Only check warp syncing for eth_getWorks

[sorpaas]

No description provided.

[5chdn]

That only affects master 2.1.0+, does it?

[sorpaas]

It affects anything after #9210. So I think that means beta and stable.

[lexfrl]

I'd like to add my review, but I need to understand some context first.. Why we don't need to check for is_major_importing but check only for is_warp_syncing here?

[sorpaas]

@fckt the issue is that using is_major_importing may break this RPC call for some miners. A peer may cause the client to occasionally switch to SyncState::Blocks (considered syncing by is_major_importing), while the client is really close to chain head.

[sorpaas]

Copied from chat, and I do appreciate if someone more familiar with our sync crate would take a review on this PR:

• In sync::chain::ChainSync::on_peer_new_hashes, when we get a newHashes message, we would set sync state to NewBlocks, and call ChainSync::sync_peer.
• In sync_peer, we go into the NewBlocks match case, and call self.new_blocks.request_block.
• If we need receipts or block bodies, the requests we received would be Some, and we go into the if statement.
• Within it, we set state to SyncState::Blocks.
• That state is considered "major importing" by eth_getWork rpc, and we would return error "still sycning".

Would an attacker / client from another network force a victim to stay in SyncState::Blocks? A peer can report having higher difficulty, and the victim would send block bodies/receipts requests to then and set its state to Blocks. The response can be invalid (from another network, for example) and the victim may choose to disconnect. But in that short period of time eth_getWorks will not be available.

[sorpaas]

I'm going to add the blocker tag for this PR, because if this is indeed an issue, then pow mining for some chains may have been broken.

[ngotchac]

There is actually already this method implemented: SyncStatus::is_snapshot_syncing that does what we want here.
https://github.com/paritytech/parity-ethereum/blob/master/ethcore/sync/src/chain/mod.rs#L246L253