DEV Community: Le Vuong

Owasp .Net Security cheetsheet

Le Vuong — Mon, 23 Feb 2026 20:58:24 +0000

https://cheatsheetseries.owasp.org/cheatsheets/DotNet_Security_Cheat_Sheet.html#encryption-for-transmission

How to send request when user close a web page?

Le Vuong — Mon, 23 Feb 2026 14:46:40 +0000

As developers, we often need to send a final request to the server when a user leaves a page — for example:

Sending final analytics data
Tracking session duration
Logging abandonment events
Saving last-known state

On older browsers, we can do this with a fetch request in the beforeunload event.

However, this approach is unreliable because browsers aggressively terminate asynchronous work when a page is closing.

On modern browsers, the navigator.sendBeacon() method can be used for this purpose.

window.addEventListener('visibilitychange', function() {
  if (document.visibilityState === 'hidden') {
    navigator.sendBeacon('/log', JSON.stringify({ event: 'page_closed' }));
  }
});

This method is built specifically for analytics-style requests.

My commonly used regex

Le Vuong — Wed, 28 Jan 2026 16:28:00 +0000

Regex is indispensable for developers. Below are some of my notes when working with Regex.

Notes:

Please try examples in this post with VSCode.
If you are on Windows, use \r\n instead of \n for line-ending.

Use OR in regex expression

Regex OR expression allow choosing 1 of multiple options.
Syntax: wrap the OR expression in parentheses.

Ex: (option1|option2)

Search/remove empty lines

Use vscode replace function (Ctrl-H or Ctrl-Shift-H)
Source: ^$\n
Target: (Leave this field empty)
Note: ^\s*$\n - use this pattern if you want to replace lines with only spaces too.

Search lines NOT matching a string

Use this pattern to search lines that NOT containing abc: ^((?!abc).)*$
?! is negative look-ahead operator. See also: look-behind, look around operators.
Note: this pattern is processing-heavy.

Shell alternatives

Many text processing tasks can be done by CLI tools, so why not use that instead? The shell commands like grep, sed, or awk are also faster and easier to maintain.
Use my Shell Command 2 extension to execute shell commands on selected text right from inside VSCode.

Regex Variants

VS Code uses JavaScript-style regex (and PCRE2 for global search)
Visual Studio use an MS specific Regex version

And, as always, use and practice a new skill frequently.

Visual Studio - How to view exception without exception variable

Le Vuong — Fri, 23 Jan 2026 14:29:18 +0000

When debugging a program and you got exception, but the catch statement don't include exception variable, like below image, what should you do?

Just use Visual Studio $exception special variable, put it in "Watch" or print in "Immediate" window, then you can view the exception.

What is state machine and how to use it - TBD

Le Vuong — Mon, 01 Dec 2025 18:45:15 +0000

TBD ...

How to scrape websites that Selenium or Playwright can't

Le Vuong — Mon, 17 Nov 2025 21:39:17 +0000

Short answer: write your own browser plugin/extension. This is not overly difficult, thanks to today's abundance of documentation and samples.

Following is a quick guide on how to do this.

Follow this Mozilla tutorial to create a simple plugin (Note: Firefox and Chrome extension) follow the same standard and so your code only need a little change to work on both.
Download and include jQuery lib in content_scripts section of manifest.json, so you can take advantages of jQuery DOM functions.
Then paste below code to content_scripts too. See how to test your plugin in the above tutorial. Open Walmart fresh fruit page, then look into the console, you can see info (price and name) for 10 products.

function getProducts() {
    /*
        Product Info
            Whole block: .mb0 a
            Name: .mb0.mt1.lh-title
            Price: .mr1.mr2-xl.lh-copy
            Image: .mb0.ph0-xl.pt0-xl .relative.overflow-hidden
    */
    let $ = jQuery;
    let blocks = $(".mb0 a");
    let names = $(".mb0.mt1.lh-title");
    let prices = $(".mr1.mr2-xl.lh-copy");

    for(let i=0; i<10; i++) {
        let name = $(names[i]).text();
        let price = $(prices[i]).text();

        console.log(`Product ${i + 1}: ${name} - ${price}`);
    }
}

$(document).ready(getProducts);

Happy coding !

