Merge pull request #46235 from droot/cmd-printer-refactor

pkg/kubectl/cmd/BUILD

@@ -92,6 +92,7 @@ go_library(
         "//pkg/kubectl/cmd/templates:go_default_library",
         "//pkg/kubectl/cmd/util:go_default_library",
         "//pkg/kubectl/cmd/util/editor:go_default_library",
+        "//pkg/kubectl/cmd/util/openapi:go_default_library",
         "//pkg/kubectl/metricsutil:go_default_library",
         "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
@@ -208,6 +209,7 @@ go_test(
         "//pkg/kubectl:go_default_library",
         "//pkg/kubectl/cmd/testing:go_default_library",
         "//pkg/kubectl/cmd/util:go_default_library",
+        "//pkg/kubectl/cmd/util/openapi:go_default_library",
         "//pkg/kubectl/plugins:go_default_library",
         "//pkg/kubectl/resource:go_default_library",
         "//pkg/printers:go_default_library",
@@ -215,6 +217,7 @@ go_test(
         "//pkg/util/i18n:go_default_library",
         "//pkg/util/strings:go_default_library",
         "//pkg/util/term:go_default_library",
+        "//vendor/github.com/go-openapi/spec:go_default_library",
         "//vendor/github.com/spf13/cobra:go_default_library",
         "//vendor/github.com/stretchr/testify/assert:go_default_library",
         "//vendor/gopkg.in/yaml.v2:go_default_library",

pkg/kubectl/cmd/config/view.go

@@ -81,7 +81,7 @@ func NewCmdConfigView(out, errOut io.Writer, ConfigAccess clientcmd.ConfigAccess
 				cmd.Flags().Set("output", defaultOutputFormat)
 			}
 
-			printer, err := cmdutil.PrinterForCommand(cmd, meta.NewDefaultRESTMapper(nil, nil), latest.Scheme, nil, []runtime.Decoder{latest.Codec}, printers.PrintOptions{})
+			printer, err := cmdutil.PrinterForCommand(cmd, nil, meta.NewDefaultRESTMapper(nil, nil), latest.Scheme, nil, []runtime.Decoder{latest.Codec}, printers.PrintOptions{})
 			cmdutil.CheckErr(err)
 			printer = printers.NewVersionedPrinter(printer, latest.Scheme, latest.ExternalVersion)
 

pkg/kubectl/cmd/convert.go

@@ -164,7 +164,7 @@ func (o *ConvertOptions) Complete(f cmdutil.Factory, out io.Writer, cmd *cobra.C
 		cmd.Flags().Set("output", outputFormat)
 	}
 	o.encoder = f.JSONEncoder()
-	o.printer, err = f.PrinterForCommand(cmd, printers.PrintOptions{})
+	o.printer, err = f.PrinterForCommand(cmd, nil, printers.PrintOptions{})
 	if err != nil {
 		return err
 	}

pkg/kubectl/cmd/get.go

@@ -19,6 +19,7 @@ package cmd
 import (
 	"fmt"
 	"io"
+	"strings"
 
 	"github.com/golang/glog"
 	"github.com/spf13/cobra"
@@ -33,6 +34,7 @@ import (
 	"k8s.io/kubernetes/pkg/kubectl"
 	"k8s.io/kubernetes/pkg/kubectl/cmd/templates"
 	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
 	"k8s.io/kubernetes/pkg/kubectl/resource"
 	"k8s.io/kubernetes/pkg/printers"
 	"k8s.io/kubernetes/pkg/util/i18n"
@@ -90,6 +92,10 @@ var (
 		kubectl get all`))
 )
 
