lang: Add file function for reading files

examples/lang/file0.mcl

@@ -0,0 +1,8 @@
+$confdir = defaultenv("CONFDIR", ".")
+$tmpdir = defaultenv("TMPDIR", "/tmp")
+
+$values = struct{somevalue => "somevalue",}
+
+file "${tmpdir}/file0.txt" {
+	content => template(file("${confdir}/examples/lang/file0.txt.tmpl"), $values),
+}

examples/lang/file0.txt.tmpl

@@ -0,0 +1 @@
+This is a template file with some value: {{.somevalue}}

integration/file_function_test.go

@@ -0,0 +1,107 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package integration
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestFileFunc verifies the file function works as expected
+func TestFileFunc(t *testing.T) {
+	// create an mgmt test environment and ensure cleanup/debug logging on failure/exit
+	m := Instance{}
+	defer m.Cleanup(t)
+
+	// start a mgmt instance running in the background
+	m.RunBackground(t)
+	m.WaitUntilConverged(t)
+
+	// create template file to be read
+	m.WorkdirWriteToFile(t, "file0.txt.tmpl", "This is a template file with some value: {{.somevalue}}")
+
+	// deploy
+	m.DeployLangFile(t, "lang/file0.mcl")
+	m.WaitUntilConverged(t)
+
+	text, _ := m.WorkdirReadFromFile(t, "file0.txt")
+	assert.Equal(t, "This is a template file with some value: somevalue", text)
+}
+
+// TestFileFuncStream verifies the file function updates when template is changed
+func TestFileFuncStream(t *testing.T) {
+	// create an mgmt test environment and ensure cleanup/debug logging on failure/exit
+	m := Instance{}
+	defer m.Cleanup(t)
+
+	// start a mgmt instance running in the background
+	m.RunBackground(t)
+	m.WaitUntilConverged(t)
+
+	// create template file to be read
+	m.WorkdirWriteToFile(t, "file0.txt.tmpl", "This is a template file with some value: {{.somevalue}}")
+
+	m.DeployLangFile(t, "lang/file0.mcl")
+	m.WaitUntilConverged(t)
+
+	text, _ := m.WorkdirReadFromFile(t, "file0.txt")
+	assert.Equal(t, "This is a template file with some value: somevalue", text)
+
+	// change template file to be read
+	m.WorkdirWriteToFile(t, "file0.txt.tmpl", "This is a template file with some other value: {{.somevalue}}")
+	m.WaitUntilConverged(t)
+
+	text2, _ := m.WorkdirReadFromFile(t, "file0.txt")
+	assert.Equal(t, "This is a template file with some other value: somevalue", text2)
+}
+
+// TestFileFuncNonExist verifies if the file function can cope with non-existing files
+func TestFileFuncNonExist(t *testing.T) {
+	// create an mgmt test environment and ensure cleanup/debug logging on failure/exit
+	m := Instance{}
+	defer m.Cleanup(t)
+
+	// start a mgmt instance running in the background
+	m.RunBackground(t)
+	m.WaitUntilConverged(t)
+
+	// deploy
+	m.DeployLangFile(t, "lang/file0.mcl")
+	m.WaitUntilConverged(t)
+
+	var text string
+
+	// TODO: file doesn't get created because file() hasn't returned output yet, inconsistent with behaviour regarding to files that go out of existence.
+	// text, _ = m.WorkdirReadFromFile(t, "file0.txt")
+	// assert.Equal(t, "", text)
+
+	// create template file to be read
+	m.WorkdirWriteToFile(t, "file0.txt.tmpl", "This is a template file with some value: {{.somevalue}}")
+	m.WaitUntilConverged(t)
+
+	text, _ = m.WorkdirReadFromFile(t, "file0.txt")
+	assert.Equal(t, "This is a template file with some value: somevalue", text)
+
+	m.WorkdirRemoveFile(t, "file0.txt.tmpl")
+	m.WaitUntilConverged(t)
+
+	text, _ = m.WorkdirReadFromFile(t, "file0.txt")
+	assert.Equal(t, "", text)
+
+}