Windows CMD Commands Cheat Sheet

Le Vuong — Fri, 17 Jan 2025 19:46:50 +0000

Files and Folders Management

COPY - Copies files to another location
DIR – Displays files and folders in current directory
DEL or ERASE - Deletes files
EDIT - Starts file editor
CD - Changes directory
EXPAND - Decompresses compressed files
FC - Compares files and shows the differences between them
FIND - Finds a text string in the file
MD or MAKEDIR - Creates a folder
MOVE - Moves files from one folder to another
PRINT - Prints out the text file contents
RD or RMDIR - Deletes a folder
REN or RENAME - Renames a file or folder
REPLACE - Replaces files in one directory with files of the same name in another directory (overwrite)
ROBOCOPY - Uses an advanced tool to copy files and directories
TREE - Shows directory structure of a disk or folder
TYPE - Displays the contents of text files
OPENFILES – Manages opened local or network files
XCOPY - Copies files and directory trees

Applications and Processes

SCHTASKS - Executes a command or start a scheduled application (Task Scheduler)
SHUTDOWN - Shutdowns or reboots your computer
TASKLIST - Lists the tasks being performed
TASKKILL - Stops or halts a task (to stop a task you use a PID which you can find out from TASKLIST)
REG – Starts registry editor
RUNAS - Launches the task as another user

Disks Management

CHKDISK - Checks disk and shows statistics
DEFRAG – Starts disk defragmentation
CHKNTFS - Displays or changes execution of disk check at boot
COMPACT - Displays and change the compression of files in NTFS partitions
CONVERT - Converts FAT disk volume to NTFS
DISKPART - Displays and adjusts disk partition properties
FORMAT - Formats the disk
FSUTIL - Displays and configures file system properties
LABEL - Creates, changes, or deletes a disk volume label
RECOVER - Recovers data from a bad or damaged disk
VOL - Displays volume label and serial number for the disk

System Information

DATE - Outputs or sets the current date
TIME - Displays or sets the system time
DRIVERQUERY - Displays the current state and properties of the device driver
HOSTNAME - Displays name of the computer
SYSTEMINFO - Shows configuration information about your computer
VER - Allows you to view the Windows version
GPRESULT – Displays current applied group policies (RSoP)
GPUPDATE – Updates group policies

Network

IPCONFIG - Shows information about network interfaces
PING – Sends ICMP requests to the target host, checks host availability
TRACERT - Finds the path for packets traveling over the network
NSLOOKUP - Finds IP address by resource name
ROUTE - Displays network route tables
ARP- Shows a table with IP addresses converted into physical addresses
NETSH – Starts is a network settings control program
GETMAC - Shows the MAC address of the network adapter
TFTP – Starts TFTP client in console

Command Line Setup

CLS - Clears screen
CMD - Displays another command prompt
COLOR - Sets the text and background color
PROMPT - Changes the command line prompt
TITLE - Assigns a title for the current session
HELP – Launches CMD help
EXIT - Exits the command line

Windows CMD Commands Cheat Sheet

Python C/C++ binding - Some notes

Le Vuong — Wed, 27 Nov 2024 22:43:20 +0000

Python binding is the connection between Python and external libraries or languages, allowing Python code to interface with C/C++, Java, or system-level libraries for extended functionality.

Source code

But why should we use Python binding

There are many cases where we may want to integrate C/C++ code with Python program, for example:

You already have a large, tested, stable library written in C++ that you’d like to take advantage of in Python. This may be a communication library or a library to talk to a specific piece of hardware. What it does is unimportant.
You want to speed up a particular section of your Python code by converting a critical section to C. Not only does C have faster execution speed, but it also allows you to break free from the limitations of the GIL, provided you’re careful.
You want to use Python test tools to do large-scale testing of their systems.

C vs C++ binding

The binding concept and principles applied similarly for both C and C++, in most cases.

Binding concepts

Marshalling Data Types

marshalling: The process of transforming the memory representation of an object to a data format suitable for storage or transmission.

In this case, we prepare data to move it from Python to C or vice versa
C stores data in the most compact form in memory possible. If you use an uint8_t, then it will only use 8 bits of memory total. In Python, on the other hand, everything is an object.

