chore: tidy up pkgs (#636)

for readability and towards potentially making helmfile usable as a go library

pkg/tmpl/context.go

@@ -0,0 +1,7 @@
+package tmpl
+
+type Context struct {
+	preRender bool
+	basePath  string
+	readFile  func(string) ([]byte, error)
+}

pkg/tmpl/context_funcs.go

@@ -0,0 +1,208 @@
+package tmpl
+
+import (
+	"fmt"
+	"gopkg.in/yaml.v2"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"text/template"
+)
+
+type Values = map[string]interface{}
+
+func (c *Context) createFuncMap() template.FuncMap {
+	funcMap := template.FuncMap{
+		"exec":           c.Exec,
+		"readFile":       c.ReadFile,
+		"toYaml":         ToYaml,
+		"fromYaml":       FromYaml,
+		"setValueAtPath": SetValueAtPath,
+		"requiredEnv":    RequiredEnv,
+		"get":            get,
+		"getOrNil":       getOrNil,
+		"tpl":            c.Tpl,
+	}
+	if c.preRender {
+		// disable potential side-effect template calls
+		funcMap["exec"] = func(string, []interface{}, ...string) (string, error) {
+			return "", nil
+		}
+		funcMap["readFile"] = func(string) (string, error) {
+			return "", nil
+		}
+	}
+
+	return funcMap
+}
+
+func (c *Context) Exec(command string, args []interface{}, inputs ...string) (string, error) {
+	var input string
+	if len(inputs) > 0 {
+		input = inputs[0]
+	}
+
+	strArgs := make([]string, len(args))
+	for i, a := range args {
+		switch a.(type) {
+		case string:
+			strArgs[i] = a.(string)
+		default:
+			return "", fmt.Errorf("unexpected type of arg \"%s\" in args %v at index %d", reflect.TypeOf(a), args, i)
+		}
+	}
+
+	cmd := exec.Command(command, strArgs...)
+	cmd.Dir = c.basePath
+
+	writeErrs := make(chan error)
+	cmdErrs := make(chan error)
+	cmdOuts := make(chan []byte)
+
+	if len(input) > 0 {
+		stdin, err := cmd.StdinPipe()
+		if err != nil {
+			return "", err
+		}
+		go func(input string, stdin io.WriteCloser) {
+			defer stdin.Close()
+			defer close(writeErrs)
+
+			size := len(input)
+
+			var n int
+			var err error
+			i := 0
+			for {
+				n, err = io.WriteString(stdin, input[i:])
+				if err != nil {
+					writeErrs <- fmt.Errorf("failed while writing %d bytes to stdin of \"%s\": %v", len(input), command, err)
+					break
+				}
+				i += n
+				if n == size {
+					break
+				}
+			}
+		}(input, stdin)
+	}
+
+	go func() {
+		defer close(cmdOuts)
+		defer close(cmdErrs)
+
+		bytes, err := cmd.Output()
+		if err != nil {
+			cmdErrs <- fmt.Errorf("exec cmd=%s args=[%s] failed: %v", command, strings.Join(strArgs, ", "), err)
+		} else {
+			cmdOuts <- bytes
+		}
+	}()
+
+	for {
+		select {
+		case bytes := <-cmdOuts:
+			return string(bytes), nil
+		case err := <-cmdErrs:
+			return "", err
+		case err := <-writeErrs:
+			return "", err
+		}
+	}
+}
+
+func (c *Context) ReadFile(filename string) (string, error) {
+	var path string
+	if filepath.IsAbs(filename) {
+		path = filename
+	} else {
+		path = filepath.Join(c.basePath, filename)
+	}
+
+	bytes, err := c.readFile(path)
+	if err != nil {
+		return "", err
+	}
+	return string(bytes), nil
+}
+
+func (c *Context) Tpl(text string, data interface{}) (string, error) {
+	buf, err := c.RenderTemplateToBuffer(text, data)
+	if err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}
+
+func ToYaml(v interface{}) (string, error) {
+	data, err := yaml.Marshal(v)
+	if err != nil {
+		return "", err
+	}
+	return string(data), nil
+}
+
+func FromYaml(str string) (Values, error) {
+	m := Values{}
+
+	if err := yaml.Unmarshal([]byte(str), &m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+func SetValueAtPath(path string, value interface{}, values Values) (Values, error) {
+	var current interface{}
+	current = values
+	components := strings.Split(path, ".")
+	pathToMap := components[:len(components)-1]
+	key := components[len(components)-1]
+	for _, k := range pathToMap {
+		var elem interface{}
+
+		switch typedCurrent := current.(type) {
+		case map[string]interface{}:
+			v, exists := typedCurrent[k]
+			if !exists {
+				return nil, fmt.Errorf("failed to set value at path \"%s\": value for key \"%s\" does not exist", path, k)
+			}
+			elem = v
+		case map[interface{}]interface{}:
+			v, exists := typedCurrent[k]
+			if !exists {
+				return nil, fmt.Errorf("failed to set value at path \"%s\": value for key \"%s\" does not exist", path, k)
+			}
+			elem = v
+		default:
+			return nil, fmt.Errorf("failed to set value at path \"%s\": value for key \"%s\" was not a map", path, k)
+		}
+
+		switch typedElem := elem.(type) {
+		case map[string]interface{}, map[interface{}]interface{}:
+			current = typedElem
+		default:
+			return nil, fmt.Errorf("failed to set value at path \"%s\": value for key \"%s\" was not a map", path, k)
+		}
+	}
+
+	switch typedCurrent := current.(type) {
+	case map[string]interface{}:
+		typedCurrent[key] = value
+	case map[interface{}]interface{}:
+		typedCurrent[key] = value
+	default:
+		return nil, fmt.Errorf("failed to set value at path \"%s\": value for key \"%s\" was not a map", path, key)
+	}
+	return values, nil
+}
+
+func RequiredEnv(name string) (string, error) {
+	if val, exists := os.LookupEnv(name); exists && len(val) > 0 {
+		return val, nil
+	}
+
+	return "", fmt.Errorf("required env var `%s` is not set", name)
+}

