feat: add multi database backend supports

README.md

@@ -61,6 +61,7 @@ Options object:
 
 | Param           | Type [= default]   | Description                                                           |
 | --------------- | ------------------ | --------------------------------------------------------------------- |
+| `backend`       | string = "idb"     | Defults to IndexedDb Store.This is the only built-in backend currently |
 | `wipe`          | boolean = false    | Delete the database and start with an empty filesystem                |
 | `url`           | string = undefined | Let `readFile` requests fall back to an HTTP request to this base URL |
 | `urlauto`       | boolean = false    | Fall back to HTTP for every read of a missing file, even if unbacked  |
@@ -190,6 +191,43 @@ Returns the size of a file or directory in bytes.
 
 All the same functions as above, but instead of passing a callback they return a promise.
 
+## Storage Backend
+
+You can create your own storage backend if the default idb storage backend does not meet your needs.
+
+You should implement these methods in your backend:
+
+```ts
+export default class YourBackend {
+  // new FS(name, options?)
+  constructor(name: string, options?) {}
+  // save the superblock to your backend
+  async saveSuperblock(superblock: Map) {}
+  // load the superblock from your backend
+  async loadSuperblock(): Map {}
+  async readFile(inode: string): Buffer {}
+  async writeFile(inode: string, data: Uint8Array) {}
+  // remove inode file
+  async unlink(inode: string) {}
+  // clean all data
+  async wipe()
+  // close backend
+  async close()
+}
+```
+
+See the `errors.js` for the error code to raise.
+
+Then register it to the `FS`
+
+```ts
+import FS from '@isomorphic-git/lightning-fs'
+FS.register('YourBackend', YourBackend)
+
+// now you can use your backend:
+const fs = new FS('your-fs-name', {backend: 'YourBackend', ...yourBackendOptions})
+```
+
 ## License
 
 MIT

src/IdbBackend.js

@@ -1,9 +1,9 @@
 const idb = require("@isomorphic-git/idb-keyval");
 
 module.exports = class IdbBackend {
-  constructor(dbname, storename) {
+  constructor(dbname, options) {
     this._database = dbname;
-    this._storename = storename;
+    this._storename = (options && options.storename) || (dbname + "_files");
     this._store = new idb.Store(this._database, this._storename);
   }
   saveSuperblock(superblock) {

src/PromisifiedFS.js

@@ -34,6 +34,16 @@ function cleanParams2(oldFilepath, newFilepath) {
 }
 
 module.exports = class PromisifiedFS {
+  static register(name, backend) {
+    if (!this.prototype.backends) this.prototype.backends = {};
+    this.prototype.backends[name] = backend;
+  }
+
+  static unregister(name) {
+    if (this.prototype.backends)
+      return delete this.prototype.backends[name];
+  }
+
   constructor(name, options) {
     this.init = this.init.bind(this)
     this.readFile = this._wrap(this.readFile, false)
@@ -69,19 +79,22 @@ module.exports = class PromisifiedFS {
     this._initPromise = this._init(...args)
     return this._initPromise
   }
-  async _init (name, {
-    wipe,
-    url,
-    urlauto,
-    fileDbName = name,
-    fileStoreName = name + "_files",
-    lockDbName = name + "_lock",
-    lockStoreName = name + "_lock",
-  } = {}) {
+  async _init (name, options = {}) {
     await this._gracefulShutdown()
+    const {
+      wipe,
+      url,
+      urlauto,
+      backend,
+      fileDbName = name,
+      fileStoreName = name + "_files",
+      lockDbName = name + "_lock",
+      lockStoreName = name + "_lock",
+    } = options
     this._name = name
-    this._idb = new IdbBackend(fileDbName, fileStoreName);
-    this._mutex = navigator.locks ? new Mutex2(name) : new Mutex(lockDbName, lockStoreName);
+    let Backend = (this.backends && this.backends[backend]) || IdbBackend;
+    this._idb = new Backend(fileDbName, {...options, storename: fileStoreName});
+    this._mutex = typeof navigator !== 'undefined' && navigator.locks ? new Mutex2(name) : new Mutex(lockDbName, lockStoreName);
     this._cache = new CacheFS(name);
     this._opts = { wipe, url };
     this._needsWipe = !!wipe;