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doc(test): Improve comments

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+ new assert helping explain why CHAIN_WORK == TARGET_BLOCKS * 2.
This commit is contained in:
Hodlinator
2025-09-03 21:21:14 +02:00
parent fe896f8faa
commit 04eeb9578c
1 changed files with 28 additions and 11 deletions
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39
src/test/headers_sync_chainwork_tests.cpp
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@@ -26,12 +26,21 @@ struct HeadersGeneratorSetup : public RegTestingSetup {
// to ensure the headers are different).
const std::vector<CBlockHeader>& FirstChain()
{
// Block header hash target is half of max uint256 (2**256 / 2), expressible
// roughly as the coefficient 0x7fffff with the exponent 0x20 (32 bytes).
// This implies around every 2nd hash attempt should succeed, which
// is why CHAIN_WORK == TARGET_BLOCKS * 2.
assert(genesis.nBits == 0x207fffff);
// Subtract 1 since the genesis block also contributes work so we reach
// the CHAIN_WORK target.
static const auto first_chain{GenerateHeaders(/*count=*/TARGET_BLOCKS - 1, genesis.GetHash(),
genesis.nVersion, genesis.nTime, /*merkle_root=*/uint256::ZERO, genesis.nBits)};
return first_chain;
}
const std::vector<CBlockHeader>& SecondChain()
{
// Subtract 2 to keep total work below the target.
static const auto second_chain{GenerateHeaders(/*count=*/TARGET_BLOCKS - 2, genesis.GetHash(),
genesis.nVersion, genesis.nTime, /*merkle_root=*/uint256::ONE, genesis.nBits)};
return second_chain;
@@ -87,10 +96,12 @@ std::vector<CBlockHeader> HeadersGeneratorSetup::GenerateHeaders(
// sufficient proof of work and one without.
// 1. We deliver the first set of headers and verify that the headers sync state
// updates to the REDOWNLOAD phase successfully.
// 2. Then we deliver the second set of headers and verify that they fail
// Then we deliver the second set of headers and verify that they fail
// processing (presumably due to commitments not matching).
// 3. Finally, we verify that repeating with the first set of headers in both
// phases is successful.
// 2. Verify that repeating with the first set of headers in both phases is
// successful.
// 3. Repeat the second set of headers in both phases to demonstrate behavior
// when the chain a peer provides has too little work.
BOOST_FIXTURE_TEST_SUITE(headers_sync_chainwork_tests, HeadersGeneratorSetup)
BOOST_AUTO_TEST_CASE(sneaky_redownload)
@@ -101,17 +112,20 @@ BOOST_AUTO_TEST_CASE(sneaky_redownload)
// Feed the first chain to HeadersSyncState, by delivering 1 header
// initially and then the rest.
HeadersSyncState hss{CreateState()};
// Just feed one header.
// Pretend the message is still "full", so we don't abort.
(void)hss.ProcessNextHeaders({{first_chain.front()}}, true);
// Pretend the first header is still "full", so we don't abort.
auto result{hss.ProcessNextHeaders(std::span{first_chain}.subspan(1), true)};
// This chain should look valid, and we should have met the proof-of-work
// requirement.
// requirement during PRESYNC and transitioned to REDOWNLOAD.
BOOST_CHECK(result.success);
BOOST_CHECK(result.request_more);
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::REDOWNLOAD);
// Try to sneakily feed back the second chain.
// Try to sneakily feed back the second chain during REDOWNLOAD.
result = hss.ProcessNextHeaders(second_chain, true);
BOOST_CHECK(!result.success); // foiled!
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::FINAL);
@@ -121,8 +135,10 @@ BOOST_AUTO_TEST_CASE(happy_path)
{
const auto& first_chain{FirstChain()};
// Now try again, this time feeding the first chain twice.
// This time we feed the first chain twice.
HeadersSyncState hss{CreateState()};
// Sufficient work transitions us from PRESYNC to REDOWNLOAD:
(void)hss.ProcessNextHeaders(first_chain, true);
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::REDOWNLOAD);
@@ -139,16 +155,17 @@ BOOST_AUTO_TEST_CASE(too_little_work)
{
const auto& second_chain{SecondChain()};
// Finally, verify that just trying to process the second chain would not
// succeed (too little work)
// Verify that just trying to process the second chain would not succeed
// (too little work).
HeadersSyncState hss{CreateState()};
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::PRESYNC);
// Pretend just the first message is "full", so we don't abort.
// Pretend just the first message is "full", so we don't abort.
(void)hss.ProcessNextHeaders({{second_chain.front()}}, true);
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::PRESYNC);
// Tell the sync logic that the headers message was not full, implying no
// more headers can be requested. For a low-work-chain, this should causes
// more headers can be requested. For a low-work-chain, this should cause
// the sync to end with no headers for acceptance.
const auto result{hss.ProcessNextHeaders(std::span{second_chain}.subspan(1), false)};
BOOST_CHECK(hss.GetState() == HeadersSyncState::State::FINAL);