Add ability to render the template config files.

config/config.go

@@ -163,27 +163,35 @@ func (cfg *rawConfig) parseTasks() ([]*tasks.Task, error) {
 	return tasks, nil
 }
 
-// ParseConfig parses a raw config flag
-func ParseConfig(configFlag string) (*Config, error) {
-	if configFlag == "" {
-		return nil, errors.New("-config flag is required")
+// RenderConfig renders the templated config in configFlag to renderFlag.
+func RenderConfig(configFlag, renderFlag string) error {
+	template, err := renderConfigTemplate(configFlag)
+	if err != nil {
+		return err
 	}
 
-	var data []byte
-	if strings.HasPrefix(configFlag, "file://") {
+	// Save the template, either to stdout or to file://...
+	if renderFlag == "-" {
+		fmt.Printf("%s", template)
+	} else if strings.HasPrefix(renderFlag, "file://") {
 		var err error
-		fName := strings.SplitAfter(configFlag, "file://")[1]
-		if data, err = ioutil.ReadFile(fName); err != nil {
-			return nil, fmt.Errorf("Could not read config file: %s", err)
+		fName := strings.SplitAfter(renderFlag, "file://")[1]
+		if err = ioutil.WriteFile(fName, template, 0644); err != nil {
+			return fmt.Errorf("Could not write config file: %s", err)
 		}
 	} else {
-		data = []byte(configFlag)
+		return fmt.Errorf("-render flag is invalid: '%s'", renderFlag)
 	}
 
-	template, err := ApplyTemplate(data)
+	return nil
+}
+
+// ParseConfig parses a raw config flag
+func ParseConfig(configFlag string) (*Config, error) {
+
+	template, err := renderConfigTemplate(configFlag)
 	if err != nil {
-		return nil, fmt.Errorf(
-			"Could not apply template to config: %v", err)
+		return nil, err
 	}
 	configMap, err := unmarshalConfig(template)
 	if err != nil {
@@ -270,6 +278,27 @@ func ParseConfig(configFlag string) (*Config, error) {
 	return cfg, nil
 }
 
+func renderConfigTemplate(configFlag string) ([]byte, error) {
+	if configFlag == "" {
+		return nil, errors.New("-config flag is required")
+	}
+	var data []byte
+	if strings.HasPrefix(configFlag, "file://") {
+		var err error
+		fName := strings.SplitAfter(configFlag, "file://")[1]
+		if data, err = ioutil.ReadFile(fName); err != nil {
+			return nil, fmt.Errorf("Could not read config file: %s", err)
+		}
+	} else {
+		data = []byte(configFlag)
+	}
+	template, err := ApplyTemplate(data)
+	if err != nil {
+		err = fmt.Errorf("Could not apply template to config: %v", err)
+	}
+	return template, err
+}
+
 func unmarshalConfig(data []byte) (map[string]interface{}, error) {
 	var config map[string]interface{}
 	if err := json.Unmarshal(data, &config); err != nil {

config/template_test.go

@@ -1,8 +1,15 @@
 package config
 
 import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"reflect"
+	"strings"
 	"testing"
+
+	// need to import this so that we have a registered backend
+	_ "github.com/joyent/containerpilot/discovery/consul"
 )
 
 func TestParseEnvironment(t *testing.T) {
@@ -28,6 +35,74 @@ func TestTemplate(t *testing.T) {
 	validateTemplate(t, "Regex Replace All", `Hello, {{.NAME | regexReplaceAll "[epa]+" "_" }}!`, env, "Hello, T_m_l_t_!")
 }
 
