lsjson: Add --hash-type parameter and use it in lsf to speed up hashing

Before this change if you specified --hash MD5 in rclone lsf it would
calculate all the hashes and just return the MD5 hash which was very
slow on the local backend.

Likewise specifying --hash on rclone lsjson was equally slow.

This change introduces the --hash-type flag (and corresponding
internal parameter) so that the hashes required can be selected in
lsjson.

This is used internally in lsf when the --hash parameter is selected
to speed up the hashing by only hashing with the one hash specified.

Fixes #4181

cmd/lsf/lsf.go

@@ -185,6 +185,7 @@ func Lsf(ctx context.Context, fsrc fs.Fs, out io.Writer) error {
 		case 'h':
 			list.AddHash(hashType)
 			opt.ShowHash = true
+			opt.HashTypes = []string{hashType.String()}
 		case 'i':
 			list.AddID()
 		case 'm':

cmd/lsjson/lsjson.go

@@ -29,6 +29,7 @@ func init() {
 	flags.BoolVarP(cmdFlags, &opt.ShowOrigIDs, "original", "", false, "Show the ID of the underlying Object.")
 	flags.BoolVarP(cmdFlags, &opt.FilesOnly, "files-only", "", false, "Show only files in the listing.")
 	flags.BoolVarP(cmdFlags, &opt.DirsOnly, "dirs-only", "", false, "Show only directories in the listing.")
+	flags.StringArrayVarP(cmdFlags, &opt.HashTypes, "hash-type", "", nil, "Show only this hash type (may be repeated).")
 }
 
 var commandDefinition = &cobra.Command{
@@ -58,17 +59,25 @@ The output is an array of Items, where each Item looks like this
       "Tier" : "hot",
    }
 
-If --hash is not specified the Hashes property won't be emitted.
+If --hash is not specified the Hashes property won't be emitted. The
+types of hash can be specified with the --hash-type parameter (which
+may be repeated). If --hash-type is set then it implies --hash.
 
-If --no-modtime is specified then ModTime will be blank. This can speed things up on remotes where reading the ModTime takes an extra request (eg s3, swift).
+If --no-modtime is specified then ModTime will be blank. This can
+speed things up on remotes where reading the ModTime takes an extra
+request (eg s3, swift).
 
-If --no-mimetype is specified then MimeType will be blank. This can speed things up on remotes where reading the MimeType takes an extra request (eg s3, swift).
+If --no-mimetype is specified then MimeType will be blank. This can
+speed things up on remotes where reading the MimeType takes an extra
+request (eg s3, swift).
 
 If --encrypted is not specified the Encrypted won't be emitted.
 
-If --dirs-only is not specified files in addition to directories are returned
+If --dirs-only is not specified files in addition to directories are
+returned
 
-If --files-only is not specified directories in addition to the files will be returned.
+If --files-only is not specified directories in addition to the files
+will be returned.
 
 The Path field will only show folders below the remote path being listed.
 If "remote:path" contains the file "subfolder/file.txt", the Path for "file.txt"

fs/operations/lsjson.go

@@ -8,6 +8,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/rclone/rclone/backend/crypt"
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/hash"
 	"github.com/rclone/rclone/fs/walk"
 )
 
@@ -77,6 +78,7 @@ type ListJSONOpt struct {
 	ShowHash      bool     `json:"showHash"`
 	DirsOnly      bool     `json:"dirsOnly"`
 	FilesOnly     bool     `json:"filesOnly"`
+	HashTypes     []string `json:"hashTypes"` // hash types to show if ShowHash is set, eg "MD5", "SHA-1"
 }
 
 // ListJSON lists fsrc using the options in opt calling callback for each item
@@ -99,6 +101,20 @@ func ListJSON(ctx context.Context, fsrc fs.Fs, remote string, opt *ListJSONOpt,
 	canGetTier := features.GetTier
 	format := formatForPrecision(fsrc.Precision())
 	isBucket := features.BucketBased && remote == "" && fsrc.Root() == "" // if bucket based remote listing the root mark directories as buckets
+	showHash := opt.ShowHash
+	hashTypes := fsrc.Hashes().Array()
+	if len(opt.HashTypes) != 0 {
+		showHash = true
+		hashTypes = []hash.Type{}
+		for _, hashType := range opt.HashTypes {
+			var ht hash.Type
+			err := ht.Set(hashType)
+			if err != nil {
+				return err
+			}
+			hashTypes = append(hashTypes, ht)
+		}
+	}
 	err := walk.ListR(ctx, fsrc, remote, false, ConfigMaxDepth(opt.Recurse), walk.ListAll, func(entries fs.DirEntries) (err error) {
 		for _, entry := range entries {
 			switch entry.(type) {
@@ -150,9 +166,9 @@ func ListJSON(ctx context.Context, fsrc fs.Fs, remote string, opt *ListJSONOpt,
 				item.IsBucket = isBucket
 			case fs.Object:
 				item.IsDir = false
-				if opt.ShowHash {
+				if showHash {
 					item.Hashes = make(map[string]string)
-					for _, hashType := range x.Fs().Hashes().Array() {
+					for _, hashType := range hashTypes {
 						hash, err := x.Hash(ctx, hashType)
 						if err != nil {
 							fs.Errorf(x, "Failed to read hash: %v", err)