get.go

/*
Copyright 2014 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 get

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/url"

	"github.com/spf13/cobra"

	corev1 "k8s.io/api/core/v1"
	kapierrors "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
	metav1beta1 "k8s.io/apimachinery/pkg/apis/meta/v1beta1"
	"k8s.io/apimachinery/pkg/runtime"
	utilerrors "k8s.io/apimachinery/pkg/util/errors"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/apimachinery/pkg/watch"
	"k8s.io/cli-runtime/pkg/genericclioptions"
	"k8s.io/cli-runtime/pkg/printers"
	"k8s.io/cli-runtime/pkg/resource"
	kubernetesscheme "k8s.io/client-go/kubernetes/scheme"
	"k8s.io/client-go/rest"
	watchtools "k8s.io/client-go/tools/watch"
	cmdutil "k8s.io/kubectl/pkg/cmd/util"
	"k8s.io/kubectl/pkg/rawhttp"
	"k8s.io/kubectl/pkg/util/i18n"
	"k8s.io/kubectl/pkg/util/interrupt"
	utilprinters "k8s.io/kubectl/pkg/util/printers"
	"k8s.io/kubectl/pkg/util/templates"
	utilpointer "k8s.io/utils/pointer"
)

// GetOptions contains the input to the get command.
type GetOptions struct {
	PrintFlags             *PrintFlags
	ToPrinter              func(*meta.RESTMapping, *bool, bool, bool) (printers.ResourcePrinterFunc, error)
	IsHumanReadablePrinter bool
	PrintWithOpenAPICols   bool

	CmdParent string

	resource.FilenameOptions

	Raw       string
	Watch     bool
	WatchOnly bool
	ChunkSize int64

	OutputWatchEvents bool

	LabelSelector     string
	FieldSelector     string
	AllNamespaces     bool
	Namespace         string
	ExplicitNamespace bool

	ServerPrint bool

	NoHeaders      bool
	Sort           bool
	IgnoreNotFound bool
	Export         bool

	genericclioptions.IOStreams
}

var (
	getLong = templates.LongDesc(`
		Display one or many resources

		Prints a table of the most important information about the specified resources.
		You can filter the list using a label selector and the --selector flag. If the
		desired resource type is namespaced you will only see results in your current
		namespace unless you pass --all-namespaces.

		Uninitialized objects are not shown unless --include-uninitialized is passed.

		By specifying the output as 'template' and providing a Go template as the value
		of the --template flag, you can filter the attributes of the fetched resources.`)

	getExample = templates.Examples(i18n.T(`
		# List all pods in ps output format.
		kubectl get pods

		# List all pods in ps output format with more information (such as node name).
		kubectl get pods -o wide

		# List a single replication controller with specified NAME in ps output format.
		kubectl get replicationcontroller web

		# List deployments in JSON output format, in the "v1" version of the "apps" API group:
		kubectl get deployments.v1.apps -o json

		# List a single pod in JSON output format.
		kubectl get -o json pod web-pod-13je7

		# List a pod identified by type and name specified in "pod.yaml" in JSON output format.
		kubectl get -f pod.yaml -o json

		# List resources from a directory with kustomization.yaml - e.g. dir/kustomization.yaml.
		kubectl get -k dir/

		# Return only the phase value of the specified pod.
		kubectl get -o template pod/web-pod-13je7 --template={{.status.phase}}

		# List resource information in custom columns.
		kubectl get pod test-pod -o custom-columns=CONTAINER:.spec.containers[0].name,IMAGE:.spec.containers[0].image

		# List all replication controllers and services together in ps output format.
		kubectl get rc,services

		# List one or more resources by their type and names.
		kubectl get rc/web service/frontend pods/web-pod-13je7`))
)

const (
	useOpenAPIPrintColumnFlagLabel = "use-openapi-print-columns"
	useServerPrintColumns          = "server-print"
)

// NewGetOptions returns a GetOptions with default chunk size 500.
func NewGetOptions(parent string, streams genericclioptions.IOStreams) *GetOptions {
	return &GetOptions{
		PrintFlags: NewGetPrintFlags(),
		CmdParent:  parent,

