MM-15480: Add server support for Range on files (#10892)

services/filesstore/filesstore.go

@@ -10,10 +10,15 @@ import (
 	"github.com/mattermost/mattermost-server/model"
 )
 
+type ReadCloseSeeker interface {
+	io.ReadCloser
+	io.Seeker
+}
+
 type FileBackend interface {
 	TestConnection() *model.AppError
 
-	Reader(path string) (io.ReadCloser, *model.AppError)
+	Reader(path string) (ReadCloseSeeker, *model.AppError)
 	ReadFile(path string) ([]byte, *model.AppError)
 	FileExists(path string) (bool, *model.AppError)
 	CopyFile(oldPath, newPath string) *model.AppError

services/filesstore/localstore.go

@@ -34,7 +34,7 @@ func (b *LocalFileBackend) TestConnection() *model.AppError {
 	return nil
 }
 
-func (b *LocalFileBackend) Reader(path string) (io.ReadCloser, *model.AppError) {
+func (b *LocalFileBackend) Reader(path string) (ReadCloseSeeker, *model.AppError) {
 	f, err := os.Open(filepath.Join(b.directory, path))
 	if err != nil {
 		return nil, model.NewAppError("Reader", "api.file.reader.reading_local.app_error", nil, err.Error(), http.StatusInternalServerError)

services/filesstore/s3store.go

@@ -84,7 +84,7 @@ func (b *S3FileBackend) TestConnection() *model.AppError {
 }
 
 // Caller must close the first return value
-func (b *S3FileBackend) Reader(path string) (io.ReadCloser, *model.AppError) {
+func (b *S3FileBackend) Reader(path string) (ReadCloseSeeker, *model.AppError) {
 	s3Clnt, err := b.s3New()
 	if err != nil {
 		return nil, model.NewAppError("Reader", "api.file.reader.s3.app_error", nil, err.Error(), http.StatusInternalServerError)