Understanding Mutable and Immutable Values

C has pass-by-value or pass-by-reference

Managing Memory

Python have garbage collector, C don't
You’ll need to be aware of where the memory for each object was allocated and ensure that it’s only freed on the same side of the language barrier.

Setting Up Your Environment

A C++ library installed and knowledge of the path for command-line invocation
Python development tools (python3-dev)
Python 3.6 or greater
The invoke tool

Using the invoke Tool

invoke is the tool you’ll be using to build and test your Python bindings in this tutorial (similar to make)

python3 -m pip install invoke

# build-cmult is build task
invoke build-cmult

# list available tasks
invoke --list

invoke all runs the build and test tasks for all tools.
invoke clean removes any generated files.

C or C++ Source

ctypes

ctypes is a tool in the standard library for creating Python bindings

Calling the Function

The steps are as following:

Load your library.
Wrap some of your input parameters.
Tell ctypes the return type of your function.

Library Loading

ctypes provides several ways for you to load a shared library

libname = pathlib.Path().absolute() / "libcmult.so"
c_lib = ctypes.CDLL(libname)

Calling Your Function

float cmult(int int_param, float float_param);

x, y = 6, 2.3

# Below command fail. Except for int, ctypes don't know how to convert other param types.
# answer = c_lib.cmult(x, y)

# below line let ctypes know that returned type is float
c_lib.cmult.restype = ctypes.c_float

answer = c_lib.cmult(x, ctypes.c_float(y))
print(f"    In Python: int: {x} float {y:.1f} return val {answer:.1f}")

CTypes Strengths and Weaknesses

Strength: ctypes is built-in
Weakness: manual works have to be done

CFFI

CFFI is the C Foreign Function Interface for Python
More automated approach to generate Python bindings

CFFI has multiple ways in which you can build and use your Python bindings:

ABI vs API: API mode uses a C compiler to generate a full Python module, whereas ABI mode loads the shared library and interacts with it directly.
in-line vs out-of-line: trade-off between speed and convenience
- In-line mode compiles the Python bindings every time your script runs
- Out-of-line mode requires an extra step to generate the Python bindings a single time and then uses them each time the program is run

This example use API out-of-line mode.

How It’s Installed

pip install cffi

Calling the Function

Write some Python code describing the bindings.
Run that code to generate a loadable module.
Modify the calling code to import and use your newly created module.

Write the Bindings

# tasks.py
import cffi

""" Build the CFFI Python bindings """
print_banner("Building CFFI Module")

# 1. Create FFI object
ffi = cffi.FFI()

# 2. Reading and processing the header file
ffi.cdef(h_file.read())

# 3. Describe the source file that CFFI will generate
ffi.set_source(
    "cffi_example",
    # Since you're calling a fully-built library directly, no custom source
    # is necessary. You need to include the .h files, though, because behind
    # the scenes cffi generates a .c file that contains a Python-friendly
    # wrapper around each of the functions.
    '#include "cmult.h"',
    # The important thing is to include the pre-built lib in the list of
    # libraries you're linking against:
    libraries=["cmult"],
    library_dirs=[this_dir.as_posix()],
    extra_link_args=["-Wl,-rpath,."],
)

# 4. Build the Python Bindings
ffi.compile()

# 5. Calling Your Function
import cffi_example
answer = cffi_example.lib.cmult(x, y)

PyBind11

Install: python3 -m pip install pybind11
Build the cppmult lib

invoke.run(
    "g++ -O3 -Wall -Werror -shared -std=c++11 -fPIC cppmult.cpp "
    "-o libcppmult.so "
)

Writing the Bindings:

#include <cppmult.hpp>

PYBIND11_MODULE(pybind11_example, m) {
    m.doc() = "pybind11 example plugin"; // Optional module docstring
    m.def("cpp_function", &cppmult, "A function that multiplies two numbers");
}

Build Python bindings

# tasks.py
invoke.run(
    "g++ -O3 -Wall -Werror -shared -std=c++11 -fPIC "
    "`python3 -m pybind11 --includes` "
    "-I /usr/include/python3.7 -I .  "
    "{0} "
    "-o {1}`python3.7-config --extension-suffix` "
    "-L. -lcppmult -Wl,-rpath,.".format(cpp_name, extension_name)
)

Calling Your Function

import pybind11_example
answer = pybind11_example.cpp_function(x, y)

Strengths and Weaknesses

PyBind11 is focused on C++ instead of C
It supports classes.
It handles polymorphic subclassing.
It allows you to add dynamic attributes to objects from Python and many other tools, which would be quite difficult to do from the C-based tools you’ve examined.