		IOStreams:   streams,
		ChunkSize:   500,
		ServerPrint: true,
	}
}

// NewCmdGet creates a command object for the generic "get" action, which
// retrieves one or more resources from a server.
func NewCmdGet(parent string, f cmdutil.Factory, streams genericclioptions.IOStreams) *cobra.Command {
	o := NewGetOptions(parent, streams)

	cmd := &cobra.Command{
		Use:                   "get [(-o|--output=)json|yaml|wide|custom-columns=...|custom-columns-file=...|go-template=...|go-template-file=...|jsonpath=...|jsonpath-file=...] (TYPE[.VERSION][.GROUP] [NAME | -l label] | TYPE[.VERSION][.GROUP]/NAME ...) [flags]",
		DisableFlagsInUseLine: true,
		Short:                 i18n.T("Display one or many resources"),
		Long:                  getLong + "\n\n" + cmdutil.SuggestAPIResources(parent),
		Example:               getExample,
		Run: func(cmd *cobra.Command, args []string) {
			cmdutil.CheckErr(o.Complete(f, cmd, args))
			cmdutil.CheckErr(o.Validate(cmd))
			cmdutil.CheckErr(o.Run(f, cmd, args))
		},
		SuggestFor: []string{"list", "ps"},
	}

	o.PrintFlags.AddFlags(cmd)

	cmd.Flags().StringVar(&o.Raw, "raw", o.Raw, "Raw URI to request from the server.  Uses the transport specified by the kubeconfig file.")
	cmd.Flags().BoolVarP(&o.Watch, "watch", "w", o.Watch, "After listing/getting the requested object, watch for changes. Uninitialized objects are excluded if no object name is provided.")
	cmd.Flags().BoolVar(&o.WatchOnly, "watch-only", o.WatchOnly, "Watch for changes to the requested object(s), without listing/getting first.")
	cmd.Flags().BoolVar(&o.OutputWatchEvents, "output-watch-events", o.OutputWatchEvents, "Output watch event objects when --watch or --watch-only is used. Existing objects are output as initial ADDED events.")
	cmd.Flags().Int64Var(&o.ChunkSize, "chunk-size", o.ChunkSize, "Return large lists in chunks rather than all at once. Pass 0 to disable. This flag is beta and may change in the future.")
	cmd.Flags().BoolVar(&o.IgnoreNotFound, "ignore-not-found", o.IgnoreNotFound, "If the requested object does not exist the command will return exit code 0.")
	cmd.Flags().StringVarP(&o.LabelSelector, "selector", "l", o.LabelSelector, "Selector (label query) to filter on, supports '=', '==', and '!='.(e.g. -l key1=value1,key2=value2)")
	cmd.Flags().StringVar(&o.FieldSelector, "field-selector", o.FieldSelector, "Selector (field query) to filter on, supports '=', '==', and '!='.(e.g. --field-selector key1=value1,key2=value2). The server only supports a limited number of field queries per type.")
	cmd.Flags().BoolVarP(&o.AllNamespaces, "all-namespaces", "A", o.AllNamespaces, "If present, list the requested object(s) across all namespaces. Namespace in current context is ignored even if specified with --namespace.")
	cmdutil.AddIncludeUninitializedFlag(cmd)
	addOpenAPIPrintColumnFlags(cmd, o)
	addServerPrintColumnFlags(cmd, o)
	cmd.Flags().BoolVar(&o.Export, "export", o.Export, "If true, use 'export' for the resources.  Exported resources are stripped of cluster-specific information.")
	cmd.Flags().MarkDeprecated("export", "This flag is deprecated and will be removed in future.")
	cmdutil.AddFilenameOptionFlags(cmd, &o.FilenameOptions, "identifying the resource to get from a server.")
	return cmd
}

// Complete takes the command arguments and factory and infers any remaining options.
func (o *GetOptions) Complete(f cmdutil.Factory, cmd *cobra.Command, args []string) error {
	if len(o.Raw) > 0 {
		if len(args) > 0 {
			return fmt.Errorf("arguments may not be passed when --raw is specified")
		}
		return nil
	}

	var err error
	o.Namespace, o.ExplicitNamespace, err = f.ToRawKubeConfigLoader().Namespace()
	if err != nil {
		return err
	}
	if o.AllNamespaces {
		o.ExplicitNamespace = false
	}

	sortBy, err := cmd.Flags().GetString("sort-by")
	if err != nil {
		return err
	}
	o.Sort = len(sortBy) > 0

	o.NoHeaders = cmdutil.GetFlagBool(cmd, "no-headers")

