use swaks now instead of nc

The wrapper is made so custon options can be applied with flags, and
common arguments are defaults. The actual invocation is easy to read but
requires the e-mail files to be adjusted. This will happen in a latter
commit.

target/scripts/build/packages.sh

@@ -80,7 +80,7 @@ function _install_packages() {
   # `bind9-dnsutils` provides the `dig` command
   # `iputils-ping` provides the `ping` command
   DEBUG_PACKAGES=(
-    bind9-dnsutils iputils-ping less nano
+    bind9-dnsutils iputils-ping less nano swaks
   )
 
   apt-get "${QUIET}" --no-install-recommends install \

test/helper/common.bash

@@ -469,5 +469,19 @@ function _print_mail_log_for_id() {
   _run_in_container grep -F "${MAIL_ID}" /var/log/mail.log
 }
 
+# A simple wrapper for netcat (`nc`). This is useful when sending
+# "raw" e-mails or doing IMAP-related work.
+#
+# @param ${1} = the file that is given to `nc`
+# @param ${1} = custom parameters for `nc` [OPTIONAL] (default: 0.0.0.0 25)
+function _nc_wrapper() {
+  local FILE=${1:?Must provide name of template file}
+  local NC_PARAMETERS=${2:-0.0.0.0 25}
+
+  [[ -v CONTAINER_NAME ]] || return 1
+
+  _run_in_container_bash "nc ${NC_PARAMETERS} < ${FILE}"
+}
+
 # ? << Miscellaneous helper functions
 # ! -------------------------------------------------------------------

test/helper/sending.bash

@@ -8,11 +8,14 @@
 # ! ATTENTION: This file requires helper functions from `common.sh`!
 
 # Sends a mail from localhost (127.0.0.1) to a container. To send
-# a custom email, create a file at `test/test-files/<TEST FILE>`,
+# a custom email, create a file at `test/files/<TEST FILE>`,
 # and provide `<TEST FILE>` as an argument to this function.
 #
-# @param ${1} = template file (path) name
+# @param ${1} = template file (path) name without .txt suffix
-# @param ${2} = parameters for `nc` [OPTIONAL] (default: `0.0.0.0 25`)
+#               and without path prefix before the emails directory
+# @param ${2} = config file path name without .cfg suffix
+#               and without path prefix before the emails directory
+#               [OPTIONAL] (default: ${1})
 #
 # ## Attention
 #
@@ -23,17 +26,32 @@
 # send the email but it will not make sure the mail queue is empty after the mail
 # has been sent.
 function _send_email() {
-  local TEMPLATE_FILE=${1:?Must provide name of template file}
+  [[ -v CONTAINER_NAME ]] || return 1
-  local NC_PARAMETERS=${2:-0.0.0.0 25}
 
-  assert_not_equal "${NC_PARAMETERS}" ''
+  local HELO='mail.external.tld'
-  assert_not_equal "${CONTAINER_NAME:-}" ''
+  local FROM='example-user@example.test'
+  local TO='user1@localhost.localdomain'
+  local SERVER='0.0.0.0'
+  local PORT=25
+  local MORE_SWAKS_OPTIONS=()
 
-  _run_in_container_bash "nc ${NC_PARAMETERS} < /tmp/docker-mailserver-test/${TEMPLATE_FILE}.txt"
+  while [[ ${#} -gt 1 ]]; do
-  assert_success
+    case "${1}" in
+      ( '--helo' )   HELO=${2:?--helo given but no argument}     ; shift 2 ;;
+      ( '--from' )   FROM=${2:?--from given but no argument}     ; shift 2 ;;
+      ( '--to' )     TO=${2:?--to given but no argument}         ; shift 2 ;;
+      ( '--server' ) SERVER=${2:?--server given but no argument} ; shift 2 ;;
+      ( '--port' )   PORT=${2:?--port given but no argument}     ; shift 2 ;;
+      ( * )          MORE_SWAKS_OPTIONS+=("${1}")                ; shift 1 ;;
+    esac
+  done
+
+  local TEMPLATE_FILE="/tmp/docker-mailserver-test/emails/${1:?Must provide name of template file}.txt"
+
+  _run_in_container_bash "swaks --server ${SERVER} --port ${PORT} --helo ${HELO} --from ${FROM} --to ${TO} ${MORE_SWAKS_OPTIONS[*]} --data - < ${TEMPLATE_FILE}"
 }
 
-# Like `_send_mail` with two major differences:
+# Like `_send_email` with two major differences:
 #
 # 1. this function waits for the mail to be processed; there is no asynchronicity
 #    because filtering the logs in a synchronous way is easier and safer!
@@ -42,8 +60,8 @@ function _send_email() {
 # No. 2 is especially useful in case you send more than one email in a single
 # test file and need to assert certain log entries for each mail individually.
 #
-# @param ${1} = template file (path) name
+# @param ${1} = template file (path) name without .txt suffix
-# @param ${2} = parameters for `nc` [OPTIONAL] (default: `0.0.0.0 25`)
+# @param ${2} = config file path name without .cfg suffix [OPTIONAL] (default: ${1})
 #
 # ## Attention
 #
@@ -57,17 +75,13 @@ function _send_email() {
 # chosen. Sending more than one mail at any given point in time with this function
 # is UNDEFINED BEHAVIOR!
 function _send_email_and_get_id() {
-  local TEMPLATE_FILE=${1:?Must provide name of template file}
+  [[ -v CONTAINER_NAME ]] || return 1
-  local NC_PARAMETERS=${2:-0.0.0.0 25}
+
+  _wait_for_empty_mail_queue_in_container
+  _send_email "${@}"
+  _wait_for_empty_mail_queue_in_container
+
   local MAIL_ID
-
-  assert_not_equal "${NC_PARAMETERS}" ''
-  assert_not_equal "${CONTAINER_NAME:-}" ''
-
-  _wait_for_empty_mail_queue_in_container
-  _send_email "${TEMPLATE_FILE}"
-  _wait_for_empty_mail_queue_in_container
-
   # The unique ID Postfix (and other services) use may be different in length
   # on different systems (e.g. amd64 (11) vs aarch64 (10)). Hence, we use a
   # range to safely capture it.