feature(show): support jsonpath output for helm show value

Signed-off-by: Dong Gang <dong.gang@daocloud.io>

cmd/helm/show.go

@@ -151,6 +151,9 @@ func addShowFlags(subCmd *cobra.Command, client *action.Show) {
 	f := subCmd.Flags()
 
 	f.BoolVar(&client.Devel, "devel", false, "use development versions, too. Equivalent to version '>0.0.0-0'. If --version is set, this is ignored")
+	if subCmd.Name() == "values" {
+		f.StringVar(&client.JsonPathTemplate, "jsonpath", "", "use jsonpath output format")
+	}
 	addChartPathOptionsFlags(f, &client.ChartPathOptions)
 
 	err := subCmd.RegisterFlagCompletionFunc("version", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {

pkg/action/show.go

@@ -20,11 +20,12 @@ import (
 	"fmt"
 	"strings"
 
+	"helm.sh/helm/v3/pkg/chartutil"
+	"k8s.io/cli-runtime/pkg/printers"
 	"sigs.k8s.io/yaml"
 
 	"helm.sh/helm/v3/pkg/chart"
 	"helm.sh/helm/v3/pkg/chart/loader"
-	"helm.sh/helm/v3/pkg/chartutil"
 )
 
 // ShowOutputFormat is the format of the output of `helm show`
@@ -52,9 +53,10 @@ func (o ShowOutputFormat) String() string {
 // It provides the implementation of 'helm show' and its respective subcommands.
 type Show struct {
 	ChartPathOptions
-	Devel        bool
-	OutputFormat ShowOutputFormat
-	chart        *chart.Chart // for testing
+	Devel            bool
+	OutputFormat     ShowOutputFormat
+	JsonPathTemplate string
+	chart            *chart.Chart // for testing
 }
 
 // NewShow creates a new Show object with the given configuration.
@@ -87,9 +89,17 @@ func (s *Show) Run(chartpath string) (string, error) {
 		if s.OutputFormat == ShowAll {
 			fmt.Fprintln(&out, "---")
 		}
-		for _, f := range s.chart.Raw {
-			if f.Name == chartutil.ValuesfileName {
-				fmt.Fprintln(&out, string(f.Data))
+		if s.JsonPathTemplate != "" {
+			printer, err := printers.NewJSONPathPrinter(s.JsonPathTemplate)
+			if err != nil {
+				return "", fmt.Errorf("error parsing jsonpath %s, %v\n", s.JsonPathTemplate, err)
+			}
+			printer.Execute(&out, s.chart.Values)
+		} else {
+			for _, f := range s.chart.Raw {
+				if f.Name == chartutil.ValuesfileName {
+					fmt.Fprintln(&out, string(f.Data))
+				}
 			}
 		}
 	}

pkg/action/show_test.go

@@ -69,3 +69,17 @@ func TestShowNoValues(t *testing.T) {
 		t.Errorf("expected empty values buffer, got %s", output)
 	}
 }
+
+func TestShowValuesByJsonPathFormat(t *testing.T) {
+	client := NewShow(ShowValues)
+	client.JsonPathTemplate = "{$.nestedKey.simpleKey}"
+	client.chart = buildChart(withSampleValues())
+	output, err := client.Run("")
+	if err != nil {
+		t.Fatal(err)
+	}
+	expect := "simpleValue"
+	if output != expect {
+		t.Errorf("Expected\n%q\nGot\n%q\n", expect, output)
+	}
+}