	// TODO (soltysh): currently we don't support custom columns
	// with server side print. So in these cases force the old behavior.
	outputOption := cmd.Flags().Lookup("output").Value.String()
	if outputOption == "custom-columns" {
		o.ServerPrint = false
	}

	templateArg := ""
	if o.PrintFlags.TemplateFlags != nil && o.PrintFlags.TemplateFlags.TemplateArgument != nil {
		templateArg = *o.PrintFlags.TemplateFlags.TemplateArgument
	}

	// human readable printers have special conversion rules, so we determine if we're using one.
	if (len(*o.PrintFlags.OutputFormat) == 0 && len(templateArg) == 0) || *o.PrintFlags.OutputFormat == "wide" {
		o.IsHumanReadablePrinter = true
	}

	o.ToPrinter = func(mapping *meta.RESTMapping, outputObjects *bool, withNamespace bool, withKind bool) (printers.ResourcePrinterFunc, error) {
		// make a new copy of current flags / opts before mutating
		printFlags := o.PrintFlags.Copy()

		if mapping != nil {
			if !cmdSpecifiesOutputFmt(cmd) && o.PrintWithOpenAPICols {
				if apiSchema, err := f.OpenAPISchema(); err == nil {
					printFlags.UseOpenAPIColumns(apiSchema, mapping)
				}
			}
			printFlags.SetKind(mapping.GroupVersionKind.GroupKind())
		}
		if withNamespace {
			printFlags.EnsureWithNamespace()
		}
		if withKind {
			printFlags.EnsureWithKind()
		}

		printer, err := printFlags.ToPrinter()
		if err != nil {
			return nil, err
		}

		if o.Sort {
			printer = &SortingPrinter{Delegate: printer, SortField: sortBy}
		}
		if outputObjects != nil {
			printer = &skipPrinter{delegate: printer, output: outputObjects}
		}
		if o.ServerPrint {
			printer = &TablePrinter{Delegate: printer}
		}
		return printer.PrintObj, nil
	}

	switch {
	case o.Watch || o.WatchOnly:
		if o.Sort {
			fmt.Fprintf(o.IOStreams.ErrOut, "warning: --watch or --watch-only requested, --sort-by will be ignored\n")
		}
	default:
		if len(args) == 0 && cmdutil.IsFilenameSliceEmpty(o.Filenames, o.Kustomize) {
			fmt.Fprintf(o.ErrOut, "You must specify the type of resource to get. %s\n\n", cmdutil.SuggestAPIResources(o.CmdParent))
			fullCmdName := cmd.Parent().CommandPath()
			usageString := "Required resource not specified."
			if len(fullCmdName) > 0 && cmdutil.IsSiblingCommandExists(cmd, "explain") {
				usageString = fmt.Sprintf("%s\nUse \"%s explain <resource>\" for a detailed description of that resource (e.g. %[2]s explain pods).", usageString, fullCmdName)
			}

			return cmdutil.UsageErrorf(cmd, usageString)
		}
	}

	// openapi printing is mutually exclusive with server side printing
	if o.PrintWithOpenAPICols && o.ServerPrint {
		fmt.Fprintf(o.IOStreams.ErrOut, "warning: --%s requested, --%s will be ignored\n", useOpenAPIPrintColumnFlagLabel, useServerPrintColumns)
	}

	return nil
}

// Validate checks the set of flags provided by the user.
func (o *GetOptions) Validate(cmd *cobra.Command) error {
	if len(o.Raw) > 0 {
		if o.Watch || o.WatchOnly || len(o.LabelSelector) > 0 || o.Export {
			return fmt.Errorf("--raw may not be specified with other flags that filter the server request or alter the output")
		}
		if len(cmdutil.GetFlagString(cmd, "output")) > 0 {
			return cmdutil.UsageErrorf(cmd, "--raw and --output are mutually exclusive")
		}
		if _, err := url.ParseRequestURI(o.Raw); err != nil {
			return cmdutil.UsageErrorf(cmd, "--raw must be a valid URL path: %v", err)
		}
	}
	if cmdutil.GetFlagBool(cmd, "show-labels") {
		outputOption := cmd.Flags().Lookup("output").Value.String()
		if outputOption != "" && outputOption != "wide" {
			return fmt.Errorf("--show-labels option cannot be used with %s printer", outputOption)
		}
	}
	if o.OutputWatchEvents && !(o.Watch || o.WatchOnly) {
		return cmdutil.UsageErrorf(cmd, "--output-watch-events option can only be used with --watch or --watch-only")
	}
	return nil
}

