Component library

A component is a piece of code which can instantiate a MsgFlo participant. By default such component code is placed in ./participants/ directory of a project.

cp ./node_modules/msgflo-nodejs/examples/ ./participants/

Declaring a command template in package.json tells MsgFlo how to instantiate them. This can be done per component, or by specifying a handler for a given file extension, which makes each matching file in the component directory (here: Repeat) automatically available as a component.

  "msgflo": {
    "handlers": {
      ".coffee": "msgflo-nodejs --name #ROLE #FILENAME"
    "components": {
      "Output": "noflo-runtime-msgflo --name out --graph core/Output --broker amqp://localhost"

The component command template supports substituting several variables, including:

Now the example service above can be started with a single command: By enabling --participants MsgFlo will start the individual participants.

msgflo-setup ./myservice.fbp --broker amqp://localhost --participants --forward=stdout

Using --forward stdout enables seeing the output from the Output participant, which is in a child process.

Send message again, and it should be repeated on stdout.

msgflo-send-message --queue repeater.IN --json '{ "foo": "bar-with-componentlib" }'

Having component handlers facilitates live-programming from Flowhub IDE: Adding a new component with Python code will get a .py file extension, and the handler for py will be used to instantiate a new process.


By default MsgFlo reads its component library configuration from the package.json (used by NPM). You can specify an alternative JSON file using --library msgflo.json. The configuration object can either exist at the top-level, or under a msgflo key.

There are default handlers specified for common supported environments. These do not need to be specified manually.