Add downward API for environment vars

pkg/fieldpath/doc.go

@@ -0,0 +1,19 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+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 fieldpath supplies methods for extracting fields from objects
+// given a path to a field.
+package fieldpath

pkg/fieldpath/fieldpath.go

@@ -0,0 +1,47 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+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 fieldpath
+
+import (
+	"fmt"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/meta"
+)
+
+// ExtractFieldPathAsString extracts the field from the given object
+// and returns it as a string.  The object must be a pointer to an
+// API type.
+//
+// Currently, this API is limited to supporting the fieldpaths:
+//
+// 1.  metadata.name - The name of an API object
+// 2.  metadata.namespace - The namespace of an API object
+func ExtractFieldPathAsString(obj interface{}, fieldPath string) (string, error) {
+	accessor, err := meta.Accessor(obj)
+	if err != nil {
+		return "", nil
+	}
+
+	switch fieldPath {
+	case "metadata.name":
+		return accessor.Name(), nil
+	case "metadata.namespace":
+		return accessor.Namespace(), nil
+	}
+
+	return "", fmt.Errorf("Unsupported fieldPath: %v", fieldPath)
+}

pkg/fieldpath/fieldpath_test.go

@@ -0,0 +1,86 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+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 fieldpath
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+)
+
+func TestExtractFieldPathAsString(t *testing.T) {
+	cases := []struct {
+		name                    string
+		fieldPath               string
+		obj                     interface{}
+		expectedValue           string
+		expectedMessageFragment string
+	}{
+		{
+			name:      "not an API object",
+			fieldPath: "metadata.name",
+			obj:       "",
+			expectedMessageFragment: "expected struct",
+		},
+		{
+			name:      "ok - namespace",
+			fieldPath: "metadata.namespace",
+			obj: &api.Pod{
+				ObjectMeta: api.ObjectMeta{
+					Namespace: "object-namespace",
+				},
+			},
+			expectedValue: "object-namespace",
+		},
+		{
+			name:      "ok - name",
+			fieldPath: "metadata.name",
+			obj: &api.Pod{
+				ObjectMeta: api.ObjectMeta{
+					Name: "object-name",
+				},
+			},
+			expectedValue: "object-name",
+		},
+		{
+			name:      "invalid expression",
+			fieldPath: "metadata.whoops",
+			obj: &api.Pod{
+				ObjectMeta: api.ObjectMeta{
+					Namespace: "object-namespace",
+				},
+			},
+			expectedMessageFragment: "Unsupported fieldPath",
+		},
+	}
+
+	for _, tc := range cases {
+		actual, err := ExtractFieldPathAsString(tc.obj, tc.fieldPath)
+		if err != nil {
+			if tc.expectedMessageFragment != "" {
+				if !strings.Contains(err.Error(), tc.expectedMessageFragment) {
+					t.Errorf("%v: Unexpected error message: %q, expected to contain %q", tc.name, err, tc.expectedMessageFragment)
+				}
+			} else {
+				t.Errorf("%v: unexpected error: %v", tc.name, err)
+			}
+		} else if e := tc.expectedValue; e != "" && e != actual {
+			t.Errorf("%v: Unexpected result; got %q, expected %q", tc.name, actual, e)
+		}
+	}
+}