Enable perfsprint linter

... and fix lints on the way.

Most of the fixes are straightforward replacements of fmt.Errorf with
errors.New and string concatenations instead of fmt.Sprintf with a
single leading or trailing %s. Single integer conversions have been
replaced with the corresponding functions from the strconv package. Used
path.Join, filepath.Join and url.URL where it made sense.

Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

.golangci.yml

@@ -10,11 +10,12 @@ run:
 
 linters:
   enable:
-    - depguard  # Checks if package imports are in a list of acceptable packages
-    - errorlint # Find code that will cause problems with Go's error wrapping scheme
-    - gofmt     # Checks whether code was gofmt-ed
-    - goheader  # Checks is file headers matche a given pattern
-    - revive    # Stricter drop-in replacement for golint
+    - depguard   # Checks if package imports are in a list of acceptable packages
+    - errorlint  # Find code that will cause problems with Go's error wrapping scheme
+    - gofmt      # Checks whether code was gofmt-ed
+    - goheader   # Checks is file headers matches a given pattern
+    - perfsprint # Checks for faster fmt.Sprintf alternatives
+    - revive     # Stricter drop-in replacement for golint
 
 linters-settings:
   depguard:

cmd/airgap/listimages.go

@@ -17,6 +17,7 @@ limitations under the License.
 package airgap
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/k0sproject/k0s/pkg/airgap"
@@ -39,7 +40,7 @@ func NewAirgapListImagesCmd() *cobra.Command {
 			}
 
 			if opts.EnableDynamicConfig {
-				return fmt.Errorf("dynamic config is not supported for airgap list-images")
+				return errors.New("dynamic config is not supported for airgap list-images")
 			}
 
 			clusterConfig, err := opts.K0sVars.NodeConfig()

cmd/api/api.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"os"
@@ -221,7 +222,7 @@ func (c *command) isValidToken(ctx context.Context, token string, usage string)
 		return false
 	}
 
-	secretName := fmt.Sprintf("bootstrap-token-%s", parts[0])
+	secretName := "bootstrap-token-" + parts[0]
 	secret, err := c.client.CoreV1().Secrets("kube-system").Get(ctx, secretName, metav1.GetOptions{})
 	if err != nil {
 		logrus.Errorf("failed to get bootstrap token: %s", err.Error())
@@ -244,19 +245,19 @@ func (c *command) authMiddleware(next http.Handler, usage string) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		auth := r.Header.Get("Authorization")
 		if auth == "" {
-			sendError(fmt.Errorf("go away"), w, http.StatusUnauthorized)
+			sendError(errors.New("go away"), w, http.StatusUnauthorized)
 			return
 		}
 
 		parts := strings.Split(auth, "Bearer ")
 		if len(parts) == 2 {
 			token := parts[1]
 			if !c.isValidToken(r.Context(), token, usage) {
-				sendError(fmt.Errorf("go away"), w, http.StatusUnauthorized)
+				sendError(errors.New("go away"), w, http.StatusUnauthorized)
 				return
 			}
 		} else {
-			sendError(fmt.Errorf("go away"), w, http.StatusUnauthorized)
+			sendError(errors.New("go away"), w, http.StatusUnauthorized)
 			return
 		}
 

cmd/backup/backup_unix.go

@@ -19,6 +19,7 @@ limitations under the License.
 package backup
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -56,7 +57,7 @@ func NewBackupCmd() *cobra.Command {
 				return err
 			}
 			if nodeConfig.Spec.Storage.Etcd.IsExternalClusterUsed() {
-				return fmt.Errorf("command 'k0s backup' does not support external etcd cluster")
+				return errors.New("command 'k0s backup' does not support external etcd cluster")
 			}
 			return c.backup(savePath, cmd.OutOrStdout())
 		},

cmd/controller/certificates.go

@@ -20,16 +20,18 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+
 	"github.com/k0sproject/k0s/internal/pkg/file"
 	"github.com/k0sproject/k0s/internal/pkg/users"
 	"github.com/k0sproject/k0s/pkg/apis/k0s/v1beta1"
 	"github.com/k0sproject/k0s/pkg/certificate"
 	"github.com/k0sproject/k0s/pkg/config"
 	"github.com/k0sproject/k0s/pkg/constant"
-	"net"
-	"os"
-	"path/filepath"
-	"strconv"
 
