bash-sock-twiddling

#

# ssh-agent + screen = mess
_sa_fixed_sock=${HOME}/.ssh/auth_sock

# check if agent socket is live (0 ==> live)
_sa_sock_is_live ()
{
	local sock=${1}
	env SSH_AUTH_SOCK=${sock} /usr/bin/ssh-add -l &>/dev/null
}

_sa_link_fixed_sock () { /bin/ln -fns "$1" "$_sa_fixed_sock" ; }

# extract from an agent's socket the sshd pid for that session
_sa_pid_of_sock ()
{
	local sock="$1"

	[ -L "$sock" ] && sock=$(readlink $sock)
	sock=$(echo $sock |egrep 'agent\.[0-9]+$')
	if [ -z "$sock" ]; then
		# empty suggests no agent was forwarded to this sussion
		return 1
	fi

	echo $sock |sed -e 's/.*\.//'
	return 0
}

_sa_current_session_pid ()
{
	if [ -n "$SA_ORIG_SOCK" ]; then
		_sa_pid_of_sock "$SA_ORIG_SOCK"
		return 0
	else
		local sshd=$(ps h -o ppid $(ps h -o sess $$))
		if ps h -o command $sshd |fgrep sshd >/dev/null; then
			echo $sshd
			return 0
		fi
		return 1
	fi
}

_sa_should_link_fixed_sock ()
{
	# interactive?  sock defined?
	[ -n "$PS1" -a -n "$SSH_AUTH_SOCK" ]		|| return 1
	[ "$SSH_AUTH_SOCK" != "$_sa_fixed_sock" ]	|| return 1

	# don't replace a live socket
	_sa_sock_is_live $_sa_fixed_sock && return 1
	# don't repoint to a dead socket
	_sa_sock_is_live $SSH_AUTH_SOCK  || return 1

	return 0
}

_sa_link_sock_if_appropriate () {
	if _sa_should_link_fixed_sock ; then
		_sa_link_fixed_sock "$SSH_AUTH_SOCK"
	fi
}

_sa_use_fixed_sock_if_appropriate ()
{
	# interactive?  sock defined?
	[ -n "$PS1" -a -n "$SSH_AUTH_SOCK" ]		|| return 1
	[ "$SSH_AUTH_SOCK" != "$_sa_fixed_sock" ]	|| return 1
	_sa_sock_is_live "$_sa_fixed_sock"			|| return 1

	export SA_ORIG_SOCK="$SSH_AUTH_SOCK"
	export SSH_AUTH_SOCK="$_sa_fixed_sock"
}

_sa_find_alternate_sock ()
{
	[ $# -eq 0 ] && return 1
	local sock= file_clauses=''

	# all remaining params are PIDs to ignore
	while [ $# -gt 0 ]; do
		file_clauses="$file_clauses -not -name agent.$1"
		shift
	done

	# search in directories that look like ssh-agent dirs
	find $( find /tmp -maxdepth 1 -type d -name ssh-\* -user $(id -un) ) -type s $file_clauses |\
		while read sock; do
			# verify socket is live
			if _sa_sock_is_live $sock; then
				echo $sock
				return 0
			fi
		done
	# no alternate found
	return 1
}

# called at logout to repoint the symlink at some socket that's not getting
#   nuked when this session ends
_sa_repoint_sock_link ()
{
	[ ! -e $_sa_fixed_sock ] && return 0

	local curr_sock_pid='' curr_fixed_pid='' alt_sock=''

	curr_sock_pid=$(_sa_current_session_pid)			|| return 1
	curr_fixed_pid=$(_sa_pid_of_sock $_sa_fixed_sock)	|| return 1

	# no-op if socket didn't come from current session
	[ -n "$curr_sock_pid" -a "$curr_sock_pid" -ne "$curr_fixed_pid" ] && return 0

	# find some other socket to use, relink
	alt_sock=$(_sa_find_alternate_sock $curr_sock_pid)	|| return 1
	_sa_link_fixed_sock "$alt_sock"
}

# done