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Cookies are filled with weird gotchas and uncomfortable behavior that works 99.95% of the time. My favorite cookie minefield is cookie shadowing - if you set cookies with the same name but different key properties (domain, path, etc.) you can get multiple near-identical cookies set at once - with no ability for the backend or JS to tell which is which.

Try going to https://example.com/somepath and entering the following into the browser console:

  document.cookie = "foo=a"; 
  document.cookie = "foo=b; domain=.example.com";
  document.cookie = "foo=c; path=/somepath";
  document.cookie

I get

  'foo=c; foo=a; foo=b'

The article mentions Rust's approach, but note that (unlike the other mentioned languages) Rust doesn't ship any cookie handling facilities in the standard library, so it's actually looking at the behavior of the third-party "cookie" crate (which includes the option to percent-encode as Ruby does): https://docs.rs/cookie/0.18.1/cookie/

About 10 years ago I implemented cookie based sessions for a project I was working on. I had a terrible time debugging why auth was working in Safari but not Chrome (or vice-versa, can't remember). Turned out that one of the browsers just wouldn't set cookies if they didn't have the right format, and I wasn't doing anything particularly weird, it was a difference of '-' vs '_' if I recall correctly.

>everything behaves differently, and it's a miracle that [it] work at all.

The web in a nutshell.

Cookies need to die. Their only legitimate use is with for which we have the Authentication header. Having a standard way to authenticate into a website in a browser would be amazing, just too bad that Basic and Digest auth wasn’t good enough at the time.

As a bonus we could get Persona-style passwordless future.

Cookies seem to be a big complicated mess, and meanwhile are almost impossible to change for backwards-compatibility reasons. Is this a case to create a new separate mechanism? For example a NewCookie mechanism could be specified instead, and redesigned from the ground-up to work consistently. It could have all the modern security measures built-in, a stricter specification, proper support for unicode, etc.

I came across a similar issue when experimenting with the Crystal language. I thought it would be fun to build a simple web scraper to test it out, only to find the default HTTP client fails to parse many cookies set by the response and aborts.

The article mocks Postel's law, but if the setter of the cookie had been conservative in what they sent, there would have been no need for the article...

Re Safari’s networking code being closed source, a good substitute might be the Swift port of Foundation. You can see checks for control and delete characters here: https://github.com/swiftlang/swift-corelibs-foundation/blob/...

> Many languages, such as PHP, don't have native functions for parsing cookies, which makes it somewhat difficult to definitively say what it allows and does not allow.

What?

Parse a cookie with http://php.adamharvey.name/manual/en/function.http-parse-coo...

Send a cookie with https://www.php.net/manual/en/function.setcookie.php or https://www.php.net/manual/en/function.setrawcookie.php

Or if you have to check how php populates the $_COOKIE superglobal I think it is somewhere is this file: https://github.com/php/php-src/blob/master/main/php_variable...

Cookie header parsing is a shitshow. The "standards" don't represent what actually exists in the wild, each back-end server and/or library and/or framework accepts something different, and browsers do something else yet.

If you are in complete control of front-end and back-end it's not a big problem, but as soon as you have to get different stuff to interoperate it gets very stupid very fast.

That is a bit of a minefield, I agree…

The way around this, as a developer, is URL-safe-base64 encode the value. Then you have a bytes primitive & you can use whatever inner representation your heart desires. But the article does also note that you're not 100% in control, either. (Nor should you be, it is a user agent, after all.)

I do wish more UAs opted for "obey the standard" over "bytes and an prayer on the wire". Those 400 responses in the screenshots … they're a conforming response. This would have been better if headers had been either UTF-8 from the start (but there are causality problems with that) or ASCII and then permitted to be UTF-8 later (but that could still cause issues since you're making values that were illegal, legal).

> ...tragedy of following Postel's Law.

The "law" is: "Be liberal in what you accept, and conservative in what you send."

But here the problem is caused by being liberal in what is sent while being more conservative in what is accepted. It's using invalid characters in the cookie value, which not everything can handle.

Following Postel's law would have avoided the problem.

Author started with throwing the results of JSON.stringify into a cookie, and I was surprised that his issue wasn't just that someone had thrown a semicolon into the JSON that was being stringified.

Most of the headaches around cookies seem to be around people trying to get them to work with arbitrary user input. Don't do that. Stick with fixed-length alphanumeric ASCII strings (the kind you use for auth tokens) and you'll be fine.

Did anyone else notice that the HTTP protocol embeds within it ten-thousand different protocols? Browsers and web servers both "add-on" a ton of functionality, which all have specifications and de-facto specifications, and all of it is delivered through the umbrella of basically one generic "HTTP" protocol. You can't have the client specify what version of these ten-thousand non-specifications it is compatible with, and the server can't either. We can't upgrade the "specs" because none of the rest of the clients will understand, and there won't be backwards-compatibility. So we just have this morass of random shit that nobody can agree on and can't fix. And there is no planned obsolescence, so we have to carry forward whatever bad decisions we made in the past.

