design.mkd

General Idea

• Run one FileWatcher on the client, and sync changes client to server
• Run one FileWatcher on the server, and sync changes server to client
• Bootstrap the process, for now with an rsync of server to client
• When a file changes, send path+time+data to other side
• State machine of the file on each side?

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• Server-side should own the state machine of path/mtime/hash
• If no client-side connection, server-side can cache changes since last client connect
• When client connects, bring up to date

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Need a state machine of the connection state:

1. Initialize
2. Get Server State

• If overflow goto 1

3. Get Client State

• If overlfow goto 1

4. Bring into sync
5. Watch server

• If overflow goto 1

6. watch client

• If overlfow goto 1

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The steady-state (post initial sync) client side would be:

• One thread listening for file changes (or overflow)
• One thread listening for server changes
• Central logic that, on each incoming Update, decides what to do

Then:

• On change from server:
  • Ensure server's mtime >= our mtime
    • If so, write file
    • If not, it's fine, we should have an incoming/outgoing Update to correct the server
• On add/change from file system:
  • Send file + mtime to server

Threads

Both sides should have:

• One thread for inotify (FileWatcher)
  • Writes to inbound queue
• grpc thread(s) listening stream
  • Writes to inbound queue
• One thread diffing trees (SyncLogic)
  • Writes to outbound queue
• One thread putting updates on the wire