hasher: fix invalid memory address error when MaxAge == 0

When f.opt.MaxAge == 0, f.db is never set, however several methods later assume
it is set and attempt to access it, causing an invalid memory address error.
This change fixes the issue in a few spots (there may still be others I haven't
yet encountered.)

backend/hasher/commands.go

@@ -80,6 +80,14 @@ func (f *Fs) dbDump(ctx context.Context, full bool, root string) error {
 		}
 		root = fspath.JoinRootPath(remoteFs.Root(), f.Root())
 	}
+	if f.db == nil {
+		if f.opt.MaxAge == 0 {
+			fs.Errorf(f, "db not found. (disabled with max_age = 0)")
+		} else {
+			fs.Errorf(f, "db not found.")
+		}
+		return kv.ErrInactive
+	}
 	op := &kvDump{
 		full: full,
 		root: root,

backend/hasher/hasher.go

@@ -418,7 +418,9 @@ func (f *Fs) DirMove(ctx context.Context, src fs.Fs, srcRemote, dstRemote string
 
 // Shutdown the backend, closing any background tasks and any cached connections.
 func (f *Fs) Shutdown(ctx context.Context) (err error) {
+	if f.db != nil {
 		err = f.db.Stop(false)
+	}
 	if do := f.Fs.Features().Shutdown; do != nil {
 		if err2 := do(ctx); err2 != nil {
 			err = err2

backend/hasher/hasher_internal_test.go

@@ -60,9 +60,11 @@ func (f *Fs) testUploadFromCrypt(t *testing.T) {
 	assert.NotNil(t, dst)
 
 	// check that hash was created
+	if f.opt.MaxAge > 0 {
 		hash, err = f.getRawHash(ctx, hashType, fileName, anyFingerprint, longTime)
 		assert.NoError(t, err)
 		assert.NotEmpty(t, hash)
+	}
 	//t.Logf("hash is %q", hash)
 	_ = operations.Purge(ctx, f, dirName)
 }

backend/hasher/hasher_test.go

@@ -37,4 +37,9 @@ func TestIntegration(t *testing.T) {
 		opt.QuickTestOK = true
 	}
 	fstests.Run(t, &opt)
+	// test again with MaxAge = 0
+	if *fstest.RemoteName == "" {
+		opt.ExtraConfig = append(opt.ExtraConfig, fstests.ExtraConfigItem{Name: "TestHasher", Key: "max_age", Value: "0"})
+		fstests.Run(t, &opt)
+	}
 }

lib/kv/bolt.go

@@ -216,7 +216,7 @@ func (db *DB) loop() {
 
 // Do a key-value operation and return error when done
 func (db *DB) Do(write bool, op Op) error {
-	if db.queue == nil {
+	if db == nil || db.queue == nil {
 		return ErrInactive
 	}
 	r := &request{