local: fix hash invalidation which caused errors with local crypt mount

Before this fix if a file was updated, but to the same length and
timestamp then the local backend would return the wrong (cached)
hashes for the object.

This happens regularly on a crypted local disk mount when the VFS
thinks files have been changed but actually their contents are
identical to that written previously. This is because when files are
uploaded their nonce changes so the contents of the file changes but
the timestamp and size remain the same because the file didn't
actually change.

This causes errors like this:

    ERROR: file: Failed to copy: corrupted on transfer: md5 crypted
    hash differ "X" vs "Y"

This turned out to be because the local backend wasn't clearing its
cache of hashes when the file was updated.

This fix clears the hash cache for Update and Remove.

It also puts a src and destination in the crypt message to make future
debugging easier.

Fixes #4031

backend/crypt/crypt.go

@@ -443,7 +443,7 @@ func (f *Fs) put(ctx context.Context, in io.Reader, src fs.ObjectInfo, options [
 				if err != nil {
 					fs.Errorf(o, "Failed to remove corrupted object: %v", err)
 				}
-				return nil, fmt.Errorf("corrupted on transfer: %v crypted hash differ %q vs %q", ht, srcHash, dstHash)
+				return nil, fmt.Errorf("corrupted on transfer: %v crypted hash differ src %q vs dst %q", ht, srcHash, dstHash)
 			}
 			fs.Debugf(src, "%v = %s OK", ht, srcHash)
 		}

backend/local/local.go

@@ -1133,6 +1133,9 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		return err
 	}
 
+	// Wipe hashes before update
+	o.clearHashCache()
+
 	var symlinkData bytes.Buffer
 	// If the object is a regular file, create it.
 	// If it is a translated link, just read in the contents, and
@@ -1295,6 +1298,13 @@ func (o *Object) setMetadata(info os.FileInfo) {
 	}
 }
 
+// clearHashCache wipes any cached hashes for the object
+func (o *Object) clearHashCache() {
+	o.fs.objectMetaMu.Lock()
+	o.hashes = nil
+	o.fs.objectMetaMu.Unlock()
+}
+
 // Stat an Object into info
 func (o *Object) lstat() error {
 	info, err := o.fs.lstat(o.path)
@@ -1306,6 +1316,7 @@ func (o *Object) lstat() error {
 
 // Remove an object
 func (o *Object) Remove(ctx context.Context) error {
+	o.clearHashCache()
 	return remove(o.path)
 }
 

backend/local/local_internal_test.go

@@ -1,6 +1,7 @@
 package local
 
 import (
+	"bytes"
 	"context"
 	"io/ioutil"
 	"os"
@@ -12,6 +13,7 @@ import (
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/config/configmap"
 	"github.com/rclone/rclone/fs/hash"
+	"github.com/rclone/rclone/fs/object"
 	"github.com/rclone/rclone/fstest"
 	"github.com/rclone/rclone/lib/file"
 	"github.com/rclone/rclone/lib/readers"
@@ -166,3 +168,64 @@ func TestSymlinkError(t *testing.T) {
 	_, err := NewFs(context.Background(), "local", "/", m)
 	assert.Equal(t, errLinksAndCopyLinks, err)
 }
+
+// Test hashes on updating an object
+func TestHashOnUpdate(t *testing.T) {
+	ctx := context.Background()
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+	const filePath = "file.txt"
+	when := time.Now()
+	r.WriteFile(filePath, "content", when)
+	f := r.Flocal.(*Fs)
+
+	// Get the object
+	o, err := f.NewObject(ctx, filePath)
+	require.NoError(t, err)
+
+	// Test the hash is as we expect
+	md5, err := o.Hash(ctx, hash.MD5)
+	require.NoError(t, err)
+	assert.Equal(t, "9a0364b9e99bb480dd25e1f0284c8555", md5)
+
+	// Reupload it with diferent contents but same size and timestamp
+	var b = bytes.NewBufferString("CONTENT")
+	src := object.NewStaticObjectInfo(filePath, when, int64(b.Len()), true, nil, f)
+	err = o.Update(ctx, b, src)
+	require.NoError(t, err)
+
+	// Check the hash is as expected
+	md5, err = o.Hash(ctx, hash.MD5)
+	require.NoError(t, err)
+	assert.Equal(t, "45685e95985e20822fb2538a522a5ccf", md5)
+}
+
+// Test hashes on deleting an object
+func TestHashOnDelete(t *testing.T) {
+	ctx := context.Background()
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+	const filePath = "file.txt"
+	when := time.Now()
+	r.WriteFile(filePath, "content", when)
+	f := r.Flocal.(*Fs)
+
+	// Get the object
+	o, err := f.NewObject(ctx, filePath)
+	require.NoError(t, err)
+
+	// Test the hash is as we expect
+	md5, err := o.Hash(ctx, hash.MD5)
+	require.NoError(t, err)
+	assert.Equal(t, "9a0364b9e99bb480dd25e1f0284c8555", md5)
+
+	// Delete the object
+	require.NoError(t, o.Remove(ctx))
+
+	// Test the hash cache is empty
+	require.Nil(t, o.(*Object).hashes)
+
+	// Test the hash returns an error
+	_, err = o.Hash(ctx, hash.MD5)
+	require.Error(t, err)
+}