feat(NODE-4815): stringify and truncate BSON documents in log messages (#3635)

Author: W-A-James

src/mongo_logger.ts

@@ -53,6 +53,8 @@ export const SeverityLevel = Object.freeze({
  OFF: 'off'
 } as const);
 
+/** @internal */
+export const DEFAULT_MAX_DOCUMENT_LENGTH = 1000;
 /** @internal */
 export type SeverityLevel = (typeof SeverityLevel)[keyof typeof SeverityLevel];
 
@@ -254,6 +256,15 @@ export interface LogConvertible extends Record<string, any> {
  toLog(): Record<string, any>;
 }
 
+/** @internal */
+export function stringifyWithMaxLen(value: any, maxDocumentLength: number): string {
+ const ejson = EJSON.stringify(value);
+
+ return maxDocumentLength !== 0 && ejson.length > maxDocumentLength
+ ? `${ejson.slice(0, maxDocumentLength)}...`
+ : ejson;
+}
+
 /** @internal */
 export type Loggable = LoggableEvent | LogConvertible;
 
@@ -292,22 +303,23 @@ function attachConnectionFields(
 }
 
 function defaultLogTransform(
- logObject: LoggableEvent | Record<string, any>
+ logObject: LoggableEvent | Record<string, any>,
+ maxDocumentLength: number = DEFAULT_MAX_DOCUMENT_LENGTH
 ): Omit<Log, 's' | 't' | 'c'> {
  let log: Omit<Log, 's' | 't' | 'c'> = Object.create(null);
 
  switch (logObject.name) {
  case COMMAND_STARTED:
  log = attachCommandFields(log, logObject);
  log.message = 'Command started';
- log.command = EJSON.stringify(logObject.command);
+ log.command = stringifyWithMaxLen(logObject.command, maxDocumentLength);
  log.databaseName = logObject.databaseName;
  return log;
  case COMMAND_SUCCEEDED:
  log = attachCommandFields(log, logObject);
  log.message = 'Command succeeded';
  log.durationMS = logObject.duration;
- log.reply = EJSON.stringify(logObject.reply);
+ log.reply = stringifyWithMaxLen(logObject.reply, maxDocumentLength);
  return log;
  case COMMAND_FAILED:
  log = attachCommandFields(log, logObject);
@@ -452,7 +464,7 @@ export class MongoLogger {
  if (isLogConvertible(message)) {
  logMessage = { ...logMessage, ...message.toLog() };
  } else {
- logMessage = { ...logMessage, ...defaultLogTransform(message) };
+ logMessage = { ...logMessage, ...defaultLogTransform(message, this.maxDocumentLength) };
  }
  }
  this.logDestination.write(logMessage);

test/unit/mongo_logger.test.ts

@@ -19,12 +19,14 @@ import {
  CONNECTION_POOL_CREATED,
  CONNECTION_POOL_READY,
  CONNECTION_READY,
+ DEFAULT_MAX_DOCUMENT_LENGTH,
  Log,
  MongoDBLogWritable,
  MongoLogger,
  MongoLoggerOptions,
  SEVERITY_LEVEL_MAP,
- SeverityLevel
+ SeverityLevel,
+ stringifyWithMaxLen
 } from '../mongodb';
 
 class BufferingStream extends Writable {
@@ -1239,4 +1241,52 @@ describe('class MongoLogger', function () {
  });
  }
  });
+
+ describe('stringifyWithMaxLen', function () {
+ const largeDoc = {};
+ const smallDoc = { test: 'Hello' };
+ before(function () {
+ for (let i = 0; i < DEFAULT_MAX_DOCUMENT_LENGTH; i++) {
+ largeDoc[`test${i}`] = `Hello_${i}`;
+ }
+ });
+
+ context('when maxDocumentLength = 0', function () {
+ it('does not truncate document', function () {
+ expect(stringifyWithMaxLen(largeDoc, 0)).to.equal(EJSON.stringify(largeDoc));
+ });
+ });
+
+ context('when maxDocumentLength is non-zero', function () {
+ context('when document has length greater than maxDocumentLength', function () {
+ it('truncates ejson string to length of maxDocumentLength + 3', function () {
+ expect(stringifyWithMaxLen(largeDoc, DEFAULT_MAX_DOCUMENT_LENGTH)).to.have.lengthOf(
+ DEFAULT_MAX_DOCUMENT_LENGTH + 3
+ );
+ });
+ it('ends with "..."', function () {
+ expect(stringifyWithMaxLen(largeDoc, DEFAULT_MAX_DOCUMENT_LENGTH)).to.match(/^.*\.\.\.$/);
+ });
+ });
+
+ context('when document has length less than or equal to maxDocumentLength', function () {
+ it('does not truncate document', function () {
+ expect(stringifyWithMaxLen(smallDoc, DEFAULT_MAX_DOCUMENT_LENGTH)).to.equal(
+ EJSON.stringify(smallDoc)
+ );
+ });
+ it('does not end with "..."', function () {
+ expect(stringifyWithMaxLen(smallDoc, DEFAULT_MAX_DOCUMENT_LENGTH)).to.not.match(
+ /^.*\.\.\./
+ );
+ });
+
+ it('produces valid relaxed EJSON', function () {
+ expect(() => {
+ EJSON.parse(stringifyWithMaxLen(smallDoc, DEFAULT_MAX_DOCUMENT_LENGTH));
+ }).to.not.throw();
+ });
+ });
+ });
+ });
 });