Check that org.freedesktop.resolve1 is available

and short-circuit with an error message about requiring systemd >= 229
if it is unavailable.

Incidental changes:

    1. Ensure that the test runner sources the "update-systemd-resolved"
       script that lives in this repository, rather than one that might
       live somewhere in PATH, and
    2. Update the test runner's "logger" function to support reading
       messages from stdin.

Author: tomeon

run-tests

@@ -31,7 +31,35 @@ RUNTEST_CALLED=0
 
 AUTOMATED_TESTING=1
 
+# Used for determining which "update-systemd-resolved" we are supposed to
+# source
+if ! TOPLEVEL="$(git rev-parse --show-toplevel 2>/dev/null)"; then
+  if ! [[ "${BASH_SOURCE[0]}" == */* ]]; then
+    if ! TOPLEVEL="${PWD:-$(pwd 2>/dev/null)}"; then
+      TOPLEVEL=.
+    fi
+  else
+    TOPLEVEL="${BASH_SOURCE[0]%/*}"
+  fi
+fi
+
 function busctl {
+  # Short-circuit if we got "busctl status <...>".  If TEST_BUSCTL_STATUS_RC is
+  # unset or empty, assume this is the call from the "main" function in
+  # update-systemd-resolved, rather than an automated test checking the
+  # behaviour of "busctl status <...>".
+  case "${1:-}" in
+    status)
+      if [[ -n "${TEST_BUSCTL_STATUS_RC:-}" ]]; then
+        busctl_called=1
+        _log "busctl status: returning ${TEST_BUSCTL_STATUS_RC}"
+        return "$TEST_BUSCTL_STATUS_RC"
+      else
+        return 0
+      fi
+      ;;
+  esac
+
   shift 4
   _log "busctl called with: ${@}"
   # Set that busctl has been called
@@ -96,9 +124,17 @@ function resolvectl {
 }
 
 function logger {
-  # Remove standard options
-  local message="$*"
-  _log "-- ${message##* -- }"
+  local message
+
+  if [[ "$*" == *' --' ]] && ! [[ -t 0 ]]; then
+    while read -r message; do
+      _log "$message"
+    done
+  else
+    # Remove standard options
+    message="$*"
+    _log "-- ${message##* -- }"
+  fi
 }
 
 function exit {
@@ -130,7 +166,7 @@ function runtest {
 
   # Source, don't run, so we don't need to export and internal functions override
   # external calls out to system commands
-  source update-systemd-resolved
+  source "${TOPLEVEL?}/update-systemd-resolved"
   exit_status="$?"
   exit_message="script exited with a ${exit_status} exit status"
 
@@ -164,6 +200,7 @@ for TEST in tests/*.sh; do
   TEST_BUSCTL_DNS=""
   TEST_BUSCTL_DOMAINS=""
   TEST_BUSCTL_DNSSEC=""
+  TEST_BUSCTL_STATUS_RC=""
   # Keep this random, as we will never know the ifindex up-front
   ip_ifindex=$((RANDOM%=64))
   # Clear foreign_option_*

tests/23_resolve1_dbus_presence.sh

@@ -0,0 +1,9 @@
+script_type="up"
+dev="tun23"
+
+TEST_TITLE='Error if "busctl status org.freedesktop.resolve1" fails'
+TEST_BUSCTL_CALLED=1
+
+# Mocked-up busctl function will return exit code 1 upon "busctl status <...>"
+TEST_BUSCTL_STATUS_RC=1
+EXPECT_FAILURE=1

update-systemd-resolved

@@ -44,6 +44,10 @@ usage() {
   err "${1:?${1}. }. Usage: ${SCRIPT_NAME} up|down device_name."
 }
 
+busctl_status() {
+  busctl status "$DBUS_DEST"
+}
+
 busctl_call() {
   # Preserve busctl's exit status
   busctl call "$DBUS_DEST" "$DBUS_NODE" "${DBUS_DEST}.Manager" "$@" || {
@@ -404,6 +408,15 @@ main() {
   local dev="${1:-$dev}"
   shift
 
+  busctl_status &>/dev/null || {
+    local -i status=$?
+    emerg <<ERR
+systemd-resolved DBus interface (${DBUS_DEST}) is not available.
+$SCRIPT_NAME requires systemd version 229 or above.
+ERR
+    return $status
+  }
+
   if [[ -z "$script_type" ]]; then
     usage 'No script type specified'
     return 1