+func TestInvalidRenderConfigFile(t *testing.T) {
+	testRenderExpectError(t, "file:///xxxx", "-",
+		"Could not read config file: open /xxxx: no such file or directory")
+}
+
+func TestInvalidRenderFileConfig(t *testing.T) {
+	var testJSON = `{"consul": "consul:8500"}`
+	testRenderExpectError(t, testJSON, "file:///a/b/c/d/e/f.json",
+		"Could not write config file: open /a/b/c/d/e/f.json: no such file or directory")
+}
+
+func TestRenderConfigFileStdout(t *testing.T) {
+
+	var testJSON = `{
+	"consul": "consul:8500",
+	"backends": [{
+					"name": "upstreamA",
+					"poll": 11,
+					"onChange": "/bin/to/onChangeEvent/for/upstream/A.sh"}]}`
+
+	// Render to file
+	defer os.Remove("testJSON.json")
+	if err := RenderConfig(testJSON, "file://testJSON.json"); err != nil {
+		t.Fatalf("Expected no error from renderConfigTemplate but got: %v", err)
+	}
+	if exists, err := fileExists("testJSON.json"); !exists || err != nil {
+		t.Errorf("Expected file testJSON.json to exist.")
+	}
+
+	// Render to stdout
+	fname := filepath.Join(os.TempDir(), "stdout")
+	temp, _ := os.Create(fname)
+	old := os.Stdout
+	os.Stdout = temp
+	if err := RenderConfig(testJSON, "-"); err != nil {
+		t.Fatalf("Expected no error from renderConfigTemplate but got: %v", err)
+	}
+	temp.Close()
+	os.Stdout = old
+
+	renderedOut, _ := ioutil.ReadFile(fname)
+	renderedFile, _ := ioutil.ReadFile("testJSON.json")
+	if string(renderedOut) != string(renderedFile) {
+		t.Fatalf("Expected the rendered file and stdout to be identical")
+	}
+}
+
+func TestRenderedConfigIsParseable(t *testing.T) {
+
+	var testJSON = `{
+	"consul": "consul:8500",
+	"backends": [{
+					"name": "upstreamA{{.TESTRENDERCONFIGISPARSEABLE}}",
+					"poll": 11,
+					"onChange": "/bin/to/onChangeEvent/for/upstream/A.sh"}]}`
+
+	os.Setenv("TESTRENDERCONFIGISPARSEABLE", "-ok")
+	template, _ := renderConfigTemplate(testJSON)
+	config, err := ParseConfig(string(template))
+	if err != nil {
+		t.Fatalf("Unexpected error in ParseConfig: %v", err)
+	}
+	name := config.Backends[0].Name
+	if name != "upstreamA-ok" {
+		t.Fatalf("Expected Backend[0] name to be upstreamA-ok but got %s", name)
+	}
+}
+
 // Helper Functions
 
 func validateParseEnvironment(t *testing.T, message string, environ []string, expected Environment) {
@@ -51,3 +126,21 @@ func validateTemplate(t *testing.T, name string, template string, env Environmen
 		t.Fatalf("%s - Expected %s but got: %s", name, expected, strRes)
 	}
 }
+
+func testRenderExpectError(t *testing.T, testJSON, render, expected string) {
+	err := RenderConfig(testJSON, render)
+	if err == nil || !strings.Contains(err.Error(), expected) {
+		t.Errorf("Expected %s but got %s", expected, err)
+	}
+}
+
+func fileExists(path string) (bool, error) {
+	_, err := os.Stat(path)
+	if err == nil {
+		return true, nil
+	}
+	if os.IsNotExist(err) {
+		return false, nil
+	}
+	return true, err
+}

core/app.go

@@ -63,10 +63,16 @@ func LoadApp() (*App, error) {
 
 	var configFlag string
 	var versionFlag bool
+	var renderFlag string
+	var templateFlag bool
 
 	if !flag.Parsed() {
 		flag.StringVar(&configFlag, "config", "",
 			"JSON config or file:// path to JSON config file.")
+		flag.BoolVar(&templateFlag, "template", false,
+			"Render template and quit. (default: false)")
+		flag.StringVar(&renderFlag, "out", "-",
+			"-(default) for stdout or file:// path where to save rendered JSON config file.")
 		flag.BoolVar(&versionFlag, "version", false, "Show version identifier and quit.")
 		flag.Parse()
 	}
@@ -77,6 +83,14 @@ func LoadApp() (*App, error) {
 	if configFlag == "" {
 		configFlag = os.Getenv("CONTAINERPILOT")
 	}
+	if templateFlag {
+
+		err := config.RenderConfig(configFlag, renderFlag)
+		if err != nil {
+			return nil, err
+		}
+		os.Exit(0)
+	}
 
 	os.Setenv("CONTAINERPILOT_PID", fmt.Sprintf("%v", os.Getpid()))
 	app, err := NewApp(configFlag)