vault-link/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

VaultLink is a self-hosted Obsidian plugin for real-time collaborative file syncing. The project consists of a Rust-based sync server and a TypeScript frontend with four main components: an Obsidian plugin, a sync client library, a test client, and a standalone CLI client.

Architecture

Core Components

• sync-server/: Rust-based WebSocket server with SQLite database for document versioning and real-time synchronization
• frontend/sync-client/: TypeScript library providing core sync functionality, WebSocket management, and file operations
• frontend/obsidian-plugin/: Obsidian plugin that integrates the sync client with Obsidian's API
• frontend/test-client/: CLI testing tool for simulating multiple concurrent users
• frontend/local-client-cli/: Standalone CLI for VaultLink sync client

Key Technologies

• Backend: Rust with Axum framework, SQLite with SQLx, WebSockets for real-time sync
• Frontend: TypeScript, Webpack for bundling, Node.js native test runner
• Sync Algorithm: Uses reconcile-text library for operational transformation

Architectural Patterns

Server Architecture:

• AppState: Central state container holding Database, Cursors, and Broadcasts
• Database: SQLite-backed document versioning with SQLx for compile-time query verification
• Broadcasts: WebSocket broadcast system for real-time updates to connected clients
• Cursors: Tracks user cursor positions across documents with background cleanup task

Client Architecture:

• SyncClient: Main entry point, orchestrates all sync operations
• SyncService: HTTP API client for CRUD operations on documents
• WebSocketManager: Manages WebSocket connection and real-time updates
• Syncer: Coordinates file synchronization between local filesystem and server
• CursorTracker: Manages local and remote cursor positions
• Database: Client-side document metadata cache
• FileOperations: Abstraction layer for filesystem operations

Dual-Bundle Strategy: The sync-client builds two separate bundles:

• sync-client.web.js: Browser-compatible UMD bundle (excludes ws package)
• sync-client.node.js: Node.js CommonJS bundle with WebSocket support

Development Commands

Initial Setup

Node.js (requires version 25):

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
nvm install 25
nvm use 25
nvm alias default 25  # Optional: set as system default

Rust:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
cargo install sqlx-cli cargo-machete cargo-edit cargo-insta

Frontend:

cd frontend
npm install

Server Development

cd sync-server
cargo run config-e2e.yml  # Start development server
cargo test --verbose      # Run all Rust tests
cargo test <test_name>    # Run specific test
cargo clippy --all-targets --all-features  # Lint Rust code
cargo clippy --all-targets --all-features --fix --allow-dirty --allow-staged  # Auto-fix clippy warnings
cargo fmt --all -- --check  # Check Rust formatting
cargo fmt --all            # Auto-format Rust code
cargo machete --with-metadata  # Detect unused dependencies

Frontend Development

cd frontend
npm run dev      # Start development mode (watches sync-client and obsidian-plugin)
npm run build    # Build all workspaces
npm run build -w sync-client     # Build specific workspace
npm run test     # Run all tests across all workspaces
npm run test -w sync-client      # Run tests for specific workspace
npm run lint     # Lint and format TypeScript code with ESLint + Prettier

Database Operations

cd sync-server
# Create/reset database for development
rm -rf db.sqlite*
sqlx database create --database-url sqlite://db.sqlite3
sqlx migrate run --source src/app_state/database/migrations --database-url sqlite://db.sqlite3
cargo sqlx prepare --workspace

# Add new migration
sqlx migrate add --source src/app_state/database/migrations <migration_name>
sqlx migrate run --source src/app_state/database/migrations --database-url sqlite://db.sqlite3

Project Scripts

• scripts/check.sh: Full CI check (builds, lints, tests both server and frontend). Run before pushing.
• scripts/check.sh --fix: Same as above but auto-fixes linting and formatting issues
• scripts/e2e.sh: End-to-end testing (e.g., scripts/e2e.sh 8 for 8 concurrent clients)
• scripts/clean-up.sh: Clean logs and database files
• scripts/bump-version.sh patch: Publish new version (options: patch, minor, major)
• scripts/update-api-types.sh: Update TypeScript bindings from Rust types (uses ts-rs)

