🏗️ fix: Agents Token Spend Race Conditions, Add Auto-refill Tx, Add Relevant Tests (#6480)

* 🏗️ refactor: Improve spendTokens logic to handle zero completion tokens and enhance test coverage

* 🏗️ test: Add tests to ensure balance does not go below zero when spending tokens

* 🏗️ fix: Ensure proper continuation in AgentClient when handling errors

* fix: spend token race conditions

* 🏗️ test: Add test for handling multiple concurrent transactions with high balance

* fix: Handle Omni models prompt prefix handling for user messages with array content in OpenAIClient

* refactor: Update checkBalance import paths to use new balanceMethods module

* refactor: Update checkBalance imports and implement updateBalance function for atomic balance updates

* fix: import from replace method

* feat: Add createAutoRefillTransaction method to handle non-balance updating transactions

* refactor: Move auto-refill logic to balanceMethods and enhance checkBalance functionality

* feat: Implement logging for auto-refill transactions in balance checks

* refactor: Remove logRefill calls from multiple client and handler files

* refactor: Move balance checking and auto-refill logic to balanceMethods for improved structure

* refactor: Simplify balance check calls by removing unnecessary balanceRecord assignments

* fix: Prevent negative rawAmount in spendTokens when promptTokens is zero

* fix: Update balanceMethods to use Balance model for findOneAndUpdate

* chore: import order

* refactor: remove unused txMethods file to streamline codebase

* feat: enhance updateBalance and createAutoRefillTransaction methods to support additional parameters for improved balance management

api/models/balanceMethods.js

@@ -0,0 +1,153 @@
+const { ViolationTypes } = require('librechat-data-provider');
+const { Transaction } = require('./Transaction');
+const { logViolation } = require('~/cache');
+const { getMultiplier } = require('./tx');
+const { logger } = require('~/config');
+const Balance = require('./Balance');
+
+/**
+ * Simple check method that calculates token cost and returns balance info.
+ * The auto-refill logic has been moved to balanceMethods.js to prevent circular dependencies.
+ */
+const checkBalanceRecord = async function ({
+  user,
+  model,
+  endpoint,
+  valueKey,
+  tokenType,
+  amount,
+  endpointTokenConfig,
+}) {
+  const multiplier = getMultiplier({ valueKey, tokenType, model, endpoint, endpointTokenConfig });
+  const tokenCost = amount * multiplier;
+
+  // Retrieve the balance record
+  let record = await Balance.findOne({ user }).lean();
+  if (!record) {
+    logger.debug('[Balance.check] No balance record found for user', { user });
+    return {
+      canSpend: false,
+      balance: 0,
+      tokenCost,
+    };
+  }
+  let balance = record.tokenCredits;
+
+  logger.debug('[Balance.check] Initial state', {
+    user,
+    model,
+    endpoint,
+    valueKey,
+    tokenType,
+    amount,
+    balance,
+    multiplier,
+    endpointTokenConfig: !!endpointTokenConfig,
+  });
+
+  // Only perform auto-refill if spending would bring the balance to 0 or below
+  if (balance - tokenCost <= 0 && record.autoRefillEnabled && record.refillAmount > 0) {
+    const lastRefillDate = new Date(record.lastRefill);
+    const nextRefillDate = addIntervalToDate(
+      lastRefillDate,
+      record.refillIntervalValue,
+      record.refillIntervalUnit,
+    );
+    const now = new Date();
+    if (now >= nextRefillDate) {
+      try {
+        /** @type {{ rate: number, user: string, balance: number, transaction: import('@librechat/data-schemas').ITransaction}} */
+        const result = await Transaction.createAutoRefillTransaction({
+          user: user,
+          tokenType: 'credits',
+          context: 'autoRefill',
+          rawAmount: record.refillAmount,
+        });
+        balance = result.balance;
+      } catch (error) {
+        logger.error('[Balance.check] Failed to record transaction for auto-refill', error);
+      }
+    }
+  }
+
+  logger.debug('[Balance.check] Token cost', { tokenCost });
+  return { canSpend: balance >= tokenCost, balance, tokenCost };
+};
+
+/**
+ * Adds a time interval to a given date.
+ * @param {Date} date - The starting date.
+ * @param {number} value - The numeric value of the interval.
+ * @param {'seconds'|'minutes'|'hours'|'days'|'weeks'|'months'} unit - The unit of time.
+ * @returns {Date} A new Date representing the starting date plus the interval.
+ */
+const addIntervalToDate = (date, value, unit) => {
+  const result = new Date(date);
+  switch (unit) {
+    case 'seconds':
+      result.setSeconds(result.getSeconds() + value);
+      break;
+    case 'minutes':
+      result.setMinutes(result.getMinutes() + value);
+      break;
+    case 'hours':
+      result.setHours(result.getHours() + value);
+      break;
+    case 'days':
+      result.setDate(result.getDate() + value);
+      break;
+    case 'weeks':
+      result.setDate(result.getDate() + value * 7);
+      break;
+    case 'months':
+      result.setMonth(result.getMonth() + value);
+      break;
+    default:
+      break;
+  }
+  return result;
+};
+
+/**
+ * Checks the balance for a user and determines if they can spend a certain amount.
+ * If the user cannot spend the amount, it logs a violation and denies the request.
+ *
+ * @async
+ * @function
+ * @param {Object} params - The function parameters.
+ * @param {Express.Request} params.req - The Express request object.
+ * @param {Express.Response} params.res - The Express response object.
+ * @param {Object} params.txData - The transaction data.
+ * @param {string} params.txData.user - The user ID or identifier.
+ * @param {('prompt' | 'completion')} params.txData.tokenType - The type of token.
+ * @param {number} params.txData.amount - The amount of tokens.
+ * @param {string} params.txData.model - The model name or identifier.
+ * @param {string} [params.txData.endpointTokenConfig] - The token configuration for the endpoint.
+ * @returns {Promise<boolean>} Throws error if the user cannot spend the amount.
+ * @throws {Error} Throws an error if there's an issue with the balance check.
+ */
+const checkBalance = async ({ req, res, txData }) => {
+  const { canSpend, balance, tokenCost } = await checkBalanceRecord(txData);
+  if (canSpend) {
+    return true;
+  }
+
+  const type = ViolationTypes.TOKEN_BALANCE;
+  const errorMessage = {
+    type,
+    balance,
+    tokenCost,
+    promptTokens: txData.amount,
+  };
+
+  if (txData.generations && txData.generations.length > 0) {
+    errorMessage.generations = txData.generations;
+  }
+
+  await logViolation(req, res, type, errorMessage, 0);
+  throw new Error(JSON.stringify(errorMessage));
+};
+
+module.exports = {
+  checkBalance,
+};