Add a package for loading Downward API metadata.

Signed-off-by: Matt Moyer <moyerm@vmware.com>

internal/downward/downward.go

@@ -0,0 +1,70 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+// Package downward implements a client interface for interacting with Kubernetes "downwardAPI" volumes.
+// See https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/.
+package downward
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"path/filepath"
+	"strconv"
+	"strings"
+)
+
+// PodInfo contains pod metadata about the current pod.
+type PodInfo struct {
+	// Namespace where the current pod is running.
+	Namespace string
+
+	// Labels of the current pod.
+	Labels map[string]string
+}
+
+// Load pod metadata from a downwardAPI volume directory.
+func Load(directory string) (*PodInfo, error) {
+	var result PodInfo
+	ns, err := ioutil.ReadFile(filepath.Join(directory, "namespace"))
+	if err != nil {
+		return nil, fmt.Errorf("could not load namespace: %w", err)
+	}
+	result.Namespace = strings.TrimSpace(string(ns))
+
+	labels, err := ioutil.ReadFile(filepath.Join(directory, "labels"))
+	if err != nil {
+		return nil, fmt.Errorf("could not load labels: %w", err)
+	}
+	result.Labels, err = parseMap(labels)
+	if err != nil {
+		return nil, fmt.Errorf("could not parse labels: %w", err)
+	}
+	return &result, nil
+}
+
+// parseMap parses the key/value format emitted by the Kubernetes Downward API for pod labels and annotations.
+// See https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/.
+// See https://github.com/kubernetes/kubernetes/blob/4b2cb072dba10227083b16731f019f096c581787/pkg/fieldpath/fieldpath.go#L28.
+func parseMap(input []byte) (map[string]string, error) {
+	result := map[string]string{}
+	for _, line := range bytes.Split(input, []byte("\n")) {
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 {
+			continue
+		}
+		parts := bytes.SplitN(line, []byte("="), 2)
+		if len(parts) != 2 {
+			return nil, fmt.Errorf("expected 2 parts, found %d: %w", len(parts), io.ErrShortBuffer)
+		}
+		value, err := strconv.Unquote(string(parts[1]))
+		if err != nil {
+			return nil, fmt.Errorf("invalid quoted value: %w", err)
+		}
+		result[string(parts[0])] = value
+	}
+	return result, nil
+}

internal/downward/downward_test.go

@@ -0,0 +1,111 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package downward
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestLoad(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		name     string
+		inputDir string
+		wantErr  string
+		want     *PodInfo
+	}{
+		{
+			name:     "missing directory",
+			inputDir: "./testdata/no-such-directory",
+			wantErr:  "could not load namespace: open testdata/no-such-directory/namespace: no such file or directory",
+		},
+		{
+			name:     "missing labels file",
+			inputDir: "./testdata/missinglabels",
+			wantErr:  "could not load labels: open testdata/missinglabels/labels: no such file or directory",
+		},
+		{
+			name:     "invalid labels file",
+			inputDir: "./testdata/invalidlabels",
+			wantErr:  "could not parse labels: expected 2 parts, found 1: short buffer",
+		},
+		{
+			name:     "valid",
+			inputDir: "./testdata/valid",
+			want: &PodInfo{
+				Namespace: "test-namespace",
+				Labels:    map[string]string{"foo": "bar", "bat": "baz"},
+			},
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Load(tt.inputDir)
+			if tt.wantErr != "" {
+				require.EqualError(t, err, tt.wantErr)
+				require.Empty(t, got)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestParseMap(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		input   []byte
+		wantErr string
+		want    map[string]string
+	}{
+		{
+			name: "empty",
+			want: map[string]string{},
+		},
+		{
+			name:    "missing equal",
+			input:   []byte(`akjhlakjh`),
+			wantErr: "expected 2 parts, found 1: short buffer",
+		},
+		{
+			name:    "missing invalid value",
+			input:   []byte(`akjhlakjh="foo\qbar"`),
+			wantErr: "invalid quoted value: invalid syntax",
+		},
+		{
+			name: "success",
+			input: []byte(`
+fooTime="2020-07-15T19:35:12.027636555Z"
+example.com/config.source="api"
+example.com/bar="baz\x01"
+`),
+			want: map[string]string{
+				"fooTime":                   "2020-07-15T19:35:12.027636555Z",
+				"example.com/config.source": "api",
+				"example.com/bar":           "baz\x01",
+			},
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := parseMap(tt.input)
+			if tt.wantErr != "" {
+				require.EqualError(t, err, tt.wantErr)
+				require.Empty(t, got)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}

internal/downward/testdata/invalidlabels/labels

@@ -0,0 +1 @@
+invalid

internal/downward/testdata/invalidlabels/namespace

@@ -0,0 +1 @@
+test-namespace

internal/downward/testdata/missinglabels/namespace

@@ -0,0 +1 @@
+test-namespace

internal/downward/testdata/valid/labels

@@ -0,0 +1,2 @@
+foo="bar"
+bat="baz"

internal/downward/testdata/valid/namespace

@@ -0,0 +1 @@
+test-namespace