[MM-26812] Add support for resumable file uploads (#15252)

* Implement AppendFile for FileBackend

* Split test into subtests

* [MM-26812] Add support for resumable file uploads (#15252)

* Implement UploadSession

* Implement UploadSessionStore

* Add error strings

* Implement resumable file uploads

* Add UploadType

* Fix retry layer tests

* Regenerate store layers

* Fix store error handling

* Use base for filename

* Prevent concurrent uploads on the same upload session

* Fix erroneus error string

* Improve error handling

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

* Fix translations

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/user.go

@@ -89,6 +89,8 @@ func (api *API) InitUser() {
 
 	api.BaseRoutes.Users.Handle("/migrate_auth/ldap", api.ApiSessionRequired(migrateAuthToLDAP)).Methods("POST")
 	api.BaseRoutes.Users.Handle("/migrate_auth/saml", api.ApiSessionRequired(migrateAuthToSaml)).Methods("POST")
+
+	api.BaseRoutes.User.Handle("/uploads", api.ApiSessionRequired(getUploadsForUser)).Methods("GET")
 }
 
 func createUser(c *Context, w http.ResponseWriter, r *http.Request) {
@@ -2601,6 +2603,26 @@ func convertUserToBot(c *Context, w http.ResponseWriter, r *http.Request) {
 	w.Write(bot.ToJson())
 }
 
+func getUploadsForUser(c *Context, w http.ResponseWriter, r *http.Request) {
+	c.RequireUserId()
+	if c.Err != nil {
+		return
+	}
+
+	if c.Params.UserId != c.App.Session().UserId {
+		c.Err = model.NewAppError("getUploadsForUser", "api.user.get_uploads_for_user.forbidden.app_error", nil, "", http.StatusForbidden)
+		return
+	}
+
+	uss, err := c.App.GetUploadSessionsForUser(c.Params.UserId)
+	if err != nil {
+		c.Err = err
+		return
+	}
+
+	w.Write([]byte(model.UploadSessionsToJson(uss)))
+}
+
 func migrateAuthToLDAP(c *Context, w http.ResponseWriter, r *http.Request) {
 	props := model.StringInterfaceFromJson(r.Body)
 	from, ok := props["from"].(string)