Code Structure

Workspace Configuration

The frontend uses npm workspaces with four packages:

• sync-client: Core synchronization logic (builds dual bundles for web and Node.js)
• obsidian-plugin: Obsidian-specific integration
• test-client: Testing utilities for E2E tests
• local-client-cli: Standalone CLI for VaultLink sync client

Type Generation and API Updates

Rust structs generate TypeScript types via ts-rs crate:

1. Rust structs annotated with #[derive(TS)] export to sync-server/bindings/
2. Run scripts/update-api-types.sh to copy bindings to frontend/sync-client/src/services/types/
3. Frontend imports these types for type-safe API communication

Important Implementation Details

SQLx Compile-Time Verification:

• SQLx verifies SQL queries at compile time against the database schema
• Run cargo sqlx prepare --workspace after schema changes to update .sqlx/ directory
• CI builds require prepared query metadata to avoid needing a live database

Testing

Running Tests

Server:

cargo test --verbose           # All tests
cargo test <test_name>         # Specific test

Frontend:

npm run test                   # All workspaces
npm run test -w sync-client    # Specific workspace

E2E:

scripts/e2e.sh 8               # 8 concurrent clients
scripts/clean-up.sh            # Clean up after tests

Test Structure

• Rust: Unit tests alongside source files, uses cargo-insta for snapshot testing
• TypeScript: .test.ts files using Node.js native test runner (not Jest)
• E2E: Uses test-client to simulate multiple concurrent users with random operations

Code Style and Formatting

Rust

• Extensive Clippy lints (see Cargo.toml)
• Pedantic linting rules enabled
• Forbids unsafe code
• Uses rustfmt.toml for formatting configuration (4 spaces, Unix line endings)
• Run cargo fmt --all to format

TypeScript

• Prettier: 4-space indentation, no trailing commas, LF line endings
• YAML/Markdown override: 2-space indentation (via prettier config)
• ESLint: Strict rules with unused imports detection
• Configuration in frontend/package.json
• Run npm run lint to format and fix issues

EditorConfig

• .editorconfig at project root defines baseline formatting rules
• rustfmt.toml and Prettier config explicitly mirror these settings
• Both formatters enforce: 4-space indent (2 for YAML/MD), LF endings, final newline, trim trailing whitespace

Sync Logic Deep Dive

Document Lifecycle

Documents go through these states on the client:

1. Pending create: metadata === undefined, idempotencyKey set. File exists locally but hasn't been confirmed by the server yet.
2. Synced: metadata has documentId, parentVersionId, hash. The server knows about this document.
3. Deleted: isDeleted === true. Locally deleted, may or may not be synced to server yet.

Pending creates are persisted to the local DB (via StoredPendingDocument) so they survive app crashes.

Create Flow and Idempotency

The create flow is designed to handle interrupted creates (lost responses, app crashes):

1. Client generates idempotencyKey (UUID) and persists it locally before sending the request
2. Client sends HTTP POST with the key and file content to the server
3. Server checks if the idempotency_key already exists — if so, returns existing document (idempotent)
4. Server stores the key in the documents table alongside the document version
5. When a create results in a merge (document already exists at that path), both the original key and the new key are preserved — they're on different version rows of the same document

On reconnect, the client calls POST /documents/resolve-keys with all pending idempotency keys. The server maps each key to a documentId. The client assigns these documentIds to pending documents so they're recognized during subsequent remote fetch, preventing duplicates.

If key resolution fails (e.g., during a SyncReset), the pending creates retry normally with the same key — the server deduplicates.

