I have grown a pattern for processing each line of Subprocess.jsm output: see https://searchfox.org/mozilla-central/search?q=const%20dumpPipe&path= for some cases. Each of these duplicates some code, with subtly different issues (are exceptions in stdin.close() handled correctly? are trailing lines handled correctly?). This ticket tracks unifying these and exposing them in the Subprocess.jsm API space so they don't need to be copy-pasted.