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| 1 | +/** |
| 2 | + * MongoDB Latency Wrapper |
| 3 | + * |
| 4 | + * Utility to inject artificial latency into MongoDB operations for performance testing. |
| 5 | + * This wrapper temporarily wraps MongoDB Collection methods to add delays before |
| 6 | + * database operations execute. |
| 7 | + * |
| 8 | + * Usage: |
| 9 | + * const { wrapMongoDBWithLatency } = require('./MongoLatencyWrapper'); |
| 10 | + * |
| 11 | + * // Before initializing Parse Server |
| 12 | + * const unwrap = wrapMongoDBWithLatency(10); // 10ms delay |
| 13 | + * |
| 14 | + * // ... run benchmarks ... |
| 15 | + * |
| 16 | + * // Cleanup when done |
| 17 | + * unwrap(); |
| 18 | + */ |
| 19 | + |
| 20 | +const { Collection } = require('mongodb'); |
| 21 | + |
| 22 | +// Store original methods for restoration |
| 23 | +const originalMethods = new Map(); |
| 24 | + |
| 25 | +/** |
| 26 | + * Wrap a Collection method to add artificial latency |
| 27 | + * @param {string} methodName - Name of the method to wrap |
| 28 | + * @param {number} latencyMs - Delay in milliseconds |
| 29 | + */ |
| 30 | +function wrapMethod(methodName, latencyMs) { |
| 31 | + if (!originalMethods.has(methodName)) { |
| 32 | + originalMethods.set(methodName, Collection.prototype[methodName]); |
| 33 | + } |
| 34 | + |
| 35 | + const originalMethod = originalMethods.get(methodName); |
| 36 | + |
| 37 | + Collection.prototype[methodName] = function (...args) { |
| 38 | + // For methods that return cursors (like find, aggregate), we need to delay the execution |
| 39 | + // but still return a cursor-like object |
| 40 | + const result = originalMethod.apply(this, args); |
| 41 | + |
| 42 | + // Check if result has cursor methods (toArray, forEach, etc.) |
| 43 | + if (result && typeof result.toArray === 'function') { |
| 44 | + // Wrap cursor methods that actually execute the query |
| 45 | + const originalToArray = result.toArray.bind(result); |
| 46 | + result.toArray = function() { |
| 47 | + // Wait for the original promise to settle, then delay the result |
| 48 | + return originalToArray().then( |
| 49 | + value => new Promise(resolve => setTimeout(() => resolve(value), latencyMs)), |
| 50 | + error => new Promise((_, reject) => setTimeout(() => reject(error), latencyMs)) |
| 51 | + ); |
| 52 | + }; |
| 53 | + return result; |
| 54 | + } |
| 55 | + |
| 56 | + // For promise-returning methods, wrap the promise with delay |
| 57 | + if (result && typeof result.then === 'function') { |
| 58 | + // Wait for the original promise to settle, then delay the result |
| 59 | + return result.then( |
| 60 | + value => new Promise(resolve => setTimeout(() => resolve(value), latencyMs)), |
| 61 | + error => new Promise((_, reject) => setTimeout(() => reject(error), latencyMs)) |
| 62 | + ); |
| 63 | + } |
| 64 | + |
| 65 | + // For synchronous methods, just add delay |
| 66 | + return new Promise((resolve) => { |
| 67 | + setTimeout(() => { |
| 68 | + resolve(result); |
| 69 | + }, latencyMs); |
| 70 | + }); |
| 71 | + }; |
| 72 | +} |
| 73 | + |
| 74 | +/** |
| 75 | + * Wrap MongoDB Collection methods with artificial latency |
| 76 | + * @param {number} latencyMs - Delay in milliseconds to inject before each operation |
| 77 | + * @returns {Function} unwrap - Function to restore original methods |
| 78 | + */ |
| 79 | +function wrapMongoDBWithLatency(latencyMs) { |
| 80 | + if (typeof latencyMs !== 'number' || latencyMs < 0) { |
| 81 | + throw new Error('latencyMs must be a non-negative number'); |
| 82 | + } |
| 83 | + |
| 84 | + if (latencyMs === 0) { |
| 85 | + // eslint-disable-next-line no-console |
| 86 | + console.log('Latency is 0ms, skipping MongoDB wrapping'); |
| 87 | + return () => {}; // No-op unwrap function |
| 88 | + } |
| 89 | + |
| 90 | + // eslint-disable-next-line no-console |
| 91 | + console.log(`Wrapping MongoDB operations with ${latencyMs}ms artificial latency`); |
| 92 | + |
| 93 | + // List of MongoDB Collection methods to wrap |
| 94 | + const methodsToWrap = [ |
| 95 | + 'find', |
| 96 | + 'findOne', |
| 97 | + 'countDocuments', |
| 98 | + 'estimatedDocumentCount', |
| 99 | + 'distinct', |
| 100 | + 'aggregate', |
| 101 | + 'insertOne', |
| 102 | + 'insertMany', |
| 103 | + 'updateOne', |
| 104 | + 'updateMany', |
| 105 | + 'replaceOne', |
| 106 | + 'deleteOne', |
| 107 | + 'deleteMany', |
| 108 | + 'findOneAndUpdate', |
| 109 | + 'findOneAndReplace', |
| 110 | + 'findOneAndDelete', |
| 111 | + 'createIndex', |
| 112 | + 'createIndexes', |
| 113 | + 'dropIndex', |
| 114 | + 'dropIndexes', |
| 115 | + 'drop', |
| 116 | + ]; |
| 117 | + |
| 118 | + methodsToWrap.forEach(methodName => { |
| 119 | + wrapMethod(methodName, latencyMs); |
| 120 | + }); |
| 121 | + |
| 122 | + // Return unwrap function to restore original methods |
| 123 | + return function unwrap() { |
| 124 | + // eslint-disable-next-line no-console |
| 125 | + console.log('Removing MongoDB latency wrapper, restoring original methods'); |
| 126 | + |
| 127 | + originalMethods.forEach((originalMethod, methodName) => { |
| 128 | + Collection.prototype[methodName] = originalMethod; |
| 129 | + }); |
| 130 | + |
| 131 | + originalMethods.clear(); |
| 132 | + }; |
| 133 | +} |
| 134 | + |
| 135 | +module.exports = { |
| 136 | + wrapMongoDBWithLatency, |
| 137 | +}; |
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