+const (
+	useOpenAPIPrintColumnFlagLabel = "experimental-use-openapi-print-columns"
+)
+
 // NewCmdGet creates a command object for the generic "get" action, which
 // retrieves one or more resources from a server.
 func NewCmdGet(f cmdutil.Factory, out io.Writer, errOut io.Writer) *cobra.Command {
@@ -128,6 +134,7 @@ func NewCmdGet(f cmdutil.Factory, out io.Writer, errOut io.Writer) *cobra.Comman
 	cmd.Flags().BoolVar(&options.IgnoreNotFound, "ignore-not-found", false, "Treat \"resource not found\" as a successful retrieval.")
 	cmd.Flags().StringSliceP("label-columns", "L", []string{}, "Accepts a comma separated list of labels that are going to be presented as columns. Names are case-sensitive. You can also use multiple flag options like -L label1 -L label2...")
 	cmd.Flags().Bool("export", false, "If true, use 'export' for the resources.  Exported resources are stripped of cluster-specific information.")
+	addOpenAPIPrintColumnFlags(cmd)
 	usage := "identifying the resource to get from a server."
 	cmdutil.AddFilenameOptionFlags(cmd, &options.FilenameOptions, usage)
 	cmdutil.AddInclude3rdPartyFlags(cmd)
@@ -219,7 +226,7 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 		}
 		info := infos[0]
 		mapping := info.ResourceMapping()
-		printer, err := f.PrinterForMapping(cmd, mapping, allNamespaces)
+		printer, err := f.PrinterForMapping(cmd, nil, mapping, allNamespaces)
 		if err != nil {
 			return err
 		}
@@ -299,7 +306,7 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 		return err
 	}
 
-	printer, err := f.PrinterForCommand(cmd, printers.PrintOptions{})
+	printer, err := f.PrinterForCommand(cmd, nil, printers.PrintOptions{})
 	if err != nil {
 		return err
 	}
@@ -418,6 +425,8 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 	var lastMapping *meta.RESTMapping
 	w := printers.GetNewTabWriter(out)
 
+	useOpenAPIPrintColumns := cmdutil.GetFlagBool(cmd, useOpenAPIPrintColumnFlagLabel)
+
 	if resource.MultipleTypesRequested(args) || cmdutil.MustPrintWithKinds(objs, infos, sorter) {
 		showKind = true
 	}
@@ -426,6 +435,7 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 	for ix := range objs {
 		var mapping *meta.RESTMapping
 		var original runtime.Object
+
 		if sorter != nil {
 			mapping = infos[sorter.OriginalPosition(ix)].Mapping
 			original = infos[sorter.OriginalPosition(ix)].Object
@@ -437,7 +447,15 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 			if printer != nil {
 				w.Flush()
 			}
-			printer, err = f.PrinterForMapping(cmd, mapping, allNamespaces)
+
+			var outputOpts *printers.OutputOptions
+			// if cmd does not specify output format and useOpenAPIPrintColumnFlagLabel flag is true,
+			// then get the default output options for this mapping from OpenAPI schema.
+			if !cmdSpecifiesOutputFmt(cmd) && useOpenAPIPrintColumns {
+				outputOpts, _ = outputOptsForMappingFromOpenAPI(f, cmdutil.GetOpenAPICacheDir(cmd), mapping)
+			}
+
+			printer, err = f.PrinterForMapping(cmd, outputOpts, mapping, allNamespaces)
 			if err != nil {
 				if !errs.Has(err.Error()) {
 					errs.Insert(err.Error())
@@ -498,7 +516,13 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 			}
 			continue
 		}
-		if err := printer.PrintObj(decodedObj, w); err != nil {
+		objToPrint := decodedObj
+		if printer.IsGeneric() {
+			// use raw object as recieved from the builder when using generic
+			// printer instead of decodedObj
+			objToPrint = original
+		}
+		if err := printer.PrintObj(objToPrint, w); err != nil {
 			if !errs.Has(err.Error()) {
 				errs.Insert(err.Error())
 				allErrs = append(allErrs, err)
@@ -511,6 +535,59 @@ func RunGet(f cmdutil.Factory, out, errOut io.Writer, cmd *cobra.Command, args [
 	return utilerrors.NewAggregate(allErrs)
 }
 
