webdav: make nextcloud only upload SHA1 checksums

When using nextcloud, before this change we only uploaded one of SHA1
or MD5 checksum in the OC-Checksum header with preference to SHA1 if
both were set.

This makes the MD5 checksums read as empty string which makes syncing
with checksums less useful than they should be as all the MD5
checksums are blank.

This change makes it so that we only upload the SHA1 to nextcloud.

The behaviour of owncloud is unchanged as owncloud uses the checksum
as an upload integrity check only and calculates its own checksums.

See: https://forum.rclone.org/t/how-to-specify-hash-method-to-checksum/13055

backend/webdav/webdav.go

@@ -113,7 +113,8 @@ type Fs struct {
 	canStream          bool          // set if can stream
 	useOCMtime         bool          // set if can use X-OC-Mtime
 	retryWithZeroDepth bool          // some vendors (sharepoint) won't list files when Depth is 1 (our default)
-	hasChecksums       bool          // set if can use owncloud style checksums
+	hasMD5             bool          // set if can use owncloud style checksums for MD5
+	hasSHA1            bool          // set if can use owncloud style checksums for SHA1
 }
 
 // Object describes a webdav object
@@ -215,7 +216,7 @@ func (f *Fs) readMetaDataForPath(ctx context.Context, path string, depth string)
 		},
 		NoRedirect: true,
 	}
-	if f.hasChecksums {
+	if f.hasMD5 || f.hasSHA1 {
 		opts.Body = bytes.NewBuffer(owncloudProps)
 	}
 	var result api.Multistatus
@@ -430,11 +431,12 @@ func (f *Fs) setQuirks(ctx context.Context, vendor string) error {
 		f.canStream = true
 		f.precision = time.Second
 		f.useOCMtime = true
-		f.hasChecksums = true
+		f.hasMD5 = true
+		f.hasSHA1 = true
 	case "nextcloud":
 		f.precision = time.Second
 		f.useOCMtime = true
-		f.hasChecksums = true
+		f.hasSHA1 = true
 	case "sharepoint":
 		// To mount sharepoint, two Cookies are required
 		// They have to be set instead of BasicAuth
@@ -536,7 +538,7 @@ func (f *Fs) listAll(ctx context.Context, dir string, directoriesOnly bool, file
 			"Depth": depth,
 		},
 	}
-	if f.hasChecksums {
+	if f.hasMD5 || f.hasSHA1 {
 		opts.Body = bytes.NewBuffer(owncloudProps)
 	}
 	var result api.Multistatus
@@ -945,10 +947,14 @@ func (f *Fs) DirMove(ctx context.Context, src fs.Fs, srcRemote, dstRemote string
 
 // Hashes returns the supported hash sets.
 func (f *Fs) Hashes() hash.Set {
-	if f.hasChecksums {
+	hashes := hash.Set(hash.None)
-		return hash.NewHashSet(hash.MD5, hash.SHA1)
+	if f.hasMD5 {
+		hashes.Add(hash.MD5)
 	}
-	return hash.Set(hash.None)
+	if f.hasSHA1 {
+		hashes.Add(hash.SHA1)
+	}
+	return hashes
 }
 
 // About gets quota information
@@ -1015,13 +1021,11 @@ func (o *Object) Remote() string {
 
 // Hash returns the SHA1 or MD5 of an object returning a lowercase hex string
 func (o *Object) Hash(ctx context.Context, t hash.Type) (string, error) {
-	if o.fs.hasChecksums {
+	if t == hash.MD5 && o.fs.hasMD5 {
-		switch t {
-		case hash.SHA1:
-			return o.sha1, nil
-		case hash.MD5:
 		return o.md5, nil
 	}
+	if t == hash.SHA1 && o.fs.hasSHA1 {
+		return o.sha1, nil
 	}
 	return "", hash.ErrUnsupported
 }
@@ -1042,11 +1046,15 @@ func (o *Object) setMetaData(info *api.Prop) (err error) {
 	o.hasMetaData = true
 	o.size = info.Size
 	o.modTime = time.Time(info.Modified)
-	if o.fs.hasChecksums {
+	if o.fs.hasMD5 || o.fs.hasSHA1 {
 		hashes := info.Hashes()
+		if o.fs.hasSHA1 {
 			o.sha1 = hashes[hash.SHA1]
+		}
+		if o.fs.hasMD5 {
 			o.md5 = hashes[hash.MD5]
 		}
+	}
 	return nil
 }
 
@@ -1126,19 +1134,21 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 		ContentLength: &size, // FIXME this isn't necessary with owncloud - See https://github.com/nextcloud/nextcloud-snap/issues/365
 		ContentType:   fs.MimeType(ctx, src),
 	}
-	if o.fs.useOCMtime || o.fs.hasChecksums {
+	if o.fs.useOCMtime || o.fs.hasMD5 || o.fs.hasSHA1 {
 		opts.ExtraHeaders = map[string]string{}
 		if o.fs.useOCMtime {
 			opts.ExtraHeaders["X-OC-Mtime"] = fmt.Sprintf("%f", float64(src.ModTime(ctx).UnixNano())/1e9)
 		}
-		if o.fs.hasChecksums {
+		// Set one upload checksum
-			// Set an upload checksum - prefer SHA1
+		// Owncloud uses one checksum only to check the upload and stores its own SHA1 and MD5
-			//
+		// Nextcloud stores the checksum you supply (SHA1 or MD5) but only stores one
-			// This is used as an upload integrity test. If we set
+		if o.fs.hasSHA1 {
-			// only SHA1 here, owncloud will calculate the MD5 too.
 			if sha1, _ := src.Hash(ctx, hash.SHA1); sha1 != "" {
 				opts.ExtraHeaders["OC-Checksum"] = "SHA1:" + sha1
-			} else if md5, _ := src.Hash(ctx, hash.MD5); md5 != "" {
+			}
+		}
+		if o.fs.hasMD5 && opts.ExtraHeaders["OC-Checksum"] == "" {
+			if md5, _ := src.Hash(ctx, hash.MD5); md5 != "" {
 				opts.ExtraHeaders["OC-Checksum"] = "MD5:" + md5
 			}
 		}