netsync: always download headers first during ibd #236
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kcalvinalvin
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We only exit headersFirstMode when we have no more checkpoints left. updateSyncPeer was resetting headersFirstMode by calling resetHeaderState only to have it turned back on with startSync(). Resetting the headers-first mode when we've not really exited the headers first mode will cause problems with later commits that add parallel block downloads so we remove it here.
We were still updating invs for peers but since during ibd new blocks and txs are irrelevant, don't bother updating either.
For headers first mode, there's no need for a global map of requested blocks since it's only used when we're caught up and need a quick way to check which blocks were requested instead of searching through all the requested blocks map for all the connected peers.
kcalvinalvin
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The headerList includes headers we've already downloaded and verified. Instead of resetting it and re-downloading them on syncPeer disconnects, we reset the startHeader to be the first header in the list so that we can re-use the headers and download the blocks associated with it.
checkpoints Even when we've synced past the checkpoint, it's possible to sync headers first. To allow for a headers-first download even past the checkpoints, we add code to verify the block headers before accepting them when we no longer have any more checkpoints.
handleBlockMsg handleBlockMsg only handled cases of headers-first mode when there are checkpoints. The added code handles cases in where there are no more checkpoints but when the sync manager is still in headers first mode.
resetHeaderState Since we can be in headers-first mode, we push the best headerNode regardless of whether or not there's still checkpoints left.
When the chainstate is current and there's no more blocks to sync up to from our peers, exit headers-first mode.
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peer has headers-first download is now always preferred over asking for blocks directly. This eliminates orphan blocks during the initial block download.
Since we're purely headers-first during ibd, we need to call resetHeaderState regardless of whether or not we have more checkpmore checkpoints.
handleUtreexoHeaderMsg
We create a requestedUtreexoHeaders local to each of the peers to be able to keep track of the utreexo headers requested from each of the peers. Just like with blocks, the global state is not used during headers-first download.
headers-first download The logic for checking if the block exists within the list of headers saved was growing and hurting readability. We refactor out the logic to a separate function.
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