+func addOpenAPIPrintColumnFlags(cmd *cobra.Command) {
+	cmd.Flags().Bool(useOpenAPIPrintColumnFlagLabel, false, "If true, use x-kubernetes-print-column metadata (if present) from openapi schema for displaying a resource.")
+	// marking it deprecated so that it is hidden from usage/help text.
+	cmd.Flags().MarkDeprecated(useOpenAPIPrintColumnFlagLabel, "its an experimental feature.")
+}
+
 func shouldGetNewPrinterForMapping(printer printers.ResourcePrinter, lastMapping, mapping *meta.RESTMapping) bool {
 	return printer == nil || lastMapping == nil || mapping == nil || mapping.Resource != lastMapping.Resource
 }
+
+func cmdSpecifiesOutputFmt(cmd *cobra.Command) bool {
+	return cmdutil.GetFlagString(cmd, "output") != ""
+}
+
+// outputOptsForMappingFromOpenAPI looks for the output format metatadata in the
+// openapi schema and returns the output options for the mapping if found.
+func outputOptsForMappingFromOpenAPI(f cmdutil.Factory, openAPIcacheDir string, mapping *meta.RESTMapping) (*printers.OutputOptions, bool) {
+
+	// user has not specified any output format, check if OpenAPI has
+	// default specification to print this resource type
+	api, err := f.OpenAPISchema(openAPIcacheDir)
+	if err != nil {
+		// Error getting schema
+		return nil, false
+	}
+	// Found openapi metadata for this resource
+	kind, found := api.LookupResource(mapping.GroupVersionKind)
+	if !found {
+		// Kind not found, return empty columns
+		return nil, false
+	}
+
+	columns, found := openapi.GetPrintColumns(kind.Extensions)
+	if !found {
+		// Extension not found, return empty columns
+		return nil, false
+	}
+
+	return outputOptsFromStr(columns)
+}
+
+// outputOptsFromStr parses the print-column metadata and generates printer.OutputOptions object.
+func outputOptsFromStr(columnStr string) (*printers.OutputOptions, bool) {
+	if columnStr == "" {
+		return nil, false
+	}
+	parts := strings.SplitN(columnStr, "=", 2)
+	if len(parts) < 2 {
+		return nil, false
+	}
+	return &printers.OutputOptions{
+		FmtType:          parts[0],
+		FmtArg:           parts[1],
+		AllowMissingKeys: true,
+	}, true
+}

pkg/kubectl/cmd/get_test.go

@@ -26,6 +26,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/go-openapi/spec"
+
 	apiequality "k8s.io/apimachinery/pkg/api/equality"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -42,6 +44,7 @@ import (
 	"k8s.io/kubernetes/pkg/api/testapi"
 	apitesting "k8s.io/kubernetes/pkg/api/testing"
 	cmdtesting "k8s.io/kubernetes/pkg/kubectl/cmd/testing"
+	"k8s.io/kubernetes/pkg/kubectl/cmd/util/openapi"
 )
 
 func testData() (*api.PodList, *api.ServiceList, *api.ReplicationControllerList) {
@@ -185,6 +188,56 @@ func TestGetSchemaObject(t *testing.T) {
 	}
 }
 
