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Improve mempool::downloads documentation (#2879) 

* Improve mempool::downloads documentation

* Apply suggestions from code review

Co-authored-by: teor <teor@riseup.net>
Co-authored-by: Alfredo Garcia <oxarbitrage@gmail.com>

Co-authored-by: teor <teor@riseup.net>
Co-authored-by: Alfredo Garcia <oxarbitrage@gmail.com>
This commit is contained in:
Conrado Gouvea 2021-10-18 17:02:40 -03:00 committed by GitHub
parent 303c8cf5ef
commit 128b8be95d
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1 changed files with 28 additions and 2 deletions
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30
zebrad/src/components/mempool/downloads.rs
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@ -1,3 +1,26 @@
//! Transaction downloader and verifier.
//!
//! The main struct [`Downloads`] allows downloading and verifying transactions.
//! It is used by the mempool to get transactions into it. It is also able to
//! just verify transactions that were directly pushed.
//!
//! The verification itself is done by the [`zebra_consensus`] crate.
//!
//! Verified transactions are returned to the caller in [`Downloads::poll_next`].
//! This is in contrast to the block downloader and verifiers which don't
//! return anything and forward the verified blocks to the state themselves.
//!
//! # Correctness
//!
//! The mempool downloader doesn't send verified transactions to the [`Mempool`] service.
//! So Zebra must spawn a task that regularly polls the downloader for ready transactions.
//! (To ensure that transactions propagate across the entire network in each 75s block interval,
//! the polling interval should be around 5-10 seconds.)
//!
//! Polling the downloader from [`Mempool::poll_ready`] is not sufficient.
//! [`Service::poll_ready`] is only called when there is a service request.
//! But we want to download and gossip transactions,
//! even when there are no other service requests.
use std::{
collections::{HashMap, HashSet},
pin::Pin,
@ -204,8 +227,11 @@ where
ZS: Service<zs::Request, Response = zs::Response, Error = BoxError> + Send + Clone + 'static,
ZS::Future: Send,
{
/// Initialize a new download stream with the provided `network` and
/// `verifier` services.
/// Initialize a new download stream with the provided services.
///
/// `network` is used to download transactions.
/// `verifier` is used to verify transactions.
/// `state` is used to check if transactions are already in the state.
///
/// The [`Downloads`] stream is agnostic to the network policy, so retry and
/// timeout limits should be applied to the `network` service passed into