Use the hardcoded protocol version by default

Fetching it from the remote repo introduces a non-negligible latency every time
a connection with Chrome is established and it is kind of breaking change since
this operation was almost immediate before. Those who desire to use this feature
will have to explicitly request it.

Related to #10

README.md

@@ -98,16 +98,16 @@ Remote Debugging Protocol versions
 
 Currently it is not possible to fetch the protocol descriptor
 ([`protocol.json`][local-json]) directly from the instrumented Chrome instance
-(see [#10][issue]); rather, that file is fetched from the proper source
-repository at every connection, and if that is not possible, the [harcoded
-version](local-json) is used. This file is fetched from time to time from the
-[Blink repo][remote-json] and pushed to this repository.
+(see [#10][issue]); rather, that file can be fetched from the proper [source
+repository][remote-json] at every connection. By default, the [hardcoded local
+version][local-json] is used.
 
 To override the above behavior there are basically three options:
 
 1. update the local copy with `make update-protocol`;
 
-2. pass a custom protocol descriptor upon
+2. pass a custom protocol descriptor (use `null` to fetch it from the remote
+   repository) upon
    [connection](https://github.com/cyrus-and/chrome-remote-interface#moduleoptions-callback);
 
 3. use the *raw* version of the [commands](#chromesendmethod-params-callback)
@@ -129,9 +129,11 @@ Protocol][rdb].
   array returned by `http://host:port/json` containing the tab list and must
   return the numeric index of a tab. Defaults to a function which returns the
   currently active tab (`function (tabs) { return 0; }`).
-- `protocol`: [Remote Debugging Protocol][rdb] descriptor object.
-  Defaults to the protocol fetched directly from the Chrome repository, if
-  available, otherwise falls back to an hardcoded version.
+- `protocol`: [Remote Debugging Protocol][rdb] descriptor object. Passing `null`
+  causes the proper protocol descriptor to be fetched from the remote Chrome
+  repository according to the version exposed by the instrumented Chrome
+  instance, falling back to the default if that is not possible. Defaults to the
+  [hardcoded local version][local-json].
 
 `callback` is a listener automatically added to the `connect` event of the
 returned `EventEmitter`.

lib/chrome.js

@@ -302,8 +302,10 @@ function connectToChrome() {
             }
         });
     };
-    // try fetching the protocol from Chrome unless not specified
-    if (typeof self.protocol === 'undefined') {
+    // fetch the protocol
+    if (self.protocol === null) {
+        // try fetching the protocol from Chrome falling back to the hardcoded
+        // version otherwise
         Chrome.Protocol(options, function (err, fromChrome, protocol) {
             if (err) {
                 self.notifier.emit('error', err);
@@ -313,6 +315,10 @@ function connectToChrome() {
             }
         });
     } else {
+        // use the one provided falling back to the hardcoded version otherwise
+        if (typeof self.protocol === 'undefined') {
+            self.protocol = require('./protocol.json');
+        }
         continueConnection();
     }
 }