evp

evp (Event Pipeline)

Listen from JSON Event sources and to process each event adapting and either forwarding it to an http/https sink or to a mssql database.

Event are processed according to rules defined in a JSON configuration file.

JSON Dsl

Configuration files are JSON files of the form:

{
  "sourceName1": {
    "type": "RabbitMQ",
    "config": {
      "host": "192.168.50.4"
    },
    "process": {
      "transform": {
        "a":  "$.nested.a",
        "b":  "$.nested.b"
      },
      "forward": {
        "uri": "http://example.com/dbo/lots"
      }
    }
  },
  "sourceName2": {
    // ...
  }
}

Built in commands

Transform

Applies a transform template to input event and send the result to the next command.

Transform pulls data from original event using JSONPath and generate a new object based on a template.

Each of the template's properties can pull a single property from the source data or an array of all results found by its JSONPath.

When pulling an array of data you can also supply a subtemplate to transform each item in the array.

JSONPath is like XPath for JavaScript objects. To learn the syntax, read the documentation for the JSONPath package on npm and the original article by Stefan Goessner.

See https://www.npmjs.com/package/jsonpath-object-transform for details.

Options

• transform: A jsonpath-object-transform object template.

"transform": {
  "a":  "$.nested.a",
  "b":  "$.nested.b"
},

Forward

Issue an HTTP requrest sending the event as body.

Options:

• forward: A request js object. See https://github.com/request/request#requestoptions-callback.

NOTE: Forward default HTTP method is POST, while request.js' one is GET.

Print

Print command just print each event to the standard output

Options:

• Print.prompt: A prompt to display along with the event
• Print.depth: depth to pass to util.Print default to null

Programmatic Api

The core is independent from specific sources and allows for different commands implementation and extension:

Source.register('mySourceName', MySource);
Command.register('myCommandName', MyCommand);
 
let Processor = new Processor();
 
Processor.configure(config);
Processor.listen();

Implementing an Source

1. Extend Source and implement listen()
2. Register the new event source into Processor;

NOTE: config for the Source will be available in this.config.

class MySource extends Source {
 
  listen() {
    setInterval(() => {
      this.event({
        time: (new Date()).getTime();
      });
    }, this.config.interval)
  }
 
}
 
Source.register('MySource', MySource);

{
  "mySource1": {
    "type": "MySource",
    "config": {
      "interval": 1000
    }
  }
}

Implementing a Command

1. Extend Command and implement run()
2. Register the new command into Processor;

NOTE: config for the Source will be available in this.config.

class MailCommand extends Command {
  run(event){
    let body = JSON.stringify(event, null, 2);
    sendMail(this.config.recipient, body);
    return Promise.resolve(event); // forward to next
  }
}
 
Command.register('email', MyCommand);

{
  "mySource1": {
    "type": "MySource",
    "config": {
      "interval": 1000
    },
    "process": {
      "email": {
        "recipient": "[e-mail]"
      }
    }
  }
}