defer bulk channel init for mongo node reuse

[jipperinbham]

• CHANGELOG.md updated (feel free to wait until changes have been reviewed by a maintainer)

When a mongodb adaptor is defined in the config.yaml with bulk=true and is used for the Source and Sink in the application.js, transporter will never shutdown properly.

The following change adds a new field to the adaptor and sets it when the Listen func is called and checked with Stop is called.

fixes #152

[trinchan]

I'm having a hard time figuring out how the bulkWriter close blocks, causing the app to hang. From what I understand, the only exit from that bulkWriter is through the quit channel and we're skipping over that here because it presumably blocks. Is the final data flush hanging? If so, I think it's more natural to leave the quit/cleanup in and attacking the bug from the bulk writer end.

If you could a quick execution path summary of the blocking state, that'd be awesome.

I don't doubt this works, I just want to make sure I understand the code path properly.

[jipperinbham]

transporter_config.yaml:

nodes:
  my_mongo:
    type: mongo
    uri: mongodb://127.0.0.1:27017/my_database
    bulk: true

transporter_app.js:

Source({name:"my_mongo", namespace: 'my_database.SomeCollection'})
  .transform({filename: 'changenamespace_and_log.js', namespace: 'my_database.SomeCollection'})
  .save({name:"my_mongo", namespace: 'my_database.OtherCollection'});\

changenamespace_and_log.js:

module.exports = function(doc) {
  console.log("transformer: " + JSON.stringify(doc));
  doc.ns = "my_database.OtherCollection";
  return doc
}

load up the my_database.SomeCollection using the following:

use my_database
for (var i=0; i<1000; i++){db.SomeCollection.insert({i: i});}

then run transporter:

./transporter run --config transporter_config.yaml transporter_app.js

you'll see the documents get transferred properly to the new collection but transporter never completes. if you add some print statements in the Listen and Stop functions of the mongodb adaptor, you'll see the sink node stop completely but the source node will just hang because the bulk flag is true.

[trinchan]

LGTM, thanks for this @jipperinbham !