// OriginalPositioner and NopPositioner is required for swap/sort operations of data in table format
type OriginalPositioner interface {
	OriginalPosition(int) int
}

// NopPositioner and OriginalPositioner is required for swap/sort operations of data in table format
type NopPositioner struct{}

// OriginalPosition returns the original position from NopPositioner object
func (t *NopPositioner) OriginalPosition(ix int) int {
	return ix
}

// RuntimeSorter holds the required objects to perform sorting of runtime objects
type RuntimeSorter struct {
	field      string
	decoder    runtime.Decoder
	objects    []runtime.Object
	positioner OriginalPositioner
}

// Sort performs the sorting of runtime objects
func (r *RuntimeSorter) Sort() error {
	// a list is only considered "sorted" if there are 0 or 1 items in it
	// AND (if 1 item) the item is not a Table object
	if len(r.objects) == 0 {
		return nil
	}
	if len(r.objects) == 1 {
		_, isTable := r.objects[0].(*metav1beta1.Table)
		if !isTable {
			return nil
		}
	}

	includesTable := false
	includesRuntimeObjs := false

	for _, obj := range r.objects {
		switch t := obj.(type) {
		case *metav1beta1.Table:
			includesTable = true

			if sorter, err := NewTableSorter(t, r.field); err != nil {
				return err
			} else if err := sorter.Sort(); err != nil {
				return err
			}
		default:
			includesRuntimeObjs = true
		}
	}

	// we use a NopPositioner when dealing with Table objects
	// because the objects themselves are not swapped, but rather
	// the rows in each object are swapped / sorted.
	r.positioner = &NopPositioner{}

	if includesRuntimeObjs && includesTable {
		return fmt.Errorf("sorting is not supported on mixed Table and non-Table object lists")
	}
	if includesTable {
		return nil
	}

	// if not dealing with a Table response from the server, assume
	// all objects are runtime.Object as usual, and sort using old method.
	var err error
	if r.positioner, err = SortObjects(r.decoder, r.objects, r.field); err != nil {
		return err
	}
	return nil
}

// OriginalPosition returns the original position of a runtime object
func (r *RuntimeSorter) OriginalPosition(ix int) int {
	if r.positioner == nil {
		return 0
	}
	return r.positioner.OriginalPosition(ix)
}

// WithDecoder allows custom decoder to be set for testing
func (r *RuntimeSorter) WithDecoder(decoder runtime.Decoder) *RuntimeSorter {
	r.decoder = decoder
	return r
}

// NewRuntimeSorter returns a new instance of RuntimeSorter
func NewRuntimeSorter(objects []runtime.Object, sortBy string) *RuntimeSorter {
	parsedField, err := RelaxedJSONPathExpression(sortBy)
	if err != nil {
		parsedField = sortBy
	}

	return &RuntimeSorter{
		field:   parsedField,
		decoder: kubernetesscheme.Codecs.UniversalDecoder(),
		objects: objects,
	}
}

func (o *GetOptions) transformRequests(req *rest.Request) {
	// We need full objects if printing with openapi columns
	if o.PrintWithOpenAPICols {
		return
	}
	if !o.ServerPrint || !o.IsHumanReadablePrinter {
		return
	}

	group := metav1beta1.GroupName
	version := metav1beta1.SchemeGroupVersion.Version

	tableParam := fmt.Sprintf("application/json;as=Table;v=%s;g=%s, application/json", version, group)
	req.SetHeader("Accept", tableParam)

	// if sorting, ensure we receive the full object in order to introspect its fields via jsonpath
	if o.Sort {
		req.Param("includeObject", "Object")
	}
}