pkg/tmpl/context_funcs_test.go

@@ -0,0 +1,135 @@
+package tmpl
+
+import (
+	"fmt"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func TestReadFile(t *testing.T) {
+	expected := `foo:
+  bar: BAR
+`
+	expectedFilename := "values.yaml"
+	ctx := &Context{basePath: ".", readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(expected), nil
+	}}
+	actual, err := ctx.ReadFile(expectedFilename)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestReadFile_PassAbsPath(t *testing.T) {
+	expected := `foo:
+  bar: BAR
+`
+	expectedFilename, _ := filepath.Abs("values.yaml")
+	ctx := &Context{basePath: ".", readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(expected), nil
+	}}
+	actual, err := ctx.ReadFile(expectedFilename)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestToYaml(t *testing.T) {
+	expected := `foo:
+  bar: BAR
+`
+	vals := Values(map[string]interface{}{
+		"foo": map[interface{}]interface{}{
+			"bar": "BAR",
+		},
+	})
+	actual, err := ToYaml(vals)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestFromYaml(t *testing.T) {
+	raw := `foo:
+  bar: BAR
+`
+	expected := Values(map[string]interface{}{
+		"foo": map[interface{}]interface{}{
+			"bar": "BAR",
+		},
+	})
+	actual, err := FromYaml(raw)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestSetValueAtPath_OneComponent(t *testing.T) {
+	input := map[string]interface{}{
+		"foo": "",
+	}
+	expected := map[string]interface{}{
+		"foo": "FOO",
+	}
+	actual, err := SetValueAtPath("foo", "FOO", input)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestSetValueAtPath_TwoComponents(t *testing.T) {
+	input := map[string]interface{}{
+		"foo": map[interface{}]interface{}{
+			"bar": "",
+		},
+	}
+	expected := map[string]interface{}{
+		"foo": map[interface{}]interface{}{
+			"bar": "FOO_BAR",
+		},
+	}
+	actual, err := SetValueAtPath("foo.bar", "FOO_BAR", input)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestTpl(t *testing.T) {
+	text := `foo: {{ .foo }}
+`
+	expected := `foo: FOO
+`
+	ctx := &Context{basePath: "."}
+	actual, err := ctx.Tpl(text, map[string]interface{}{"foo": "FOO"})
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}

