local: don't calculate any hashes by default #3419

Before this change, if the caller didn't provide a hint, we would
calculate all hashes for reads and writes.

The new whirlpool hash is particularly expensive and that has become noticeable.

Now we don't calculate any hashes on upload or download unless hints are provided.

This means that some operations may run slower and these will need to be discovered!

It does not affect anything calling operations.Copy which already puts
the corrects hints in.

backend/local/local.go

@@ -917,7 +917,7 @@ func (o *Object) openTranslatedLink(offset, limit int64) (lrc io.ReadCloser, err
 // Open an object for read
 func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.ReadCloser, err error) {
 	var offset, limit int64 = 0, -1
-	hashes := hash.Supported
+	var hasher *hash.MultiHasher
 	for _, option := range options {
 		switch x := option.(type) {
 		case *fs.SeekOption:
@@ -925,7 +925,12 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 		case *fs.RangeOption:
 			offset, limit = x.Decode(o.size)
 		case *fs.HashesOption:
-			hashes = x.Hashes
+			if x.Hashes.Count() > 0 {
+				hasher, err = hash.NewMultiHasherTypes(x.Hashes)
+				if err != nil {
+					return nil, err
+				}
+			}
 		default:
 			if option.Mandatory() {
 				fs.Logf(o, "Unsupported mandatory option: %v", option)
@@ -949,15 +954,15 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 		// don't attempt to make checksums
 		return wrappedFd, err
 	}
-	hash, err := hash.NewMultiHasherTypes(hashes)
-	if err != nil {
-		return nil, err
+	if hasher == nil {
+		// no need to wrap since we don't need checksums
+		return wrappedFd, nil
 	}
-	// Update the md5sum as we go along
+	// Update the hashes as we go along
 	in = &localOpenFile{
 		o:    o,
 		in:   wrappedFd,
-		hash: hash,
+		hash: hasher,
 		fd:   fd,
 	}
 	return in, nil
@@ -979,18 +984,23 @@ func (nwc nopWriterCloser) Close() error {
 }
 
 // Update the object from in with modTime and size
-func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) error {
+func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (err error) {
 	var out io.WriteCloser
+	var hasher *hash.MultiHasher
 
-	hashes := hash.Supported
 	for _, option := range options {
 		switch x := option.(type) {
 		case *fs.HashesOption:
-			hashes = x.Hashes
+			if x.Hashes.Count() > 0 {
+				hasher, err = hash.NewMultiHasherTypes(x.Hashes)
+				if err != nil {
+					return err
+				}
+			}
 		}
 	}
 
-	err := o.mkdirAll()
+	err = o.mkdirAll()
 	if err != nil {
 		return err
 	}
@@ -1015,11 +1025,9 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	}
 
 	// Calculate the hash of the object we are reading as we go along
-	hash, err := hash.NewMultiHasherTypes(hashes)
-	if err != nil {
-		return err
+	if hasher != nil {
+		in = io.TeeReader(in, hasher)
 	}
-	in = io.TeeReader(in, hash)
 
 	_, err = io.Copy(out, in)
 	closeErr := out.Close()
@@ -1055,9 +1063,11 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	}
 
 	// All successful so update the hashes
-	o.fs.objectHashesMu.Lock()
-	o.hashes = hash.Sums()
-	o.fs.objectHashesMu.Unlock()
+	if hasher != nil {
+		o.fs.objectHashesMu.Lock()
+		o.hashes = hasher.Sums()
+		o.fs.objectHashesMu.Unlock()
+	}
 
 	// Set the mtime
 	err = o.SetModTime(ctx, src.ModTime(ctx))