{ "number": 35271, "repo": "bitcoin/bitcoin", "url": "https://github.com/bitcoin/bitcoin/pull/35271", "title": "Update CoinsView::NeedsUpgrade to add additional checks", "author": "tomt1664", "author_association": "NONE", "created_at": "2026-05-12T13:53:22Z", "updated_at": "2026-05-21T14:02:00Z", "age_days": 128, "draft": true, "labels": [ "CI failed" ], "milestone": null, "base": "master", "head_sha": "697ffa196e6852520d0011e55334f86f0e81ac0c", "head_ref": "fix_coinsview_upgrade", "head_repo": "tomt1664/bitcoin", "head_history": [], "additions": 2, "deletions": 1, "changed_files": 1, "commit_count": 1, "size_bucket": "S", "mergeable_state": "blocked", "bot": { "drahtbot": { "present": true, "reviews": {}, "conflicts": [] } }, "acks_parsed": {}, "acks_tally": { "ack": 0, "stale_ack": 0, "concept_ack": 0, "approach_ack": 0, "nack": 0, "concept_nack": 0, "approach_nack": 0 }, "reviews": { "approved": 0, "changes_requested": 0, "distinct_reviewers": [ "l0rinc", "maflcko", "sedited" ] }, "signals": { "needs_rebase": false, "ci_failed": true, "mergeable_state": "blocked", "last_author_activity": "2026-05-12T15:37:32Z", "last_reviewer_activity": "2026-05-21T14:02:00Z", "last_reviewer": "maflcko", "author_silent_days": 128, "waiting_on_author_days": 119, "days_since_update": 119 }, "refs": { "mentioned": [ 24236 ], "depends_on": [], "fixes": [], "linked_issues": [], "references": [ { "number": 24236, "type": "pull", "state": "closed", "merged": true, "merged_at": "2022-04-05", "title": "Remove utxo db upgrade code" } ], "conflicts": [] }, "stack": { "shares_commits_with": [], "based_on": [], "base_for": [] }, "review_paths": [], "body": "Additional two checks after cursor->Valid():\n\nSeek() in LevelDB finds the first key \u2265 the target. If no DB_COINS entry exists but there happens to be another key whose byte value is greater than DB_COINS, cursor->Valid() returns true \u2014 even though no legacy coins are present.\nThe original code would incorrectly signal an upgrade is needed. The new code explicitly verifies the found key's prefix is DB_COINS.", "commits": [ { "sha": "697ffa196e6852520d0011e55334f86f0e81ac0c", "date": "2026-05-12T13:29:54Z", "message": "update CoinsView::NeedsUpgrade check for correctness" } ], "timeline": [ { "t": "2026-05-12T15:11:23Z", "kind": "comment", "who": "sedited", "assoc": "CONTRIBUTOR", "text": "Thank you for your contribution, but I don't think this needs fixing. This is logic that has been there for a long time and has served its purpose as such. If a change to the db format is ever repeated, it can be re-investigated then.\n\nEDIT: If there is a motivation for this in the form of an actual bug report or down stream issue, I'll be happy to re-open this." }, { "t": "2026-05-12T15:11:42Z", "kind": "comment", "who": "l0rinc", "assoc": "CONTRIBUTOR", "text": "This check disappeared in https://github.com/bitcoin/bitcoin/pull/24236/changes#diff-cafbe1353eff6084b73fd3b6c3dee603e0827348fdd2fe12dfad1e01003a84edR52-R60\n\nCan you please explain why `there happens to be another key whose byte value is greater than DB_COINS` can happen for a Bitcoin Core-produced chainstate? Did you encounter this on an actual datadir, or is this based on reasoning from LevelDB's `Seek()` semantics? Could you please check historically whether any Bitcoin Core version ever wrote another chainstate key that sorts after `DB_COINS`?\n\n@maflcko, do you remember if #24236 intentionally simplified this because `cursor->Valid()` implied the only possible key at that position was a legacy `DB_COINS` key?