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Design Overview

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dcyoung edited this page Aug 30, 2017 · 12 revisions

Concept

The RaspberryPi creates a local WiFi access point and hosts a small webserver. Users can connect to the app from any device (phone or computer) without internet access.

  • User connects to the RaspberryPi's WiFi access point
  • User navigates to the hosted webpage using an internet browser
  • User interacts with scanner via webpage GUI
    • Specify scan parameters
    • Submit scan requests
    • View list of recorded scan files
    • Download a specific file
    • Delete a specific file
    • Trigger small troubleshooting scripts that test various components. To be used during device assembly or on error states.
    • Shutdown or restart the RaspberryPi

Design Philosophy

  • Simple dependencies or platform requirements
  • Simple messaging and IPC (ie: printing stringied JSON)
  • Simple languages (Javascript + python)
  • Familiar/standard environments (Node + express)

Application Structure + Design

  • node webserver (app)
    • express routing
    • jade templates for front-end
    • standard view + route directory structure
  • simple client side JavaScript for user interaction
  • app uses node's child_process module to spawn child processes that execute simple compartmentalized python scripts which interact with the sweep device (ie: perform scan)
  • stdin of the main process (node) and the stdout of the child process (python) are piped together, such that print statements in python code are essentially messages received as JS events
  • python code provides updates about the scan progress using a simple message format encoded as stringified JSON, which the back-end JavaScript can easily decode and feed right off to the client side JavaScript at the client’s request

Directory structure

  • output_scans/: where .csv output scan files are stored
  • js/: contains custom node modules used by various routes
  • public/: contains client-side static files (express will look here)
    • javascript/
      • pages/: browser/client-side JavaScript (1 script for every page)
      • scanner/: a library for code shared by various pages (front-end scanner settings, helper functions etc).
    • lib/: libraries like jQuery
    • stylesheets/: style related stuff
  • routes/: contains scripts which handle routing + back-end logic
  • scanner/: contains python scripts controlling the actual scanner
  • views/: contains jade templates (1 per page) which handle the front end view
  • app.js: the main entry point to the app

Main Dependencies

The idea is to let other libraries do all the heavy lifting (ie: libsweep + sweeppy should handle all the low level communication with the device).

Alternative Directions

Simplicity is the overarching design philosophy for the main scanner application. But there are a lot of interesting directions to take the application in the future.

More powerful and expandable solutions could easily be explored. Distributed zeromq patterns with a message schema like protobuff could extend the capabilities beyond IPC, to messaging multiple external applications for real time viewing of data etc. A more simple upgrade might involve switching to a python app that runs in parallel and communicating between node and python via zeroRPC (see discussion here).

The sweeppy python bindings don't seem as robust as a well organized c++ application that uses libsweep directly. The scanner code could likely be cleaned up and re-written in c++ without too much effort.

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