From b09eb3451192ca82b8d841de73b80d7e4b23caec Mon Sep 17 00:00:00 2001
From: Erich Eckner <git@eckner.net>
Date: Mon, 9 Apr 2018 12:59:39 +0200
Subject: digest-mailer.in: -f = flush new

---
 digest-mailer.in | 97 +++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 75 insertions(+), 22 deletions(-)

diff --git a/digest-mailer.in b/digest-mailer.in
index ec333c8..b62b57c 100644
--- a/digest-mailer.in
+++ b/digest-mailer.in
@@ -6,11 +6,26 @@ verwendung() {
   >&2 echo 'digest-mailer collects emails into digests before sending them.'
   >&2 echo ''
   >&2 echo 'Usage: digest-mailer [OPTIONS]'
+  >&2 echo '  -f:'
+  >&2 echo '    flush all pending emails'
+  >&2 echo '  -f $receiver:'
+  >&2 echo '    flush pending emails to $receiver (hash)'
   >&2 echo \
 '#HELPTEXT#    #'
   exit 1
 }
 
+extract_receiver_hash() {
+  sed -n '
+    /^$/q
+    s/^To:\s*//
+    T
+    p
+  ' | \
+    sha224sum | \
+    awk '{print $1}'
+}
+
 if [ "x$1" = 'x--help' ]; then
   verwendung
 fi
@@ -20,6 +35,19 @@ if [ "x$1" = 'x--version' ]; then
   exit
 fi
 
+if [ "x$1" = 'x-f' ]; then
+  flush=true
+  shift
+  if [ $# -eq 0 ]; then
+    receiver=''
+  else
+    receiver="$1"
+    shift
+  fi
+else
+  flush=false
+fi
+
 if [ $# -ne 0 ]; then
   verwendung
 fi
@@ -34,33 +62,56 @@ then
   . '#ETCDIR#/digest-mailer.conf'
 fi
 
-message=$(
-  cat
-)
 sender=$(
   whoami | \
     sha224sum | \
     awk '{print $1}'
 )
-receiver=$(
-  printf '%s\n' "${message}" | \
-    sed -n '
-      /^$/q
-      s/^To:\s*//
-      T
-      p
-    ' | \
-    sha224sum | \
-    awk '{print $1}'
-)
+if ${flush} && \
+  [ -z "${receiver}" ]; then
+  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.flush.from.'"${sender}"'.lock'
+  if ! flock -n 9; then
+    # silently fail if lock is not available ("flush" is not _that_ important)
+    exit
+  fi
+  find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
+    -regex ".*/${sender}\.[0-9a-f]\+\.[0-9]\+\.[0-9a-f]\+\$" | \
+    while read -r file; do
+      extract_receiver_hash < "${file}"
+    done | \
+    sort -u | \
+    xargs -rn1 "$0" -f
+  exit
+fi
+
 time=$(
   date +%s
 )
-hash=$(
-  printf '%s' "${message}" | \
-    sha224sum | \
-    awk '{print $1}'
-)
+if ! ${flush}; then
+  message=$(
+    cat
+  )
+  receiver=$(
+    printf '%s\n' "${message}" | \
+      extract_receiver_hash
+  )
+  hash=$(
+    printf '%s' "${message}" | \
+      sha224sum | \
+      awk '{print $1}'
+  )
+  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.from.'"${sender}"'.to.'"${receiver}"'.lock'
+  flock 9
+  # we block if that lock is not available - the sender expects his mails delivered!
+  printf '%s' "${message}" > "#LIBDIR#/digest-mailer/${sender}.${receiver}.${time}.${hash}"
+else
+  exec 9> '#LIBDIR#/digest-mailer/digest-mailer.from.'"${sender}"'.to.'"${receiver}"'.lock'
+  if ! flock -n 9; then
+    # silently fail if lock is not available ("flush" is not _that_ important)
+    exit
+  fi
+fi
+
 if [ -s "#LIBDIR#/digest-mailer/${sender}.${receiver}.last-sent" ]; then
   last_sent=$(
     cat "#LIBDIR#/digest-mailer/${sender}.${receiver}.last-sent"
@@ -69,8 +120,6 @@ else
   last_sent='0'
 fi
 
-printf '%s' "${message}" > "#LIBDIR#/digest-mailer/${sender}.${receiver}.${time}.${hash}"
-
 first_unsent=$(
   find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
     -regex ".*/${sender}\.${receiver}\.[0-9]\+\.[0-9a-f]\+\$" \
@@ -79,7 +128,11 @@ first_unsent=$(
     sort -nr | \
     tail -n1
 )
-
+if ${flush} && \
+  [ -z "${first_unsent}" ]; then
+  # no pending emails at all
+  exit
+fi
 to_send=$(
   find '#LIBDIR#/digest-mailer' -regextype grep -maxdepth 1 -mindepth 1 \
     -regex ".*/${sender}\.${receiver}\.[0-9]\+\.[0-9a-f]\+\$" | \
-- 
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