pkg/tmpl/context_tmpl.go

@@ -0,0 +1,41 @@
+package tmpl
+
+import (
+	"bytes"
+	"github.com/Masterminds/sprig"
+	"text/template"
+)
+
+func (c *Context) stringTemplate() *template.Template {
+	funcMap := sprig.TxtFuncMap()
+	for name, f := range c.createFuncMap() {
+		funcMap[name] = f
+	}
+	tmpl := template.New("stringTemplate").Funcs(funcMap)
+	if c.preRender {
+		tmpl.Option("missingkey=zero")
+	} else {
+		tmpl.Option("missingkey=error")
+	}
+	return tmpl
+}
+
+func (c *Context) RenderTemplateToBuffer(s string, data ...interface{}) (*bytes.Buffer, error) {
+	var t, parseErr = c.stringTemplate().Parse(s)
+	if parseErr != nil {
+		return nil, parseErr
+	}
+
+	var tplString bytes.Buffer
+	var d interface{}
+	if len(data) > 0 {
+		d = data[0]
+	}
+	var execErr = t.Execute(&tplString, d)
+
+	if execErr != nil {
+		return &tplString, execErr
+	}
+
+	return &tplString, nil
+}

pkg/tmpl/context_tmpl_test.go

@@ -0,0 +1,252 @@
+package tmpl
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestRenderTemplate_Values(t *testing.T) {
+	valuesYamlContent := `foo:
+  bar: BAR
+`
+	expected := `foo:
+  bar: FOO_BAR
+`
+	expectedFilename := "values.yaml"
+	ctx := &Context{readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(valuesYamlContent), nil
+	}}
+	buf, err := ctx.RenderTemplateToBuffer(`{{ readFile "values.yaml" | fromYaml | setValueAtPath "foo.bar" "FOO_BAR" | toYaml }}`)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := buf.String()
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestRenderTemplate_WithData(t *testing.T) {
+	valuesYamlContent := `foo:
+  bar: {{ .foo.bar }}
+`
+	expected := `foo:
+  bar: FOO_BAR
+`
+	expectedFilename := "values.yaml"
+	data := map[string]interface{}{
+		"foo": map[string]interface{}{
+			"bar": "FOO_BAR",
+		},
+	}
+	ctx := &Context{readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(valuesYamlContent), nil
+	}}
+	buf, err := ctx.RenderTemplateToBuffer(valuesYamlContent, data)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := buf.String()
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestRenderTemplate_AccessingMissingKeyWithGetOrNil(t *testing.T) {
+	valuesYamlContent := `foo:
+  bar: {{ . | getOrNil "foo.bar" }}
+`
+	expected := `foo:
+  bar: <no value>
+`
+	expectedFilename := "values.yaml"
+	data := map[string]interface{}{}
+	ctx := &Context{readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(valuesYamlContent), nil
+	}}
+	buf, err := ctx.RenderTemplateToBuffer(valuesYamlContent, data)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := buf.String()
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestRenderTemplate_Defaulting(t *testing.T) {
+	valuesYamlContent := `foo:
+  bar: {{ . | getOrNil "foo.bar" | default "DEFAULT" }}
+`
+	expected := `foo:
+  bar: DEFAULT
+`
+	expectedFilename := "values.yaml"
+	data := map[string]interface{}{}
+	ctx := &Context{readFile: func(filename string) ([]byte, error) {
+		if filename != expectedFilename {
+			return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", expectedFilename, filename)
+		}
+		return []byte(valuesYamlContent), nil
+	}}
+	buf, err := ctx.RenderTemplateToBuffer(valuesYamlContent, data)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := buf.String()
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func renderTemplateToString(s string, data ...interface{}) (string, error) {
+	ctx := &Context{readFile: func(filename string) ([]byte, error) {
+		return nil, fmt.Errorf("unexpected call to readFile: filename=%s", filename)
+	}}
+	tplString, err := ctx.RenderTemplateToBuffer(s, data...)
+	if err != nil {
+		return "", err
+	}
+	return tplString.String(), nil
+}
+
+func Test_renderTemplateToString(t *testing.T) {
+	type args struct {
+		s    string
+		envs map[string]string
+		data interface{}
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    string
+		wantErr bool
+	}{
+		{
+			name: "simple replacement",
+			args: args{
+				s: "{{ env \"HF_TEST_VAR\" }}",
+				envs: map[string]string{
+					"HF_TEST_VAR": "content",
+				},
+			},
+			want:    "content",
+			wantErr: false,
+		},
+		{
+			name: "two replacements",
+			args: args{
+				s: "{{ env \"HF_TEST_ALPHA\" }}{{ env \"HF_TEST_BETA\" }}",
+				envs: map[string]string{
+					"HF_TEST_ALPHA": "first",
+					"HF_TEST_BETA":  "second",
+				},
+			},
+			want:    "firstsecond",
+			wantErr: false,
+		},
+		{
+			name: "replacement and comment",
+			args: args{
+				s: "{{ env \"HF_TEST_ALPHA\" }}{{/* comment */}}",
+				envs: map[string]string{
+					"HF_TEST_ALPHA": "first",
+				},
+			},
+			want:    "first",
+			wantErr: false,
+		},
+		{
+			name: "global template function",
+			args: args{
+				s: "{{ env \"HF_TEST_ALPHA\" | len }}",
+				envs: map[string]string{
+					"HF_TEST_ALPHA": "abcdefg",
+				},
+			},
+			want:    "7",
+			wantErr: false,
+		},
+		{
+			name: "get",
+			args: args{
+				s:    `{{ . | get "Foo" }}, {{ . | get "Bar" "2" }}`,
+				envs: map[string]string{},
+				data: map[string]interface{}{
+					"Foo": "1",
+				},
+			},
+			want:    "1, 2",
+			wantErr: false,
+		},
+		{
+			name: "env var not set",
+			args: args{
+				s: "{{ env \"HF_TEST_NONE\" }}",
+				envs: map[string]string{
+					"HF_TEST_THIS": "first",
+				},
+			},
+			want: "",
+		},
+		{
+			name: "undefined function",
+			args: args{
+				s: "{{ env foo }}",
+				envs: map[string]string{
+					"foo": "bar",
+				},
+			},
+			wantErr: true,
+		},
+		{
+			name: "required env var",
+			args: args{
+				s: "{{ requiredEnv \"HF_TEST\" }}",
+				envs: map[string]string{
+					"HF_TEST": "value",
+				},
+			},
+			want:    "value",
+			wantErr: false,
+		},
+		{
+			name: "required env var not set",
+			args: args{
+				s:    "{{ requiredEnv \"HF_TEST_NONE\" }}",
+				envs: map[string]string{},
+			},
+			wantErr: true,
+		},
+	}
+	for i := range tests {
+		tt := tests[i]
+		t.Run(tt.name, func(t *testing.T) {
+			for k, v := range tt.args.envs {
+				err := os.Setenv(k, v)
+				if err != nil {
+					t.Error("renderTemplateToString() could not set env var for testing")
+				}
+			}
+			got, err := renderTemplateToString(tt.args.s, tt.args.data)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("renderTemplateToString() for %s error = %v, wantErr %v", tt.name, err, tt.wantErr)
+				return
+			}
+			if got != tt.want {
+				t.Errorf("renderTemplateToString() for %s = %v, want %v", tt.name, got, tt.want)
+			}
+		})
+	}
+}

