wire through json/yaml print flags

pkg/printers/BUILD

@@ -13,6 +13,7 @@ go_library(
         "humanreadable.go",
         "interface.go",
         "json.go",
+        "json_yaml_flags.go",
         "jsonpath.go",
         "name.go",
         "printers.go",
@@ -24,6 +25,7 @@ go_library(
     deps = [
         "//vendor/github.com/ghodss/yaml:go_default_library",
         "//vendor/github.com/golang/glog:go_default_library",
+        "//vendor/github.com/spf13/cobra:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/api/meta:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1/unstructured:go_default_library",
@@ -39,7 +41,10 @@ go_library(
 
 go_test(
     name = "go_default_xtest",
-    srcs = ["customcolumn_test.go"],
+    srcs = [
+        "customcolumn_test.go",
+        "json_yaml_flags_test.go",
+    ],
     deps = [
         ":go_default_library",
         "//pkg/api/legacyscheme:go_default_library",

pkg/printers/json_yaml_flags.go

@@ -0,0 +1,57 @@
+/*
+Copyright 2018 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 printers
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+// JSONYamlPrintFlags provides default flags necessary for json/yaml printing.
+// Given the following flag values, a printer can be requested that knows
+// how to handle printing based on these values.
+type JSONYamlPrintFlags struct{}
+
+// ToPrinter receives an outputFormat and returns a printer capable of
+// handling --output=(yaml|json) printing.
+// Returns false if the specified outputFormat does not match a supported format.
+// Supported Format types can be found in pkg/printers/printers.go
+func (f *JSONYamlPrintFlags) ToPrinter(outputFormat string) (ResourcePrinter, bool, error) {
+	outputFormat = strings.ToLower(outputFormat)
+	switch outputFormat {
+	case "json":
+		return &JSONPrinter{}, true, nil
+	case "yaml":
+		return &YAMLPrinter{}, true, nil
+	case "":
+		return nil, false, fmt.Errorf("missing output format")
+	default:
+		return nil, false, nil
+	}
+}
+
+// AddFlags receives a *cobra.Command reference and binds
+// flags related to JSON or Yaml printing to it
+func (f *JSONYamlPrintFlags) AddFlags(c *cobra.Command) {}
+
+// NewJSONYamlPrintFlags returns flags associated with
+// yaml or json printing, with default values set.
+func NewJSONYamlPrintFlags() *JSONYamlPrintFlags {
+	return &JSONYamlPrintFlags{}
+}

pkg/printers/json_yaml_flags_test.go

@@ -0,0 +1,89 @@
+/*
+Copyright 2018 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 printers_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/kubernetes/pkg/printers"
+)
+
+func TestPrinterSupportsExpectedJSONYamlFormats(t *testing.T) {
+	testObject := &v1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "foo"}}
+
+	testCases := []struct {
+		name           string
+		outputFormat   string
+		expectedOutput string
+		expectNoMatch  bool
+	}{
+		{
+			name:           "json output format matches a json printer",
+			outputFormat:   "json",
+			expectedOutput: "\"name\": \"foo\"",
+		},
+		{
+			name:           "yaml output format matches a yaml printer",
+			outputFormat:   "yaml",
+			expectedOutput: "name: foo",
+		},
+		{
+			name:          "output format for another printer does not match a json/yaml printer",
+			outputFormat:  "jsonpath",
+			expectNoMatch: true,
+		},
+		{
+			name:          "invalid output format results in no match",
+			outputFormat:  "invalid",
+			expectNoMatch: true,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			printFlags := printers.JSONYamlPrintFlags{}
+
+			p, matched, err := printFlags.ToPrinter(tc.outputFormat)
+			if tc.expectNoMatch {
+				if matched {
+					t.Fatalf("expected no printer matches for output format %q", tc.outputFormat)
+				}
+				return
+			}
+			if !matched {
+				t.Fatalf("expected to match template printer for output format %q", tc.outputFormat)
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+
+			out := bytes.NewBuffer([]byte{})
+			err = p.PrintObj(testObject, out)
+			if err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+
+			if !strings.Contains(out.String(), tc.expectedOutput) {
+				t.Errorf("unexpected output: expecting %q, got %q", tc.expectedOutput, out.String())
+			}
+		})
+	}
+}

pkg/printers/printers.go

@@ -34,11 +34,17 @@ func GetStandardPrinter(typer runtime.ObjectTyper, encoder runtime.Encoder, deco
 	var printer ResourcePrinter
 	switch format {
 
-	case "json":
-		printer = &JSONPrinter{}
+	case "json", "yaml":
+		jsonYamlFlags := NewJSONYamlPrintFlags()
+		p, matched, err := jsonYamlFlags.ToPrinter(format)
+		if !matched {
+			return nil, fmt.Errorf("unable to match a printer to handle current print options")
+		}
+		if err != nil {
+			return nil, err
+		}
 
-	case "yaml":
-		printer = &YAMLPrinter{}
+		printer = p
 
 	case "name":
 		printer = &NamePrinter{