 	"k8s.io/client-go/tools/clientcmd"
 	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
@@ -66,7 +68,7 @@ func (c *Certificates) Init(ctx context.Context) error {
 	c.CACert = string(cert)
 	// Changing the URL here also requires changes in the "k0s kubeconfig admin" subcommand.
 	apiAddress := net.JoinHostPort(c.ClusterSpec.API.Address, strconv.Itoa(c.ClusterSpec.API.Port))
-	kubeConfigAPIUrl := fmt.Sprintf("https://%s", apiAddress)
+	kubeConfigAPIUrl := (&url.URL{Scheme: "https", Host: apiAddress}).String()
 
 	apiServerUID, err := users.LookupUID(constant.ApiserverUser)
 	if err != nil {
@@ -197,7 +199,7 @@ func (c *Certificates) Init(ctx context.Context) error {
 		"kubernetes.default",
 		"kubernetes.default.svc",
 		"kubernetes.default.svc.cluster",
-		fmt.Sprintf("kubernetes.svc.%s", c.ClusterSpec.Network.ClusterDomain),
+		"kubernetes.svc." + c.ClusterSpec.Network.ClusterDomain,
 		"localhost",
 		"127.0.0.1",
 	}

cmd/controller/controller.go

@@ -24,6 +24,7 @@ import (
 	"net"
 	"os"
 	"os/signal"
+	"path"
 	"path/filepath"
 	"slices"
 	"syscall"
@@ -58,6 +59,7 @@ import (
 	"github.com/k0sproject/k0s/pkg/token"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
+	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/client-go/rest"
 )
 
@@ -94,7 +96,7 @@ func NewControllerCmd() *cobra.Command {
 				c.TokenArg = args[0]
 			}
 			if c.TokenArg != "" && c.TokenFile != "" {
-				return fmt.Errorf("you can only pass one token argument either as a CLI argument 'k0s controller [join-token]' or as a flag 'k0s controller --token-file [path]'")
+				return errors.New("you can only pass one token argument either as a CLI argument 'k0s controller [join-token]' or as a flag 'k0s controller --token-file [path]'")
 			}
 			if err := c.ControllerOptions.Normalize(); err != nil {
 				return err
@@ -659,9 +661,11 @@ func (c *command) startWorker(ctx context.Context, profile string, nodeConfig *v
 	wc := workercmd.Command(*(*config.CLIOptions)(c))
 	wc.TokenArg = bootstrapConfig
 	wc.WorkerProfile = profile
-	wc.Labels = append(wc.Labels, fmt.Sprintf("%s=control-plane", constant.K0SNodeRoleLabel))
+	wc.Labels = append(wc.Labels, fields.OneTermEqualSelector(constant.K0SNodeRoleLabel, "control-plane").String())
 	if !c.SingleNode && !c.NoTaints {
-		wc.Taints = append(wc.Taints, fmt.Sprintf("%s/master=:NoSchedule", constant.NodeRoleLabelNamespace))
+		key := path.Join(constant.NodeRoleLabelNamespace, "master")
+		taint := fields.OneTermEqualSelector(key, ":NoSchedule")
+		wc.Taints = append(wc.Taints, taint.String())
 	}
 	return wc.Start(ctx)
 }

cmd/etcd/etcd.go

@@ -17,6 +17,7 @@ limitations under the License.
 package etcd
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/k0sproject/k0s/pkg/apis/k0s/v1beta1"
@@ -46,7 +47,7 @@ func NewEtcdCmd() *cobra.Command {
 				return fmt.Errorf("wrong storage type: %s", nodeConfig.Spec.Storage.Type)
 			}
 			if nodeConfig.Spec.Storage.Etcd.IsExternalClusterUsed() {
-				return fmt.Errorf("command 'k0s etcd' does not support external etcd cluster")
+				return errors.New("command 'k0s etcd' does not support external etcd cluster")
 			}
 			return nil
 		},

cmd/etcd/leave.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"strconv"
 
 	"github.com/k0sproject/k0s/pkg/config"
 	"github.com/k0sproject/k0s/pkg/etcd"
@@ -52,7 +53,7 @@ func etcdLeaveCmd() *cobra.Command {
 			peerAddress := nodeConfig.Spec.Storage.Etcd.PeerAddress
 			if peerAddressArg == "" {
 				if peerAddress == "" {
-					return fmt.Errorf("can't leave etcd cluster: this node doesn't have an etcd peer address, check the k0s configuration or use --peer-address")
+					return errors.New("can't leave etcd cluster: this node doesn't have an etcd peer address, check the k0s configuration or use --peer-address")
 				}
 			} else {
 				peerAddress = peerAddressArg
@@ -73,13 +74,13 @@ func etcdLeaveCmd() *cobra.Command {
 			if err := etcdClient.DeleteMember(ctx, peerID); err != nil {
 				logrus.
 					WithField("peerURL", peerURL).
-					WithField("peerID", fmt.Sprintf("%x", peerID)).
+					WithField("peerID", strconv.FormatUint(peerID, 16)).
 					Errorf("Failed to delete node from cluster")
 				return err
 			}
 
 			logrus.
-				WithField("peerID", fmt.Sprintf("%x", peerID)).
+				WithField("peerID", strconv.FormatUint(peerID, 16)).
 				Info("Successfully deleted")
 			return nil
 		},

cmd/install/install.go

@@ -17,6 +17,7 @@ limitations under the License.
 package install
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -54,7 +55,7 @@ func NewInstallCmd() *cobra.Command {
 //   - Sets up startup and logging for k0s.
 func (c *command) setup(role string, args []string, installFlags *installFlags) error {
 	if os.Geteuid() != 0 {
-		return fmt.Errorf("this command must be run as root")
+		return errors.New("this command must be run as root")
 	}
 
