Test task

Test task for Node.js developers.

Task

The main goal is to create a small Web application with only one API processing input binary data and returning aggregated statistics for this data. Application should be able to process relatively big amounts of data and high number of concurrent requests (i.e. use all you can to achieve higher performance, but still use Node as a platform :P).

Configuration

Configuration depends on environment (NODE_ENV environment variable). Default configuration is kept in some JSON / JSON5 file. Environment configuration should be taken from corresponding JSON / JSON5 file (e.g.config.ENV.json). Default environment is development. When configuration is loaded default one is merged with environment, so that env configuration overrides defaults.

If configuration can't be read application should crash.

API

Endpoint URL: /api/v1/process Endpoint method: 'POST'

(requests to any other endpoint should return 501 with error message)

Handler of this API checks if Content-Type header is set to application/octet-stream. If header value is different, request must be aborted with 406 error and error message.

Incoming data should be parsed and aggregated as specified below. If there is a parsing error, request should be aborted with 415 and error describing error.

The result of processing should be returned with 200 as JSON message. Assume, that client always expects JSON output from this Web application.

Input data

Input data is a history of payment transactions. Each record has following fields:

• Sender name (string, 32 bytes)
• Receiver name (string, 32 bytes)
• Amount in cents (4 bytes)
• Date as timestamp in ms (6 bytes)

Each record is coded into a binary frame. Frame structure is configurable and specified in application configuration, so it can be used for parsing frames before processing.

Assumptions:

• Strings are UTF-8 strings
• Numbers are unsigned integers in big endian

Frame configuration specifies its size and offsets for fields.

{
  "frameSize": 128,
  "offset": {
    "sender": 0,
    "receiver": 32,
    "amount": 72,
    "timestamp": 80
  }
}

The rationale of having this frame specification is that frame can have other fields coded inside, and these fields are not of concern of this application, but still mentioned fields can be coded and positioned in whatever way.

Note: if configuration is invalid, application should crash. Examples of invalid configuration: - Overlapping fields - Field offset + size exceeds frame size

Processing

Statistics calculated per request. Processing of all the frames in request should result in aggregated statistics:

• Total amount (sum of amount values)
• Number of transactions (i.e. number of frames)
• Stats per each user:
  • Number of transactions
  • Total sent amount
  • Total received amount
• Stats per each day:
  • Number of transactions

This can be done in a free form, the formatting below can be used as a reference:

{
  "total": {
    "amount": 10050000,
    "transactions": 100
  },
  "customerStatistics": {
    "alex": {
      "transactions": 10,
      "totalSent": 1000,
      "totalReceived": 100
    }
  },
  "dayStatistics": {
    "2016-09-01T00:00:00Z": {
      "transactions": 100
    }
  }
}

Error messages

In case of any error API should return JSON message representing Error object with name and message fields. Optionally, error objects can be custom errors with corresponding HTTP status codes put into JSON output as well.

Assumptions

• Size of input data frame can be quite big
• Client making HTTP requests sets indefinite request timeout

Testing

Server

For run server please do:

yarn install
yarn start

Server runs on port 3000 by default

Utility for sending test content

Execute client/bin/client for usage.

For testing you can use following command:

client/bin/client -u http://127.0.0.1:3000/api/v1/process -f 128 -s 0 -r 40 -a 80 -t 120 -m 10000 -c 1

For stress-testing you can add -S option, plus play with -c and -m.