Cython

The approach Cython takes to creating Python bindings uses a Python-like language to define the bindings and then generates C or C++ code that can be compiled into the module.
Cython can support both C and C++
Install:

python3 -m pip install cython

Write the Bindings

# cython_example.pyx
""" Example cython interface definition """

cdef extern from "cppmult.hpp":
    float cppmult(int int_param, float float_param)

def pymult( int_param, float_param ):
    return cppmult( int_param, float_param )

The language used here is a special mix of C, C++, and Python
Build the Python Bindings:

# tasks.py
def compile_python_module(cpp_name, extension_name):
    invoke.run(
        "g++ -O3 -Wall -Werror -shared -std=c++11 -fPIC "
        "`python3 -m pybind11 --includes` "
        "-I /usr/include/python3.7 -I .  "
        "{0} "
        "-o {1}`python3.7-config --extension-suffix` "
        "-L. -lcppmult -Wl,-rpath,.".format(cpp_name, extension_name)
    )

def build_cython(c):
    """ Build the cython extension module """
    print_banner("Building Cython Module")
    # Run cython on the pyx file to create a .cpp file
    invoke.run("cython --cplus -3 cython_example.pyx -o cython_wrapper.cpp")

    # Compile and link the cython wrapper library
    compile_python_module("cython_wrapper.cpp", "cython_example")
    print("* Complete")

Calling Your Function

import cython_example
answer = cython_example.pymult(x, y)

Strengths and Weaknesses

Cython is a relatively complex tool that can provide you a deep level of control when creating Python bindings for either C or C++.

References

Lodash - a javascript power tool

Le Vuong — Wed, 13 Nov 2024 17:05:04 +0000

Lodash, a lightweight replacement for Underscore.js, is a popular JavaScript utility library that simplifies common programming tasks. Explore the top 20 Lodash functions below to enhance your JavaScript skills:

1. `_.get`

Safely retrieves a nested property from an object, avoiding errors if the property doesn't exist.

const obj = { a: { b: { c: 42 } } }; _.get(obj, 'a.b.c', 'default'); // 42

2. `_.set`

Sets the value of a nested property in an object, creating intermediate properties if they don’t exist.

const obj = {}; _.set(obj, 'a.b.c', 42); console.log(obj); // { a: { b: { c: 42 } } }

3. `_.cloneDeep`

Creates a deep copy of an object or array.

const arr = [{ a: 1 }]; const deepClone = _.cloneDeep(arr);

4. `_.debounce`

Delays the execution of a function until after a specified time has passed since its last call.

const log = _.debounce(() => console.log('Debounced!'), 300); window.addEventListener('resize', log);

5. `_.throttle`

Ensures a function is executed at most once in a specified time interval.

const log = _.throttle(() => console.log('Throttled!'), 1000); window.addEventListener('scroll', log);

6. `_.isEmpty`

Checks if a value is an empty object, array, or falsy value.

_.isEmpty([]); // true _.isEmpty({}); // true _.isEmpty(''); // true

7. `_.merge`

Deeply merges two or more objects, combining their properties.

const obj1 = { a: { b: 1 } }; const obj2 = { a: { c: 2 } }; _.merge(obj1, obj2); // { a: { b: 1, c: 2 } }

8. `_.pick`

Creates an object composed of the selected properties.

const obj = { a: 1, b: 2, c: 3 }; _.pick(obj, ['a', 'c']); // { a: 1, c: 3 }

9. `_.omit`

Creates an object excluding the specified properties.

const obj = { a: 1, b: 2, c: 3 }; _.omit(obj, ['b']); // { a: 1, c: 3 }

10. `_.uniq`

Removes duplicate values from an array.