Server-Side Smart Create

When a client sends a create request for a path where a document already exists:

1. Server calls merge_with_stored_version instead of creating a new document
2. Content is 3-way merged using reconcile-text (for text files) or last-write-wins (for binary)
3. The response uses the EXISTING document's documentId — the client adopts it
4. The idempotency_key from the create request is stored on the new merged version

Concurrency Model (Client)

The client uses two layers of concurrency control:

1. PQueue (syncQueue): Limits concurrent sync operations (configurable via syncConcurrency)
2. Locks (updatedDocumentsByPathAndKeysLocks): Per-document locks keyed by relativePath and documentId

Critical ordering: Locks are acquired INSIDE the queue, not outside. Acquiring locks while waiting for queue slots causes deadlocks (two operations hold locks on different keys while both waiting for queue capacity).

syncQueue.add(async () =>
    locks.withLock(keys, operation)  // lock acquired only when queue slot is available
)

Sync Reset and Recovery

A SyncResetError is thrown when the WebSocket disconnects or sync is toggled off. This:

• Clears the sync queue
• Rejects all pending lock waiters
• On reconnect, scheduleSyncForOfflineChanges() runs to reconcile local state with server

Important: SyncResetError during syncRemotelyUpdatedFile must be caught and logged as INFO, not ERROR. The test client exits on ERROR-level logs (except retries), so logging SyncResetError as ERROR during expected resets causes false test failures.

The Offline Sync Algorithm (scheduleSyncForOfflineChanges)

Runs on reconnect to detect what changed while offline:

1. Resolve idempotency keys first: Call resolveIdempotencyKeys() to map pending creates to server-side documentIds before scanning files
2. List all local files
3. For each file with metadata: schedule as update (hash comparison will skip unchanged)
4. For each file without metadata: try to match against "deleted" DB records by content hash (detects moves). If no match, schedule as create.
5. For DB records whose files don't exist locally: schedule as delete
6. Deletes and updates run first, THEN creates — to avoid the server merging creates with about-to-be-deleted docs

Remote Update Processing

When the server broadcasts updates via WebSocket:

1. scheduleSyncForOfflineChanges() runs first (ensures local changes are queued)
2. For each remote document update:
   • If client knows the documentId: treat as update to existing doc
   • If client doesn't know the documentId: it's a new remote document — create locally
3. Before creating a new local file for an unknown remote doc, check if a pending local create exists at the same originalCreationPath. If so, skip (the pending retry with idempotency key will handle it).

Known Concurrency Pitfalls

1. Interrupted create + rename + modify: A create request succeeds on the server but the response is lost. The file is renamed and modified locally. On reconnect, the idempotency key resolution maps the pending doc to the server's documentId, preventing a duplicate.

2. Two clients create at same path: Both send creates with different idempotency keys. Server merges them under one documentId. Each key is stored on its respective version row. Both clients can resolve their keys to the same document.

3. Lock ordering: Multi-key locks are sorted alphabetically to prevent deadlocks. Lock acquisition is sequential (not concurrent) even for multiple keys.

4. resolvedDocuments vs pendingDocuments: resolvedDocuments only includes docs with metadata (filters by metadata !== undefined). pendingDocuments returns docs with metadata === undefined && !isDeleted. Never confuse the two — scanning resolvedDocuments for pending docs returns nothing.

5. saveInTheBackground triggers ensureConsistency: The consistency check calls resolvedDocuments which can throw if there are duplicate paths with the same parallelVersion. Avoid calling saveInTheBackground during operations that temporarily create inconsistent state — use save() directly instead. This is why createNewPendingDocument calls save() directly.

6. Pending doc parallelVersion on load: When loading pending documents from storage, compute parallelVersion based on existing docs at the same path (use getLatestDocumentByRelativePath to find the current max). Setting all to 0 causes collisions if a resolved doc at the same path also has parallelVersion: 0.

7. Key resolution with stale documentIds: When resolveIdempotencyKeys returns a documentId, check getDocumentByDocumentId first. If another document already has that ID (assigned through normal sync), remove the stale pending doc instead of creating a duplicate.