pkg/tmpl/file_renderer.go

@@ -0,0 +1,78 @@
+package tmpl
+
+import (
+	"bytes"
+	"io/ioutil"
+
+	"fmt"
+	"strings"
+)
+
+type FileRenderer struct {
+	ReadFile func(string) ([]byte, error)
+	Context  *Context
+	Data     interface{}
+}
+
+func NewFileRenderer(readFile func(filename string) ([]byte, error), basePath string, data interface{}) *FileRenderer {
+	return &FileRenderer{
+		ReadFile: readFile,
+		Context: &Context{
+			basePath: basePath,
+			readFile: readFile,
+		},
+		Data: data,
+	}
+}
+
+func NewFirstPassRenderer(basePath string, data interface{}) *FileRenderer {
+	return &FileRenderer{
+		ReadFile: ioutil.ReadFile,
+		Context: &Context{
+			preRender: true,
+			basePath:  basePath,
+			readFile:  ioutil.ReadFile,
+		},
+		Data: data,
+	}
+}
+
+func (r *FileRenderer) RenderTemplateFileToBuffer(file string) (*bytes.Buffer, error) {
+	content, err := r.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+
+	return r.RenderTemplateContentToBuffer(content)
+}
+
+func (r *FileRenderer) RenderToBytes(path string) ([]byte, error) {
+	var yamlBytes []byte
+	splits := strings.Split(path, ".")
+	if len(splits) > 0 && splits[len(splits)-1] == "gotmpl" {
+		yamlBuf, err := r.RenderTemplateFileToBuffer(path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to render [%s], because of %v", path, err)
+		}
+		yamlBytes = yamlBuf.Bytes()
+	} else {
+		var err error
+		yamlBytes, err = r.ReadFile(path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to load [%s]: %v", path, err)
+		}
+	}
+	return yamlBytes, nil
+}
+
+func (r *FileRenderer) RenderTemplateContentToBuffer(content []byte) (*bytes.Buffer, error) {
+	return r.Context.RenderTemplateToBuffer(string(content), r.Data)
+}
+
+func (r *FileRenderer) RenderTemplateContentToString(content []byte) (string, error) {
+	buf, err := r.Context.RenderTemplateToBuffer(string(content), r.Data)
+	if err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}

