Merge pull request #1017 from mvk/sshagent_plugin

reference implementation of #1016

plugins/available/sshagent.plugin.bash

@@ -0,0 +1,144 @@
+#!/usr/bin/env bash
+cite about-plugin
+about-plugin 'sshagent helper functions'
+
+function _get_sshagent_pid_from_env_file() {
+  local env_file="${1}"
+  [[ -r "${env_file}" ]] || {
+    echo "";
+    return
+  }
+  tail -1 "${env_file}" \
+  | cut -d' ' -f4 \
+  | cut -d';' -f1
+}
+
+function _get_process_status_field() {
+  # uses /proc filesystem
+  local \
+    pid \
+    status_file \
+    field
+  pid="${1}"
+  field="${2}"
+  status_file="/proc/${pid}/status"
+  if ! ([[ -d "${status_file%/*}" ]] \
+    && [[ -r "${status_file}" ]]); then
+    echo ""; return;
+  fi
+  grep "${field}:" "${status_file}" \
+  | cut -d':' -f2 \
+  | sed -e 's/[[:space:]]\+//g' \
+  | cut -d'(' -f1
+}
+
+function _is_item_in_list() {
+  local item
+  for item in "${@:1}"; do
+    if [[ "${item}" == "${1}" ]]; then
+      return 1
+    fi
+  done
+  return 0
+}
+
+
+function _is_proc_alive_at_pid() {
+  local \
+    pid \
+    expected_name \
+    actual_name \
+    actual_state
+  pid="${1?}"
+  expected_name="ssh-agent"
+  # we want to exclude: X (killed), T (traced), Z (zombie)
+  actual_name=$(_get_process_status_field "${pid}" "Name")
+  [[ "${expected_name}" == "${actual_name}" ]] || return 1
+  actual_state=$(_get_process_status_field "${pid}" "State")
+  if _is_item_in_list "${actual_state}" "X" "T" "Z"; then
+    return 1
+  fi
+  return 0
+}
+
+
+function _ensure_valid_sshagent_env() {
+  local \
+    agent_pid \
+    tmp_res
+
+  mkdir -p "${HOME}/.ssh"
+  type restorecon &> /dev/null
+  tmp_res="$?"
+
+  if [[ "${tmp_res}" -eq 0 ]]; then
+    restorecon -rv "${HOME}/.ssh"
+  fi
+
+  # no env file -> shoot a new agent
+  if ! [[ -r "${SSH_AGENT_ENV}" ]]; then
+    ssh-agent > "${SSH_AGENT_ENV}"
+    return
+  fi
+
+  ## do not trust pre-existing SSH_AGENT_ENV
+  agent_pid=$(_get_sshagent_pid_from_env_file "${SSH_AGENT_ENV}")
+  if [[ -z "${agent_pid}" ]]; then
+    # no pid detected -> shoot a new agent
+    ssh-agent > "${SSH_AGENT_ENV}"
+    return
+  fi
+
+  ## do not trust SSH_AGENT_PID
+  if _is_proc_alive_at_pid "${agent_pid}"; then
+    return
+  fi
+
+  echo "There's a dead ssh-agent at the landing..."
+  ssh-agent > "${SSH_AGENT_ENV}"
+  return
+}
+
+
+function _ensure_sshagent_dead() {
+  [[ -r "${SSH_AGENT_ENV}" ]] \
+  || return ## no agent file - no problems
+  ## ensure the file indeed points to a really running agent:
+  agent_pid=$(
+    _get_sshagent_pid_from_env_file \
+    "${SSH_AGENT_ENV}"
+  )
+
+  [[ -n "${agent_pid}" ]] \
+  || return # no pid - no problem
+
+  _is_proc_alive_at_pid "${agent_pid}" \
+  || return # process is not alive - no problem
+
+  echo -e -n "Killing ssh-agent (pid:${agent_pid}) ... "
+  kill -9 "${agent_pid}" && echo "DONE" || echo "FAILED"
+  rm -f "${SSH_AGENT_ENV}"
+}
+
+
+function sshagent() {
+  about 'ensures ssh-agent is up and running'
+  param '1: on|off '
+  example '$ sshagent on'
+  group 'ssh'    
+  [[ -v SSH_AGENT_ENV ]] \
+  || export SSH_AGENT_ENV="${HOME}/.ssh/agent_env.${HOSTNAME}"
+
+  case "${1}" in
+    on) _ensure_valid_sshagent_env;
+      # shellcheck disable=SC1090
+      source "${SSH_AGENT_ENV}" > /dev/null;
+      ;;
+    off) _ensure_sshagent_dead
+      ;;
+    *)
+      ;;
+  esac
+}
+
+sshagent on