feat: Enable reading env vars from files (#4359)

Co-authored-by: Brennan Kinney <5098581+polarathene@users.noreply.github.com>
Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

test/tests/parallel/set3/container_configuration/env_vars_from_files.bats

@@ -0,0 +1,89 @@
+load "${REPOSITORY_ROOT}/test/helper/setup"
+load "${REPOSITORY_ROOT}/test/helper/common"
+
+# Feature (ENV value sourced from file):
+# - An ENV with a `__FILE` suffix will read a value from a referenced file path to set the actual ENV (assuming it is empty)
+# - Feature implemented at: `variables-stack.sh:__environment_variables_from_files()`
+# - Feature PR: https://github.com/docker-mailserver/docker-mailserver/pull/4359
+
+BATS_TEST_NAME_PREFIX='[Configuration] (ENV __FILE support) '
+CONTAINER1_NAME='dms-test_env-files_success'
+CONTAINER2_NAME='dms-test_env-files_warning'
+CONTAINER3_NAME='dms-test_env-files_error'
+
+function setup_file() {
+  export CONTAINER_NAME
+  export FILEPATH_VALID='/tmp/file-with-value'
+  export FILEPATH_INVALID='/path/to/non-existent-file'
+  # Each `_init_with_defaults` call updates the `TEST_TMP_CONFIG` location to create a container specific file:
+  local FILE_WITH_VALUE
+
+  # ENV is set via file content (valid file path):
+  CONTAINER_NAME=${CONTAINER1_NAME}
+  _init_with_defaults
+  FILE_WITH_VALUE=${TEST_TMP_CONFIG}/test_secret
+  echo 1 > "${FILE_WITH_VALUE}"
+  local CUSTOM_SETUP_ARGUMENTS=(
+    --env ENABLE_POP3__FILE="${FILEPATH_VALID}"
+    -v "${FILE_WITH_VALUE}:${FILEPATH_VALID}"
+  )
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
+
+  # ENV is already set explicitly, a warning should be logged:
+  CONTAINER_NAME=${CONTAINER2_NAME}
+  _init_with_defaults
+  FILE_WITH_VALUE=${TEST_TMP_CONFIG}/test_secret
+  echo 1 > "${FILE_WITH_VALUE}"
+  local CUSTOM_SETUP_ARGUMENTS=(
+    --env ENABLE_POP3="0"
+    --env ENABLE_POP3__FILE="${FILEPATH_VALID}"
+    -v "${FILE_WITH_VALUE}:${FILEPATH_VALID}"
+  )
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
+
+  # ENV is not set by file content (invalid file path):
+  CONTAINER_NAME=${CONTAINER3_NAME}
+  _init_with_defaults
+  local CUSTOM_SETUP_ARGUMENTS=(
+    --env ENABLE_POP3__FILE="${FILEPATH_INVALID}"
+  )
+  _common_container_setup 'CUSTOM_SETUP_ARGUMENTS'
+}
+
+function teardown_file() {
+  docker rm -f "${CONTAINER1_NAME}" "${CONTAINER2_NAME}" "${CONTAINER3_NAME}"
+}
+
+@test "ENV can be set from a file" {
+  export CONTAINER_NAME=${CONTAINER1_NAME}
+
+  # /var/log/mail/mail.log is not equivalent to stdout content,
+  # Relevant log content only available via docker logs:
+  run docker logs "${CONTAINER_NAME}"
+  assert_success
+  assert_line --partial "Getting secret 'ENABLE_POP3' from '${FILEPATH_VALID}'"
+
+  # Verify ENABLE_POP3 was enabled (disabled by default), by checking this file path is valid:
+  _run_in_container [ -f /etc/dovecot/protocols.d/pop3d.protocol ]
+  assert_success
+}
+
+@test "Non-empty ENV have precedence over their __FILE variant" {
+  export CONTAINER_NAME=${CONTAINER2_NAME}
+
+  # /var/log/mail/mail.log is not equivalent to stdout content,
+  # Relevant log content only available via docker logs:
+  run docker logs "${CONTAINER_NAME}"
+  assert_success
+  assert_line --partial "ENV value will not be sourced from 'ENABLE_POP3__FILE' since 'ENABLE_POP3' is already set"
+}
+
+@test "Referencing a non-existent file logs an error" {
+  export CONTAINER_NAME=${CONTAINER3_NAME}
+
+  # /var/log/mail/mail.log is not equivalent to stdout content,
+  # Relevant log content only available via docker logs:
+  run docker logs "${CONTAINER_NAME}"
+  assert_success
+  assert_line --partial "File defined for secret 'ENABLE_POP3' with path '${FILEPATH_INVALID}' does not exist"
+}