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joule

0.1.5 • Public • Published

Joule

Inspired by Mule (http://www.mulesoft.com), Joule is a collection of built-in configurable components that help you get your REST service up and running quickly! These components include common things like setting headers and variables, logging, file parsing, consuming external web services, etc. Joule also supports custom components, allowing you to write your own code and inject it anywhere in the component flow. Joule takes care of all of the scaffolding and setup required for a REST service, letting you concentrate on your own code. Read on to see how easy it is to create a REST service with Joule!

Table of Contents

Download

$ cd my_app_dir
$ npm install joule

Run the sample app

Joule comes with a sample configuration used mostly for tests, tho you can use it to run the app to see how it works. To start Joule with the sample/test config:

$ cd my_app_dir
$ node node_modules/joule/src/app.js -c node_modules/joule/sample/test-config.json

You should see the following output:

Loading config file: node_modules/joule/sample/test-config.json
Starting app on localhost:8081
Registered route: /setHeaders
Registered route: /setVariable
Registered route: /customFunction
Registered route: /parseTemplate
Registered route: /parseTemplate2/:id
Registered route: /webServiceConsumer
Registered route: /webServiceConsumerDynamicUrl
Registered route: /webServiceConsumerBadEndPoint
Registered route: /customErrorHandler
Registered route: /genericErrorHandler
Registered route: /choiceHandler
Starting app on localhost:8082
Registered route: /json
App listening on localhost:8081
App listening on localhost:8082

Once the app is running, you can try hitting the various sample/test end-points to see their output:

You can take a look at node_modules/joule/sample/test-config.json to see how each of these end-points are configured and also see the documentation below.

Once you're familiar with how the various components are configured, you can try your hand at your own configuration. Just run the app with:

$ node node_modules/joule/src/app.js -c relative_path_to_your_config.json

Configuration

A Joule app is configured via a JSON config file where you define your app, its routes, and the component flow for each route. Here's an example where we define two apps, one running on port 8081, and one running on 8082. Each app has a /hello route defined.

{
    "apps": [
        {
            "host": "localhost",
            "port": 8081,
            "routes": [
                {
                    "path": "/hello",
                    "components": [
                        {
                            "type": "setPayload",
                            "value": "Hello World!"
                        }
                    ]
                }
            ]
        },
        {
            "host": "localhost",
            "port": 8082,
            "routes": [
                {
                    "path": "/hello",
                    "components": [
                        {
                            "type": "setPayload",
                            "value": {
                                "Hello": "World!",
                            }
                        }
                    ]
                }
            ]
        }
    ]
}

Hitting http://localhost:8081/hello will respond with the plain text string:

Hello World!

Hitting http://localhost:8082/hello will respond with a json object:

{"Hello": "World!"}

Routes

Joule sits on top of ExpressJS, so routing configuration follows ExpressJS conventions. I.e, any route supported by ExpressJS is also supported by Joule.

That's really it for the app and route configuration. Let's dive into the heart of Joule - components!

Components

SetHeaders

Sets one or more headers on the response. Here's an example that sets the common no-cache response headers:

{
    "type": "setHeaders",
    "headers": {
        "Cache-Control": "no-cache, no-store, must-revalidate",
        "Pragma": "no-cache",
        "Expires": "0"
    }
}

SetVariable

Sets a variable within the scope of the request/response flow. You can use these variables in your own custom code or in other components using res.getVariable(varName). Examples:

Set the airline variable to "delta":

{
    "type": "setVariable",
    "name": "airline",
    "value": "delta"
}

The value attribute can also take javascript code that will be evaluated. Just surround the code with $$ tokens. This example sets the passedInId variable to the value of the 'id' request parameter:

{
    "type": "setVariable",
    "name": "passedInId",
    "value": "$$req.getParam('id')$$"
}

Logger

Lets you add logging at any point in the flow. Examples:

{
    "type": "logger",
    "message": "Looking up user ..."
}

The message attribute can also take javascript code that will be evaluated. Just surround the code with $$ tokens:

{
    "type": "logger",
    "message": "Looking up user $$res.getParam('userid')$$ ..."
}

ParseTemplate

Parses a file using underscore's built-in template engine. Examples:

