Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="Pkg-IO-capture-BufferStream")
julia> using Pluto

This PR seems to fix the issue! Except it stalls forever when doing Pkg operations, unless I add lots of logs to debug this, and then it magically works. So I need to figure out which log fixed it and why? (Maybe I need a yield or something?)

pankgeorg suggested flush(some_io)

The problem was that I was doing readavailable on a stream that was already fully read, so it was waiting forever for the next byte. The logs "fixed" it because the logs were also printed in this stream, adding bytes.

This fixed it! There is one more Pkg issue that I will maybe do in a separate PR

last failure is julia-actions/setup-julia#240