8. resolveIdempotencyKeys uses retryForever: The HTTP call to /documents/resolve-keys retries forever like all other sync service calls. SyncResetError is re-thrown by retryForever, so the pipeline properly aborts on WebSocket disconnect without deadlocking.

E2E Test Configuration

The test client (frontend/test-client/src/cli.ts) runs 5 iterations of 9 test configurations per process:

• 2 agents, concurrency 16 and 1, with/without deletes, with/without resets, with/without slow file events
• Tests assert: file system consistency between agents AND no duplicate content across files
• Uses jitterScaleInSeconds: 0.75 to simulate network latency

Running E2E: Requires a server running with config-e2e.yml. Always clean the server databases before running. Use scripts/e2e.sh 8 for 8 concurrent processes (each running the full test suite independently).

E2E test harness known issue: The named pipe mechanism for log collection can cause processes to hang when debug output exceeds the pipe buffer size. This is an infrastructure issue, not a sync bug. If processes appear stuck with logs that stopped growing, it's likely a pipe buffer issue.

File Operations Abstraction

FileOperations has an ensureClearPath method that renames existing files to (1).md, (2).md etc. if a file already exists at the target path. This prevents data loss but can create apparent duplicates if the sync logic doesn't handle it.

The write method does a 3-way merge: write(path, oldContent, newContent). It reads the current file, computes a diff from oldContent to newContent, and applies that diff to the current file content. This preserves local changes that happened between the read and write. If the old content doesn't match what's expected, the merge can fail with "Part X not found in new content".

Approaches That Were Tried and Failed

When fixing the duplicate-document-after-interrupted-create problem, several heuristic approaches were attempted before landing on idempotency keys:

1. Content-hash matching during remote fetch: Scan all pending docs, read each file, hash it, and compare against incoming remote document. Failed because: (a) local content can be modified between the create and the fetch, so hashes don't match; (b) O(pending × remote) file I/O; (c) the resolvedDocuments getter was used instead of pendingDocuments, which filtered out all pending docs — a silent no-op bug.

2. originalCreationPath matching: Track where each pending doc was originally created. When a remote doc arrives at that path, assign metadata. Failed because: (a) two different clients can create at the same path — false matches assign wrong metadata, causing 3-way merge errors on the other client; (b) adding a deviceId check to limit false matches broke the case where another client updated the document (changing the deviceId in the broadcast).

3. In-memory tracking (e.g., pendingLocalId): Any in-memory state is lost on app crash. The whole point of the fix is to handle interrupted creates, which include crashes.

The idempotency key approach works because it's: (a) crash-safe (persisted locally); (b) deterministic (UUID lookup, no heuristics); (c) server-authoritative (the server resolves keys to documentIds).

Critical Implementation Invariants (Learned from Bugs)

These invariants were discovered through deep auditing and E2E testing. Violating any of them causes data loss, sync stalls, or test failures.

1. waitUntilFinished must loop until both sync queue AND WebSocket handlers are simultaneously idle. WebSocket message handlers (onRemoteVaultUpdateReceived) enqueue new sync operations. If you wait for the sync queue first, then WebSocket handlers, the handlers may have enqueued new operations that aren't awaited. The correct implementation loops: wait for WS handlers → wait for sync queue → check if WS has new work → repeat if needed. See SyncClient.waitUntilFinished().

2. enqueueSyncOperation must catch ALL errors, not just SyncResetError. executeSync re-throws non-SyncReset/non-FileNotFound errors (they're logged in sync history as ERROR). If enqueueSyncOperation doesn't catch these, they become unhandled promise rejections that crash the process. The catch logs the error and returns undefined — failed operations will be retried on the next WebSocket reconnect (which clears runningScheduleSyncForOfflineChanges and triggers a fresh filesystem scan).

3. Locks.reset() must NOT clear this.locked. In-flight operations (currently executing their callback) still hold conceptual locks. If reset() clears this.locked, new operations can acquire the same key and run concurrently with the still-running old operation. Only clear this.waiters (to reject pending waiters with SyncResetError). Let running operations release their locks naturally via the finally block in withLock.

