Update will cleanup unneeded artifacts.

The update process will cleanup unneeded artifacts. When an update
starts all artifacts that do not have the current version number in it's
name will be removed. If artifact retrieval fails, downloaded artifacts
are removed. On a successful upgrade, all contents of the downloads dir
will be removed.

CHANGELOG.next.asciidoc

@@ -110,6 +110,7 @@
 - Allow ':' characters in dynamic variables {issue}624[624] {pull}680[680]
 - Allow the - char to appear as part of variable names in eql expressions. {issue}709[709] {pull}710[710]
 - Allow the / char in variable names in eql and transpiler. {issue}715[715] {pull}718[718]
+- Agent updates will clean up unneeded artifacts. {issue}693[693] {issue}694[694] {pull}752[752]
 
 ==== New features
 

internal/pkg/agent/application/upgrade/cleanup.go

@@ -0,0 +1,49 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package upgrade
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
+)
+
+// preUpgradeCleanup will remove files that do not have the passed version number from the downloads directory.
+func preUpgradeCleanup(version string) error {
+	files, err := os.ReadDir(paths.Downloads())
+	if err != nil {
+		return err
+	}
+	for _, file := range files {
+		if file.IsDir() {
+			continue
+		}
+		if !strings.Contains(file.Name(), version) {
+			if err := os.Remove(filepath.Join(paths.Downloads(), file.Name())); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// cleanAllDownloads will remove all files from the downloads directory
+func cleanAllDownloads() error {
+	files, err := os.ReadDir(paths.Downloads())
+	if err != nil {
+		return err
+	}
+	for _, file := range files {
+		if file.IsDir() {
+			continue
+		}
+		if err := os.Remove(filepath.Join(paths.Downloads(), file.Name())); err != nil {
+			return err
+		}
+	}
+	return nil
+}

internal/pkg/agent/application/upgrade/cleanup_test.go

@@ -0,0 +1,61 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package upgrade
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
+
+	"github.com/stretchr/testify/require"
+)
+
+func setupDir(t *testing.T) {
+	t.Helper()
+	dir := t.TempDir()
+	paths.SetDownloads(dir)
+
+	err := os.WriteFile(filepath.Join(dir, "test-8.3.0-file"), []byte("hello, world!"), 0640)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.WriteFile(filepath.Join(dir, "test-8.4.0-file"), []byte("hello, world!"), 0640)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.WriteFile(filepath.Join(dir, "test-8.5.0-file"), []byte("hello, world!"), 0640)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = os.WriteFile(filepath.Join(dir, "test-hash-file"), []byte("hello, world!"), 0640)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestPreUpgradeCleanup(t *testing.T) {
+	setupDir(t)
+	err := preUpgradeCleanup("8.4.0")
+	require.NoError(t, err)
+
+	files, err := os.ReadDir(paths.Downloads())
+	require.NoError(t, err)
+	require.Len(t, files, 1)
+	require.Equal(t, "test-8.4.0-file", files[0].Name())
+	fi, err := files[0].Info()
+	require.NoError(t, err)
+	require.Greater(t, fi.Size(), int64(0))
+}
+
+func TestCleanAllDownloads(t *testing.T) {
+	setupDir(t)
+	err := cleanAllDownloads()
+	require.NoError(t, err)
+	files, err := os.ReadDir(paths.Downloads())
+	require.NoError(t, err)
+	require.Len(t, files, 0)
+}

internal/pkg/agent/application/upgrade/upgrade.go

@@ -126,6 +126,11 @@ func (u *Upgrader) Upgrade(ctx context.Context, a Action, reexecNow bool) (_ ree
 				"running under control of the systems supervisor")
 	}
 
+	err = preUpgradeCleanup(a.Version())
+	if err != nil {
+		u.log.Errorf("Unable to clean downloads dir %q before update: %v", paths.Downloads(), err)
+	}
+
 	if u.caps != nil {
 		if _, err := u.caps.Apply(a); errors.Is(err, capabilities.ErrBlocked) {
 			return nil, nil
@@ -137,6 +142,11 @@ func (u *Upgrader) Upgrade(ctx context.Context, a Action, reexecNow bool) (_ ree
 	sourceURI := u.sourceURI(a.SourceURI())
 	archivePath, err := u.downloadArtifact(ctx, a.Version(), sourceURI)
 	if err != nil {
+		// Run the same preUpgradeCleanup task to get rid of any newly downloaded files
+		// This may have an issue if users are upgrading to the same version number.
+		if dErr := preUpgradeCleanup(a.Version()); dErr != nil {
+			u.log.Errorf("Unable to remove file after verification failure: %v", dErr)
+		}
 		return nil, err
 	}
 
@@ -184,6 +194,13 @@ func (u *Upgrader) Upgrade(ctx context.Context, a Action, reexecNow bool) (_ ree
 		return nil, nil
 	}
 
+	// Clean everything from the downloads dir
+	// If we wanted to be a bit simpler we could call os.RemoveAll to remove the dir + children
+	err = cleanAllDownloads()
+	if err != nil {
+		u.log.Errorf("Unable to clean downloads dir %q after update: %v", paths.Downloads(), err)
+	}
+
 	return cb, nil
 }