Merge pull request #148 from megawac/streaming

Make registering as a subscriber or publisher an option for the streaming API

src/node/TopicStream.js

@@ -5,10 +5,19 @@ var DuplexStream = require('stream').Duplex;
  * Publish a connected ROS topic to a duplex
  * stream. This stream can be piped to, which will
  * publish to the topic
+ *
+ * @options
+ *   * subscribe: whether to subscribe to the topic and start emitting
+ *              Data
+ *   * publish: whether to register the stream as a publisher to the topic
+ *   * transform: a function to change the data to be published
+ *              or filter it if false is returned
  */
-Topic.prototype.toStream = function(transform) {
+Topic.prototype.toStream = function(options) {
+    options = options || {subscribe: true, publish: true};
+
     var topic = this;
-    var hasTransform = typeof transform === 'function';
+    var hasTransform = typeof options.transform === 'function';
 
     var stream = new DuplexStream({
         objectMode: true
@@ -18,18 +27,24 @@ Topic.prototype.toStream = function(transform) {
     // Publish to the topic if someone pipes to stream
     stream._write = function(chunk, encoding, callback) {
         if (hasTransform) {
-            chunk = transform(chunk);
+            chunk = options.transform(chunk);
         }
-        if (chunk) {
+        if (chunk === false) {
             topic.publish(chunk);
         }
         callback();
     };
 
-    this.subscribe(function(message) {
-        stream.push(message);
-    });
-    this.on('unsubscribe', stream.push.bind(stream, null));
+    if (options.subscribe) {
+        this.subscribe(function(message) {
+            stream.push(message);
+        });
+        this.on('unsubscribe', stream.push.bind(stream, null));
+    }
+
+    if (options.publish) {
+        this.advertise();
+    }
 
     return stream;
 };