• back-end developer and team lead at DA-14
  • ~ 3.5 years in software development area
  • hold tech meetups

ABOUT ME

  1. Definition of error
  2. Error types
  3. Source of errors
  4. Error handling patterns
  5. Exceptions 
  6. Security issues
  7. In context of Node.js
  8. Other

CONTENTS

DEFINITION OF ERROR

  • something goes wrong
  • something doesn't work the way it should
  • something does strange things
  • something comes with things you don't even know what to do with
  • you do something wrong, so consequently, it does everything from above
  • you have got issues in DNA

DEFINITION OF ERROR: IN LIFE

  • error resulting from bad code within some program involved in producing the erroneous result
  • unexpected conditions which aren’t a part of program’s normal operation
  • bug in a program that causes it to operate incorrectly, but not to terminate abnormally (or crash).

DEFINITION OF ERROR: PROGRAMMING

ERROR TYPES

Operation Errors

Developer Errors

ERROR TYPES

Operation Errors

  • Run-time issues experienced by correctly-written software
  • Not bugs
  • Problems with environment or external things​
    • system itself
    • system configuration
    • hardware
    • network
    • etc.

ERROR TYPES

Developer Errors

  • Bugs
  • Something that can be fixed by changing a code
  • Can never be handled properly becuase a code is under the question

ERROR TYPES

SOURCE OF ERRORS

"I think I've got an awesome idea.
Frank, take your chainsaw and a flamethrower,let's have fun"

  • Typo
  • Not validated data
  • Incompetence
  • Carelessness
  • Unsuitable environment
  • Overconfidence
  • Superstition
  • Corrupted library / service / module
  • Environment problems

SOURCE OF ERRORS

ERROR HANDLING PATTERNS

Return a neutral value

ERROR HANDLING PATTERNS

Return the same answer as the previous time

ERROR HANDLING PATTERNS

Substitute the next piece of valid data

ERROR HANDLING PATTERNS

Substitute the closest legal value

ERROR HANDLING PATTERNS

Log a warning message

ERROR HANDLING PATTERNS

Return an error code

ERROR HANDLING PATTERNS

Call an error-processing routine/object

ERROR HANDLING PATTERNS

Display an error message wherever the error
is encountered

ERROR HANDLING PATTERNS

Handle the error in whatever way works best locally

ERROR HANDLING PATTERNS

Shut down

ERROR HANDLING PATTERNS

EXCEPTIONS

  • ​anomalous or exceptional conditions
  • requires special processing
  • breaks a normal system flow

EXCEPTIONS

Handling:

  • ​use catch, try-catch
  • use events (event emitter)

EXCEPTIONS

Important:

  • ​shut down a system because of unclear app state

EXCEPTIONS

SECURITY ISSUES

SECURITY ISSUES: INFORMATION LEAKAGE

Syntax error message

ReferenceError: foo is not defined\n    at /home/roman_sachenko/Projects/API/app/controllers/main.js:28:9\n    at wrapped (/home/roman_sachenko/Projects/API/node_modules/newrelic/lib/transaction/tracer/index.js:183:28)\n    at wrappedPromise.linkTransaction (/home/roman_sachenko/Projects/API/node_modules/newrelic/lib/instrumentation/promise.js:273:65)\n    at wrappedPromise.wrapped [as __NR_wrapper]

SECURITY ISSUES: INFORMATION LEAKAGE

Application error message

Authentication: "Email doesn't exist"

 

SECURITY ISSUES: INFORMATION LEAKAGE

SECURITY ISSUES: INFORMATION LEAKAGE

Painkiller

  • limit stack trace
  • map error messages

SECURITY ISSUES: INFORMATION LEAKAGE

IN CONTEXT OF NODE.JS

Assert API is not for tests only

IN CONTEXT OF NODE.JS

Assert API is not for tests only

const assert = require('assert');

const getResult = () => {
  return {
    err: 'error message',
    value: null,
  };
};


const result = getResult();

assert.ifError(result.err);

//do something else

IN CONTEXT OF NODE.JS

Yes, we've got more than just new Error();

IN CONTEXT OF NODE.JS

Yes, we've got more than just new Error();

Error

AssertionError

Range
Error

ReferenceError

Syntax

Error

Type

Error

IN CONTEXT OF NODE.JS

Still not enough? Let's extend the Error object

IN CONTEXT OF NODE.JS

Error

Still not enough? Let's extend the Error object

IN CONTEXT OF NODE.JS

Error

API
Error

Custom features

Bad
Request

Not
Found

Oops

Extend the Error object? How does it look like?

const httpStatus = require('http-status');


module.exports = class ApiError extends Error {
  constructor(message, status) {
    super(message);

    this.name = this.constructor.name;

    Error.captureStackTrace(this, this.constructor);

    this.status = status || httpStatus.INTERNAL_SERVER_ERROR;

    this.message = message;
  }
};

IN CONTEXT OF NODE.JS

Want more? Events are everywhere

IN CONTEXT OF NODE.JS

Want more? Events are everywhere

IN CONTEXT OF NODE.JS

Event Emitter

Main Service

Error

Handling

Service

0

Service

1

Service

n

Events? Show me the code -_-

const EventEmitter = require('events');

class MainService extends EventEmitter {
  constructor(serviceName) {
    super();

    this._serviceName = serviceName;

    this.on('error', (err) => {
      // handle ${err}
      // from ${this._serviceName}
    });
  }
};

IN CONTEXT OF NODE.JS

class MyService extends MainService {
  constructor() {
    super('My Service');
  }

  foo() {
    try {
      // do something
    } catch (err) {
      this.emit('error', err);
    }
  }
};

Don't forget to catch exceptions and shut down the system

IN CONTEXT OF NODE.JS

Don't forget to catch exceptions and shut down the system

process
    .on('uncaughtException', (err) => {
      //log error
      //do asynchronous OR synchronous stuff
      process.exit(1) //shut down the system
    })
    .on('exit', () => {
      //do synchronous stuff only - last chance 
    });

IN CONTEXT OF NODE.JS

And don't reveal too much

IN CONTEXT OF NODE.JS

And don't reveal too much

const applicationStartupFunction = () => {

  if (process.env.NODE_ENV = 'production') {

    Error.stackTraceLimit = -1;

  }

};

IN CONTEXT OF NODE.JS

BEST PRACTICES

BEST PRACTICES

CHECKLIST

  • Setup uncaught exception handler
    • Log
    • Stop/Kill process because of unknown state
  • Setup and configure single point of error processing
  • Create custom error object
    • Extend from existing NodeJS Error object 
  • limit stack trace size for Production Environment
    • Error.stackTraceLimit

CHECKLIST

HELPFUL TOOLS

HELPFUL TOOLS

System Analysts

 

Logging

 

Security

 

Git Hooks

ARTICLES AND LINKS

ARTICLES AND LINKS

Questions

roman.sachenko@gmail.com

https://www.facebook.com/rsachenko

roman.sachenko

https://twitter.com/RSachenko

https://github.com/roman-sachenko

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