+func TestGetObjectsWithOpenAPIOutputFormatPresent(t *testing.T) {
+	pods, _, _ := testData()
+
+	f, tf, codec, _ := cmdtesting.NewAPIFactory()
+	tf.Printer = &testPrinter{}
+	// overide the openAPISchema function to return custom output
+	// for Pod type.
+	tf.OpenAPISchemaFunc = testOpenAPISchemaData
+	tf.UnstructuredClient = &fake.RESTClient{
+		APIRegistry:          api.Registry,
+		NegotiatedSerializer: unstructuredSerializer,
+		Resp:                 &http.Response{StatusCode: 200, Header: defaultHeader(), Body: objBody(codec, &pods.Items[0])},
+	}
+	tf.Namespace = "test"
+	buf := bytes.NewBuffer([]byte{})
+	errBuf := bytes.NewBuffer([]byte{})
+
+	cmd := NewCmdGet(f, buf, errBuf)
+	cmd.SetOutput(buf)
+	cmd.Flags().Set(useOpenAPIPrintColumnFlagLabel, "true")
+	cmd.Run(cmd, []string{"pods", "foo"})
+
+	expected := []runtime.Object{&pods.Items[0]}
+	verifyObjects(t, expected, tf.Printer.(*testPrinter).Objects)
+
+	if len(buf.String()) == 0 {
+		t.Errorf("unexpected empty output")
+	}
+}
+
+func testOpenAPISchemaData() (*openapi.Resources, error) {
+	return &openapi.Resources{
+		GroupVersionKindToName: map[schema.GroupVersionKind]string{
+			{
+				Version: "v1",
+				Kind:    "Pod",
+			}: "io.k8s.kubernetes.pkg.api.v1.Pod",
+		},
+		NameToDefinition: map[string]openapi.Kind{
+			"io.k8s.kubernetes.pkg.api.v1.Pod": {
+				Name:       "io.k8s.kubernetes.pkg.api.v1.Pod",
+				IsResource: false,
+				Extensions: spec.Extensions{
+					"x-kubernetes-print-columns": "custom-columns=NAME:.metadata.name,RSRC:.metadata.resourceVersion",
+				},
+			},
+		},
+	}, nil
+}
+
 func TestGetObjects(t *testing.T) {
 	pods, _, _ := testData()
 

pkg/kubectl/cmd/testing/fake.go

@@ -23,7 +23,7 @@ import (
 	"path/filepath"
 	"time"
 
-	"github.com/emicklei/go-restful-swagger12"
+	swagger "github.com/emicklei/go-restful-swagger12"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 
@@ -230,6 +230,7 @@ type TestFactory struct {
 
 	ClientForMappingFunc             func(mapping *meta.RESTMapping) (resource.RESTClient, error)
 	UnstructuredClientForMappingFunc func(mapping *meta.RESTMapping) (resource.RESTClient, error)
+	OpenAPISchemaFunc                func() (*openapi.Resources, error)
 }
 
 type FakeFactory struct {
@@ -336,7 +337,7 @@ func (f *FakeFactory) Describer(*meta.RESTMapping) (printers.Describer, error) {
 	return f.tf.Describer, f.tf.Err
 }
 
-func (f *FakeFactory) PrinterForCommand(cmd *cobra.Command, options printers.PrintOptions) (printers.ResourcePrinter, error) {
+func (f *FakeFactory) PrinterForCommand(cmd *cobra.Command, outputOpts *printers.OutputOptions, options printers.PrintOptions) (printers.ResourcePrinter, error) {
 	return f.tf.Printer, f.tf.Err
 }
 
@@ -460,7 +461,7 @@ func (f *FakeFactory) PrintObject(cmd *cobra.Command, mapper meta.RESTMapper, ob
 	return nil
 }
 
-func (f *FakeFactory) PrinterForMapping(cmd *cobra.Command, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
+func (f *FakeFactory) PrinterForMapping(cmd *cobra.Command, outputOpts *printers.OutputOptions, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
 	return f.tf.Printer, f.tf.Err
 }
 
@@ -617,7 +618,7 @@ func (f *fakeAPIFactory) UnstructuredClientForMapping(m *meta.RESTMapping) (reso
 	return f.tf.UnstructuredClient, f.tf.Err
 }
 
-func (f *fakeAPIFactory) PrinterForCommand(cmd *cobra.Command, options printers.PrintOptions) (printers.ResourcePrinter, error) {
+func (f *fakeAPIFactory) PrinterForCommand(cmd *cobra.Command, outputOpts *printers.OutputOptions, options printers.PrintOptions) (printers.ResourcePrinter, error) {
 	return f.tf.Printer, f.tf.Err
 }
 
@@ -691,14 +692,14 @@ func (f *fakeAPIFactory) PrintObject(cmd *cobra.Command, mapper meta.RESTMapper,
 		return err
 	}
 
-	printer, err := f.PrinterForMapping(cmd, mapping, false)
+	printer, err := f.PrinterForMapping(cmd, nil, mapping, false)
 	if err != nil {
 		return err
 	}
 	return printer.PrintObj(obj, out)
 }
 
