Add a ParseTemplate util function for parsing go text templates easily

cmd/kubeadm/app/util/BUILD

@@ -12,6 +12,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "error.go",
+        "template.go",
         "tokens.go",
         "version.go",
     ],
@@ -32,6 +33,7 @@ go_test(
     name = "go_default_test",
     srcs = [
         "error_test.go",
+        "template_test.go",
         "tokens_test.go",
         "version_test.go",
     ],

cmd/kubeadm/app/util/template.go

@@ -0,0 +1,37 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+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 util
+
+import (
+	"bytes"
+	"fmt"
+	"text/template"
+)
+
+// TODO: Should be unit-tested
+func ParseTemplate(strtmpl string, obj interface{}) ([]byte, error) {
+	var buf bytes.Buffer
+	tmpl, err := template.New("template").Parse(strtmpl)
+	if err != nil {
+		return nil, fmt.Errorf("error when parsing template: %v", err)
+	}
+	err = tmpl.Execute(&buf, obj)
+	if err != nil {
+		return nil, fmt.Errorf("error when executing template: %v", err)
+	}
+	return buf.Bytes(), nil
+}

cmd/kubeadm/app/util/template_test.go

@@ -0,0 +1,90 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+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 util
+
+import (
+	"testing"
+)
+
+const (
+	validTmpl    = "image: {{ .ImageRepository }}/pause-{{ .Arch }}:3.0"
+	validTmplOut = "image: gcr.io/google_containers/pause-amd64:3.0"
+	doNothing    = "image: gcr.io/google_containers/pause-amd64:3.0"
+	invalidTmpl1 = "{{ .baz }/d}"
+	invalidTmpl2 = "{{ !foobar }}"
+)
+
+func TestParseTemplate(t *testing.T) {
+	var tmplTests = []struct {
+		template    string
+		data        interface{}
+		output      string
+		errExpected bool
+	}{
+		// should parse a valid template and set the right values
+		{
+			template: validTmpl,
+			data: struct{ ImageRepository, Arch string }{
+				ImageRepository: "gcr.io/google_containers",
+				Arch:            "amd64",
+			},
+			output:      validTmplOut,
+			errExpected: false,
+		},
+		// should noop if there aren't any {{ .foo }} present
+		{
+			template: doNothing,
+			data: struct{ ImageRepository, Arch string }{
+				ImageRepository: "gcr.io/google_containers",
+				Arch:            "amd64",
+			},
+			output:      doNothing,
+			errExpected: false,
+		},
+		// invalid syntax, passing nil
+		{
+			template:    invalidTmpl1,
+			data:        nil,
+			output:      "",
+			errExpected: true,
+		},
+		// invalid syntax
+		{
+			template:    invalidTmpl2,
+			data:        struct{}{},
+			output:      "",
+			errExpected: true,
+		},
+	}
+	for _, tt := range tmplTests {
+		outbytes, err := ParseTemplate(tt.template, tt.data)
+		if tt.errExpected != (err != nil) {
+			t.Errorf(
+				"failed TestParseTemplate:\n\texpected err: %s\n\t  actual: %s",
+				tt.errExpected,
+				err,
+			)
+		}
+		if tt.output != string(outbytes) {
+			t.Errorf(
+				"failed TestParseTemplate:\n\texpected bytes: %s\n\t  actual: %s",
+				tt.output,
+				outbytes,
+			)
+		}
+	}
+}