 	nodeConfig, err := c.K0sVars.NodeConfig()

cmd/kubectl/kubectl.go

@@ -17,6 +17,7 @@ limitations under the License.
 package kubectl
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
@@ -171,7 +172,7 @@ func handleKubectlPlugins(kubectlCmd *cobra.Command) {
 func fallbackToK0sKubeconfig(cmd *cobra.Command) error {
 	kubeconfigFlag := cmd.Flags().Lookup("kubeconfig")
 	if kubeconfigFlag == nil {
-		return fmt.Errorf("kubeconfig flag not found")
+		return errors.New("kubeconfig flag not found")
 	}
 
 	if kubeconfigFlag.Changed {

cmd/restore/restore_unix.go

@@ -19,6 +19,7 @@ limitations under the License.
 package restore
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -74,7 +75,7 @@ func NewRestoreCmd() *cobra.Command {
 
 func (c *command) restore(path string, out io.Writer) error {
 	if os.Geteuid() != 0 {
-		return fmt.Errorf("this command must be run as root")
+		return errors.New("this command must be run as root")
 	}
 
 	k0sStatus, _ := status.GetStatusInfo(c.K0sVars.StatusSocketPath)

cmd/root.go

@@ -18,7 +18,6 @@ package cmd
 
 import (
 	"errors"
-	"fmt"
 	"net/http"
 	"os"
 	"runtime"
@@ -135,7 +134,7 @@ func newDocsCmd() *cobra.Command {
 			case "man":
 				return doc.GenManTree(NewRootCmd(), &doc.GenManHeader{Title: "k0s", Section: "1"}, "./man")
 			}
-			return fmt.Errorf("invalid format")
+			return errors.New("invalid format")
 		},
 	}
 }

cmd/start/start.go

@@ -17,7 +17,7 @@ limitations under the License.
 package start
 
 import (
-	"fmt"
+	"errors"
 	"os"
 
 	"github.com/k0sproject/k0s/pkg/install"
@@ -32,15 +32,15 @@ func NewStartCmd() *cobra.Command {
 		Short: "Start the k0s service configured on this host. Must be run as root (or with sudo)",
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if os.Geteuid() != 0 {
-				return fmt.Errorf("this command must be run as root")
+				return errors.New("this command must be run as root")
 			}
 			svc, err := install.InstalledService()
 			if err != nil {
 				return err
 			}
 			status, _ := svc.Status()
 			if status == service.StatusRunning {
-				return fmt.Errorf("already running")
+				return errors.New("already running")
 			}
 			return svc.Start()
 		},

cmd/stop/stop.go

@@ -17,7 +17,7 @@ limitations under the License.
 package stop
 
 import (
-	"fmt"
+	"errors"
 	"os"
 
 	"github.com/k0sproject/k0s/pkg/install"
@@ -32,7 +32,7 @@ func NewStopCmd() *cobra.Command {
 		Short: "Stop the k0s service configured on this host. Must be run as root (or with sudo)",
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if os.Geteuid() != 0 {
-				return fmt.Errorf("this command must be run as root")
+				return errors.New("this command must be run as root")
 			}
 			svc, err := install.InstalledService()
 			if err != nil {
@@ -43,7 +43,7 @@ func NewStopCmd() *cobra.Command {
 				return err
 			}
 			if status == service.StatusStopped {
-				return fmt.Errorf("already stopped")
+				return errors.New("already stopped")
 			}
 			return svc.Stop()
 		},

cmd/token/preshared.go

@@ -19,6 +19,7 @@ package token
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -55,10 +56,10 @@ func preSharedCmd() *cobra.Command {
 				return err
 			}
 			if certPath == "" {
-				return fmt.Errorf("please, provide --cert argument")
+				return errors.New("please, provide --cert argument")
 			}
 			if joinURL == "" {
-				return fmt.Errorf("please, provide --url argument")
+				return errors.New("please, provide --url argument")
 			}
 
 			return nil

cmd/worker/worker.go

@@ -74,7 +74,7 @@ func NewWorkerCmd() *cobra.Command {
 			}
 
 			if c.TokenArg != "" && c.TokenFile != "" {
-				return fmt.Errorf("you can only pass one token argument either as a CLI argument 'k0s worker [token]' or as a flag 'k0s worker --token-file [path]'")
+				return errors.New("you can only pass one token argument either as a CLI argument 'k0s worker [token]' or as a flag 'k0s worker --token-file [path]'")
 			}
 
 			if err := (&sysinfo.K0sSysinfoSpec{

hack/tool/cmd/aws/provision/provision.go

@@ -17,6 +17,7 @@ package provision
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
@@ -100,7 +101,7 @@ func bugfixK0sctlNullImages(k0sctlConfigFile string) error {
 	cmd.Stdout = os.Stdout
 
 	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("failed to post-process k0sctl.yaml")
+		return errors.New("failed to post-process k0sctl.yaml")
 	}
 
 	return nil