_.uniq([1, 2, 2, 3]); // [1, 2, 3]

11. `_.groupBy`

Groups the elements of an array based on a provided criterion.

_.groupBy([6.1, 4.2, 6.3], Math.floor); // { '4': [4.2], '6': [6.1, 6.3] }

12. `_.sortBy`

Sorts an array of objects based on specific properties or criteria.

const users = [{ name: 'Tom', age: 30 }, { name: 'Jerry', age: 20 }]; _.sortBy(users, 'age'); // [{ name: 'Jerry', age: 20 }, { name: 'Tom', age: 30 }]

13. `_.map`

Creates a new array by transforming each element in a collection.

_.map([1, 2, 3], n => n * 2); // [2, 4, 6]

14. `_.filter`

Creates an array with elements that pass the provided condition.

_.filter([1, 2, 3, 4], n => n % 2 === 0); // [2, 4]

15. `_.find`

Finds the first element that satisfies a condition.

_.find([1, 2, 3, 4], n => n > 2); // 3

16. `_.flatten`

Flattens a nested array into a single-level array.

_.flatten([1, [2, [3, [4]]]]); // [1, 2, [3, [4]]]

17. `_.flattenDeep`

Flattens a nested array into a fully single-level array.

_.flattenDeep([1, [2, [3, [4]]]]); // [1, 2, 3, 4]

18. `_.difference`

Returns the values from the first array that are not in the second array.

_.difference([2, 1, 3], [2, 3]); // [1]

19. `_.chunk`

Splits an array into groups of the specified size.

_.chunk([1, 2, 3, 4, 5], 2); // [[1, 2], [3, 4], [5]]

20. `_.isEqual`

Performs a deep comparison to determine if two values are equivalent.

_.isEqual({ a: 1 }, { a: 1 }); // true

Keep learning and having FUN !

10 questions developers should ask our self

Le Vuong — Fri, 08 Nov 2024 19:48:36 +0000

Here are 10 common questions developers often face, ranging from technical challenges to career advice:

How do I efficiently debug code?

Debugging is essential for developers. Many ask about strategies and tools to help them identify and resolve issues faster. Techniques like setting breakpoints, using logging, or leveraging tools like Chrome DevTools or debugging features in IDEs (e.g., Visual Studio Code, PyCharm) are popular.
How can I improve the performance of my code?

Performance optimization often involves refactoring code, optimizing algorithms, reducing memory usage, or minimizing network requests. Developers often seek guidance on balancing performance improvements with readability and maintainability.
How do I stay updated with new technologies and best practices?

With tech evolving quickly, developers wonder how to keep their skills relevant. Strategies like following trusted blogs, taking online courses, attending conferences, or participating in communities (e.g., GitHub, Stack Overflow) are common approaches.
What are the best practices for version control, especially in Git?

Many developers seek tips on managing branches, making efficient commits, writing meaningful commit messages, and handling merge conflicts. Following Git best practices ensures smooth collaboration in team environments.
How do I manage dependencies and packages in my project?

Developers frequently encounter issues with package compatibility, outdated dependencies, and package security. Tools like npm, yarn, pip, and Docker (for containerization) are commonly used to manage these challenges.
What should I know about testing and test-driven development (TDD)?

Testing ensures software reliability, but implementing it effectively can be challenging. Developers seek advice on unit testing, integration testing, end-to-end testing, and TDD approaches, along with tools like Jest, Mocha, JUnit, or pytest.
How do I design and structure a scalable database?

Many wonder how to create databases that can grow with the application, considering scalability, efficiency, and maintainability. Topics include SQL vs. NoSQL, normalization, indexing, and database partitioning.
How do I secure my application against common vulnerabilities?

Security is a significant concern, especially with growing cyber threats. Developers often seek advice on preventing vulnerabilities like SQL injection, cross-site scripting (XSS), and cross-site request forgery (CSRF), along with implementing HTTPS and OAuth.
How do I manage work-life balance as a developer?

Many developers struggle with long hours and burnout, particularly in high-demand tech environments. They ask about setting boundaries, improving productivity, and maintaining a healthy work-life balance.
What’s the best way to get hired or advance in a developer career?

