Add option to automatically create a topic and re-use a subscription.

lib/pubsub/index.js

@@ -196,18 +196,25 @@ PubSub.prototype.createTopic = function(name, callback) {
  * @throws {Error} If a name is not provided.
  *
  * @param {string} name - The name of the topic.
+ * @param {object=} options - Configuration object.
+ * @param {bool=} options.autoCreate - Automatically create topic if
+ *     it doesn't exist. Note that messages published to a topic with
+ *     no subscribers will not be delivered.
  * @return {module:pubsub/topic}
  *
  * @example
  * var topic = pubsub.topic('my-existing-topic');
+ * var topic = pubsub.topic('topic-that-maybe-exists', {autoCreate: true});
  * topic.publish('New message!');
  */
-PubSub.prototype.topic = function(name) {
+PubSub.prototype.topic = function(name, options) {
   if (!name) {
     throw new Error('A name must be specified for a new topic.');
   }
+  options = options || {};
   return new Topic(this, {
-    name: name
+    name: name,
+    autoCreate: options.autoCreate
   });
 };
 

lib/pubsub/topic.js

@@ -60,6 +60,12 @@ function Topic(pubsub, options) {
   this.name = Topic.formatName_(pubsub.projectId, options.name);
   this.projectId = pubsub.projectId;
   this.pubsub = pubsub;
+
+  if (options.autoCreate) {
+    this.unformattedName = options.name;
+    this.origMakeReq_ = this.makeReq_;
+    this.makeReq_ = this.autoCreateWrapper_;
+  }
 }
 
 /**
@@ -95,6 +101,37 @@ Topic.formatName_ = function(projectId, name) {
   return 'projects/' + projectId + '/topics/' + name;
 };
 
+/**
+ * Wrapper for makeReq_ that automatically attempts to create a topic if it
+ * does not yet exist.
+ *
+ * @private
+ */
+Topic.prototype.autoCreateWrapper_ = function(method, path, q, body, callback) {
+  var self = this;
+
+  var createAndRetry = function(){
+    self.pubsub.createTopic(self.unformattedName, function(err) {
+      if (err) {
+        callback(err);
+        return;
+      }
+      self.origMakeReq_(method, path, q, body, callback);
+    });
+  };
+
+  this.origMakeReq_(method, path, q, body, function(err, res) {
+    if (err && err.code === 404 && method !== 'DELETE') {
+      createAndRetry();
+      return;
+    }
+    else {
+      callback(err, res);
+      return;
+    }
+  });
+};
+
 /**
  * Publish the provided message or array of messages. A message can be of any
  * type. On success, an array of messageIds is returned in the response.
@@ -276,7 +313,10 @@ Topic.prototype.subscribe = function(name, options, callback) {
 
   var path = Subscription.formatName_(this.projectId, name);
   this.makeReq_('PUT', path, null, body, function(err) {
-    if (err) {
+    if (options.reuseExisting && err && err.code === 409) {
+      callback(null, self.subscription(name, options));
+    }
+    else if (err) {
       callback(err);
       return;
     }

test/pubsub/topic.js

@@ -161,6 +161,44 @@ describe('Topic', function() {
     });
   });
 
+  describe('publish to non-existing topic', function(){
+    var messageObject = { data: 'howdy' };
+
+    it('should generate 404 error without autoCreate', function(done) {
+      topic.makeReq_ = function(method, path, query, body, callback) {
+        callback({code: 404});
+      };
+
+      topic.publish(messageObject, function(err){
+        assert.equal(err.code, 404);
+        done();
+      });
+    });
+
+    it('should publish successfully with autoCreate', function(done) {
+      var acTopic = new Topic(pubsubMock, {
+        name: TOPIC_NAME, autoCreate: true
+      });
+      var created = false;
+
+      acTopic.origMakeReq_ = function(method, path, query, body, callback) {
+        if (!created) {
+          callback({code: 404});
+        }
+        else {
+          callback(null);
+        }
+      };
+
+      pubsubMock.createTopic = function(name, callback) {
+        created = true;
+        callback();
+      };
+
+      acTopic.publish(messageObject, done);
+    });
+  });
+
   describe('delete', function() {
     it('should delete a topic', function(done) {
       topic.makeReq_ = function(method, path) {