syncguard/firestore/operations/release.js

Functional TypeScript library for distributed locking across microservices. Prevents race conditions with Redis, Firestore, and custom backends. Features automatic lock management, timeout handling, and extensible architecture.

/* SPDX-FileCopyrightText: 2025-present Kriasoft */
/* SPDX-License-Identifier: MIT */
import { withRetries } from "../retry.js";
/**
 * Creates a release operation for Firestore backend
 */
export function createReleaseOperation(db, locksCollection, config) {
    return async (lockId) => {
        return withRetries(async () => {
            // First, find the document by querying for lockId to get the key
            const querySnapshot = await locksCollection
                .where("lockId", "==", lockId)
                .limit(1)
                .get();
            if (querySnapshot.empty) {
                return false;
            }
            const doc = querySnapshot.docs[0];
            const data = doc.data();
            // Use transaction for atomic ownership verification and deletion
            const result = await db.runTransaction(async (trx) => {
                // Use the exact document reference from the query to avoid TOCTOU issues
                const docRef = doc.ref;
                const currentDoc = await trx.get(docRef);
                // Handle race condition: document might have been deleted between query and transaction
                if (!currentDoc.exists) {
                    // Document was deleted between query and transaction - treat as success
                    // since our lockId was found initially but document no longer exists
                    return true;
                }
                const currentData = currentDoc.data();
                // Verify ownership by lockId - this is critical for safety
                if (currentData.lockId !== lockId) {
                    // Document exists but lockId changed - another lock took this key
                    return false;
                }
                trx.delete(docRef);
                return true;
            });
            return result;
        }, config);
    };
}