[fallbackstorage] allow to support browser without IndexedDB

Makefile

@@ -132,6 +132,7 @@ ${JIOVERSION}: ${EXTERNALDIR}/URI.js \
 	${SRCDIR}/jio.js \
 	${EXTERNALDIR}/rusha.js \
 	${SRCDIR}/jio.storage/replicatestorage.js \
+	${SRCDIR}/jio.storage/fallbackstorage.js \
 	${SRCDIR}/jio.storage/shastorage.js \
 	${SRCDIR}/jio.storage/uuidstorage.js \
 	${SRCDIR}/jio.storage/memorystorage.js \
@@ -179,6 +180,7 @@ ${JIONODEVERSION}: ${SRCDIR}/node/jio-start.js \
 	${SRCDIR}/jio.js \
 	${SRCDIR}/node/jio.js \
 	${SRCDIR}/jio.storage/replicatestorage.js \
+	${SRCDIR}/jio.storage/fallbackstorage.js \
 	${SRCDIR}/jio.storage/shastorage.js \
 	${SRCDIR}/jio.storage/uuidstorage.js \
 	${SRCDIR}/jio.storage/memorystorage.js \

src/jio.storage/fallbackstorage.js

+/*
+ * JIO extension for resource replication.
+ * Copyright (C) 2021  Nexedi SA
+ *
+ * This program is free software: you can Use, Study, Modify and Redistribute
+ * it under the terms of the GNU General Public License version 3, or (at your
+ * option) any later version, as published by the Free Software Foundation.
+ *
+ * You can also Link and Combine this program with other software covered by
+ * the terms of any of the Free Software licenses or any of the Open Source
+ * Initiative approved licenses and Convey the resulting work. Corresponding
+ * source of such a combination shall include the source code for all other
+ * software used.
+ *
+ * This program is distributed WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * See COPYING file for full licensing terms.
+ * See https://www.nexedi.com/licensing for rationale and options.
+ */
+
+/*jslint nomen: true*/
+/*global jIO*/
+
+(function (jIO) {
+  "use strict";
+
+  function FallbackStorage(spec) {
+    this._sub_storage = this._current_storage = jIO.createJIO(spec.sub_storage);
+    if (spec.hasOwnProperty('fallback_storage')) {
+      this._fallback_storage = jIO.createJIO(spec.fallback_storage);
+      this._checked = false;
+    } else {
+      this._checked = true;
+    }
+  }
+
+  var method_name_list = [
+    'get',
+    'put',
+    'post',
+    'remove',
+    'buildQuery',
+    'getAttachment',
+    'putAttachment',
+    'allAttachments',
+    'repair'
+  ],
+    i;
+
+  function methodFallback(method_name) {
+    return function () {
+      var storage = this,
+        queue =  storage._current_storage[method_name].apply(
+          storage._current_storage,
+          arguments
+        ),
+        argument_list = arguments;
+      if (!storage._checked) {
+        queue
+          .push(function (result) {
+            storage._checked = true;
+            return result;
+          }, function (error) {
+            storage._checked = true;
+            if ((error instanceof jIO.util.jIOError) &&
+                (error.status_code === 500)) {
+              // If storage is not working, use fallback instead
+              storage._current_storage = storage._fallback_storage;
+              return storage._current_storage[method_name].apply(
+                storage._current_storage,
+                argument_list
+              );
+            }
+            throw error;
+          });
+      }
+      return queue;
+    };
+  }
+
+  for (i = 0; i < method_name_list.length; i += 1) {
+    FallbackStorage.prototype[method_name_list[i]] =
+      methodFallback(method_name_list[i]);
+  }
+
+  FallbackStorage.prototype.hasCapacity = function hasCapacity(name) {
+    return (this._sub_storage.hasCapacity(name) &&
+      this._fallback_storage.hasCapacity(name));
+  };
+
+  jIO.addStorage('fallback', FallbackStorage);
+
+}(jIO));

test/tests.html

@@ -64,6 +64,7 @@ See https://www.nexedi.com/licensing for rationale and options.
   <script src="jio.storage/replicatestorage_repairattachment.tests.js"></script>
   <script src="jio.storage/replicatestorage_fastrepair.tests.js"></script>
   <script src="jio.storage/replicatestorage_fastrepairattachment.tests.js"></script>
+  <script src="jio.storage/fallbackstorage.tests.js"></script>
   <script src="jio.storage/shastorage.tests.js"></script>
   <script src="jio.storage/parserstorage.tests.js"></script>