// Run performs the get operation.
// TODO: remove the need to pass these arguments, like other commands.
func (o *GetOptions) Run(f cmdutil.Factory, cmd *cobra.Command, args []string) error {
	if len(o.Raw) > 0 {
		restClient, err := f.RESTClient()
		if err != nil {
			return err
		}
		return rawhttp.RawGet(restClient, o.IOStreams, o.Raw)
	}
	if o.Watch || o.WatchOnly {
		return o.watch(f, cmd, args)
	}

	chunkSize := o.ChunkSize
	if o.Sort {
		// TODO(juanvallejo): in the future, we could have the client use chunking
		// to gather all results, then sort them all at the end to reduce server load.
		chunkSize = 0
	}

	r := f.NewBuilder().
		Unstructured().
		NamespaceParam(o.Namespace).DefaultNamespace().AllNamespaces(o.AllNamespaces).
		FilenameParam(o.ExplicitNamespace, &o.FilenameOptions).
		LabelSelectorParam(o.LabelSelector).
		FieldSelectorParam(o.FieldSelector).
		ExportParam(o.Export).
		RequestChunksOf(chunkSize).
		ResourceTypeOrNameArgs(true, args...).
		ContinueOnError().
		Latest().
		Flatten().
		TransformRequests(o.transformRequests).
		Do()

	if o.IgnoreNotFound {
		r.IgnoreErrors(kapierrors.IsNotFound)
	}
	if err := r.Err(); err != nil {
		return err
	}

	if !o.IsHumanReadablePrinter {
		return o.printGeneric(r)
	}

	allErrs := []error{}
	errs := sets.NewString()
	infos, err := r.Infos()
	if err != nil {
		allErrs = append(allErrs, err)
	}
	printWithKind := multipleGVKsRequested(infos)

	objs := make([]runtime.Object, len(infos))
	for ix := range infos {
		objs[ix] = infos[ix].Object
	}

	sorting, err := cmd.Flags().GetString("sort-by")
	if err != nil {
		return err
	}

	var positioner OriginalPositioner
	if o.Sort {
		sorter := NewRuntimeSorter(objs, sorting)
		if err := sorter.Sort(); err != nil {
			return err
		}
		positioner = sorter
	}

	var printer printers.ResourcePrinter
	var lastMapping *meta.RESTMapping

	// track if we write any output
	trackingWriter := &trackingWriterWrapper{Delegate: o.Out}
	// output an empty line separating output
	separatorWriter := &separatorWriterWrapper{Delegate: trackingWriter}

	w := utilprinters.GetNewTabWriter(separatorWriter)
	for ix := range objs {
		var mapping *meta.RESTMapping
		var info *resource.Info
		if positioner != nil {
			info = infos[positioner.OriginalPosition(ix)]
			mapping = info.Mapping
		} else {
			info = infos[ix]
			mapping = info.Mapping
		}

		printWithNamespace := o.AllNamespaces

		if mapping != nil && mapping.Scope.Name() == meta.RESTScopeNameRoot {
			printWithNamespace = false
		}

		if shouldGetNewPrinterForMapping(printer, lastMapping, mapping) {
			w.Flush()
			w.SetRememberedWidths(nil)

			// add linebreaks between resource groups (if there is more than one)
			// when it satisfies all following 3 conditions:
			// 1) it's not the first resource group
			// 2) it has row header
			// 3) we've written output since the last time we started a new set of headers
			if lastMapping != nil && !o.NoHeaders && trackingWriter.Written > 0 {
				separatorWriter.SetReady(true)
			}

			printer, err = o.ToPrinter(mapping, nil, printWithNamespace, printWithKind)
			if err != nil {
				if !errs.Has(err.Error()) {
					errs.Insert(err.Error())
					allErrs = append(allErrs, err)
				}
				continue
			}

			lastMapping = mapping
		}

		// ensure a versioned object is passed to the custom-columns printer
		// if we are using OpenAPI columns to print
		if o.PrintWithOpenAPICols {
			printer.PrintObj(info.Object, w)
			continue
		}

		printer.PrintObj(info.Object, w)
	}
	w.Flush()
	if trackingWriter.Written == 0 && !o.IgnoreNotFound && len(allErrs) == 0 {
		// if we wrote no output, and had no errors, and are not ignoring NotFound, be sure we output something
		if !o.AllNamespaces {
			fmt.Fprintln(o.ErrOut, fmt.Sprintf("No resources found in %s namespace.", o.Namespace))
		} else {
			fmt.Fprintln(o.ErrOut, fmt.Sprintf("No resources found"))
		}
	}
	return utilerrors.NewAggregate(allErrs)
}

