serve webdav: fix incorrect Content-Type immediately after upload

Before this change, if the Content-Type for an object was read
immediately after upload (before the object had been uploaded to the
backing store) then the Content-Type would be returned incorrectly.

This error would be more likely with `--vfs-cache-mode full` and
`writes` but may have been possible with the other
`--vfs-cache-mode`s.

This fixes the problem by always returning a sensible guess at the
content type - the same guess we would use for uploading the object.

Fixes #6433

backend/union/union.go

@@ -222,19 +222,19 @@ func (f *Fs) Purge(ctx context.Context, dir string) error {
 //
 // If it isn't possible then return fs.ErrorCantCopy
 func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (fs.Object, error) {
-	var srcFs fs.Info
-	if srcObj, ok := src.(*Object); ok {
-		// Have a union object - unwrap
-		o := srcObj.UnWrapUpstream()
-		srcFs = o.UpstreamFs()
-		src = o
-	} else {
-		// Have a non union object - it might be compatible with a union member
-		srcFs = src.Fs()
+	srcObj, ok := src.(*Object)
+	if !ok {
+		fs.Debugf(src, "Can't copy - not same remote type")
+		return nil, fs.ErrorCantCopy
+	}
+	o := srcObj.UnWrapUpstream()
+	su := o.UpstreamFs()
+	if su.Features().Copy == nil {
+		return nil, fs.ErrorCantCopy
 	}
 	var du *upstream.Fs
 	for _, u := range f.upstreams {
-		if u.Features().Copy != nil && operations.Same(u.RootFs, srcFs) {
+		if operations.Same(u.RootFs, su.RootFs) {
 			du = u
 		}
 	}
@@ -244,7 +244,7 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (fs.Object,
 	if !du.IsCreatable() {
 		return nil, fs.ErrorPermissionDenied
 	}
-	co, err := du.Features().Copy(ctx, src, remote)
+	co, err := du.Features().Copy(ctx, o, remote)
 	if err != nil || co == nil {
 		return nil, err
 	}

cmd/serve/webdav/webdav.go

@@ -377,18 +377,21 @@ func (fi FileInfo) ETag(ctx context.Context) (etag string, err error) {
 // ContentType returns a content type for the FileInfo
 func (fi FileInfo) ContentType(ctx context.Context) (contentType string, err error) {
 	// defer log.Trace(fi, "")("etag=%q, err=%v", &contentType, &err)
-	node, ok := (fi.FileInfo).(vfs.Node)
-	if !ok {
-		fs.Errorf(fi, "Expecting vfs.Node, got %T", fi.FileInfo)
-		return "application/octet-stream", nil
-	}
-	entry := node.DirEntry()
-	switch x := entry.(type) {
-	case fs.Object:
-		return fs.MimeType(ctx, x), nil
-	case fs.Directory:
+	if fi.IsDir() {
 		return "inode/directory", nil
 	}
-	fs.Errorf(fi, "Expecting fs.Object or fs.Directory, got %T", entry)
-	return "application/octet-stream", nil
+	if node, ok := (fi.FileInfo).(vfs.Node); !ok {
+		fs.Errorf(fi, "Expecting vfs.Node, got %T", fi.FileInfo)
+	} else {
+		entry := node.DirEntry()
+		switch x := entry.(type) {
+		case nil:
+			// object hasn't been uploaded yet if entry is nil
+		case fs.Object:
+			return fs.MimeType(ctx, x), nil
+		default:
+			fs.Errorf(fi, "Expecting fs.Object or nil, got %T", entry)
+		}
+	}
+	return fs.MimeTypeFromName(fi.Name()), nil
 }

fs/operations/operations.go

@@ -383,20 +383,6 @@ func CommonHash(ctx context.Context, fa, fb fs.Info) (hash.Type, *fs.HashesOptio
 	return hashType, &fs.HashesOption{Hashes: common}
 }
 
-// Is it OK to server side move/copy from src to dst
-func serverSideOK(ci *fs.ConfigInfo, fDst, fSrc fs.Info) bool {
-	if ci.ServerSideAcrossConfigs {
-		return true
-	}
-	if SameConfig(fSrc, fDst) {
-		return true
-	}
-	if SameRemoteType(fSrc, fDst) {
-		return fDst.Features().ServerSideAcrossConfigs
-	}
-	return false
-}
-
 // Copy src object to dst or f if nil.  If dst is nil then it uses
 // remote as the name of the new object.
 //
@@ -438,7 +424,7 @@ func Copy(ctx context.Context, f fs.Fs, dst fs.Object, remote string, src fs.Obj
 				return nil, accounting.ErrorMaxTransferLimitReachedGraceful
 			}
 		}
-		if doCopy := f.Features().Copy; doCopy != nil && serverSideOK(ci, f, src.Fs()) {
+		if doCopy := f.Features().Copy; doCopy != nil && (SameConfig(src.Fs(), f) || (SameRemoteType(src.Fs(), f) && (f.Features().ServerSideAcrossConfigs || ci.ServerSideAcrossConfigs))) {
 			in := tr.Account(ctx, nil) // account the transfer
 			in.ServerSideCopyStart()
 			newDst, err = doCopy(ctx, src, remote)
@@ -633,7 +619,7 @@ func Move(ctx context.Context, fdst fs.Fs, dst fs.Object, remote string, src fs.
 		return newDst, nil
 	}
 	// See if we have Move available
-	if doMove := fdst.Features().Move; doMove != nil && serverSideOK(ci, fdst, src.Fs()) {
+	if doMove := fdst.Features().Move; doMove != nil && (SameConfig(src.Fs(), fdst) || (SameRemoteType(src.Fs(), fdst) && (fdst.Features().ServerSideAcrossConfigs || ci.ServerSideAcrossConfigs))) {
 		// Delete destination if it exists and is not the same file as src (could be same file while seemingly different if the remote is case insensitive)
 		if dst != nil && !SameObject(src, dst) {
 			err = DeleteFile(ctx, dst)