Beam Streaming Mechanism
The core mechanism of streaming all happens in the Beam service canister. It is driven by Internet Computer's scheduling service called Timer API. The initial version of BeamFi uses IC Heartbeat to trigger the streaming. However, it is more heavy-weighted and consumes more cycles.
Here is the brief walkthrough of the mechanism:
Schedule Timer
IC Timer API triggers timer() which would schedule to run processActiveBeams every timerBeamPaymentEveryN secs (30 secs currently).
system func timer(setGlobalTimer : Nat64 -> ()) : async ()Find and Process Active Beams
Find and process the top 5 active BeamModels (opens in a new tab) ordered by #lastProcessedDate.
func processActiveBeams() : async ()Beam Payment
Beam streams payment to recipient (opens in a new tab) over time following Checks-Effects-Interactions-Rollback pattern.
It will calculate the elapsed time since the last payment and update the allocations of each party (BeamEscrow, sender, recipient) accordingly.
One of the reasons to follow Checks-Effects-Interactions-Rollback pattern is to avoid the reentrancy attack since another party can interact with the Canister actor during its async processing.
One of the steps it does is to call BeamEscrow Canister to update allocation which is an inter-canister remote async call. If the call fails, it will roll back the allocation changes done in the Beam Canister.
func beamPayment(beam : BeamModelV2) : async ()