Implement JS flipper client

Summary:
Standardize WS implementation for JS environments.

Why do we need a separate server implementation for browsers?
Browser targets cannot authenticate via the default certificate exchange flow. We need a dedicated client for them that works over an insecure channel (without the cert exchange).

Major changes:
1. Renamed `flipper-js-client-sdk` to `js-flipper` for consistency with `react-native-flipper`
2. Updated `js-flipper` implementation to match our other existing clients

Documentation will be updated in a separate subsequent PR.

https://fb.quip.com/2mboA0xbgoxl

Reviewed By: mweststrate

Differential Revision: D31688105

fbshipit-source-id: 418aa80e0fd86361c089cf54b0d44a8b4f748efa

js/js-flipper/src/connection.ts

@@ -0,0 +1,74 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {FlipperErrorMessage, FlipperMessageBus} from './message';
+import {FlipperPluginConnection, FlipperPluginReceiver} from './plugin';
+import {FlipperResponder} from './responder';
+import {isPromise, safeJSONStringify} from './util';
+
+type FlipperReceiver = (data: unknown, responder: FlipperResponder) => void;
+
+export class FlipperConnection implements FlipperPluginConnection {
+  pluginId: string;
+  private client: FlipperMessageBus;
+  private subscriptions: Map<string, FlipperReceiver> = new Map();
+
+  constructor(pluginId: string, client: FlipperMessageBus) {
+    this.pluginId = pluginId;
+    this.client = client;
+  }
+
+  send(method: string, params?: unknown) {
+    this.client.sendData({
+      method: 'execute',
+      params: {
+        api: this.pluginId,
+        method,
+        params,
+      },
+    });
+  }
+
+  receive(method: string, receiver: FlipperPluginReceiver) {
+    const wrappedReceiver: FlipperReceiver = (data, responder) => {
+      const handleError = (e: unknown) => {
+        const errorMessage: FlipperErrorMessage =
+          e instanceof Error
+            ? {name: e.name, message: e.message, stacktrace: e.stack}
+            : {name: 'Unknown', message: safeJSONStringify(e)};
+        responder.error(errorMessage);
+      };
+      try {
+        const response = receiver(data);
+        if (isPromise(response)) {
+          response.then((data) => responder.success(data)).catch(handleError);
+          return;
+        }
+        responder.success(response);
+      } catch (e) {
+        handleError(e);
+      }
+    };
+    this.subscriptions.set(method, wrappedReceiver);
+  }
+
+  call(method: string, params: unknown, responder: FlipperResponder) {
+    const receiver = this.subscriptions.get(method);
+    if (receiver == null) {
+      const errorMessage = `Receiver ${method} not found.`;
+      responder.error({message: errorMessage});
+      return;
+    }
+    receiver.call(receiver, params, responder);
+  }
+
+  hasReceiver(method: string): boolean {
+    return this.subscriptions.has(method);
+  }
+}