type trackingWriterWrapper struct {
	Delegate io.Writer
	Written  int
}

func (t *trackingWriterWrapper) Write(p []byte) (n int, err error) {
	t.Written += len(p)
	return t.Delegate.Write(p)
}

type separatorWriterWrapper struct {
	Delegate io.Writer
	Ready    bool
}

func (s *separatorWriterWrapper) Write(p []byte) (n int, err error) {
	// If we're about to write non-empty bytes and `s` is ready,
	// we prepend an empty line to `p` and reset `s.Read`.
	if len(p) != 0 && s.Ready {
		fmt.Fprintln(s.Delegate)
		s.Ready = false
	}
	return s.Delegate.Write(p)
}

func (s *separatorWriterWrapper) SetReady(state bool) {
	s.Ready = state
}

// watch starts a client-side watch of one or more resources.
// TODO: remove the need for arguments here.
func (o *GetOptions) watch(f cmdutil.Factory, cmd *cobra.Command, args []string) error {
	r := f.NewBuilder().
		Unstructured().
		NamespaceParam(o.Namespace).DefaultNamespace().AllNamespaces(o.AllNamespaces).
		FilenameParam(o.ExplicitNamespace, &o.FilenameOptions).
		LabelSelectorParam(o.LabelSelector).
		FieldSelectorParam(o.FieldSelector).
		ExportParam(o.Export).
		RequestChunksOf(o.ChunkSize).
		ResourceTypeOrNameArgs(true, args...).
		SingleResourceType().
		Latest().
		TransformRequests(o.transformRequests).
		Do()
	if err := r.Err(); err != nil {
		return err
	}
	infos, err := r.Infos()
	if err != nil {
		return err
	}
	if multipleGVKsRequested(infos) {
		return i18n.Errorf("watch is only supported on individual resources and resource collections - more than 1 resource was found")
	}

	info := infos[0]
	mapping := info.ResourceMapping()
	outputObjects := utilpointer.BoolPtr(!o.WatchOnly)
	printer, err := o.ToPrinter(mapping, outputObjects, o.AllNamespaces, false)
	if err != nil {
		return err
	}
	obj, err := r.Object()
	if err != nil {
		return err
	}

	// watching from resourceVersion 0, starts the watch at ~now and
	// will return an initial watch event.  Starting form ~now, rather
	// the rv of the object will insure that we start the watch from
	// inside the watch window, which the rv of the object might not be.
	rv := "0"
	isList := meta.IsListType(obj)
	if isList {
		// the resourceVersion of list objects is ~now but won't return
		// an initial watch event
		rv, err = meta.NewAccessor().ResourceVersion(obj)
		if err != nil {
			return err
		}
	}

	writer := utilprinters.GetNewTabWriter(o.Out)

	// print the current object
	var objsToPrint []runtime.Object
	if isList {
		objsToPrint, _ = meta.ExtractList(obj)
	} else {
		objsToPrint = append(objsToPrint, obj)
	}
	for _, objToPrint := range objsToPrint {
		if o.OutputWatchEvents {
			objToPrint = &metav1.WatchEvent{Type: string(watch.Added), Object: runtime.RawExtension{Object: objToPrint}}
		}
		if err := printer.PrintObj(objToPrint, writer); err != nil {
			return fmt.Errorf("unable to output the provided object: %v", err)
		}
	}
	writer.Flush()
	if isList {
		// we can start outputting objects now, watches started from lists don't emit synthetic added events
		*outputObjects = true
	} else {
		// suppress output, since watches started for individual items emit a synthetic ADDED event first
		*outputObjects = false
	}

