Disable grab download resume

This is to mitigate cases like #4296

By default grab tries to resume the download if the file name determined from either the url or from content-type headers already exists. This makes things go side ways, if the existing file is smaller than the new one, the old content would still be there and only the "extra" new bytes would get written. I.e. the download would be "resumed". 🤦

So this change disables resuming altogether fro grab.

To be able to download and replace k0s without resuming, i.e. "truncate" the file in-between. We need to force the download to download it as k0s.tmp first. Only after that we can safely move the file as truncating a running binary is not allowed and will error with `text file busy`.

This is a minimal possible fix that we can easily backport. @twz123 is already working on bigger refactoring of autopilot download functionality that gets rid of grab. Grab seems to bring more (bad) surprises than real benefits. In the end, we just download files and we should pretty much always just replace them. No need for full library dependecy for that.

Signed-off-by: Jussi Nummelin <[email protected]>

pkg/autopilot/constant/static.go

@@ -19,6 +19,7 @@ const (
 	AutopilotNamespace                 = "k0s-autopilot"
 	AutopilotConfigName                = AutopilotName
 	K0sBinaryDir                       = "/usr/local/bin"
+	K0sTempFilename                    = "k0s.tmp"
 	K0sDefaultDataDir                  = "/var/lib/k0s"
 	K0sManifestSubDir                  = "manifests"
 	K0sImagesDir                       = "images"

pkg/autopilot/controller/signal/common/download.go

@@ -90,7 +90,6 @@ func (r *downloadController) Reconcile(ctx context.Context, req cr.Request) (cr.
 
 	} else {
 		logger.Infof("Download of '%s' successful", manifest.URL)
-
 		// When the download is complete move the status to the success state
 		signalData.Status = apsigv2.NewStatus(manifest.SuccessState)
 	}

pkg/autopilot/controller/signal/k0s/apply.go

@@ -18,12 +18,12 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"net/url"
 	"os"
 	"path"
 	"path/filepath"
 
 	apcomm "github.com/k0sproject/k0s/pkg/autopilot/common"
+	apconst "github.com/k0sproject/k0s/pkg/autopilot/constant"
 	apdel "github.com/k0sproject/k0s/pkg/autopilot/controller/delegate"
 	apsigpred "github.com/k0sproject/k0s/pkg/autopilot/controller/signal/common/predicate"
 	apsigv2 "github.com/k0sproject/k0s/pkg/autopilot/signaling/v2"
@@ -102,30 +102,23 @@ func (r *applyingUpdate) Reconcile(ctx context.Context, req cr.Request) (cr.Resu
 	}
 
 	logger := r.log.WithField("signalnode", signalNode.GetName())
+	logger.Info("Applying update")
 
 	var signalData apsigv2.SignalData
 	if err := signalData.Unmarshal(signalNode.GetAnnotations()); err != nil {
 		return cr.Result{}, fmt.Errorf("unable to unmarshal signal data for node='%s': %w", req.NamespacedName.Name, err)
 	}
 
-	// Get the filename fragment from the URL
-	updateURL, err := url.Parse(signalData.Command.K0sUpdate.URL)
-	if err != nil {
-		return cr.Result{}, fmt.Errorf("unable to get update request URL: %w", err)
-	}
-
-	// TODO: make the filename part random
-	updateFilename := path.Base(updateURL.Path)
-	updateFilenamePath := path.Join(r.k0sBinaryDir, updateFilename)
+	updateFilenamePath := path.Join(r.k0sBinaryDir, apconst.K0sTempFilename)
 
 	// Ensure that the expected file exists
 	if _, err := os.Stat(updateFilenamePath); errors.Is(err, os.ErrNotExist) {
-		return cr.Result{}, fmt.Errorf("unable to find update file '%s': %w", updateFilename, err)
+		return cr.Result{}, fmt.Errorf("unable to find update file '%s': %w", apconst.K0sTempFilename, err)
 	}
 
 	// Ensure that the new file is executable
 	if err := os.Chmod(updateFilenamePath, 0755); err != nil {
-		return cr.Result{}, fmt.Errorf("unable to chmod update file '%s': %w", updateFilename, err)
+		return cr.Result{}, fmt.Errorf("unable to chmod update file '%s': %w", apconst.K0sTempFilename, err)
 	}
 
 	// Perform the update atomically

pkg/autopilot/controller/signal/k0s/download.go

@@ -16,8 +16,10 @@ package k0s
 
 import (
 	"crypto/sha256"
+	"path/filepath"
 
 	apcomm "github.com/k0sproject/k0s/pkg/autopilot/common"
+	apconst "github.com/k0sproject/k0s/pkg/autopilot/constant"
 	apdel "github.com/k0sproject/k0s/pkg/autopilot/controller/delegate"
 	apsigcomm "github.com/k0sproject/k0s/pkg/autopilot/controller/signal/common"
 	apsigpred "github.com/k0sproject/k0s/pkg/autopilot/controller/signal/common/predicate"
@@ -88,6 +90,7 @@ func (b downloadManifestBuilderK0s) Build(signalNode crcli.Object, signalData ap
 			ExpectedHash: signalData.Command.K0sUpdate.Sha256,
 			Hasher:       sha256.New(),
 			DownloadDir:  b.k0sBinaryDir,
+			Filename:     filepath.Join(b.k0sBinaryDir, apconst.K0sTempFilename),
 		},
 		SuccessState: Cordoning,
 	}

pkg/autopilot/download/downloader.go

@@ -34,6 +34,7 @@ type Config struct {
 	ExpectedHash string
 	Hasher       hash.Hash
 	DownloadDir  string
+	Filename     string
 }
 
 type downloader struct {
@@ -72,6 +73,15 @@ func (d *downloader) Download(ctx context.Context) error {
 		dlreq.SetChecksum(d.config.Hasher, expectedHash, true)
 	}
 
+	// We're never really resuming downloads, so disable this feature.
+	// This also allows to re-download the file if it's already present.
+	dlreq.NoResume = true
+
+	if d.config.Filename != "" {
+		d.logger.Infof("Setting filename to %s", d.config.Filename)
+		dlreq.Filename = d.config.Filename
+	}
+
 	client := grab.NewClient()
 	// Set user agent to mitigate 403 errors from GitHub
 	// See https://github.com/cavaliergopher/grab/issues/104