-func (f *fakeAPIFactory) PrinterForMapping(cmd *cobra.Command, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
+func (f *fakeAPIFactory) PrinterForMapping(cmd *cobra.Command, outputOpts *printers.OutputOptions, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
 	return f.tf.Printer, f.tf.Err
 }
 
@@ -712,6 +713,17 @@ func (f *fakeAPIFactory) SuggestedPodTemplateResources() []schema.GroupResource
 	return []schema.GroupResource{}
 }
 
+func (f *fakeAPIFactory) SwaggerSchema(schema.GroupVersionKind) (*swagger.ApiDeclaration, error) {
+	return nil, nil
+}
+
+func (f *fakeAPIFactory) OpenAPISchema(cacheDir string) (*openapi.Resources, error) {
+	if f.tf.OpenAPISchemaFunc != nil {
+		return f.tf.OpenAPISchemaFunc()
+	}
+	return &openapi.Resources{}, nil
+}
+
 func NewAPIFactory() (cmdutil.Factory, *TestFactory, runtime.Codec, runtime.NegotiatedSerializer) {
 	t := &TestFactory{
 		Validator: validation.NullSchema{},

pkg/kubectl/cmd/util/factory.go

@@ -233,10 +233,12 @@ type BuilderFactory interface {
 	// are declared on the command (see AddPrinterFlags). Returns a printer, or an error if a printer
 	// could not be found.
 	// TODO: Break the dependency on cmd here.
-	PrinterForCommand(cmd *cobra.Command, options printers.PrintOptions) (printers.ResourcePrinter, error)
+	PrinterForCommand(cmd *cobra.Command, outputOpts *printers.OutputOptions, options printers.PrintOptions) (printers.ResourcePrinter, error)
 	// PrinterForMapping returns a printer suitable for displaying the provided resource type.
 	// Requires that printer flags have been added to cmd (see AddPrinterFlags).
-	PrinterForMapping(cmd *cobra.Command, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error)
+	// Returns a printer, true if the printer is generic (is not internal), or
+	// an error if a printer could not be found.
+	PrinterForMapping(cmd *cobra.Command, outputOpts *printers.OutputOptions, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error)
 	// PrintObject prints an api object given command line flags to modify the output format
 	PrintObject(cmd *cobra.Command, mapper meta.RESTMapper, obj runtime.Object, out io.Writer) error
 	// One stop shopping for a Builder

pkg/kubectl/cmd/util/factory_builder.go

@@ -48,7 +48,7 @@ func NewBuilderFactory(clientAccessFactory ClientAccessFactory, objectMappingFac
 	return f
 }
 
-func (f *ring2Factory) PrinterForCommand(cmd *cobra.Command, options printers.PrintOptions) (printers.ResourcePrinter, error) {
+func (f *ring2Factory) PrinterForCommand(cmd *cobra.Command, outputOpts *printers.OutputOptions, options printers.PrintOptions) (printers.ResourcePrinter, error) {
 	mapper, typer, err := f.objectMappingFactory.UnstructuredObject()
 	if err != nil {
 		return nil, err
@@ -56,10 +56,10 @@ func (f *ring2Factory) PrinterForCommand(cmd *cobra.Command, options printers.Pr
 	// TODO: used by the custom column implementation and the name implementation, break this dependency
 	decoders := []runtime.Decoder{f.clientAccessFactory.Decoder(true), unstructured.UnstructuredJSONScheme}
 	encoder := f.clientAccessFactory.JSONEncoder()
-	return PrinterForCommand(cmd, mapper, typer, encoder, decoders, options)
+	return PrinterForCommand(cmd, outputOpts, mapper, typer, encoder, decoders, options)
 }
 
