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chromium-format.md

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Chromium LevelDB Format Notes

Quick reference for the on-disk layout and gotchas when reading Chromium's leveldb stores.

File Layout

A leveldb directory contains:

File Purpose
*.ldb Sorted runs (immutable SST tables). Numbered by sequence.
*.log Write-ahead log. Contains recent writes not yet compacted into .ldb.
MANIFEST-<n> Metadata: which .ldb files are live, version edits
CURRENT Tiny pointer file naming the active MANIFEST
LOCK File lock; held by the running app. Blocks readers.
LOG, LOG.old Diagnostic text logs (human-readable)

To read while the app runs: copy the dir, delete the LOCK file from your copy, open the copy.

Append-Only Semantics

LevelDB is log-structured. A write to key foo doesn't overwrite — it appends a new entry. Compaction eventually drops older versions.

When iterating raw records (as ccl_chromium_reader does), you can see multiple entries for the same key. The last one in iteration order is the current value.

# Wrong — uses first match
for rec in ls.iter_records_for_storage_key(origin):
    if rec.script_key == "default-model":
        return rec.value  # might be stale

# Right — iterate all, keep last
latest = {}
for rec in ls.iter_records_for_storage_key(origin):
    latest[rec.script_key] = rec.value
return latest["default-model"]

Chromium's Layers on Top

Local Storage (simple)

Keys in the underlying leveldb look like:

META:<origin>\x00\x00\x01<script_key>

Values are UTF-8 strings (the actual localStorage.setItem payload). ccl_chromium_localstorage.LocalStoreDb decodes the META prefix and yields (origin, script_key, value) triples.

Session Storage (per-tab)

Same shape but partitioned per browsing session/tab. Use ccl_chromium_sessionstorage.

IndexedDB (complex)

  • Multiple databases per origin
  • Each DB has versioned object stores
  • Keys are typed (string, number, array, date, binary)
  • Values are v8-serialized (not JSON) — the same format Chromium's StructuredClone uses
  • Indexes maintained as separate keyspaces

ccl_chromium_indexeddb.WrappedIndexDB handles all of this. Walk: db.database_ids → db[id] → wdb.object_store_names → wdb[name].iterate_records().

Locking Specifics

  • Windows: LOCK uses LockFile Win32 API. Robust, no stale locks.
  • macOS/Linux: flock(2) advisory lock. Crashed apps may leave stale LOCK files; safe to delete.
  • Reading concurrently: Strictly speaking, leveldb supports multiple readers if openers use the same lock. In practice, copy-and-read is safest because ccl_chromium_reader doesn't take any lock — it just reads the bytes.

Encryption / DPAPI Note

Local State JSON in the same parent dir contains os_crypt.encrypted_key — DPAPI-encrypted on Windows, used by Chrome to encrypt cookies and saved passwords. Local Storage and IndexedDB themselves are NOT encrypted at rest. They're plain leveldb. Only the cookie store and password store use that key.

When to Reach for a Different Tool

Tool When
strings + grep Quick grep for known string. No structure needed.
ccl_chromium_reader Structured Local Storage / IndexedDB. Default choice.
Node level package You need to write to leveldb. Better wheels than Python on Windows.
Electron remote DevTools Mutate live state without taking the app down. --remote-debugging-port=<n> then DevTools Protocol.
leveldb-cli (Go) Raw leveldb, no Chromium decoding. Good for non-Chromium leveldb stores.

References