Check that cached script execution results are only valid for the same
script flags; that script execution checks are returned for non-cached
transactions; and that cached results are only valid for transactions
with the same witness hash.
This requires that we not access pcoinsTip in InitBlockIndex's
FlushStateToDisk (so we just skip it until later in AppInitMain)
and the LoadChainTip in LoadBlockIndex (which there is already one
later in AppinitMain, after ReplayBlocks, so skipping it there is
fine).
Includes some simplifications by Suhas Daftuar and Pieter Wuille.
This wraps CheckInputs in ATMP's cache-inputs call to check that
each scriptPubKey the CCoinsViewCache provides is the one which
was committed to by the input's transaction hash.
A few "a->an" and "an->a".
"Shows, if the supplied default SOCKS5 proxy" -> "Shows if the supplied default SOCKS5 proxy". Change made on 3 occurrences.
"without fully understanding the ramification of a command" -> "without fully understanding the ramifications of a command".
Removed duplicate words such as "the the".
CCoinsViewCache doesn't actually support cursor iteration returning the
current contents of the cache, so raise an error when the cursor method is
called instead of returning a cursor that iterates over stale data.
Also update the gettxoutsetinfo RPC which was relying on the old behavior to be
explicit about which view it is returning data about.
This adds a new CuckooCache in validation, caching whether all of a
transaction's scripts were valid with a given set of script flags.
Unlike previous attempts at caching an entire transaction's
validity, which have nearly universally introduced consensus
failures, this only caches the validity of a transaction's
scriptSigs. As these are pure functions of the transaction and
data it commits to, this should be much safer.
This is somewhat duplicative with the sigcache, as entries in the
new cache will also have several entries in the sigcache. However,
the sigcache is kept both as ATMP relies on it and because it
prevents malleability-based DoS attacks on the new higher-level
cache. Instead, the -sigcachesize option is re-used - cutting the
sigcache size in half and using the newly freed memory for the
script execution cache.
Transactions which match the script execution cache never even have
entries in the script check thread's workqueue created.
Note that the cache is indexed only on the script execution flags
and the transaction's witness hash. While this is sufficient to
make the CScriptCheck() calls pure functions, this introduces
dependancies on the mempool calculating things such as the
PrecomputedTransactionData object, filling the CCoinsViewCache, etc
in the exact same way as ConnectBlock. I belive this is a reasonable
assumption, but should be noted carefully.
In a rather naive benchmark (reindex-chainstate up to block 284k
with cuckoocache always returning true for contains(),
-assumevalid=0 and a very large dbcache), this connected blocks
~1.7x faster.
As the maximum amount of data that can be pulled into the cache due to
a block validation is much lower now (at most one CCoin entry per input
and per output), reduce the conservative estimate used to determine
flushing time.
This patch makes several related changes:
* Changes the CCoinsView virtual methods (GetCoins, HaveCoins, ...)
to be COutPoint/Coin-based rather than txid/CCoins-based.
* Changes the chainstate db to a new incompatible format that is also
COutPoint/Coin based.
* Implements reconstruction code for hash_serialized_2.
* Adapts the coins_tests unit tests (thanks to Russell Yanofsky).
A side effect of the new CCoinsView model is that we can no longer
use the (unreliable) test for transaction outputs in the UTXO set
to determine whether we already have a particular transaction.
This clarifies a bit more the ways in which the new script execution
cache could break consensus in the future if additional data from
the CCoins object were to be used as a part of script execution.
After this change, any such consensus breaks should be very visible
to reviewers, hopefully ensuring no such changes can be made.
The earlier CTxInUndo class now holds the same information as the Coin
class. Instead of duplicating functionality, replace CTxInUndo with a
serialization adapter for Coin.
Previously, transaction metadata (height, coinbase or not, and before
the previous commit also nVersion) was only stored for undo records
that correspond to the last output of a transaction being spent.
This only saves 2 bytes per undo record. Change this to storing this
information for every undo record, and stop complaining for having it
in non-last output spends. This means that undo dat written with
this patch won't be readable by older versions anymore.
This makes the following changes:
* In undo data and the chainstate database, the transaction nVersion
field is removed from the data structures, always written as 0, and
ignored when reading.
* The definition of hash_serialized in gettxoutsetinfo is changed to no
longer incude the nVersion field. It is renamed to hash_serialized_2
to avoid confusion. The new definition also includes transaction
height and coinbase information, as this information was missing
before.
This depends on having a CHashVerifier-based undo data checksum
verifier.
Apart from changing the definition of serialized_hash, downgrading
after using this patch is supported, as no release ever used the value
of nVersion field in UTXO entries.
This is necessary later, when we drop the nVersion field from the undo
data. At that point deserializing and reserializing the data won't
roundtrip anymore, and thus that approach can't be used to verify
checksums anymore.
With this CHashVerifier approach, we can deserialize while hashing the
exact serialized form that was used. This is both more efficient and
more correct in that case.
The error() function unconditionally reports an error. It should only
be used for actually exception situations, and not for the type of
inconsistencies that ApplyTxInUndo/DisconnectBlock can graciously deal
with.
This also makes a subtle semantics change: in ApplyTxInUndo, when a
record with metadata is encountered (indicating it is the last spend
from a tx), don't wipe the CCoins record if it wasn't empty at that
point. This makes sure that UTXO operations never affect any other
UTXOs (including those from the same tx).
Rather than re-add disconnected block transactions back to the mempool
immediately, store them in a separate disconnectpool for later processing,
because we expect most such transactions to reappear in the chain that is
still to be connected (and thus we can avoid the work of reprocessing those
transactions through the mempool altogether).
DisconnectBlock currently has a complicated interface:
Situation Return value
pfClean != nullptr pfClean == nullptr
All good: true true
Failure: false false
Unclean rewind: true false
with *pfClean=false
Change this to return a tristate enum instead. As an added bonus,
remove the ValidationState& argument which was unused.
This removes another callback from block connection logic, making it
easier to reason about the wallet-RPCs-returns-stale-info issue.
UpdatedTransaction was previously used by the GUI to display
coinbase transactions only after they have a block built on top of
them. This worked fine for in most cases, but only worked due to a
corner case if the user received a coinbase payout in a block
immediately prior to restart. In that case, the normal process of
caching the most recent coinbase transaction's hash would not work,
and instead it would only work because of the on-load -checkblocks
calling DisconnectBlock and ConnectBlock on the current tip.
In order to make this more robust, a full mapWallet loop after the
first block which is connected after restart was added.
practicalswift