1 files changed, 117 insertions, 0 deletions
diff --git a/remote/domains/DomainCache.jsm b/remote/domains/DomainCache.jsm
new file mode 100644
index 0000000000..8f240d7c89
--- /dev/null
+++ b/remote/domains/DomainCache.jsm
@@ -0,0 +1,117 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["DomainCache"];
+
+const { Domain } = ChromeUtils.import(
+  "chrome://remote/content/domains/Domain.jsm"
+);
+const { UnknownMethodError } = ChromeUtils.import(
+  "chrome://remote/content/Error.jsm"
+);
+
+/**
+ * Lazy domain instance cache.
+ *
+ * Domains are loaded into each target's realm, and consequently
+ * there exists one domain cache per realm.  Domains are preregistered
+ * with this cache and then constructed lazily upon request.
+ *
+ * @param {Session} session
+ *     Session that domains should be associated with as they
+ *     are constructed.
+ * @param {Map.<string, string>} modules
+ *     Table defining JS modules available to this domain cache.
+ *     This should be a mapping between domain name
+ *     and JS module path passed to ChromeUtils.import.
+ */
+class DomainCache {
+  constructor(session, modules) {
+    this.session = session;
+    this.modules = modules;
+    this.instances = new Map();
+  }
+
+  /** Test if domain supports method. */
+  domainSupportsMethod(name, method) {
+    const domain = this.modules[name];
+    if (domain) {
+      return domain.implements(method);
+    }
+    return false;
+  }
+
+  /**
+   * Gets the current instance of the domain, or creates a new one,
+   * and associates it with the predefined session.
+   *
+   * @throws {UnknownMethodError}
+   *     If domain is not preregistered with this domain cache.
+   */
+  get(name) {
+    let inst = this.instances.get(name);
+    if (!inst) {
+      const Cls = this.modules[name];
+      if (!Cls) {
+        throw new UnknownMethodError(name);
+      }
+      if (!isConstructor(Cls)) {
+        throw new TypeError("Domain cannot be constructed");
+      }
+
+      inst = new Cls(this.session);
+      if (!(inst instanceof Domain)) {
+        throw new TypeError("Instance not a domain");
+      }
+
+      inst.addEventListener(this.session);
+
+      this.instances.set(name, inst);
+    }
+
+    return inst;
+  }
+
+  /**
+   * Tells if a Domain of the given name is available
+   */
+  has(name) {
+    return name in this.modules;
+  }
+
+  get size() {
+    return this.instances.size;
+  }
+
+  /**
+   * Execute the given command (function) of a given domain with the given parameters.
+   * If the command doesn't exists, it will throw.
+   * It returns the returned value of the command, which is most likely a promise.
+   */
+  execute(domain, command, params) {
+    if (!this.domainSupportsMethod(domain, command)) {
+      throw new UnknownMethodError(domain, command);
+    }
+    const inst = this.get(domain);
+    return inst[command](params);
+  }
+
+  /** Calls destructor on each domain and clears the cache. */
+  clear() {
+    for (const inst of this.instances.values()) {
+      inst.destructor();
+    }
+    this.instances.clear();
+  }
+
+  toString() {
+    return `[object DomainCache ${this.size}]`;
+  }
+}
+
+function isConstructor(obj) {
+  return !!obj.prototype && !!obj.prototype.constructor.name;
+}