build: Add example bitcoin-chainstate executable

The bitcoin-chainstate executable serves to surface the dependencies
required by a program wishing to use Bitcoin Core's consensus engine as
it is right now.

More broadly, the _SOURCES list serves as a guiding "North Star" for the
libbitcoinkernel project: as we decouple more and more modules of the
codebase from our consensus engine, this _SOURCES list will grow shorter
and shorter. One day, only what is critical to our consensus engine will
remain. Right now, it's "the minimal list of files to link in to even
use our consensus engine".

[META] In a future commit the libbitcoinkernel library will be extracted
       from bitcoin-chainstate, and the libbitcoinkernel library's
       _SOURCES list will be the list that we aim to shrink.

1 files changed, 262 insertions, 0 deletions

diff --git a/src/bitcoin-chainstate.cpp b/src/bitcoin-chainstate.cpp
new file mode 100644
index 0000000000..f93197350d
--- /dev/null
+++ b/src/bitcoin-chainstate.cpp
@@ -0,0 +1,262 @@
+// Copyright (c) 2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+//
+// The bitcoin-chainstate executable serves to surface the dependencies required
+// by a program wishing to use Bitcoin Core's consensus engine as it is right
+// now.
+//
+// DEVELOPER NOTE: Since this is a "demo-only", experimental, etc. executable,
+//                 it may diverge from Bitcoin Core's coding style.
+//
+// It is part of the libbitcoinkernel project.
+
+#include <chainparams.h>
+#include <consensus/validation.h>
+#include <core_io.h>
+#include <init/common.h>
+#include <node/blockstorage.h>
+#include <node/chainstate.h>
+#include <scheduler.h>
+#include <script/sigcache.h>
+#include <util/system.h>
+#include <util/thread.h>
+#include <validation.h>
+#include <validationinterface.h>
+
+#include <filesystem>
+#include <functional>
+#include <iosfwd>
+
+const std::function<std::string(const char*)> G_TRANSLATION_FUN = nullptr;
+
+int main(int argc, char* argv[])
+{
+    // SETUP: Argument parsing and handling
+    if (argc != 2) {
+        std::cerr
+            << "Usage: " << argv[0] << " DATADIR" << std::endl
+            << "Display DATADIR information, and process hex-encoded blocks on standard input." << std::endl
+            << std::endl
+            << "IMPORTANT: THIS EXECUTABLE IS EXPERIMENTAL, FOR TESTING ONLY, AND EXPECTED TO" << std::endl
+            << "           BREAK IN FUTURE VERSIONS. DO NOT USE ON YOUR ACTUAL DATADIR." << std::endl;
+        return 1;
+    }
+    std::filesystem::path abs_datadir = std::filesystem::absolute(argv[1]);
+    std::filesystem::create_directories(abs_datadir);
+    gArgs.ForceSetArg("-datadir", abs_datadir.string());
+
+
+    // SETUP: Misc Globals
+    SelectParams(CBaseChainParams::MAIN);
+    const CChainParams& chainparams = Params();
+
+    init::SetGlobals(); // ECC_Start, etc.
+
+    // Necessary for CheckInputScripts (eventually called by ProcessNewBlock),
+    // which will try the script cache first and fall back to actually
+    // performing the check with the signature cache.
+    InitSignatureCache();
+    InitScriptExecutionCache();
+
+
+    // SETUP: Scheduling and Background Signals
+    CScheduler scheduler{};
+    // Start the lightweight task scheduler thread
+    scheduler.m_service_thread = std::thread(util::TraceThread, "scheduler", [&] { scheduler.serviceQueue(); });
+
+    // Gather some entropy once per minute.
+    scheduler.scheduleEvery(RandAddPeriodic, std::chrono::minutes{1});
+
+    GetMainSignals().RegisterBackgroundSignalScheduler(scheduler);
+
+
+    // SETUP: Chainstate
+    ChainstateManager chainman;
+
+    auto rv = node::LoadChainstate(false,
+                                   std::ref(chainman),
+                                   nullptr,
+                                   false,
+                                   chainparams.GetConsensus(),
+                                   false,
+                                   2 << 20,
+                                   2 << 22,
+                                   (450 << 20) - (2 << 20) - (2 << 22),
+                                   false,
+                                   false,
+                                   []() { return false; });
+    if (rv.has_value()) {
+        std::cerr << "Failed to load Chain state from your datadir." << std::endl;
+        goto epilogue;
+    } else {
+        auto maybe_verify_error = node::VerifyLoadedChainstate(std::ref(chainman),
+                                                               false,
+                                                               false,
+                                                               chainparams.GetConsensus(),
+                                                               DEFAULT_CHECKBLOCKS,
+                                                               DEFAULT_CHECKLEVEL,
+                                                               /*get_unix_time_seconds=*/static_cast<int64_t (*)()>(GetTime));
+        if (maybe_verify_error.has_value()) {
+            std::cerr << "Failed to verify loaded Chain state from your datadir." << std::endl;
+            goto epilogue;
+        }
+    }
+
+    for (CChainState* chainstate : WITH_LOCK(::cs_main, return chainman.GetAll())) {
+        BlockValidationState state;
+        if (!chainstate->ActivateBestChain(state, nullptr)) {
+            std::cerr << "Failed to connect best block (" << state.ToString() << ")" << std::endl;
+            goto epilogue;
+        }
+    }
+
+    // Main program logic starts here
+    std::cout
+        << "Hello! I'm going to print out some information about your datadir." << std::endl
