Support JSON-RPC 2.0-compatible VM service events.

This adds a parameter to streamListen that will cause it to produce JSON-RPC
2.0-compatible events.

R=turnidge@google.com

Review URL: https://codereview.chromium.org//1257943003 .

CHANGELOG.md

@@ -81,6 +81,9 @@
 
 ### VM Service Protocol Changes
 
+* **BREAKING** The service protocol now sends JSON-RPC 2.0-compatible
+  server-to-client events.
+
 * The service protocol now includes a `"jsonrpc"` property in its responses, as
   opposed to `"json-rpc"`.
 

runtime/observatory/lib/service_common.dart

@@ -204,11 +204,11 @@ abstract class CommonWebSocketVM extends VM {
           bytes.offsetInBytes + offset,
           bytes.lengthInBytes - offset);
       var map = _parseJSON(meta);
-      if (map == null) {
+      if (map == null || map['method'] != 'streamNotify') {
         return;
       }
-      var event = map['event'];
-      var streamId = map['streamId'];
+      var event = map['params']['event'];
+      var streamId = map['params']['streamId'];
       postServiceEvent(streamId, event, data);
     });
   }
@@ -218,9 +218,10 @@ abstract class CommonWebSocketVM extends VM {
     if (map == null) {
       return;
     }
-    var event = map['event'];
-    if (event != null) {
-      var streamId = map['streamId'];
+
+    if (map['method'] == 'streamNotify') {
+      var event = map['params']['event'];
+      var streamId = map['params']['streamId'];
       postServiceEvent(streamId, event, null);
       return;
     }

runtime/vm/service.cc

@@ -681,8 +681,11 @@ void Service::HandleEvent(ServiceEvent* event) {
   ASSERT(stream_id != NULL);
   {
     JSONObject jsobj(&js);
-    jsobj.AddProperty("event", event);
-    jsobj.AddProperty("streamId", stream_id);
+    jsobj.AddProperty("jsonrpc", "2.0");
+    jsobj.AddProperty("method", "streamNotify");
+    JSONObject params(&jsobj, "params");
+    params.AddProperty("streamId", stream_id);
+    params.AddProperty("event", event);
   }
   PostEvent(stream_id, event->KindAsCString(), &js);
 }

runtime/vm/service/service.md

@@ -12,10 +12,9 @@ It is possible to make HTTP (non-WebSocket) requests,
 but this does not allow access to VM _events_ and is not documented
 here.
 
-The Service Protocol is based on JSON-RPC 2.0
-(http://www.jsonrpc.org/specification). The Service Protocol has been
-extended to support pushing _events_ to the client, which is
-apparently outside the scope of the JSON-RPC specification.
+The Service Protocol uses [JSON-RPC 2.0][].
+
+[JSON-RPC 2.0]: http://www.jsonrpc.org/specification
 
 **Table of Contents**
 
@@ -189,22 +188,27 @@ Each stream provides access to certain kinds of events. For example the _Isolate
 access to events pertaining to isolate births, deaths, and name changes. See [streamListen](#streamlisten)
 for a list of the well-known stream ids and their associated events.
 
-Events arrive asynchronously over the WebSocket and always have the
-_streamId_ and _event_ properties:
+Stream events arrive asynchronously over the WebSocket. They're structured as
+JSON-RPC 2.0 requests with no _id_ property. The _method_ property will be
+_streamNotify_, and the _params_ will have _streamId_ and _event_ properties:
 
-```
+```json
 {
-  "event": {
-    "type": "Event",
-    "kind": "IsolateExit",
-    "isolate": {
-      "type": "@Isolate",
-      "id": "isolates/33",
-      "number": "51048743613",
-      "name": "worker-isolate"
+  "json-rpc": "2.0",
+  "method": "streamNotify",
+  "params": {
+    "streamId": "Isolate",
+    "event": {
+      "type": "Event",
+      "kind": "IsolateExit",
+      "isolate": {
+        "type": "@Isolate",
+        "id": "isolates/33",
+        "number": "51048743613",
+        "name": "worker-isolate"
+      }
     }
   }
-  "streamId": "Isolate"
 }
 ```
 
@@ -212,6 +216,7 @@ It is considered a _backwards compatible_ change to add a new type of event to a
 Clients should be written to handle this gracefully.
 
 
+
 ## Types
 
 By convention, every result and event provided by the Service Protocol