\n\nIf we do decide this defensive change makes sense for corrupt/foreign/past/future keys, I think it would be useful to add a [first commit documenting the current behavior](https://github.com/bitcoin/bitcoin/pull/35260):\n```patch\ndiff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp\n--- a/src/test/coins_tests.cpp\t(revision 10ca73c02cbff59f2134c0c7da3b8d0a7e727475)\n+++ b/src/test/coins_tests.cpp\t(revision 786432696f5e702529bbc8becd3483c8b595c929)\n@@ -5,6 +5,7 @@\n#include \n#include \n#include \n+#include \n#include \n#include \n#include \n@@ -16,8 +17,10 @@\n#include \n#include \n\n+#include \n#include \n#include \n+#include \n#include \n#include \n\n@@ -305,6 +308,25 @@\n\nBOOST_FIXTURE_TEST_SUITE(coins_tests, BasicTestingSetup)\n\n+BOOST_AUTO_TEST_CASE(coins_view_db_needs_upgrade)\n+{\n+ static constexpr uint8_t LEGACY_COINS_KEY{'c'};\n+ static constexpr uint8_t INVALID_KEY{'x'};\n+\n+ auto needs_upgrade_with_first_key{[&](const char* name, uint8_t key) {\n+ const fs::path path{m_args.GetDataDirBase() / name};\n+ {\n+ CDBWrapper db{{.path = path, .cache_bytes = 1_MiB, .wipe_data = true, .obfuscate = false}};\n+ db.Write(std::make_pair(key, uint256{}), uint256{});\n+ }\n+ CCoinsViewDB coins_view{{.path = path, .cache_bytes = 1_MiB, .obfuscate = false}, {}};\n+ return coins_view.NeedsUpgrade();\n+ }};\n+\n+ BOOST_CHECK(needs_upgrade_with_first_key(\"coins_view_db_needs_upgrade_legacy\", LEGACY_COINS_KEY));\n+ BOOST_CHECK(needs_upgrade_with_first_key(\"coins_view_db_needs_upgrade_invalid\", INVALID_KEY));\n+}\n+\nstruct UpdateTest : BasicTestingSetup {\n// Store of all necessary tx and undo data for next test\ntypedef std::map> UtxoData;\n```\nwhich could be flipped on the second commit with the fix:\n```C++\n BOOST_CHECK(!needs_upgrade_with_first_key(\"coins_view_db_needs_upgrade_invalid\", INVALID_KEY));\n```\nAlso, if the intended check is only the key prefix, `GetKey()` does not need to deserialize the whole `(prefix, uint256)` pair:\n```C++\n uint8_t key;\n return cursor->Valid() && cursor->GetKey(key) && key == DB_COINS;\n```\n(But if the goal is instead to recognize only well-formed legacy coins keys, then the current pair decode is more precise.)" }, { "t": "2026-05-12T15:37:32Z", "kind": "comment", "who": "tomt1664", "assoc": "NONE", "text": "[quoted text omitted]\n\nMotivation is that it is needed downstream in Elements (https://github.com/tomt1664/elements/commit/697f03a17e714ebca15f732bae83b0f2e4f0c05a) and thought it may be relevant in other contexts. But fine if it is not appropriate to address here." }, { "t": "2026-05-12T15:39:27Z", "kind": "comment", "who": "sedited", "assoc": "CONTRIBUTOR", "text": "Thanks for the reply and motivation @tomt1664. I'll re-open this then, given that it is a rather small change." }, { "t": "2026-05-12T15:52:06Z", "kind": "comment", "who": "l0rinc", "assoc": "CONTRIBUTOR", "text": "Was there a corresponding value in Core for https://github.com/tomt1664/elements/blob/60cf64e07053b6a1bac89d9d3fa25f354ad82933/src/txdb.cpp#L36? Regardless, if we add it here the test key could be adjusted to `static constexpr uint8_t INVALID_KEY{'w'};` adding a comment to the corresponding repo.\n\nnit: the linter fails for the trailing spaces in `return cursor->Valid() && cursor->GetKey(key) && key.first == DB_COINS; `" }, { "t": "2026-05-21T14:02:00Z", "kind": "comment", "who": "maflcko", "assoc": "MEMBER", "text": "are you still working on this, or can it be closed?" } ], "labels_log": [ { "t": "2026-05-12T16:04:48Z", "action": "labeled", "label": "CI failed", "who": "DrahtBot" } ], "state_log": [ { "t": "2026-05-12T15:11:23Z", "kind": "closed", "who": "sedited" }, { "t": "2026-05-12T15:39:27Z", "kind": "reopened", "who": "sedited" }, { "t": "2026-05-15T08:28:50Z", "kind": "convert_to_draft", "who": "DrahtBot" } ], "text_chars": 4933, "text_tokens_estimate": 1233, "changed_paths": [ "src/txdb.cpp" ], "files": [ { "path": "src/txdb.cpp", "add": 2, "del": 1 } ], "test_lines": 0, "git": { "head": "697ffa196e6852520d0011e55334f86f0e81ac0c", "head_matches_backup": true, "base": "10ca73c02cbff59f2134c0c7da3b8d0a7e727475", "commits": [ { "sha": "697ffa196e", "subject": "update CoinsView::NeedsUpgrade check for correctness", "files": 1, "add": 2, "del": 1 } ], "patch_truncated": false }, "input_hash": "eea22e23b9746260", "extracted_at": "2026-09-17T16:15:31+00:00" }