+        << "\t" << "Path: " << gArgs.GetDataDirNet() << std::endl
+        << "\t" << "Reindexing: " << std::boolalpha << node::fReindex.load() << std::noboolalpha << std::endl
+        << "\t" << "Snapshot Active: " << std::boolalpha << chainman.IsSnapshotActive() << std::noboolalpha << std::endl
+        << "\t" << "Active Height: " << chainman.ActiveHeight() << std::endl
+        << "\t" << "Active IBD: " << std::boolalpha << chainman.ActiveChainstate().IsInitialBlockDownload() << std::noboolalpha << std::endl;
+    {
+        CBlockIndex* tip = chainman.ActiveTip();
+        if (tip) {
+            std::cout << "\t" << tip->ToString() << std::endl;
+        }
+    }
+
+    for (std::string line; std::getline(std::cin, line);) {
+        if (line.empty()) {
+            std::cerr << "Empty line found" << std::endl;
+            break;
+        }
+
+        std::shared_ptr<CBlock> blockptr = std::make_shared<CBlock>();
+        CBlock& block = *blockptr;
+
+        if (!DecodeHexBlk(block, line)) {
+            std::cerr << "Block decode failed" << std::endl;
+            break;
+        }
+
+        if (block.vtx.empty() || !block.vtx[0]->IsCoinBase()) {
+            std::cerr << "Block does not start with a coinbase" << std::endl;
+            break;
+        }
+
+        uint256 hash = block.GetHash();
+        {
+            LOCK(cs_main);
+            const CBlockIndex* pindex = chainman.m_blockman.LookupBlockIndex(hash);
+            if (pindex) {
+                if (pindex->IsValid(BLOCK_VALID_SCRIPTS)) {
+                    std::cerr << "duplicate" << std::endl;
+                    break;
+                }
+                if (pindex->nStatus & BLOCK_FAILED_MASK) {
+                    std::cerr << "duplicate-invalid" << std::endl;
+                    break;
+                }
+            }
+        }
+
+        {
+            LOCK(cs_main);
+            const CBlockIndex* pindex = chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock);
+            if (pindex) {
+                UpdateUncommittedBlockStructures(block, pindex, chainparams.GetConsensus());
+            }
+        }
+
+        // Adapted from rpc/mining.cpp
+        class submitblock_StateCatcher final : public CValidationInterface
+        {
+        public:
+            uint256 hash;
+            bool found;
+            BlockValidationState state;
+
+            explicit submitblock_StateCatcher(const uint256& hashIn) : hash(hashIn), found(false), state() {}
+
+        protected:
+            void BlockChecked(const CBlock& block, const BlockValidationState& stateIn) override
+            {
+                if (block.GetHash() != hash)
+                    return;
+                found = true;
+                state = stateIn;
+            }
+        };
+
+        bool new_block;
+        auto sc = std::make_shared<submitblock_StateCatcher>(block.GetHash());
+        RegisterSharedValidationInterface(sc);
+        bool accepted = chainman.ProcessNewBlock(chainparams, blockptr, /* force_processing */ true, /* new_block */ &new_block);
+        UnregisterSharedValidationInterface(sc);
+        if (!new_block && accepted) {
+            std::cerr << "duplicate" << std::endl;
+            break;
+        }
+        if (!sc->found) {
+            std::cerr << "inconclusive" << std::endl;
+            break;
+        }
+        std::cout << sc->state.ToString() << std::endl;
+        switch (sc->state.GetResult()) {
+        case BlockValidationResult::BLOCK_RESULT_UNSET:
+            std::cerr << "initial value. Block has not yet been rejected" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_CONSENSUS:
+            std::cerr << "invalid by consensus rules (excluding any below reasons)" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_RECENT_CONSENSUS_CHANGE:
+            std::cerr << "Invalid by a change to consensus rules more recent than SegWit." << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_CACHED_INVALID:
+            std::cerr << "this block was cached as being invalid and we didn't store the reason why" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_INVALID_HEADER:
+            std::cerr << "invalid proof of work or time too old" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_MUTATED:
+            std::cerr << "the block's data didn't match the data committed to by the PoW" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_MISSING_PREV:
+            std::cerr << "We don't have the previous block the checked one is built on" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_INVALID_PREV:
+            std::cerr << "A block this one builds on is invalid" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_TIME_FUTURE:
+            std::cerr << "block timestamp was > 2 hours in the future (or our clock is bad)" << std::endl;
+            break;
+        case BlockValidationResult::BLOCK_CHECKPOINT:
+            std::cerr << "the block failed to meet one of our checkpoints" << std::endl;
+            break;
+        }
+    }
+
+epilogue:
+    // Without this precise shutdown sequence, there will be a lot of nullptr
+    // dereferencing and UB.
+    scheduler.stop();
+    if (chainman.m_load_block.joinable()) chainman.m_load_block.join();
+    StopScriptCheckWorkerThreads();
+
+    GetMainSignals().FlushBackgroundCallbacks();
+    {
+        LOCK(cs_main);
+        for (CChainState* chainstate : chainman.GetAll()) {
+            if (chainstate->CanFlushToDisk()) {
+                chainstate->ForceFlushStateToDisk();
+                chainstate->ResetCoinsViews();
+            }
+        }
+    }
+    GetMainSignals().UnregisterBackgroundSignalScheduler();
+
+    UnloadBlockIndex(nullptr, chainman);
+
+    init::UnsetGlobals();
+}