TopCoder Challenge Notifier Backend

Sends notifications to users at their specified time through email, by filtering out previously notified challenges and filtering in by specified tags(Ex: NodeJs, Java) from TopCoder RSS Feed.

TRY IT OUT https://custom-built.dev/app/tpcn

Framework: Spring Boot.
Databse: MongoDB.

How does it schedule

• On app start up, a notification task is scheduled at a fixed rate, set through schedule_rate property.
• This will at each invocation divides the schedule_rate into equal sections, set through schedule_sections property.
• For each section it schedules an task using java.util.concurrent.ScheduledExecutorService.
• These tasks wake up at their intervals and fetch all users scheduled in this interval from the database and send notifications to them through their emails.

Note:

• The variance between user scheduled time and actual notification time can be tuned by adjusting schedule_sections property.
• For example: If a variance of +/- 10 min is acceptable, then you can set schedule_rate as 1800000(30 min in ms) and schedule_sections as 3.
• schedule_sections property should be inline with task_scheduler max pool size in AppConfig.

Authentication

• This app uses JWT access tokens to identify users between requests, signed using SHA256withECDSA.
• Implementation of JWT access token authentication is based on RFC7519.

Admin Endpoint

• App has admin endpoint which can be accessed by admin users to get error log and summary of successful/un-successful messages.
• When exceptions are raised in the app, they are gracefully handled and details are asynchronously logged in db.

Setup

• Install and start mongodb, and update db.host and db.port properties in application.properties file.
• Create 256 bit EC key and store it in JKS format.

$ keytool -genkeypair -keyalg EC -keysize 256 -sigalg SHA256withECDSA -storetype JKS -keystore test.jks -alias test

• Update keystore alias, file and password in JKS_KEYSTORE_ALIAS, JKS_KEYSTORE_FILE and JKS_KEYSTORE_PASSWORD properties in application.properties file or as ENV variables.
• App uses Gmail STMP server to send mail, please provide Gmail credentials as APP_SENDER_MAIL and APP_SENDER_MAIL_PASSWORD ENV variables.
• Update schedule_rate in milliseconds and schedule_sections properties in application.properties to your choice.
• Set the app log level by logging.level.com.app property.
• Run the db init scripts in build-scripts/mongodb folder

$ cd build-scripts/mongodb
$ mongo db-colls-test-init.js
$ mongo db-colls-init.js

• db-colls-test-init.js creates collections for unit test cases.
• Build the app using mvn install command and run the jar file by providing LOG_HOME system property to store logs or run by AppRunner main method from your IDE.
• To run as docker container cd into build-scripts/server paste the jar previously built into this folder and from build folder run build.sh by providing these three arguments:
  • path to store mongodb database data
  • path to store logs
  • app version

Example

$ ./build.sh /var/app/tpcn/db /var/app/tpcn/logs 2.3

• Import postman collection and environment in POST_MAN folder to check and get info about API.

Architecture

• App main root package is com.app which contains AppRunner which initializes the app.
• Sub packages com.app.config for app configuration, com.app.controller for app REST controllers, com.app.controlleradvice for controller advices, com.app.converters for http message converters, com.app.dao for app data access objects, com.app.exception for app exception classes, com.app.interceptors for app http interceptors, com.app.model for app models, com.app.notifier for app user notifier, com.app.scheduler for app scheduler, com.app.service for app services, com.app.util for app util classes.

Implementation

• AccessTokenService creates and verifies JWT access tokens.
• StatusService contains async methods to log successful/un-successful events.
• ChallengeNotificationScheduler schedules notifications at fixed rate.
• ChallengeNotifier notifies new challenges by filtering out old challenges and filtering in by tags.
• AuthInterceptor verifies the access token of incoming requests.

TODO

• Add option to change challenge type to develop/design.
• Make build script for windows.