AbortController and AbortSignal globals

[TaylorBeeston]

Hi there 👋 I'm Taylor from the LEF, working on making a LearnCard snap!

While building out the snap, I managed to work around every issue I came across except one: AbortController and AbortSignal not being globally available. @learncard/core internally depends on Ceramic libraries, which internally have a wrapper function around fetch that automatically times out via the use of an AbortController. In the past I've managed to get around environments that don't have the AbortController global available by using the abort-controller package to polyfill it, but when doing this inside of the SES runtime, I am running into this error when the fetch call gets made:

I dug around a lot to try and find where this error is thrown, and I eventually found myself in the Chromium source code, where it seems like the native fetch object will only want to accept native AbortSignal objects (not "fake" AbortSignal objects created by a polyfill library with JS 😥). I'm not very good at reading C++ code (particularly a codebase as complicated as that!), so I could be wrong in that assumption, but that is where I landed!

So, for now, I am using sed against my bundled snap file to actually remove that AbortSignal object from being passed in when calling fetch, and everything is happy! This is, however, a pretty bad hack, and I would love it if we could instead just expose the browser's native AbortController and AbortSignal objects inside of the snap's SES runtime, as I believe that will fix the problem!

AFAIK, there's really no harm that one could cause if they got access to these two globals, though I am also definitely not a security expert, and I am aware of how seemingly innocuous things can become malicious quickly with JS, so I understand that there would probably need to be some research into what possible security risks could be associated with adding these in.

tl;dr My snap is in a hacky, potentially buggy state until AbortController and AbortSignal can become globally available inside the snap runtime!

[ritave]

Hey @TaylorBeeston, we already had AbortController exposed, but we didn't expose AbortSignal.

I've added it now in #682, and so the next release of Flask should fix your errors.