell (mostly fish, but sometimes Bash or Zsh).
Today I found the need to look through all old versions of a file in S3 that had versioning turned on. You can do it through the AWS Console, but I prefer command line tools. You can do it with awscli, but the flags are long and I can never quite remember them. So let’s write up a quick script using boto3 (and as a bonus, try out click)!
Part 1: Create an infinite stream of numbers, by starting with [3, 7] with two pointers: 0 and 1. To add values to the list:
- Add the current values of the two pointers
- If the value is less than ten, add that value to the end of the list
- If the value is greater or equal to ten, add 1 and then the ones digits to the end of the list
- Update each pointer by adding the value it is pointing at to its current index plus one
With that algorithm, find the ten digits after a given index.
Part 1: Load a minecart track that looks like this:
/->-\ | | /----\ | /-+--+-\ | | | | | v | \-+-/ \-+--/ \------/Assuming minecarts follow the tracks and alternate turning left, going straight, and turning right on each intersection (
+), where does the first collision occur?NOTE: Update carts top to bottom, left to right. Carts can collide mid update.
Part 1: Create an infinite 2D cellular automaton with transition rules based on two points to each side, starting with initial state at index 0 to the right.
After 20 generations, what is the sum of indexes of points turned on?