Module progress 

Progress event emission helpers for transfers.

Design

emit_progress throttles emissions to at most one per 250 ms or per 256 KB transferred, whichever condition is met first. This avoids flooding the IPC channel while still giving the frontend a responsive progress bar.

emit_state is unthrottled — state transitions (Queued → Running → Done / Failed / Canceled) must always reach the frontend.

OCP contract

The same helpers are reused for uploads (task 32) — the throttle logic lives in one place and is called identically from both download.rs and upload.rs.

Structs

ProgressThrottle

Tracks when the last progress event was emitted so emit_progress can apply the 250 ms / 256 KB throttle.

TransferProgressPayload

Payload for transfer:progress.

TransferStatePayload

Payload for transfer:state.

Constants

PROGRESS_THROTTLE_BYTES

Minimum bytes transferred between progress events.

PROGRESS_THROTTLE_MS

Minimum milliseconds between progress events for one transfer.

Functions

emit_progress

Emit a transfer:progress event if the throttle gate is open.

emit_state

Emit a transfer:state event (unthrottled). Use emit_state_with_error on Failed transitions to attach the underlying AppError to the payload so the frontend can render the failure reason.

emit_state_with_error

Emit a transfer:state event with an optional AppError attached.