Add bin/mbsync_cron.sh: Make mbsync+pass works well with cron

This script is suitable with a `cron` task to periodically sync emails using
the `mbsync`, which invokes `pass` to get the account password stored in
GPG-encrypted format.

This script works around the `gpg-agent` usage with `cron`.

1 files changed, 177 insertions, 0 deletions

diff --git a/bin/mbsync_cron.sh b/bin/mbsync_cron.sh
new file mode 100755
index 0000000..fd435db
--- /dev/null
+++ b/bin/mbsync_cron.sh
@@ -0,0 +1,177 @@
+#!/bin/sh
+#
+# Copyright (c) 2017 Aaron LI <aly@aaronly.me>
+# MIT license
+#
+# Get new mails and sync IMAP folders using `mbsync` with `cron`.
+#
+# Since the passwords are managed using `pass` which encrypts them using
+# `gpg`, therefore, `gpg-agent` will be periodically triggered to ask user
+# for the passphrase to decrypt the stored passwords, which is annoying
+# for the cron tasks.
+#
+# Workaround the `gpg-agent` asking for passphrase by testing its current
+# status about the cached passphrase, i.e., with *pinentry* disabled
+# (by passing the `--pinentry-mode error` to `gpg`), invoke `gpg` to try
+# to sign a message, if it succeed, then the necessary passphrase has
+# already been cached by `gpg-agent`.
+#
+# Reference:
+# * Programmatically determine if gpg-agent will ask for passphrase
+#   https://superuser.com/a/1212720/731908
+#
+# Aaron LI
+# 2017-05-28
+#
+
+set -e
+
+# Workaround to make `notify-send` work with cron
+# Credit: https://stackoverflow.com/a/16520076
+export DISPLAY=:0
+export XAUTHORITY="${HOME}/.Xauthority"
+
+PROG="${0##*/}"
+
+LOGFILE="/dev/null"
+
+# The GPG key used by `pass`
+GPG_KEY="aly@aaronly.me"
+
+# Command to send notification
+NOTIFY_CMD="notify-send"
+
+
+error() {
+    echo "$*" >&2
+}
+
+log() {
+    echo "[$(date --iso-8601=seconds)] $*" >> ${LOGFILE}
+}
+
+exists() {
+    command -v "$1" >/dev/null 2>&1
+}
+
+# Check if a process id (PID) exists
+# Credit: https://stackoverflow.com/a/3044045
+is_running() {
+    kill -0 "$1" >/dev/null 2>&1
+}
+
+notify() {
+    local message="$1"
+    if exists ${NOTIFY_CMD}; then
+        command ${NOTIFY_CMD} ${PROG} "${message}"
+    fi
+}
+
+usage() {
+    error "usage: ${PROG} <account>"
+}
+
+
+# Check whether `gpg-agent` already cached the needed passphrase,
+# if return 0 (i.e., success), then the passphrase is already cached,
+# then `pass` can decrypt the password without triggering `gpg-agent`
+# to ask user for the passphrase.
+check_cached_passphrase() {
+    local key="$1"
+    echo "test" | \
+        gpg2 --sign --batch --no-tty --pinentry-mode error \
+             --local-user ${key} -o /dev/null >/dev/null 2>&1
+}
+
+
+# Check the network availability and remote server online status.
+# FIXME: need test IMAP connection instead of ping the server...
+check_server() {
+    local server="$1"
+    ping -c 3 ${server} >/dev/null 2>&1
+}
+
+
+case "$1" in
+    aly|weitian|webmaster)
+        ACCOUNT="$1"
+        SERVER="mail.aaronly.me"
+        ;;
+    autistici)
+        ACCOUNT="$1"
+        SERVER="mail.autistici.org"
+        ;;
+    lavabit)
+        ACCOUNT="$1"
+        SERVER="imap.lavabit.com"
+        ;;
+    outlook-aly|outlook-li)
+        ACCOUNT="$1"
+        SERVER="imap-mail.outlook.com"
+        ;;
+    gmail-aly|gmail-li)
+        ACCOUNT="$1"
+        SERVER="imap.gmail.com"
+        ;;
+    sjtu)
+        ACCOUNT="$1"
+        SERVER="imap.sjtu.edu.cn"
+        ;;
+    foxmail)
+        ACCOUNT="$1"
+        SERVER="imap.qq.com"
+        ;;
+    -h|--help)
+        usage
+        exit 1
+        ;;
+    *)
+        error "Invalid account name!"
+        usage
+        exit 1
+        ;;
+esac
+
+# PID file for `mbsync`, which may just hang and lock the mailbox
+PIDFILE="${HOME}/.cache/mbsync.${ACCOUNT}.pid"
+
+# Log file to record the sync information
+LOGFILE="${HOME}/.cache/mbsync.${ACCOUNT}.log"
+[ ! -f ${LOGFILE} ] && touch ${LOGFILE}
+log "-----------------------------------"
+
+
+if ! check_cached_passphrase ${GPG_KEY}; then
+    log "GPG passphrase not cached! Skip sync mail."
+    notify "GPG passphrase not cached! Skip sync mail."
+    exit 2
+fi
+
+#if ! check_server ${SERVER}; then
+#    log "Network not available or remote server ${SERVER} is offline!"
+#    notify "Network not available or remote server ${SERVER} is offline!"
+#    exit 3
+#fi
+
+if [ -f "${PIDFILE}" ]; then
+    PID=$(cat ${PIDFILE})
+    if is_running ${PID} && ! kill ${PID} >/dev/null 2>&1; then
+        log "Cannot kill process: ${PID}"
+        notify "Cannot kill process: ${PID}"
+    else
+        log "Killed previous instance: ${PID}"
+        notify "Killed previous instance: ${PID}"
+    fi
+fi
+
+log "Sync mail for account: ${ACCOUNT} ..."
+notify "Sync mail for account: ${ACCOUNT} ..."
+mbsync -V "${ACCOUNT}" >>${LOGFILE} 2>&1 &
+#sleep 10 &
+PID=$!
+echo ${PID} > ${PIDFILE}
+wait ${PID}
+rm ${PIDFILE}
+
+log "Finish syncing mail for account: ${ACCOUNT}!"
+notify "Finish syncing mail for account: ${ACCOUNT}!"