-func (f *ring2Factory) PrinterForMapping(cmd *cobra.Command, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
+func (f *ring2Factory) PrinterForMapping(cmd *cobra.Command, outputOpts *printers.OutputOptions, mapping *meta.RESTMapping, withNamespace bool) (printers.ResourcePrinter, error) {
 	// Some callers do not have "label-columns" so we can't use the GetFlagStringSlice() helper
 	columnLabel, err := cmd.Flags().GetStringSlice("label-columns")
 	if err != nil {
@@ -76,7 +76,7 @@ func (f *ring2Factory) PrinterForMapping(cmd *cobra.Command, mapping *meta.RESTM
 		ColumnLabels:       columnLabel,
 	}
 
-	printer, err := f.PrinterForCommand(cmd, options)
+	printer, err := f.PrinterForCommand(cmd, outputOpts, options)
 	if err != nil {
 		return nil, err
 	}
@@ -132,7 +132,7 @@ func (f *ring2Factory) PrintObject(cmd *cobra.Command, mapper meta.RESTMapper, o
 		return err
 	}
 
-	printer, err := f.PrinterForMapping(cmd, mapping, false)
+	printer, err := f.PrinterForMapping(cmd, nil, mapping, false)
 	if err != nil {
 		return err
 	}

pkg/kubectl/cmd/util/factory_object_mapping.go

@@ -27,7 +27,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/emicklei/go-restful-swagger12"
+	swagger "github.com/emicklei/go-restful-swagger12"
 
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

pkg/kubectl/cmd/util/helpers.go

@@ -417,6 +417,10 @@ func AddOpenAPIFlags(cmd *cobra.Command) {
 	cmd.MarkFlagFilename("schema-cache-dir")
 }
 
+func GetOpenAPICacheDir(cmd *cobra.Command) string {
+	return GetFlagString(cmd, "schema-cache-dir")
+}
+
 func AddFilenameOptionFlags(cmd *cobra.Command, options *resource.FilenameOptions, usage string) {
 	kubectl.AddJsonFilenameFlag(cmd, &options.Filenames, "Filename, directory, or URL to files "+usage)
 	cmd.Flags().BoolVarP(&options.Recursive, "recursive", "R", options.Recursive, "Process the directory used in -f, --filename recursively. Useful when you want to manage related manifests organized within the same directory.")

pkg/kubectl/cmd/util/openapi/BUILD

@@ -12,6 +12,7 @@ go_library(
     name = "go_default_library",
     srcs = [
         "doc.go",
+        "extensions.go",
         "openapi.go",
         "openapi_cache.go",
         "openapi_getter.go",

pkg/kubectl/cmd/util/openapi/extensions.go

+/*
+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 openapi
+
+import "github.com/go-openapi/spec"
+
+const PrintColumnsKey = "x-kubernetes-print-columns"
+
+// GetPrintColumns looks for the open API extension for the display columns.
+func GetPrintColumns(extensions spec.Extensions) (string, bool) {
+	return extensions.GetString(PrintColumnsKey)
+}

pkg/kubectl/cmd/util/openapi/openapi.go

@@ -194,7 +194,7 @@ func (o *Resources) parseDefinition(name string, s spec.Schema) Kind {
 		Fields:           map[string]Type{},
 	}
 	if err != nil {
-		glog.Warning(err)
+		glog.V(2).Info(err)
 	}
 
 	// Definition represents a primitive type - e.g.

pkg/kubectl/cmd/util/printing.go

@@ -105,38 +105,18 @@ func ValidateOutputArgs(cmd *cobra.Command) error {
 	return nil
 }
 
