Merge pull request #399 from aywan/multi-template

Nested templates and include function

Author: buchdag

README.md

@@ -214,6 +214,8 @@ e75a60548dc9 = 1  # a key can be either container name (nginx) or ID
 
 The templates used by docker-gen are written using the Go [text/template](http://golang.org/pkg/text/template/) language. In addition to the [built-in functions](http://golang.org/pkg/text/template/#hdr-Functions) supplied by Go, docker-gen uses [sprig](https://masterminds.github.io/sprig/) and some additional functions to make it simpler (or possible) to generate your desired output. Some templates rely on environment variables within the container to make decisions on what to generate from the template.
 
+For parsing several templates, split path with `;` (for example `template = "nginx.tmpl;header.tmpl"`). This makes possible to use go nested templates through standard `template` function.
+
 #### Emit Structure
 
 Within the templates, the object emitted by docker-gen will be a structure consisting of following Go structs:
@@ -378,6 +380,7 @@ For example, this is a JSON version of an emitted RuntimeContainer struct:
 * *`groupByKeys $containers $fieldPath`*: Returns the same as `groupBy` but only returns the keys of the map.
 * *`groupByMulti $containers $fieldPath $sep`*: Like `groupBy`, but the string value specified by `$fieldPath` is first split by `$sep` into a list of strings. A container whose `$fieldPath` value contains a list of strings will show up in the map output under each of those strings.
 * *`groupByLabel $containers $label`*: Returns the same as `groupBy` but grouping by the given label's value.
+* *`include $file`*: Returns content of `$file`, and empty string if file reading error.
 * *`intersect $slice1 $slice2`*: Returns the strings that exist in both string slices.
 * *`json $value`*: Returns the JSON representation of `$value` as a `string`.
 * *`keys $map`*: Returns the keys from `$map`. If `$map` is `nil`, a `nil` is returned. If `$map` is not a `map`, an error will be thrown.

internal/template/functions.go

@@ -31,6 +31,14 @@ func keys(input interface{}) (interface{}, error) {
 	return k, nil
 }
 
+func include(file string) string {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return ""
+	}
+	return string(data)
+}
+
 func intersect(l1, l2 []string) []string {
 	m := make(map[string]bool)
 	m2 := make(map[string]bool)

internal/template/functions_test.go

@@ -77,6 +77,16 @@ func TestKeysNil(t *testing.T) {
 	}
 }
 
+func TestInclude(t *testing.T) {
+	data := include("some_random_file")
+	assert.Equal(t, "", data)
+
+	_ = os.WriteFile("/tmp/docker-gen-test-temp-file", []byte("some string"), 0o777)
+	data = include("/tmp/docker-gen-test-temp-file")
+	assert.Equal(t, "some string", data)
+	_ = os.Remove("/tmp/docker-gen-test-temp-file")
+}
+
 func TestIntersect(t *testing.T) {
 	i := intersect([]string{"foo.fo.com", "bar.com"}, []string{"foo.bar.com"})
 	assert.Len(t, i, 0, "Expected no match")

internal/template/template.go

@@ -69,6 +69,7 @@ func newTemplate(name string) *template.Template {
 		"groupByMulti":           groupByMulti,
 		"groupByLabel":           groupByLabel,
 		"json":                   marshalJson,
+		"include":                include,
 		"intersect":              intersect,
 		"keys":                   keys,
 		"replace":                strings.Replace,
@@ -223,13 +224,14 @@ func GenerateFile(config config.Config, containers context.Context) bool {
 }
 
 func executeTemplate(templatePath string, containers context.Context) []byte {
-	tmpl, err := newTemplate(filepath.Base(templatePath)).ParseFiles(templatePath)
+	templatePathList := strings.Split(templatePath, ";")
+	tmpl, err := newTemplate(filepath.Base(templatePath)).ParseFiles(templatePathList...)
 	if err != nil {
 		log.Fatalf("Unable to parse template: %s", err)
 	}
 
 	buf := new(bytes.Buffer)
-	err = tmpl.ExecuteTemplate(buf, filepath.Base(templatePath), &containers)
+	err = tmpl.ExecuteTemplate(buf, filepath.Base(templatePathList[0]), &containers)
 	if err != nil {
 		log.Fatalf("Template error: %s\n", err)
 	}