pkg/tmpl/file_renderer_test.go

@@ -0,0 +1,67 @@
+package tmpl
+
+import (
+	"fmt"
+	"github.com/roboll/helmfile/pkg/environment"
+	"reflect"
+	"testing"
+)
+
+var emptyEnvTmplData = map[string]interface{}{
+	"Environment": environment.EmptyEnvironment,
+	"Namespace":   "",
+}
+
+func TestRenderToBytes_Gotmpl(t *testing.T) {
+	valuesYamlTmplContent := `foo:
+  bar: '{{ readFile "data.txt" }}'
+`
+	dataFileContent := "FOO_BAR"
+	expected := `foo:
+  bar: 'FOO_BAR'
+`
+	dataFile := "data.txt"
+	valuesTmplFile := "values.yaml.gotmpl"
+	r := NewFileRenderer(func(filename string) ([]byte, error) {
+		switch filename {
+		case valuesTmplFile:
+			return []byte(valuesYamlTmplContent), nil
+		case dataFile:
+			return []byte(dataFileContent), nil
+		}
+		return nil, fmt.Errorf("unexpected filename: expected=%v or %v, actual=%s", dataFile, valuesTmplFile, filename)
+	}, "", emptyEnvTmplData)
+	buf, err := r.RenderToBytes(valuesTmplFile)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := string(buf)
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}
+
+func TestRenderToBytes_Yaml(t *testing.T) {
+	valuesYamlContent := `foo:
+  bar: '{{ readFile "data.txt" }}'
+`
+	expected := `foo:
+  bar: '{{ readFile "data.txt" }}'
+`
+	valuesFile := "values.yaml"
+	r := NewFileRenderer(func(filename string) ([]byte, error) {
+		switch filename {
+		case valuesFile:
+			return []byte(valuesYamlContent), nil
+		}
+		return nil, fmt.Errorf("unexpected filename: expected=%v, actual=%s", valuesFile, filename)
+	}, "", emptyEnvTmplData)
+	buf, err := r.RenderToBytes(valuesFile)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	actual := string(buf)
+	if !reflect.DeepEqual(actual, expected) {
+		t.Errorf("unexpected result: expected=%v, actual=%v", expected, actual)
+	}
+}

pkg/tmpl/get_or_nil.go

@@ -0,0 +1,91 @@
+package tmpl
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+type noValueError struct {
+	msg string
+}
+
+func (e *noValueError) Error() string {
+	return e.msg
+}
+
+func get(path string, varArgs ...interface{}) (interface{}, error) {
+	var defSet bool
+	var def interface{}
+	var obj interface{}
+	switch len(varArgs) {
+	case 1:
+		defSet = false
+		def = nil
+		obj = varArgs[0]
+	case 2:
+		defSet = true
+		def = varArgs[0]
+		obj = varArgs[1]
+	default:
+		return nil, fmt.Errorf("unexpected number of args pased to the template function get(path, [def, ]obj): expected 1 or 2, got %d, args was %v", len(varArgs), varArgs)
+	}
+
+	if path == "" {
+		return obj, nil
+	}
+	keys := strings.Split(path, ".")
+	var v interface{}
+	var ok bool
+	switch typedObj := obj.(type) {
+	case map[string]interface{}:
+		v, ok = typedObj[keys[0]]
+		if !ok {
+			if defSet {
+				return def, nil
+			}
+			return nil, &noValueError{fmt.Sprintf("no value exist for key \"%s\" in %v", keys[0], typedObj)}
+		}
+	case map[interface{}]interface{}:
+		v, ok = typedObj[keys[0]]
+		if !ok {
+			if defSet {
+				return def, nil
+			}
+			return nil, &noValueError{fmt.Sprintf("no value exist for key \"%s\" in %v", keys[0], typedObj)}
+		}
+	default:
+		maybeStruct := reflect.ValueOf(typedObj)
+		if maybeStruct.Kind() != reflect.Struct {
+			return nil, &noValueError{fmt.Sprintf("unexpected type(%v) of value for key \"%s\": it must be either map[string]interface{} or any struct", reflect.TypeOf(obj), keys[0])}
+		} else if maybeStruct.NumField() < 1 {
+			return nil, &noValueError{fmt.Sprintf("no accessible struct fields for key \"%s\"", keys[0])}
+		}
+		f := maybeStruct.FieldByName(keys[0])
+		if !f.IsValid() {
+			if defSet {
+				return def, nil
+			}
+			return nil, &noValueError{fmt.Sprintf("no field named \"%s\" exist in %v", keys[0], typedObj)}
+		}
+		v = f.Interface()
+	}
+
+	if defSet {
+		return get(strings.Join(keys[1:], "."), def, v)
+	}
+	return get(strings.Join(keys[1:], "."), v)
+}
+
+func getOrNil(path string, o interface{}) (interface{}, error) {
+	v, err := get(path, o)
+	if err != nil {
+		switch err.(type) {
+		case *noValueError:
+			return nil, nil
+		default:
+			return nil, err
+		}
+	}
+	return v, nil
+}