Developers frequently look for advice on building portfolios, acing technical interviews, learning soft skills, and advancing in their careers. Tips often include contributing to open-source projects, networking, and preparing for coding challenges.

Do any of these questions resonate with you or relate to what you're working on right now?

Simple steps to debug docker build

Le Vuong — Wed, 06 Nov 2024 15:09:09 +0000

Below are steps to debug docker build. In this example, docker is a python app, but the same logic apply to other languages and frameworks.

In the Dockerfile, comment the lines that cause the build to fail and all other lines below that; Then add below line to the end of the Dockerfile.

CMD ["bash"]

Build again (this time it should success) and start the container.
docker run <image name>
Connect to the container: docker exec -it <container> bash
Run the steps that cause the build error (in Dockerfile).
Eg. pip install -s requirements.txt
Investigate and try to fix the failed commands.
Continue with next other commands in the Dockerfile until everything is ok.
When finished, uncomment the commented lines in Dockerfile in step 1.
Try and build Dockerfile again.

References:

How to build docker
How to dockerize an app

Script for converting Markdown with bold text to Unicode, retaining the bold text.

Le Vuong — Mon, 28 Oct 2024 14:19:17 +0000

Hello developers,

Have you ever needed to convert Markdown text to a bold/italic text that you can post to Facebook, Instagram ?

Here’s how it works:

It looks through text for any parts that are wrapped in **bold text**.
Using regex, it breaks up each segment into "normal" and "bold" parts.
Each letter in the bold section gets replaced with its corresponding Unicode "bold" version. For example, A becomes a Unicode-bold 𝐀, and a becomes 𝐚.
Finally, it puts everything back together and gives you the bolded version of the whole text.

This script is perfect for converting text so that it looks bold across platforms that don’t directly support rich text formatting, like some messaging apps. Simple and effective!

Code snippet

Side Notes:

If you need to get the Html output of some formatted text, use CopyQ. Windows have similar "buffer" tools like Free Clipboard Viewer
VSCode have "Paste" extension that allows you to paste different format of the Clipboard content.
Also, for VSCode, you have extensions for converting Markdown to Html and vice verse.
Take a look at the code comment if you want to extent the script to process Italic or Bold and Italic text.

DEV Community: Le Vuong

Owasp .Net Security cheetsheet

How to send request when user close a web page?

My commonly used regex

Use OR in regex expression

Search/remove empty lines

Search lines NOT matching a string

Shell alternatives

Regex Variants

Visual Studio - How to view exception without exception variable

What is state machine and how to use it - TBD

How to scrape websites that Selenium or Playwright can't

Windows CMD Commands Cheat Sheet

Python C/C++ binding - Some notes

But why should we use Python binding

C vs C++ binding

Binding concepts

Marshalling Data Types

Understanding Mutable and Immutable Values

Managing Memory

Setting Up Your Environment

Using the invoke Tool

C or C++ Source

ctypes

Calling the Function

Library Loading

Calling Your Function

CTypes Strengths and Weaknesses

CFFI

How It’s Installed

Calling the Function

Write the Bindings

PyBind11

Strengths and Weaknesses

Cython

Strengths and Weaknesses

Other Solutions

References

Lodash - a javascript power tool

1. _.get

2. _.set

3. _.cloneDeep

4. _.debounce

5. _.throttle

6. _.isEmpty

7. _.merge

8. _.pick

9. _.omit

10. _.uniq

11. _.groupBy

12. _.sortBy

13. _.map

14. _.filter

15. _.find

16. _.flatten

17. _.flattenDeep

18. _.difference

19. _.chunk

20. _.isEqual

10 questions developers should ask our self

Simple steps to debug docker build

Script for converting Markdown with bold text to Unicode, retaining the bold text.

1. `_.get`

2. `_.set`

3. `_.cloneDeep`

4. `_.debounce`

5. `_.throttle`

6. `_.isEmpty`

7. `_.merge`

8. `_.pick`

9. `_.omit`

10. `_.uniq`

11. `_.groupBy`

12. `_.sortBy`

13. `_.map`

14. `_.filter`

15. `_.find`

16. `_.flatten`

17. `_.flattenDeep`

18. `_.difference`

19. `_.chunk`

20. `_.isEqual`