Fix sample with Routing metadata changes

Prior to this commit, changes in the routing metadata mechanism had
broken this sample application.
The routing metadata is now transmitted over the wire and the metadata
must be encoded/decoded according to the MIME type used.

See https://github.com/rsocket/rsocket/blob/master/Extensions/Routing.md

This commit implements a new Serializer that writes the metadata length
and then the metadata itself as an UTF8 string.

This only supports a single type of metadata.
We'll need to use Composite metadata if we want to send other metadata,
such as authentication.

flight-client/src/metadata.js

@@ -0,0 +1,29 @@
+import {
+    createBuffer,
+    byteLength
+} from 'rsocket-core';
+
+/**
+ * Serializer for Routing metadata
+ * @see https://github.com/rsocket/rsocket/blob/master/Extensions/Routing.md
+ */
+export class RoutingMetadataSerializer {
+
+    deserialize(data) {
+        throw 'Not implemented!';
+    }
+
+    serialize(data) {
+        if (data == null) {
+            return null;
+        }
+        let dataLength = byteLength(data, 'utf8');
+        let outBuffer = createBuffer(1 + dataLength);
+        outBuffer.writeUInt8(dataLength, 0);
+        outBuffer.write(data, 1, data.length, 'utf8');
+        return outBuffer;
+    }
+}
+
+RoutingMetadataSerializer.MIME_TYPE = "message/x.rsocket.routing.v0";
+RoutingMetadataSerializer.MIME_TYPE_ID = 0x7E;

flight-client/src/radars.js

@@ -1,27 +1,39 @@
 import {
     RSocketClient,
     JsonSerializer,
-    IdentitySerializer
+    IdentitySerializer,
+    BufferEncoder,
+    UTF8Encoder
 } from 'rsocket-core';
 import RSocketWebSocketClient from 'rsocket-websocket-client';
+import {RoutingMetadataSerializer} from './metadata'
+
+const CustomEncoders = {
+    data: UTF8Encoder,
+    dataMimeType: UTF8Encoder,
+    message: UTF8Encoder,
+    metadata: BufferEncoder,
+    metadataMimeType: UTF8Encoder,
+    resumeToken: UTF8Encoder,
+};
 
 export class RadarClient {
 
     constructor(url, responder) {
         this.client = new RSocketClient({
             serializers: {
                 data: JsonSerializer,
-                metadata: IdentitySerializer,
+                metadata: new RoutingMetadataSerializer(),
             },
             setup: {
                 // ms btw sending keepalive to server
                 keepAlive: 10000,
                 // ms timeout if no keepalive response
                 lifetime: 20000,
                 dataMimeType: 'application/json',
-                metadataMimeType: 'message/x.rsocket.routing.v0',
+                metadataMimeType: RoutingMetadataSerializer.MIME_TYPE,
             },
-            transport: new RSocketWebSocketClient({url: url}),
+            transport: new RSocketWebSocketClient({url: url}, CustomEncoders),
             responder: responder
         });
     }