Questions and Answers
What is the primary purpose of logging in an application?
What type of data is typically logged in a large system?
What is the name of the HTTP request logger middleware for Node.js?
What is the purpose of the format argument in the Morgan API?
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What is the purpose of the tokens object in the Morgan format function?
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What is the purpose of the :date token in Morgan?
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How do you install Morgan using npm?
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What is the purpose of the morgan(format, options) API?
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What does the :remote-addr token represent in a Morgan log format?
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Which of the following predefined log formats is a color-coded log format by request status?
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What does the :response-time token represent in a Morgan log format?
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How do you specify the tokens you want in your log format when using Morgan?
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What is the purpose of the :req[header] token in a Morgan log format?
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What does the :total-time token represent in a Morgan log format?
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What is the purpose of the 'flags: a' option when creating a file stream using the fs library?
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What is the main advantage of using the rotating-file-stream module for log file rotation?
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What is the purpose of the 'interval: 1d' option when creating a rotating write stream using the rotating-file-stream module?
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What is the correct syntax for applying a custom token in a morgan logger?
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What is the purpose of the 'path.join(__dirname, 'log')' option when creating a rotating write stream using the rotating-file-stream module?
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What is the correct way to define a custom token in morgan?
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Study Notes
Logging
- Logging is the collection and storing of data over a time period for analysis, used to gain insights, resolve bugs, and detect problems in an application.
- Simplest form of logging is using console.log to log data to the command line for debugging.
Importance of Logging
- Debugging: document steps leading up to an error
- Security Audits: detect and log suspicious activities or important events
What to Log
- Timestamp or log entry
- Timing data for the request
- Request endpoint data (e.g. paths: "/users" or verbs: GET, POST, PUT, DELETE)
- IP of the requesting party
- Exceptions
How to Log
- Manually write code to log required info to console, file, or database
- Use libraries like Morgan, Winson, or Log4JS
Morgan Library
- HTTP request logger middleware for Node.js
- Simplifies logging requests to an application
- Can be installed using npm install morgan --save
- Import with var morgan = require('morgan')
Using Morgan
- Create a new Morgan logger middleware function using format and options
- Format argument can be a string of a predefined name, a string of a format string, or a function that produces a log entry
- Tokens can be used to customize log format
Morgan Pre-defined Tokens
- :date - current date and time in UTC
- :http-version - HTTP version of the request
- :method - HTTP method of the request
- :referrer - Referrer header of the request
- :remote-addr - remote address (IP) of the request
- :remote-user - user authenticated as part of Basic auth for the request
- :req[header] - given header of the request
- :res[header] - given header of the response
- :response-time - time between request and response headers being written (in milliseconds)
- :status - status code of the response
- :total-time - time between request and response being written (in milliseconds)
- :url - URL of the request
- :user-agent - User-Agent header of the request
Predefined Log Formats
- combined - Apache standard combined format
- common - Apache standard common format
- dev - color-coded log format by request status
- short - shorter than default format
- tiny - even shorter, just response time and a few items
Creating Custom Tokens
- morgan.token('myToken', function(req, res) { ... return ...; })
- Custom token name and function that returns value representing token output in log
Applying Custom Token
- app.use(morgan(':myToken :method :url :date'));
- Apply and test the code to observe output in console
Applying Logging to File
- Use fs library to create a file stream and apply it to Morgan
- var fs = require('fs');
- const appLogStream = fs.createWriteStream(path.join(__dirname, 'app.log'), { flags: 'a' })
- app.use(morgan("combined", { stream: appLogStream }));
Log File Rotation
- Log file can grow to a large size, need to create multiple log files (e.g. one each day)
- Use rotating-file-stream module
- npm install rotating-file-stream --save
- var rfs = require('rotating-file-stream');
- Create a rotating write stream
- var appLogStream = rfs.createStream('access.log', { interval: '1d', // rotate daily path: path.join(__dirname, 'log') // write to a subdir log })
- app.use(morgan("combined", { stream: appLogStream }));
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Description
This quiz covers the concepts of logging in secure coding, including collecting and storing data for analysis, debugging, and security audits.