Constant SCRIPT 

pub const SCRIPT: &str = "#!/bin/sh\n\
                          # Hands the address to QCode, which shows it in a window of this container.\n\
                          set -eu\n\
                          [ -n \"${1:-}\" ] || exit 1\n\
                          [ -d \"$0_DIR\" ] || exit 1\n\
                          name=\"$0_DIR/$(date +%s%N)\"\n\
                          printf '%s\\n' \"$1\" > \"$name.part\"\n\
                          mv \"$name.part\" \"$name.url\"\n";

The program the image installs at OPEN_PROGRAM.

It is a shell script rather than anything larger because the base image is the only thing it may rely on. It writes beside the final name and moves it into place so that a reader never sees half an address, and it says nothing on its output: whatever it printed would land in the application’s own log, not in front of the person.