-// PrinterForCommand returns the default printer for this command.
-// Requires that printer flags have been added to cmd (see AddPrinterFlags).
-func PrinterForCommand(cmd *cobra.Command, mapper meta.RESTMapper, typer runtime.ObjectTyper, encoder runtime.Encoder, decoders []runtime.Decoder, options printers.PrintOptions) (printers.ResourcePrinter, error) {
-	outputFormat := GetFlagString(cmd, "output")
-
-	// templates are logically optional for specifying a format.
-	// TODO once https://github.com/kubernetes/kubernetes/issues/12668 is fixed, this should fall back to GetFlagString
-	templateFile, _ := cmd.Flags().GetString("template")
-	if len(outputFormat) == 0 && len(templateFile) != 0 {
-		outputFormat = "template"
+// PrinterForCommand returns the printer for the outputOptions (if given) or
+// returns the default printer for the command. Requires that printer flags have
+// been added to cmd (see AddPrinterFlags).
+// TODO: remove the dependency on cmd object
+func PrinterForCommand(cmd *cobra.Command, outputOpts *printers.OutputOptions, mapper meta.RESTMapper, typer runtime.ObjectTyper, encoder runtime.Encoder, decoders []runtime.Decoder, options printers.PrintOptions) (printers.ResourcePrinter, error) {
+
+	if outputOpts == nil {
+		outputOpts = extractOutputOptions(cmd)
 	}
 
-	templateFormat := []string{
-		"go-template=", "go-template-file=", "jsonpath=", "jsonpath-file=", "custom-columns=", "custom-columns-file=",
-	}
-	for _, format := range templateFormat {
-		if strings.HasPrefix(outputFormat, format) {
-			templateFile = outputFormat[len(format):]
-			outputFormat = format[:len(format)-1]
-		}
-	}
-
-	// this function may be invoked by a command that did not call AddPrinterFlags first, so we need
-	// to be safe about how we access the allow-missing-template-keys flag
-	allowMissingTemplateKeys := false
-	if cmd.Flags().Lookup("allow-missing-template-keys") != nil {
-		allowMissingTemplateKeys = GetFlagBool(cmd, "allow-missing-template-keys")
-	}
-	printer, err := printers.GetStandardPrinter(
-		outputFormat, templateFile, GetFlagBool(cmd, "no-headers"), allowMissingTemplateKeys,
-		mapper, typer, encoder, decoders, options,
-	)
+	printer, err := printers.GetStandardPrinter(outputOpts,
+		GetFlagBool(cmd, "no-headers"), mapper, typer, encoder, decoders, options)
 	if err != nil {
 		return nil, err
 	}
@@ -149,12 +129,12 @@ func PrinterForCommand(cmd *cobra.Command, mapper meta.RESTMapper, typer runtime
 // object passed is non-generic, it attempts to print the object using a HumanReadablePrinter.
 // Requires that printer flags have been added to cmd (see AddPrinterFlags).
 func PrintResourceInfoForCommand(cmd *cobra.Command, info *resource.Info, f Factory, out io.Writer) error {
-	printer, err := f.PrinterForCommand(cmd, printers.PrintOptions{})
+	printer, err := f.PrinterForCommand(cmd, nil, printers.PrintOptions{})
 	if err != nil {
 		return err
 	}
 	if !printer.IsGeneric() {
-		printer, err = f.PrinterForMapping(cmd, nil, false)
+		printer, err = f.PrinterForMapping(cmd, nil, nil, false)
 		if err != nil {
 			return err
 		}
@@ -162,6 +142,50 @@ func PrintResourceInfoForCommand(cmd *cobra.Command, info *resource.Info, f Fact
 	return printer.PrintObj(info.Object, out)
 }
 
