Friday, 1 February 2013

Local WebHooks with Mule Cloud Connect and LocalTunnel v2

When using an external API for WebHooks or Callbacks as discussed in Chapters 3 and 5 of Getting Started with Mule Cloud Connect; The API provider running somewhere out there on the web needs to callback your application that is happily running in isolation on your local machine. For an API provider to callback your application, the application must be accessible over the web. Sure, you could upload and test your application on a public facing server, but you may find it quicker and easier to work on your local development machine and these are typically behind firewalls, NAT, or otherwise not able to provide a public URL. You need a way to make your local application available over the web.

There are a few good services and tools out there to help with this. Examples include ProxyLocal, and Alternatively, you can set up your own reverse SSH Tunnel if you already have a remote system to forward your requests, but this is cumbersome to say the least. I find Localtunnel to be an excellent fit for this need and localtunnel have just recently released v2 of its service with a host of new features and enhancements. More information can be found here:

Installing Localtunnel

Those familiar with version 1 of the service will know that the v1 Localtunnel client was written in Ruby and required Rubygems to install it. The v2 client is now written in Python and can instead be installed via easy_install or pip.

If instead you're interested in using Localtunnel v1, then I have wrote a previous blog post on the subject here:

To get started, you will first need to check that you have Python installed. Localtunnel requires Python 2.6 or later. Most systems come with Python installed as standard, but if not you can check via the following command:

$ python -version

More info on installing Python can be found here:

Once complete, you will need easy_install to install the Localtunnel client.If you don't have easy_install after you install Python, you can install it with this bootstrap script:

$ curl | python

Once complete, you can install the Localtunnel client using the following command:

$ easy_install localtunnel

First run with LocalTunnel

Once installed, creating a tunnel is as simple as running the following command:

$ localtunnel-beta 8082

The parameter after the command: "8000" is the local port we want Localtunnel to forward to. So whatever port your app is running on should replace this value. Each time you run the command you should get output similar to the following:

Port 8082 is now accessible from ...
Note: As v2 is still in beta; the command local-tunnel-beta will eventually be installed as just localtunnel. This lets you keep the v1 just in case anything goes wrong with v2 during the beta.

Configuring the Connector

Now onto Mule! To demonstrate I will use the Twilio Cloud Connector example from Chapter 5. Twilio has an awesome WebHook implementation with great debugging tools. Twilio uses callbacks to tell you about the status of your requests; When you use Twilio to a place a phone call or send an SMS the Twilio API allows you to send a URL where you'll receive information about the phone call once it ends or the status of the outbound SMS message after it's processed.

This example uses the Twilio Cloud Connector to send a simple SMS message. The most important thing to note is that the "status-callback-flow-ref" attribute. All connector operations that support callback's will have an optional attribute ending in "-flow-ref". In this case : "status-callback-flow-ref". As the name suggests, this attribute should reference a flow. This value must be a valid flow id from within your configuration. It is this flow that will be used to listen for the callback.

Notice that the flow has no inbound endpoint? This is where the magic happens; when Twilio process the SMS message it will send a callback automatically to that flow without you having to define an inbound endpoint. The connector automatically generates an inbound endpoint and sends the auto generated URL to Twilio for you.

Customizing the Callback

The URL generated for the callback URL is built using 'localhost' as the host, the 'http.port' environment variable or 'localPort' value as the port and the path of the URL is typically just a random generated string or static value. So if I run this locally it would send Twilio my non public address, something like: http://localhost:80/...vv3v3er342fvvn. Each connector that accepts HTTP callbacks will provide you with an optional http-callback-config child element to override these settings. These settings can be set at the connector's config level as follows:

Here we have amended the previous example to add the additonal http-callback-config configuration. The configuration takes three additional arguments: domain, localPort and remotePort. These settings will be used to constuct the URL that is passed to the external system. The URL will be the same as the default generated URL of the HTTP inbound-endpoint except that the host is replaced by the 'domain' setting (or its default value) and the port is replaced by the 'remotePort' setting (or its default value).

In this case we have used the domain from the URL that Localtunnel generated for us earlier: and set the localPort to 8082 as we run the Localtunnel command using port 8082 and the remotePort to 80 as the localtunnel server just runs on port 80.

And that's it! If you run this configuration you should start seeing your callback being printed to the console. The same goes for any OAuth connectors too. If your using any OAuth connectors built using the DevKit OAuth modules, you can configure the OAuth callback in a similar fashion.

A full Mule/Twilio WebHook project can be found here:

1 comment:

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