Consensus: Decouple ContextualCheckBlockHeader from checkpoints #5975

jtimon · 2015-04-06T16:08:13Z

By separating a new CheckIndexAgainstCheckpoint() from ContextualCheckBlockHeader().
@theuni you will probably be interested in this since you were doing some work on the checkpoints. I hope it doesn't conflict with what you've done.

The checkpoints shouldn't be used to check a new block header. Instead, they should be used to check the index (the chain) that it's going to be used to check new block header.

jtimon · 2015-04-08T13:26:55Z

fixed after a discussion with @theuni on IRC
Now CheckIndexAgainstCheckpoint() takes CChainParams instead of uint256& hashGenesisBlock as parameter to avoid conflicts with work that he is doing in parallel related to checkpoints.
Ready for squash.
#5968 and #5970 probably need to be adapted to CheckIndexAgainstCheckpoint depending on CChainParams.

theuni · 2015-04-08T16:35:01Z

src/main.cpp

@@ -2640,6 +2642,8 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
        if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
            return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
    }
+    if (!CheckIndexAgainstCheckpoint(pindexPrev, state, params, mapBlockIndex))


Shouldn't these just return false? state is already set in CheckIndexAgainstCheckpoint().

jtimon · 2015-04-08T17:12:56Z

2 more fixes, ready to squash

jtimon · 2015-04-15T12:00:18Z

Needed rebase.

jtimon · 2015-04-19T21:35:20Z

Somehow I missed this one. Renamed params to chainparams like everywhere else.

jtimon · 2015-04-22T10:01:08Z

ping @theuni

theuni · 2015-04-22T22:28:53Z

src/main.cpp

@@ -2540,19 +2540,30 @@ bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW, bo
    return true;
 }

-bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& state, CBlockIndex * const pindexPrev)
+static bool CheckIndexAgainstCheckpoint(const CBlockIndex* pindexPrev, CValidationState& state, const CChainParams& chainparams, const BlockMap& mapBlockIndex)


nit: mapBlockIndex shadows the global, will be confusing when it's used.

theuni · 2015-04-22T23:14:47Z

ut ack other than the nit

jtimon · 2015-04-22T23:32:26Z

nit solved

theuni · 2015-04-23T21:06:37Z

Thanks, looks good.

sipa · 2015-04-24T10:11:39Z

src/main.cpp

    assert(pindexPrev);
+    if (*pindexPrev->phashBlock == chainparams.GetConsensus().hashGenesisBlock)


I'd rather keep comparisons with the genesis block out of the "checkpoints" logic. That's purely philosophical, but we may get rid of checkpoints at some point, though the genesis block will always remain part of consensus.

Well, the question is, should we validate the genesis block?
I don't think so, the genesis block is hardcoded, no need to check it redundantly from many computers.
So this is more moving that check out of consensus than "moving it to the checkpoints logic".

But of course, if your the tip of the chain index you're using (your pindexPrev) is the genesis block (that is, if you're validating the second block), you can skip the other checkpoint tests.

What you want to check is that your chain index contains the genesis block. Or with checkpoints, you may even want to just check that your chain index contains the previous checkpoint (you have to be certain that all your checkpoints contain the genesis block when your hardcode them).
In that sense you can see the genesis block just as the oldest checkpoint possible.

But thanks for bringing this up, this is the only change in logic and what needs discussion.

jtimon · 2015-05-06T10:45:42Z

Needed rebase

theuni · 2015-05-06T16:29:42Z

@jtimon I think #6055 was a big improvement in readability for the checkpoint functions because it moved the "what if checkpoints aren't enabled" case out of the actual checkpoint logic. This would undo some of that.

How about removing the early return from CheckIndexAgainstCheckpoint() and instead calling into it like if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(...)) ?

jtimon · 2015-05-06T16:52:07Z

I disagree that this undoes part of #6055 but I'm ok with your proposed alternative. I thought about it too but I didn't wanted to take the assert(pindexPrev); out of the function as well.

theuni · 2015-05-06T17:09:02Z

Sorry, that was poorly worded. It wouldn't undo any of #6055, but it would negate one of the beneficial side-effects of it.

As for not removing the assert, I don't follow. pindexPrev is used whether checkpoints are enabled or not, so relying on the assert in CheckIndexAgainstCheckpoint() even if checkpoints are disabled makes no sense to me.

jtimon · 2015-05-06T17:15:42Z

I still disagree that it is removing one of the beneficial side effects of it, I don't think the negated condition is less readable...

Anyway, what I mean is that if I want to maintain it almost equivalent (is not completely equivalent functionally because I'm changing the genesis check as discussed in the outdated comment by @sipa), I can't do just

if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(...))

It would need to be something like

assert(pindexPrev);
if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(...))

because pindexPrev shouldn't arrive NULL to ContextualCheckBlockHeader.
But I'm fine with that, should I change it to that, then?

theuni · 2015-05-06T17:27:16Z

Yes, that looks good. Thanks.

jtimon · 2015-05-06T17:44:19Z

Done, changed as suggested by @theuni

sipa · 2015-05-07T23:10:59Z

src/main.cpp

@@ -2715,6 +2712,9 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
        if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
            return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
    }
+    assert(pindexPrev);


Any reason why the checkpoints check is moved?

I think it's harmless to do so, but I was wondering if there is a reason.

Apparently having the check of the global boolean outside of the function is more readable according to @theuni.

@sipa if you're referring to fCheckpointsEnabled moving out of CheckIndexAgainstCheckpoint(), I requested that to reduce the side-effects of CheckIndexAgainstCheckpoint(). Imo if possible the checkpoint functions should be side-effect free so that we know it's consensus-safe to simply not call them at all.

