shc-decode.rb

# Smart Health Card decoder
# This decodes the SHC url thing that is stored in smart health card QR codes

str = DATA.readline

require "base64"
require "zlib"
require "json"
require "pp"

payload = str.delete_prefix("shc:/").scan(/\d\d/).map { |x| (x.to_i + 45).chr }.join
payload = payload.split(".").map { |x|
  pad = x.bytesize % 4
  Base64.urlsafe_decode64("#{x}#{pad == 0 ? nil : '=' * (4-pad)}")
}
pp JSON.load payload.first
zlib = Zlib::Inflate.new(-15)
pp JSON.load zlib.inflate payload[1]

__END__
shc:/1234...

Decode your health card QR code and paste the shc "URL" above

present code attempted to add ==== as a padding when x.bytesize % 4 is zero...

payload = payload.split(".").map { |x|
  pad = x.bytesize % 4
  Base64.urlsafe_decode64("#{x}#{pad == 0 ? nil : '=' * (4-pad)}")
}

@sorah fixed! Thank you!