	// print watched changes
	w, err := r.Watch(rv)
	if err != nil {
		return err
	}

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	intr := interrupt.New(nil, cancel)
	intr.Run(func() error {
		_, err := watchtools.UntilWithoutRetry(ctx, w, func(e watch.Event) (bool, error) {
			objToPrint := e.Object
			if o.OutputWatchEvents {
				objToPrint = &metav1.WatchEvent{Type: string(e.Type), Object: runtime.RawExtension{Object: objToPrint}}
			}
			if err := printer.PrintObj(objToPrint, writer); err != nil {
				return false, err
			}
			writer.Flush()
			// after processing at least one event, start outputting objects
			*outputObjects = true
			return false, nil
		})
		return err
	})
	return nil
}

func (o *GetOptions) printGeneric(r *resource.Result) error {
	// we flattened the data from the builder, so we have individual items, but now we'd like to either:
	// 1. if there is more than one item, combine them all into a single list
	// 2. if there is a single item and that item is a list, leave it as its specific list
	// 3. if there is a single item and it is not a list, leave it as a single item
	var errs []error
	singleItemImplied := false
	infos, err := r.IntoSingleItemImplied(&singleItemImplied).Infos()
	if err != nil {
		if singleItemImplied {
			return err
		}
		errs = append(errs, err)
	}

	if len(infos) == 0 && o.IgnoreNotFound {
		return utilerrors.Reduce(utilerrors.Flatten(utilerrors.NewAggregate(errs)))
	}

	printer, err := o.ToPrinter(nil, nil, false, false)
	if err != nil {
		return err
	}

	var obj runtime.Object
	if !singleItemImplied || len(infos) != 1 {
		// we have zero or multple items, so coerce all items into a list.
		// we don't want an *unstructured.Unstructured list yet, as we
		// may be dealing with non-unstructured objects. Compose all items
		// into an corev1.List, and then decode using an unstructured scheme.
		list := corev1.List{
			TypeMeta: metav1.TypeMeta{
				Kind:       "List",
				APIVersion: "v1",
			},
			ListMeta: metav1.ListMeta{},
		}
		for _, info := range infos {
			list.Items = append(list.Items, runtime.RawExtension{Object: info.Object})
		}

		listData, err := json.Marshal(list)
		if err != nil {
			return err
		}

		converted, err := runtime.Decode(unstructured.UnstructuredJSONScheme, listData)
		if err != nil {
			return err
		}

		obj = converted
	} else {
		obj = infos[0].Object
	}

	isList := meta.IsListType(obj)
	if isList {
		items, err := meta.ExtractList(obj)
		if err != nil {
			return err
		}

		// take the items and create a new list for display
		list := &unstructured.UnstructuredList{
			Object: map[string]interface{}{
				"kind":       "List",
				"apiVersion": "v1",
				"metadata":   map[string]interface{}{},
			},
		}
		if listMeta, err := meta.ListAccessor(obj); err == nil {
			list.Object["metadata"] = map[string]interface{}{
				"selfLink":        listMeta.GetSelfLink(),
				"resourceVersion": listMeta.GetResourceVersion(),
			}
		}

		for _, item := range items {
			list.Items = append(list.Items, *item.(*unstructured.Unstructured))
		}
		if err := printer.PrintObj(list, o.Out); err != nil {
			errs = append(errs, err)
		}
		return utilerrors.Reduce(utilerrors.Flatten(utilerrors.NewAggregate(errs)))
	}

	if printErr := printer.PrintObj(obj, o.Out); printErr != nil {
		errs = append(errs, printErr)
	}

	return utilerrors.Reduce(utilerrors.Flatten(utilerrors.NewAggregate(errs)))
}

func addOpenAPIPrintColumnFlags(cmd *cobra.Command, opt *GetOptions) {
	cmd.Flags().BoolVar(&opt.PrintWithOpenAPICols, useOpenAPIPrintColumnFlagLabel, opt.PrintWithOpenAPICols, "If true, use x-kubernetes-print-column metadata (if present) from the OpenAPI schema for displaying a resource.")
	cmd.Flags().MarkDeprecated(useOpenAPIPrintColumnFlagLabel, "deprecated in favor of server-side printing")
}

func addServerPrintColumnFlags(cmd *cobra.Command, opt *GetOptions) {
	cmd.Flags().BoolVar(&opt.ServerPrint, useServerPrintColumns, opt.ServerPrint, "If true, have the server return the appropriate table output. Supports extension APIs and CRDs.")
}

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") != ""
}

func multipleGVKsRequested(infos []*resource.Info) bool {
	if len(infos) < 2 {
		return false
	}
	gvk := infos[0].Mapping.GroupVersionKind
	for _, info := range infos {
		if info.Mapping.GroupVersionKind != gvk {
			return true
		}
	}
	return false
}