all: Use slices.Backward for reverse iteration

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

cmd/containerd/server/server.go

@@ -24,6 +24,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"slices"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -280,8 +281,7 @@ func (s *Server) Start(ctx context.Context) error {
 
 // Stop the containerd server canceling any open connections
 func (s *Server) Stop() {
-	for i := len(s.plugins) - 1; i >= 0; i-- {
-		p := s.plugins[i]
+	for _, p := range slices.Backward(s.plugins) {
 		instance, err := p.Instance()
 		if err != nil {
 			log.L.WithFields(log.Fields{"error": err, "id": p.Registration.URI()}).Error("could not get plugin instance")

core/diff/stream.go

@@ -21,6 +21,7 @@ import (
 	"errors"
 	"io"
 	"os"
+	"slices"
 
 	"github.com/containerd/containerd/v2/core/images"
 	"github.com/containerd/containerd/v2/pkg/archive/compression"
@@ -48,8 +49,8 @@ func RegisterProcessor(handler Handler) {
 // GetProcessor returns the processor for a media-type
 func GetProcessor(ctx context.Context, stream StreamProcessor, payloads map[string]typeurl.Any) (StreamProcessor, error) {
 	// reverse this list so that user configured handlers come up first
-	for i := len(handlers) - 1; i >= 0; i-- {
-		processor, ok := handlers[i](ctx, stream.MediaType())
+	for _, handler := range slices.Backward(handlers) {
+		processor, ok := handler(ctx, stream.MediaType())
 		if ok {
 			return processor(ctx, stream, payloads)
 		}

core/mount/manager/manager.go

@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -720,12 +721,12 @@ func (mm *mountManager) Deactivate(ctx context.Context, name string) error {
 
 	// TODO: Should this also be backgrounded, no much can do on failure to unmount
 	var mountErrors error
-	for i := len(allActive) - 1; i >= 0; i-- {
+	for _, active := range slices.Backward(allActive) {
 		var err error
-		if h := mm.handlers[allActive[i].Type]; h != nil {
-			err = h.Unmount(ctx, allActive[i].MountPoint)
+		if h := mm.handlers[active.Type]; h != nil {
+			err = h.Unmount(ctx, active.MountPoint)
 		} else {
-			err = mount.Unmount(allActive[i].MountPoint, 0)
+			err = mount.Unmount(active.MountPoint, 0)
 		}
 		if err != nil {
 			mountErrors = errors.Join(mountErrors, err)

core/mount/mount.go

@@ -66,8 +66,8 @@ func All(mounts []Mount, target string) error {
 // UnmountMounts unmounts all the mounts under a target in the reverse order of
 // the mounts array provided.
 func UnmountMounts(mounts []Mount, target string, flags int) error {
-	for i := len(mounts) - 1; i >= 0; i-- {
-		mountpoint, err := fs.RootPath(target, mounts[i].Target)
+	for i, m := range slices.Backward(mounts) {
+		mountpoint, err := fs.RootPath(target, m.Target)
 		if err != nil {
 			return err
 		}

core/remotes/docker/fetcher.go

@@ -26,6 +26,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"slices"
 	"strings"
 	"sync"
 
@@ -637,8 +638,8 @@ func (r dockerFetcher) open(ctx context.Context, req *request, mediatype string,
 		}
 	}
 
-	for i := len(encoding) - 1; i >= 0; i-- {
-		algorithm := strings.ToLower(encoding[i])
+	for _, value := range slices.Backward(encoding) {
+		algorithm := strings.ToLower(value)
 		switch algorithm {
 		case "zstd":
 			r, err := zstd.NewReader(body.ReadCloser,

core/remotes/handlers.go

@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"io"
 	"maps"
+	"slices"
 	"strings"
 	"sync"
 
@@ -286,8 +287,8 @@ func PushContent(ctx context.Context, pusher Pusher, desc ocispec.Descriptor, st
 	}
 
 	// Iterate in reverse order as seen, parent always uploaded after child
-	for i := len(indexStack) - 1; i >= 0; i-- {
-		err := images.Dispatch(ctx, pushHandler, limiter, indexStack[i])
+	for _, index := range slices.Backward(indexStack) {
+		err := images.Dispatch(ctx, pushHandler, limiter, index)
 		if err != nil {
 			// TODO(estesp): until we have a more complete method for index push, we need to report
 			// missing dependencies in an index/manifest list by sensing the "400 Bad Request"

plugins/cri/cri.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"slices"
 	"strings"
 
 	"github.com/containerd/log"
@@ -141,9 +142,9 @@ func initCRIService(ic *plugin.InitContext) (any, error) {
 	}
 	if hasEnv, ok := shimPlugin.(interface{ Env() []string }); ok {
 		env := hasEnv.Env()
-		for i := len(env) - 1; i >= 0; i-- {
+		for _, value := range slices.Backward(env) {
 			// iterate backwards to grab the last PATH=
-			if path, ok := strings.CutPrefix(env[i], "PATH="); ok {
+			if path, ok := strings.CutPrefix(value, "PATH="); ok {
 				shimPath = path
 				break
 			}