I attached a possible fix for this. It will timeout if avahi-browse doesn't respond in 250 miliseconds. This seems reasonable; if the answer takes longer than that it's not useful for interactive use. This will still work for people who care about avahi.
This seems more like a big in avahi or avahi's configuration in debian, but I don't really care about why avahi takes a long time to answer. I believe it's reasonable for bash-completion to include workarounds for bugs in other programs. It's useful for the shell to work reliably even if the system is otherwise misconfigured. It seems that bash-completion debian bug mail also goes to the bash-completion-devel upstream list. Patch is against latest upstream, any feedback is welcome. I had to mangle +o posix to get tests to pass. I don't know why the test suite puts the shell into posix mode anyway.
diff --git a/CHANGES b/CHANGES index 3845158..19a7696 100644 --- a/CHANGES +++ b/CHANGES @@ -78,6 +78,7 @@ bash-completion (2.x) Make it possible to run tests from any directory. * Add a --debug-xtrace option to test/run using BASH_XTRACEFD from bash-4.1. * Add a --timeout option to test/run to override the default expect timeout. + * Timeout when reading avahi-browse output to avoid hangs (Debian #551780). [ Raphaƫl Droz ] * Add xsltproc completion (Alioth: #311843). diff --git a/bash_completion b/bash_completion index 41197ac..f030847 100644 --- a/bash_completion +++ b/bash_completion @@ -1564,15 +1564,47 @@ _known_hosts_real() fi # Add hosts reported by avahi-browse, if it's available. - # The original call to avahi-browse also had "-k", to avoid lookups into - # avahi's services DB. We don't need the name of the service, and if it - # contains ";", it may mistify the result. But on Gentoo (at least), - # -k isn't available (even if mentioned in the manpage), so... if type avahi-browse >&/dev/null; then - COMPREPLY=( "${comprep...@]}" $( \ - compgen -P "$prefix$user" -S "$suffix" -W \ - "$( avahi-browse -cpr _workstation._tcp 2>/dev/null | \ - awk -F';' '/^=/ { print $7 }' | sort -u )" -- "$cur" ) ) + # Process substitution is not available when set -o posix. + local posix_on=$(set -o | awk '/^posix/ { print $2 }') + + set +o posix + # Sometimes avahi can take a long time to respond. + # If we don't get a response quickly just kill it and move on. + # + # The original call to avahi-browse also had "-k", to avoid lookups into + # avahi's services DB. We don't need the name of the service, and if it + # contains ";", it may mistify the result. But on Gentoo (at least), + # -k isn't available (even if mentioned in the manpage), so... + local avahi_fd=<( + echo $BASHPID + avahi-browse -cpr _workstation._tcp 2>/dev/null | \ + awk -F';' '/^=/ { print $7 }' | sort -u + ) + + # Read the pid of the avahi pipe. + # The processes will die on their own anyway but we don't want to leak + # one process every time the users tabs after "ssh " + local avahi_pid + read avahi_pid < $avahi_fd + + local -a avahi_reply + while true; do + # Read with a timeout of 250 miliseconds + local read_reply read_ret + read -t 0.250 read_reply < $avahi_fd + read_ret=$? + [[ $read_ret -gt 128 ]] && kill $avahi_pid + [[ $read_ret -ne 0 ]] && break + #echo "Found avahi host $read_reply" + avahi_reply+=("$read_reply") + done + + [[ $posix_on = 'on' ]] && set -o posix + + COMPREPLY=( "${comprep...@]}" + $( compgen -P "$prefix$user" -S "$suffix" \ + -W "${avahi_reply[*]}" -- "$cur" ) ) fi # Add results of normal hostname completion, unless
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