pkg/tmpl/get_or_nil_test.go

@@ -0,0 +1,128 @@
+package tmpl
+
+import (
+	"testing"
+)
+
+type EmptyStruct struct {
+}
+
+func TestGetStruct(t *testing.T) {
+	type Foo struct{ Bar string }
+
+	obj := struct{ Foo }{Foo{Bar: "Bar"}}
+
+	v1, err := get("Foo.Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	_, err = get("Foo.baz", obj)
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
+
+	_, err = get("foo", EmptyStruct{})
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
+}
+
+func TestGetMap(t *testing.T) {
+	obj := map[string]interface{}{"Foo": map[string]interface{}{"Bar": "Bar"}}
+
+	v1, err := get("Foo.Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	_, err = get("Foo.baz", obj)
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
+}
+
+func TestGet_Default(t *testing.T) {
+	obj := map[string]interface{}{"Foo": map[string]interface{}{}, "foo": 1}
+
+	v1, err := get("Foo.Bar", "Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	v2, err := get("Baz", "Baz", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v2 != "Baz" {
+		t.Errorf("unexpected value for path Baz in %v: expected=Baz, actual=%v", obj, v2)
+	}
+
+	_, err = get("foo.Bar", "fooBar", obj)
+
+	if err == nil {
+		t.Errorf("expected error but was not occurred")
+	}
+}
+
+func TestGetOrNilStruct(t *testing.T) {
+	type Foo struct{ Bar string }
+
+	obj := struct{ Foo }{Foo{Bar: "Bar"}}
+
+	v1, err := getOrNil("Foo.Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	v2, err := getOrNil("Foo.baz", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v2 != nil {
+		t.Errorf("unexpected value for path Foo.baz in %v: expected=nil, actual=%v", obj, v2)
+	}
+}
+
+func TestGetOrNilMap(t *testing.T) {
+	obj := map[string]interface{}{"Foo": map[string]interface{}{"Bar": "Bar"}}
+
+	v1, err := getOrNil("Foo.Bar", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v1 != "Bar" {
+		t.Errorf("unexpected value for path Foo.Bar in %v: expected=Bar, actual=%v", obj, v1)
+	}
+
+	v2, err := getOrNil("Foo.baz", obj)
+
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+	if v2 != nil {
+		t.Errorf("unexpected value for path Foo.baz in %v: expected=nil, actual=%v", obj, v2)
+	}
+}

pkg/tmpl/text_renderer.go

@@ -0,0 +1,30 @@
+package tmpl
+
+type templateTextRenderer struct {
+	ReadText func(string) ([]byte, error)
+	Context  *Context
+	Data     interface{}
+}
+
+type TextRenderer interface {
+	RenderTemplateText(text string) (string, error)
+}
+
+func NewTextRenderer(readFile func(filename string) ([]byte, error), basePath string, data interface{}) *templateTextRenderer {
+	return &templateTextRenderer{
+		ReadText: readFile,
+		Context: &Context{
+			basePath: basePath,
+			readFile: readFile,
+		},
+		Data: data,
+	}
+}
+
+func (r *templateTextRenderer) RenderTemplateText(text string) (string, error) {
+	buf, err := r.Context.RenderTemplateToBuffer(text, r.Data)
+	if err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}