zjkmxy / pyndn-json-patch

An example on using JSON patch, SVS and AFrame to sync on VR/AR scenes.

An example on using JSON patch, SVS and AFrame to sync on VR/AR scenes.

Run the application

Setup poetry environment:

poetry install

Run the application (needs local NFD):

poetry run python -m uvicorn main:app --port 8000

Then, browse http://127.0.0.1:8000/ to see the scene.

Examples on aincraft

• Run an instance on 8000: poetry run python -m uvicorn main:app --port 8000
• Run an instance on 8001: poetry run python -m uvicorn main:app --port 8001
• Connect to the 8000 instance http://127.0.0.1:8000/
• Connect to the 8001 instance http://127.0.0.1:8001/
• Use cursor left click to create boxes on the ground.
  • Right click to move the camera.
• Verify that boxes are synced.

Alternatively, an NDNts version is deployed at https://zjkmxy.web.app/, which is a static webpage compatible with the python-ndn version.

Note: you still need a running localhost NFD instance to use the NDNts web for now.

Examples on operating objects (V1)

Get the JSON representation of the box

curl http://127.0.0.1:8000/objects/root/theBox

The path /root/theBox can be replaced with any object. This endpoint will automatically resolve sub-entities and return the full JSON representation.

Change the box color to red

curl http://127.0.0.1:8000/patches/root/theBox -H 'Content-Type: application/json' \
  -d '{"op": "replace", "path": "/color", "value":"#EE0000"}'

Create an octahedron

curl http://127.0.0.1:8000/patches/root/theOctahedron -H 'Content-Type: application/json' \
  -d '{"op":"new","value":{"@type":"a-octahedron","@children":{},"color":"#FF926B","radius":1,"position": "2 1.5 -4"}}'
curl http://127.0.0.1:8000/patches/root -H 'Content-Type: application/json' \
  -d '{"op": "add", "path": "/@children/theOctahedron", "value":-1}'

Examples with SVS

• Run an instance on 8000: poetry run python -m uvicorn main:app --port 8000
• Run an instance on 8001: poetry run python -m uvicorn main:app --port 8001
• Manipulate objects on the 8000 instance. For example, add an octahedron.
• Check the 8001 scene at http://127.0.0.1:8001/, verify the modification is fetched.

Discussion

• Serverless
  • Though this demo requires python-ndn and local NFD instance to run, all operations can be executed in a browser with ndn-ts. There is nothing must be executed on the backend. It is possible to migrate to ndn-ts and use textbed or WebRTC for connectivity Also, this demo requires manual reloading the page to see new changes, but no reload is required if we migrate to TS.
• Decentralized
  • This demo does not handle consensus problem properly. However, JSON patch can be extended to a conflict-free replicated data types (CRDT), which means eventual consensus is "automagically" reached irrelevant of the order of receiving the patches. No master server or leader election is needed.
• Hierarchical namespace
  • There are two kinds of data objects: scene objects (a-entities) and JSON patches (i.e. diffential updates of scene objects). Scene objects can be named in any hierarchical way according to application's need. Patches are named like /<producer>/<sequence-number>, according to the security's need.
  • Peers in the sync group will fetch all patches. Since scene objects can be recovered by JSON patches, they do not need to fetch scene objects directly.
• Security
  • Patches are signed by their producers.
  • Patches are immutable. Scene objects are updated via applying patches.