This parses the templates/products.html file passing in optional attributes for token replacement. Setting setPayload to true causes the parsed output to be sent as the response body:

{
    "type": "parseTemplate",
    "file": "templates/products.html", // The relative path/file of the template
    "attrs": {
        "title": "Our Products",
        "id": "$$req.getParam('id')$$"
    },
    "setPayload": true
}

Same as above but stores the parsed output in a variable called productsHtml:

{
    "type": "parseTemplate",
    "file": "templates/products.html", // The relative path/file of the template
    "attrs": {
        "title": "Our Products",
        "id": "$$req.getParam('id')$$"
    },
    "varName": "productsHtml"
}

Note that the file must be configured as relative to the directory where the app is started. For example, if you start the app from ~/node/myApp, and your file is in ~/node/myApp/src/templates, you would need to configure it as:

"file": "src/templates/file.html"

WebServiceConsumer

Calls a web service. Examples:

Make a get request to an end-point, expecting the response type to be JSON. Setting setPayload to true causes the parsed output to be sent as the response body:

{
    "type": "webServiceConsumer",
    "method": "get", // Optional. If not supplied, 'get' will be used by default.
    "endPoint": "http://api.data.gov/census/american-community-survey/v1/2011/populations/states?api_key=DEMO_KEY",
    "responseType": "json",
    "setPayload": true
}

Same as above but stores the parsed output in a variable called statePolpulations:

{
    "type": "webServiceConsumer",
    "endPoint": "http://api.data.gov/census/american-community-survey/v1/2011/populations/states?api_key=DEMO_KEY",
    "responseType": "json",
    "varName": "statePolpulations"
}

The end-point can also contain javascript expressions. In this example, the year can be passed in as a request parameter:

{
    "type": "webServiceConsumer",
    "method": "get", // Optional. If not supplied, 'get' will be used by default.
    "endPoint": "http://api.data.gov/census/american-community-survey/v1/$$req.getParam('year')$$/populations/states?api_key=DEMO_KEY",
    "responseType": "json",
    "setPayload": true
}

Choice

The choice component lets you dynamically decide what to do based on the outcome of the conditions you define. Each condition contains an 'if' attribute with your logic (surrouned by $$ tokens as seen above). The 'then' attribute can contain one or more components to call based on the outcome of the 'if' logic. If a condition's logic evaluates to true, the components defined in the 'then' attribute will be called, in order. All other conditions will be ignored. A final condition with '$$true$$' for the 'if' attribute acts as the default condition to perform if no others evaluated to true.

{
    "type": "choice",
    "conditions": [
        {
            "if": "$$req.getParam('airline') === 'delta'$$",
            "then": [
                {
                    "type": "logger",
                    "message": "Calling delta web svc ..."
                },
                {
                    "type": "webServiceConsumer",
                    "endPoint": "http://www.delta.com/api/flights",
                    "responseType": "json",
                    "varName": "flights"
                }
            ]
        },
        {
            "if": "$$req.getParam('airline') === 'jetblue'$$",
            "then": [
                {
                    "type": "logger",
                    "message": "Calling jetblue web svc ..."
                },
                {
                    "type": "webServiceConsumer",
                    "endPoint": "http://www.jetblue.com/apis/flights",
                    "responseType": "json",
                    "varName": "flights"
                }
            ]
        },
        {
            "if": "$$true$$",
            "then": [
                {
                    "type": "setPayload",
                    "value": "Missing required parameter: airline"
                }
            ]
        }
    ]
}

CustomFunction

Allows you to call your own custom function. Example:

{
    "type": "customFunction",
    "require": "src/customFunctions", // The relative file where the custom function lives
    "function": "myCustomFunction" // The function name
}

Note that the component file must be configured as relative to the directory where the app is started. For example, if you start the app from ~/node/myApp, and your file is at ~/node/myApp/src/customFunctions.js, you would need to configure it as:

"file": "src/customFunctions"

When writing a custom function, it must accept three arguments:

  • req - The request
  • res - The response
  • callback - The next component to call