> Handling cookies is a minefield

I know! You gotta let them cool down first. Learned this the hard way.

> Apple Support

Are we sure the website wasn't just broken normally? I kid, a bit, but good lord does Apple _suck_ at websites. Apple Developer and, more often, App Store Connect is broken for no good reason with zero or a confusing error message.

Note: I'm typing this on a M3 Max MBP (via a Magic Keyboard and Magic Mouse) with an iPhone 16 Pro and iPad Mini (N-1 version) on the desk next to me with an Apple Watch Series 10 on my wrist and AirPods Pro in my pocket. I'm a huge Apple fanboy, but their websites are hot garbage.

Go and failing to parse http headers correctly should become a meme at some point.

One issue we had was the reverse proxy inserting headers about the origin of the request to the server behind. Like ip, ip city lookup etc. And that parsed through a service written in go that just crashed whenever the city had a Norwegians letter in it, took ages to understand why some of our (luckily only internal) services didn't work for coworkers working from Røros for instance. And that was again not the fault of the Go software, but how the stdlib handled it.

That reminds me of the Frog and Toad story about willpower vs eating cookies. Yes, handling cookies is a mine field!

I read the collected stories with my two year old, though I made sure we skipped the scary ones with the Dark Frog. I think the cookies ending was a little over his head, but we had fun taking turns acting out Toad pulling his blankets over his head when Frog tells him it's spring.

Need to alternate background color-code (61e272 / e26161 + 63b754 / b75454) tables because reading a sea of Yes and No requires too much effort.

I got the impression that almost as soon as they were introduced people thought the only sensible use of cookies is to set an opaque token so the server can recognize the client when it sees it again, and store everything else server side.

I don;t understand why it's a problem that the client (in principle) can handle values that the server will never send. Just don't send them, and you don;t have to worry about perplexing riddles like "but what would happen if I did?"

Everything about the web is a minefield. It's an exercise in "how many unnecessary layers can we put between users and their content"?

[comment intended for a different post, but too old to delete]

One of the things I’ve always found frustrating about cookies is that you have to do your own encoding instead of the API doing it for you. I’m sure someone somewhere does but too often I’m doing my own urlencode calls.

There’s a nasty bug in the python cookie parser, cookies after a cookie with quotes will be dropped: https://github.com/python/cpython/pull/113663

Zoom or some other website our customers use was writing a cookie with quotes that would break the site. Amazingly hard to reproduce and debug.

And the article isn't even about the proliferation of attributes cookies have, that browsers honor, and in some cases are just mandatory. I was trying to explain SameSite to a coworker, and scrolled down a bit... https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#co... wait, cookie prefixes? What the heck are those? The draft appears to date to 2016, but I've been trying to write secure cookie code for longer than that, hadn't heard of it until recently, and I can't really find when they went in to browsers (because there's a lot more drafts than there are implemented drafts and the date doesn't mean much necessarily), replies explaining that welcome.

Seems like every time I look at cookies they've grown a new wrinkle. They're just a nightmare to keep up with.

> minefield

Cookies are a bit of a mess, but if you're going to use them, you can follow the standard and all will be well. Not so much a minefield, but a hammer; you just need to take some care not to hit yourself on the thumb.

I guess the confusion here is that the browser is taking on the role of the server in setting the cookie value. In doing so it should follow the same rules any server should in setting a cookie value, which don't generally allow for raw JSON (no double-quote! no comma!).

Either use a decent higher-level API for something like this (which will take care of any necessary encoding/escaping), or learn exactly what low-level encoding/escaping is needed. Pretty much the same thing you face in nearly anything to do with information communication.

Wait til you have a legacy system and a newer system and need to, among other things:

- Implement redirects from the old login screen to the new one - Keep sessions in sync - Make sure all internal and external users know how to clear cookies - Remind everyone to update bookmarks on all devices - Troubleshoot edge cases

    Firefox accepts five characters which RFC recommends that servers not send:

    0x09 (horizontal tab)
    0x20 (spaces)
    0x22 (double quotes)
    0x2C (commas)
    0x5C (backslashes)

I agree with at least some of these. Cookies without commas? Quotes?

IT IS a mess, but I never saw json inside a cookie. For json I use local storage or indexeddb.

I got a trick.

Just dont make them, and dont accept them.

Almost nobody uses SimpleCookie.load for python. Flask, FastAPI, Django have own more relaxed parsers which doesn't break on invalid byte.

Literally everything in IT runs on decades old principles and technologies. The world simply refuses to fix things because "if ain't broken, don't fix it" philosophy. Look at TCP, HTML, JSON, SMTP..all good tech but insanely old and outdated and overtaxed for that it was invented for. When people joke that the entire banking industry runs on excel sheets, they are really not far from truth. Things will be shitty until they completely break down and people are forced to fix them. Look at JavaScript, this horribly stinking steaming pile of green diarrhea that rules over the entire front-end is still being worked on and developed and billions of money and countless work-hours have been wasted in order to make it somewhat usable, instead of just coming up with entirely new tech suitable for the 21st century. This is the entire internet and tech in general.