4. handleMaybeMergingResponse must write the file BEFORE updating metadata. If metadata is updated first and the write fails (crash, OS error), the metadata points to a server version whose content was never written locally. On recovery, the stale local content is uploaded, potentially overwriting other clients' changes that were part of the merge. Order: write file → re-read + re-hash → update metadata → update cache.

5. After a MergingUpdate, cache the SERVER's content (responseBytes), not the local content. The content cache is used to compute diffs for subsequent updates: diff(cached, newFileContent). The server applies this diff against its content at parentVersionId. If the cache stores the local content (which may differ from the server's due to the 3-way merge in FileOperations.write), the diff won't match the server's state and the update will fail with "Invalid diff".

6. After a MergingUpdate, re-read the file and re-hash. The 3-way merge in operations.write() may produce content different from responseBytes (because the user edited the file between the read and the write). The stored hash must match the actual on-disk content, not the server's merged content. Otherwise, the next sync cycle incorrectly detects "no changes" (phantom hash match) or always detects changes (phantom hash mismatch).

7. Snapshot parentVersionId before computing diffs. document.metadata is a mutable shared reference. A concurrent operation (via a WebSocket handler running during an await in the same sync operation) can update parentVersionId between the cache lookup and the putText call. Always capture const parentVersionIdForUpdate = document.metadata.parentVersionId and use that value for both the cache lookup and the HTTP request.

8. Guard updateDocumentMetadata against concurrently removed documents. After any await (file write, re-read, HTTP call), the document may have been removed from the database by a concurrent delete operation. Always check database.containsDocument(document) before calling updateDocumentMetadata if there was an await since the document reference was obtained. Return gracefully if removed — the file is on disk and scheduleSyncForOfflineChanges will re-detect it.

9. When assigning a documentId to a pending doc, check for duplicates first. Both resolveIdempotencyKeys and handleMaybeMergingResponse (for deleted pending docs) assign documentIds. Before setting metadata, call getDocumentByDocumentId(id). If another document already has that ID, remove the stale pending doc instead of creating a duplicate. ensureConsistency checks for duplicate documentIds across ALL documents (not just resolvedDocuments).

10. resolveIdempotencyKeys sets parentVersionId: 0 — treat this as a create, not an update. When resolveIdempotencyKeys assigns a documentId to a pending doc, it uses parentVersionId: 0 as a placeholder. The sync path must check for parentVersionId === 0 and take the CREATE path (sending a create with the idempotency key), not the UPDATE path (which would fail because version 0 doesn't exist on the server).

11. Idempotent create returns can have stale content — check contentSize. When the server returns a FastForwardUpdate for a create with an idempotency key, it may return the ORIGINAL version (from the first create), not a new version with the current content. The response's contentSize may not match originalContentBytes.length. If they differ, fetch the actual server content for that version and use it for the cache and hash, so subsequent diffs are correct.

12. SyncClient.pause() must swallow SyncResetError. pause() calls fetchController.startReset() which rejects in-flight fetches. Those rejections propagate through waitUntilFinished(). Since pause() CAUSED the reset, the resulting SyncResetError is expected and must be caught (not re-thrown). Only re-throw non-SyncResetError exceptions. Also call fetchController.finishReset() in the catch block to prevent the FetchController from getting stuck in resetting state.

13. runningScheduleSyncForOfflineChanges must be cleared on WebSocket disconnect. After the initial scheduleSyncForOfflineChanges() completes, the field retains the resolved promise. On WebSocket disconnect/reconnect (without a full client reset), the field must be cleared so the next call triggers a fresh filesystem scan. Add a handler on onWebSocketStatusChanged that sets the field to undefined when isConnected is false.

