add yaml helper functions

docs/guides-templating.md

@@ -93,6 +93,8 @@ In addition to that you can use over 200+ [sprig functions](http://masterminds.g
 
 | jwkPublicKeyPem | Takes an json-serialized JWK and returns an PEM block of type `PUBLIC KEY` that contains the public key. [See here](https://golang.org/pkg/crypto/x509/#MarshalPKIXPublicKey) for details. |
 | jwkPrivateKeyPem | Takes an json-serialized JWK as `string` and returns an PEM block of type `PRIVATE KEY` that contains the private key in PKCS #8 format. [See here](https://golang.org/pkg/crypto/x509/#MarshalPKCS8PrivateKey) for details. |
+| toYaml | Takes an interface, marshals it to yaml. It returns a string, even on marshal error (empty string). |
+| fromYaml | Function converts a YAML document into a map[string]interface{}. |
 
 ## Migrating from v1
 

pkg/template/v2/template.go

@@ -32,6 +32,9 @@ var tplFuncs = tpl.FuncMap{
 
 	"jwkPublicKeyPem":  jwkPublicKeyPem,
 	"jwkPrivateKeyPem": jwkPrivateKeyPem,
+
+	"toYaml":        toYAML,
+	"fromYaml":      fromYAML,
 }
 
 // So other templating calls can use the same extra functions.

pkg/template/v2/yaml.go

@@ -0,0 +1,48 @@
+/*
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package template
+
+import (
+	"strings"
+
+	"sigs.k8s.io/yaml"
+)
+
+// toYAML takes an interface, marshals it to yaml, and returns a string. It will
+// always return a string, even on marshal error (empty string).
+//
+// This is designed to be called from a template.
+func toYAML(v interface{}) string {
+	data, err := yaml.Marshal(v)
+	if err != nil {
+		// Swallow errors inside of a template.
+		return ""
+	}
+	return strings.TrimSuffix(string(data), "\n")
+}
+
+// fromYAML converts a YAML document into a map[string]interface{}.
+//
+// This is not a general-purpose YAML parser, and will not parse all valid
+// YAML documents. Additionally, because its intended use is within templates
+// it tolerates errors. It will insert the returned error message string into
+// m["Error"] in the returned map.
+func fromYAML(str string) map[string]interface{} {
+	m := map[string]interface{}{}
+
+	if err := yaml.Unmarshal([]byte(str), &m); err != nil {
+		m["Error"] = err.Error()
+	}
+	return m
+}