+// extractOutputOptions parses printer specific commandline args and returns
+// printers.OutputsOptions object.
+func extractOutputOptions(cmd *cobra.Command) *printers.OutputOptions {
+	flags := cmd.Flags()
+
+	var outputFormat string
+	if flags.Lookup("output") != nil {
+		outputFormat = GetFlagString(cmd, "output")
+	}
+
+	// templates are logically optional for specifying a format.
+	// TODO once https://github.com/kubernetes/kubernetes/issues/12668 is fixed, this should fall back to GetFlagString
+	var templateFile string
+	if flags.Lookup("template") != nil {
+		templateFile = GetFlagString(cmd, "template")
+	}
+	if len(outputFormat) == 0 && len(templateFile) != 0 {
+		outputFormat = "template"
+	}
+
+	templateFormats := []string{
+		"go-template=", "go-template-file=", "jsonpath=", "jsonpath-file=", "custom-columns=", "custom-columns-file=",
+	}
+	for _, format := range templateFormats {
+		if strings.HasPrefix(outputFormat, format) {
+			templateFile = outputFormat[len(format):]
+			outputFormat = format[:len(format)-1]
+		}
+	}
+
+	// this function may be invoked by a command that did not call AddPrinterFlags first, so we need
+	// to be safe about how we access the allow-missing-template-keys flag
+	allowMissingTemplateKeys := false
+	if flags.Lookup("allow-missing-template-keys") != nil {
+		allowMissingTemplateKeys = GetFlagBool(cmd, "allow-missing-template-keys")
+	}
+
+	return &printers.OutputOptions{
+		FmtType:          outputFormat,
+		FmtArg:           templateFile,
+		AllowMissingKeys: allowMissingTemplateKeys,
+	}
+}
+
 func maybeWrapSortingPrinter(cmd *cobra.Command, printer printers.ResourcePrinter) printers.ResourcePrinter {
 	sorting, err := cmd.Flags().GetString("sort-by")
 	if err != nil {

pkg/printers/customcolumn.go

@@ -153,6 +153,9 @@ type CustomColumnsPrinter struct {
 	Columns   []Column
 	Decoder   runtime.Decoder
 	NoHeaders bool
+	// lastType records type of resource printed last so that we don't repeat
+	// header while printing same type of resources.
+	lastType reflect.Type
 }
 
 func (s *CustomColumnsPrinter) AfterPrint(w io.Writer, res string) error {
@@ -162,12 +165,14 @@ func (s *CustomColumnsPrinter) AfterPrint(w io.Writer, res string) error {
 func (s *CustomColumnsPrinter) PrintObj(obj runtime.Object, out io.Writer) error {
 	w := tabwriter.NewWriter(out, columnwidth, tabwidth, padding, padding_character, flags)
 
-	if !s.NoHeaders {
+	t := reflect.TypeOf(obj)
+	if !s.NoHeaders && t != s.lastType {
 		headers := make([]string, len(s.Columns))
 		for ix := range s.Columns {
 			headers[ix] = s.Columns[ix].Header
 		}
 		fmt.Fprintln(w, strings.Join(headers, "\t"))
+		s.lastType = t
 	}
 	parsers := make([]*jsonpath.JSONPath, len(s.Columns))
 	for ix := range s.Columns {

pkg/printers/interface.go

@@ -100,3 +100,13 @@ type ErrNoDescriber struct {
 func (e ErrNoDescriber) Error() string {
 	return fmt.Sprintf("no describer has been defined for %v", e.Types)
 }
+
+// OutputOptions represents resource output options which is used to generate a resource printer.
+type OutputOptions struct {
+	// supported Format types can be found in pkg/printers/printers.go
+	FmtType string
+	FmtArg  string
+
+	// indicates if it is OK to ignore missing keys for rendering an output template.
+	AllowMissingKeys bool
+}

pkg/printers/printers.go

@@ -29,7 +29,13 @@ import (
 // a printer or an error. The printer is agnostic to schema versions, so you must
 // send arguments to PrintObj in the version you wish them to be shown using a
 // VersionedPrinter (typically when generic is true).
-func GetStandardPrinter(format, formatArgument string, noHeaders, allowMissingTemplateKeys bool, mapper meta.RESTMapper, typer runtime.ObjectTyper, encoder runtime.Encoder, decoders []runtime.Decoder, options PrintOptions) (ResourcePrinter, error) {
+func GetStandardPrinter(outputOpts *OutputOptions, noHeaders bool, mapper meta.RESTMapper, typer runtime.ObjectTyper, encoder runtime.Encoder, decoders []runtime.Decoder, options PrintOptions) (ResourcePrinter, error) {
+	if outputOpts == nil {
+		return nil, fmt.Errorf("no output options specified")
+	}
+
+	format, formatArgument, allowMissingTemplateKeys := outputOpts.FmtType, outputOpts.FmtArg, outputOpts.AllowMissingKeys
+
 	var printer ResourcePrinter
 	switch format {