I'm referring to the fCheckpointsEnabled conditional. Just to the fact that the checkpoints-checking point in this function moving.

@sipa I'm still not sure what you mean.
The checkpoints checks are moved out of ContextualCheckBlockHeader to keep them out of consensus.
Then is moved up in the functions, because you should have your index checked before checking a new block, maybe they can be moved upper (and earlier in time) later. I suspect the index is checked in this way redundantly.
If this is an issue I can maintain the calls to CheckIndexAgainstCheckpoint right before the calls to ContextualCheckBlockHeader.

Sorry, I missed this was in AcceptBlockHeader already, and not in ContextualCheckBlockHeader anymore. Looks good.

jtimon · 2015-05-08T10:34:16Z

@sipa I answered to your worries on checking the genesis block. You never answered back so I assume you were satisfied by my answer.

sipa · 2015-05-10T21:30:56Z

Untested ACK

jtimon · 2015-05-27T13:45:51Z

Updated without the unused blockIndexMap parameter.
It may take long until it gets used so better to just introduce it at that point.

laanwj · 2015-06-10T08:42:43Z

Sorry: needs rebase after #5927, will merge after that.

…kBlockHeader

jtimon · 2015-06-10T11:13:53Z

No worries, it was an easy rebase.

425c3a8 Consensus: Separate CheckIndexAgainstCheckpoint() from ContextualCheckBlockHeader (Jorge Timón)

sdaftuar · 2015-06-16T18:56:18Z

This appears to have broken running bitcoind with -reindex(!); it appears the assert(pindexPrev) in AcceptBlockHeader can be reached when processing the genesis block from disk. Can be reproduced by running qa/rpc-tests/reindex.py.

jtimon · 2015-06-17T19:30:45Z

@sdaftuar created #6299 to fix the bug.

This fixes an error triggered when running with -reindex after bitcoin#5975

laanwj added the Refactoring label Apr 7, 2015

jtimon mentioned this pull request Apr 8, 2015

Chainparams: Refactor: Decouple IsSuperMajority from Params() #5968

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theuni reviewed Apr 8, 2015
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jtimon force-pushed the consensus_checkpoints branch 4 times, most recently from 9c38309 to 54f2e9d Compare April 9, 2015 16:50

jtimon mentioned this pull request Apr 10, 2015

DEPENDENT: API: Expose bitcoinconsensus_verify_header() in libconsensus #5995

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jtimon force-pushed the consensus_checkpoints branch from 54f2e9d to 55b98a2 Compare April 15, 2015 11:59

jtimon force-pushed the consensus_checkpoints branch from 55b98a2 to e55ad48 Compare April 19, 2015 21:34

theuni reviewed Apr 22, 2015
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jtimon force-pushed the consensus_checkpoints branch from e55ad48 to b00583b Compare April 22, 2015 23:31

jtimon mentioned this pull request Apr 23, 2015

MOVEONLY: Consensus: Move most of consensus functions (pre-block) #6051

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jtimon mentioned this pull request Apr 24, 2015

Decouple checkpoints from Params() #6055

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sipa reviewed Apr 24, 2015
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jtimon mentioned this pull request Apr 24, 2015

MOVEONLY-ish: Move most block header validation function defintions to consensus/blockverify.cpp #6048

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jtimon force-pushed the consensus_checkpoints branch from b00583b to ae6de26 Compare May 6, 2015 10:45

jtimon force-pushed the consensus_checkpoints branch 2 times, most recently from 3b008ef to 6e55325 Compare May 6, 2015 14:36

jtimon mentioned this pull request May 6, 2015

Pow: Refactor: Encapsulate miner-related pow in GenerateProof (was ScanHash) and use it for regtest mining #4793

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jtimon force-pushed the consensus_checkpoints branch from 6e55325 to 102b09b Compare May 6, 2015 17:43

sipa reviewed May 7, 2015
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sipa mentioned this pull request May 10, 2015

Reduce checkpoints' effect on consensus. #5927

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jtimon force-pushed the consensus_checkpoints branch from 102b09b to 8d834ec Compare May 27, 2015 13:44

Consensus: Separate CheckIndexAgainstCheckpoint() from ContextualChec…

425c3a8

…kBlockHeader

jtimon force-pushed the consensus_checkpoints branch from 8d834ec to 425c3a8 Compare June 10, 2015 11:05

laanwj merged commit 425c3a8 into bitcoin:master Jun 10, 2015

laanwj added a commit that referenced this pull request Jun 10, 2015

Merge pull request #5975

1fea667

425c3a8 Consensus: Separate CheckIndexAgainstCheckpoint() from ContextualCheckBlockHeader (Jorge Timón)

sdaftuar mentioned this pull request Jun 16, 2015

Reindex broken in master #6294

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laanwj mentioned this pull request Jun 17, 2015

test: Move reindex test to standard tests #6298

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jtimon mentioned this pull request Jun 17, 2015

Bugfix: Don't check the genesis block header before accepting it #6299

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jtimon added a commit to jtimon/bitcoin that referenced this pull request Jun 20, 2015

Bugfix: Don't check the genesis block header before accepting it

36c97b4

This fixes an error triggered when running with -reindex after bitcoin#5975

str4d mentioned this pull request Feb 14, 2017

Bitcoin 0.12 misc PRs 1 zcash/zcash#2099

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Consensus: Decouple ContextualCheckBlockHeader from checkpoints #5975

Consensus: Decouple ContextualCheckBlockHeader from checkpoints #5975

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		assert(pindexPrev);
		if (*pindexPrev->phashBlock == chainparams.GetConsensus().hashGenesisBlock)

Consensus: Decouple ContextualCheckBlockHeader from checkpoints #5975

Consensus: Decouple ContextualCheckBlockHeader from checkpoints #5975

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