Joule takes care of passing these arguments in to each component/function. Also, make sure to call the next callback when your function is done. Example:

module.exports.myCustomFunction = function (req, res, callback) {
    // Use setTimeout to prove that async function calls work within the framework
    setTimeout(function(){
        console.log('in custom function');
        res.setVariable('myVar', 'this is a test');
        callback(req, res);
    }, 1000);
}

Also, when writing a custom function, it's crucial to detect and handle errors properly. Joule provides a res.setError() function that can aid with this. In your code, if you detect an error, calling this function will result in the error handler being invoked. In this example, if fs.readFileSync() throws an error, calling res.setError(e) followed by a return will bypass all remaining components in the flow and invoke the error handler:

try {
    var file = fs.readFileSync(component.file, {encoding: encoding});
} catch (e) {
    res.setError(e);
    return;
}

SetPayload

Sets the response body to return to the client. This typically comes at the end of a route's flow. Examples:

Set a plain text response body (the Content-Type response header will automatically be set to text/plain):

{
    "type": "setPayload",
    "value": "You passed in id: $$res.getVariable('passedInId')$$"
}

Set a JSON object as the response body (the Content-Type response header will automatically be set to application/json):

{
    "type": "setPayload",
    "value": {
        "1": "test",
        "2": "test2"
    }
}

CustomErrorHandler

By default, Joule handles errors by logging the stack trace and sending a '500 Internal Server Error' back to the caller along with the error message. If you need your own behaviour, you can specify a custom error handler like so:

{
    "type": "customErrorHandler",
    "require": "app/customFunctions", // The relative file where the custom error handler lives
    "function": "myErrorHandler" // The error handler function name
}

Note that the component file must be configured as relative to the directory where the app is started. For example, if you start the app from ~/node/myApp, and your file is at ~/node/myApp/src/customFunctions.js, you would need to configure it as:

"file": "src/customFunctions"

When writing a custom error handler function, it must accept three arguments:

  • req - The request
  • res - The response
  • err - The error object

Example:

module.exports.myErrorHandler = function (req, res, err) {
    console.error("In custom error handler\n" + err.stack);
    res.status(500).send("In custom error handler: " + err.message);
}

GlobalComponents

You may find the need to configure the same type of component(s) with the same attribute(s) over and over again (e.g., a setHeader component for setting no-cache headers). To aid with this, Joule supports the notion of global components. Simply define these components in the globalComponents namespace, and you can then reference them elsewhere in the configuration. In this example, we define two global components with the names/IDs setNoCacheHeaders and setHeadersLogger:

"globalComponents": {
    "setNoCacheHeaders": {
        "type": "setHeaders",
        "headers": {
            "Cache-Control": "no-cache, no-store, must-revalidate",
            "Pragma": "no-cache",
            "Expires": "0"
        }
    },
    "headersLogger": {
        "type": "logger",
        "message": "Headers: $$JSON.stringify(res._headers)$$"
    }
}

We can then reference these in a component flow like so:

{
    "path": "/hello",
    "components": [
        "setNoCacheHeaders",
        "headersLogger",
        {
            "type": "setPayload",
            "value": "Hello World!"
        }
    ]
}

As you can see, we first set the no-cache headers, then the headers logger, and finally, we set the payload.

Enhancements to request and response objects

Joule modifies the request and response objects with the following handy functions:

req.getParam(name)

Gets the value of a request parameter by name. This can be a parameter passed in as:

req.getParams()

Returns a hash of all request parameters.

res.setVariable(name, value)

Set a variable for later use in your app.

res.getVariable(name)

Get a variable set with res.setVariable().

res.setPayload(payload)

Set the payload of the response.

res.getPayload()

Get the payload set with res.setPayload().

res.setError(err)

When an error occurs in a custom component, calling this function will invoke the error handler. Note that you must also explicitely return after calling this function:

res.setError(err);
return;

Commit History

  • 0.1.0 - Initial release.

  • 0.1.2 - Modified parseTemplate test config to work in both dev and node_module contexts.

  • 0.1.3 - Fixed a relative path issues, which caused customFunctionHandler, customErrorHandler, and parsefile to not work properly.

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Install

npm i joule

Repository

github.com/dcpf/joule

Homepage

github.com/dcpf/joule

Weekly Downloads

0

Version

0.1.5

License

BSD-2-Clause

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Collaborators

  • dpf
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