fetch collation

[EclesioMeloJunior]

Description

• Retrieves the collation from network

• The collator validator-side subsystem uses a field called collation_requests to receive responses from dispatch requests

• The function request_collation creates the request and a return channel, the request is sent to network-bridge and the return channel keeps in the collation_requests as well as a cancellation token so at any time we can cancel/shutdown the ongoing request.

• The collator validator-side has a field called collation_fetch_timeouts that is a unordered future (channel) that is populated when a new request collation is sent and will trigger after 1 second (MAX_UNSHARED_DOWNLOAD_TIME) to cancel the related ongoing request.

• It supports versioned requests depending on the peer's version we are requesting.

• Supports cancelation (through context.Context)

• Make sure to start the timeout based on MAX_UNSHARED_DOWNLOAD_TIME

• Supports request_v2::CollationFetchingRequest ({ relay_parent, para_id })

• Supports request_v1::CollationFetchingRequest ({ relay_parent, para_id, candidate_hash })

Approach

Using the same struct that is used by availability-distribution with NewOutgoingRequest, just need to forward the request.Result channel to the subsytem main loop (maybe using a new goroutine)

gossamer/dot/parachain/availability-distribution/fetch_chunk_task.go

Line 92 in 6d3e72d

request := networkbridgemessages.NewOutgoingRequest(

Links

• https://github.com/paritytech/polkadot-sdk/blob/c679ed79a1de575d4c3d5b8878b3e401b024f2f2/polkadot/node/network/collator-protocol/src/validator_side/mod.rs#L578

[Yuri0405]

Hi @EclesioMeloJunior ! I found there's a feat/parachain branch with existing parachain infrastructure including collator-protocol. Should I base my implementation on this branch or start fresh from development? The issue mentions studying availability-distribution code which exists in the feature branch.

[P1sar]

Hey @Yuri0405 yeah you should base you branch from feat/parachain .