14. The server must not expect() / panic on UTF-8 conversion — return a client error. In update_text, the parent version's content may be binary (if another client uploaded binary via putBinary). Using .expect() on str::from_utf8() panics the server. Use .context(...).map_err(client_error)? to return a 4xx error, allowing the client to fall back to putBinary.

15. The create-merge parent content must be latest_version.content, not empty. In create_document.rs, when a create merges with an existing document, the 3-way merge parent must be the latest version's content (&latest_version.content), not an empty vector (&Vec::new()). An empty parent causes reconcile("", existing, new) to treat all content as additions, producing garbled interleaved text.

16. retryForever must not retry 4xx HTTP errors. 4xx errors indicate the request itself is wrong (e.g., invalid diff, missing parent version). Retrying won't help. The HttpClientError class (in errors/http-client-error.ts) carries the status code. retryForever checks for it and re-throws immediately. Only 5xx errors (transient server failures) are retried.

17. The broadcast channel's RecvError::Lagged must be handled explicitly. The while let Ok(update) = broadcast_receiver.recv().await pattern silently exits the loop on Lagged, disconnecting the client without logging. Handle Lagged explicitly with a warn! log and break. The channel capacity (broadcast_channel_capacity in config, default 1024) is separate from max_clients_per_vault.

E2E Test Debugging Guide

How to run E2E tests:

cd sync-server && rm -rf databases && ./target/release/sync_server config-e2e.yml &
sleep 3
cd /volumes/syncthing/Projects/vault-link && scripts/e2e.sh 8

Always clean the databases directory before running. The server must be running separately.

Common E2E failure patterns:

1. SyncResetError unhandled rejection: Check that enqueueSyncOperation catches all errors and that pause() swallows SyncResetError. The test client's unhandledRejection handler checks error.name === "SyncResetError" — if the error message changes, update the filter in test-client/src/cli.ts.

2. "Files from agent-X missing in agent-Y": This is a consistency assertion. Check the agent's LOCAL file list (now correctly logged per-agent after a logging bug fix). Common causes:

   • Broadcasts lost during shutdown: Operations completed on one agent but the WebSocket broadcast didn't reach the other before destroy. The 5-second sleep between finish and destroy helps.
   • Path deconfliction: Both agents have the same DOCUMENT but at different LOCAL paths (e.g., binary-10.bin vs binary-10 (1).bin). This is a known limitation with concurrent creates at the same path.
   • Failed sync operations not retried: If executeSync throws, the failed file won't be retried until the next WebSocket reconnect (which clears runningScheduleSyncForOfflineChanges and triggers a fresh filesystem scan).

3. "Document not found in database": A concurrent operation removed the document between the last await and the updateDocumentMetadata call. Add a containsDocument guard.

4. "Duplicate documentId found in database": Two documents have the same documentId. Usually caused by resolveIdempotencyKeys or handleMaybeMergingResponse assigning a documentId without checking if another doc already has it.

5. "Invalid diff: attempting to access N characters...": The content cache has wrong content for a parentVersionId. Common causes: (a) cached local content instead of server content after MergingUpdate; (b) idempotent create returned a stale version but the client cached its current content under that version ID; (c) parentVersionId changed between cache lookup and putText call due to mutable shared reference.

6. "Parent version with id 0 not found": A document's parentVersionId is 0 (set by resolveIdempotencyKeys). The sync path should treat parentVersionId === 0 as a create, not an update.

Test client internals (test-client/src/agent/mock-agent.ts):

• files: InMemoryFileSystem map — the ACTUAL filesystem state
• data: Map of expected file contents — what the agent CREATED/UPDATED
• assertFileSystemsAreConsistent: Compares files maps between two agents
• assertAllContentIsPresentOnce: Checks no duplicate content across files
• The finish() and destroy() methods use withTimeout(TIMEOUT_MS) — operations that exceed 30s are killed

Logging bug (fixed): In assertFileSystemsAreConsistent, the error handler's "Local files" log previously printed otherAgent.files.keys() for BOTH agents. Now correctly prints this.files.keys() for the current agent.