Monthly Archives: November 2023

Understanding the cURL Command for Performance Metrics

 in Applications / GNU/Linux  tagged curl by

Breaking Down the Command

In the world of web development and network administration, the cURL command is a versatile tool used for transferring data using various protocols. One interesting application of this command is to measure the performance of a web server. Let’s dissect a specific cURL command to understand how it works:

curl -svo /dev/null -w "Connect: %{time_connect} \n TTFB: %{time_starttransfer} \n Total time: %{time_total} \n" https://bytefreaks.net/;

Components of the Command

  1. curl: This is the basic command call for using cURL, which initiates the data transfer.
  2. -sv: The -s flag stands for ‘silent’, which makes cURL less talkative by hiding the progress meter and error messages. The -v flag is for ‘verbose’, providing more information about the transaction. These flags might seem contradictory, but together, they suppress unnecessary details while keeping the essential info visible.
  3. /dev/null: This part redirects the output of the command to a special file that discards all data written to it. In essence, it’s used here to ignore the body of the response.
  4. -w: This flag is used to specify what data to display on the screen after the execution of the command. It stands for ‘write-out’.
  5. "Connect: %{time_connect} \n TTFB: %{time_starttransfer} \n Total time: %{time_total} \n": This is a formatted string that curl will use to display the timing statistics:
    • %{time_connect}: Shows the time it took to establish the connection to the server.
    • %{time_starttransfer}: Stands for ‘Time to First Byte’ (TTFB), indicating the time from the start until the first byte is received.
    • %{time_total}: Displays the total time taken for the operation.
  6. https://bytefreaks.net/: This is the URL to which the cURL request is made.

Practical Use

This command is particularly useful for testing the performance of web servers. By analyzing the connect time, TTFB, and total time, administrators and developers can get insights into potential bottlenecks or performance issues. For instance, a long TTFB might suggest server-side delays in processing requests.

Conclusion

The cURL command demonstrated here is a powerful tool for performance testing. It’s concise yet provides crucial metrics for understanding how a web server responds to requests. By mastering such commands, one can effectively monitor and optimize web server performance, ensuring better user experiences and efficient server management.

Bug Fix: Resolving TypeError in Face Descriptor Computation

 in Programming / Python  tagged cvtColor / opencv / python by

In the realm of facial recognition software development, it’s not uncommon to encounter a TypeError when integrating different libraries. We recently addressed an issue with the following error message:

TypeError: compute_face_descriptor(): incompatible function arguments.

This error resulted from a misalignment in the expected color format of image data between OpenCV and the face_recognition library. Here’s how we resolved it.

The Problem

OpenCV, a powerful library for image processing, represents images in BGR (Blue, Green, Red) color space by default. Conversely, the face_recognition library, which excels at recognizing and manipulating faces in images, expects images in RGB (Red, Green, Blue) format. When the image data does not match the expected color format, the compute_face_descriptor() function raises a TypeError.

Our Solution

To fix this issue, we modified how we convert the image from OpenCV’s BGR format to the RGB format required by the face_recognition library. Previously, we used a slicing technique to reverse the color channels:

# Incorrect color conversion
rgb_frame = frame[:, :, ::-1]

However, this approach led to the aforementioned TypeError. We realized that using OpenCV’s cvtColor function provides a more reliable conversion:

# Correct color conversion
rgb_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)

The cvtColor function is explicitly designed for color space conversions, ensuring the image data is properly formatted for the face_recognition library.

Conclusion

With this small but crucial change, we eliminated the TypeError and improved the robustness of our facial recognition pipeline. This example serves as a reminder that understanding the intricacies of our libraries is essential for creating seamless and error-free integrations.For developers facing similar issues, consider the specific requirements of each function and library you’re using. It’s these details that can make or break your application.

Solving the ‘numpy._DTypeMeta’ Subscriptable Error in Python

 in Programming / Python  tagged numpy / pip / python by

Are you struggling with an unexpected TypeError when working with the OpenCV library in Python? If you’ve encountered the error message TypeError: ‘numpy._DTypeMeta’ object is not subscriptable and wonder what went wrong, you’re not alone. This error can be a significant roadblock when you’re trying to import the cv2 module, which is essential for computer vision tasks.

The root of this problem lies in a compatibility issue between numpy and other packages that rely on it, such as OpenCV. The ‘numpy._DTypeMeta’ object is a part of numpy’s core system, and when it’s not subscriptable, it suggests that the version of numpy you’re using is not playing nicely with the version of OpenCV.

Fortunately, the fix for this is often straightforward. By updating numpy to the latest version, you ensure that all the subscriptable features OpenCV needs are available. Here’s the magic command that usually does the trick:

pip install -U numpy;

This command asks pip, Python’s package installer, to upgrade numpy to the latest version available. The -U flag is short for --upgrade, which tells pip to overwrite the current version with the newest one.

Why does updating numpy work? It’s because newer versions of libraries like OpenCV often require the latest features and bug fixes from their dependencies. An outdated numpy package might not have the necessary functionality, leading to errors like the one mentioned.

So next time you face this TypeError, remember that a quick update of numpy could save the day. Keep your packages up to date, and you’ll minimize these sorts of issues significantly.

Remember, it’s good practice to keep your development environment updated. But always back up your work before doing so, as sometimes new versions can introduce their own issues. Happy coding!

Beware of Phishing Links on Viber: A Security Alert

 in Applications  tagged phishing / scam / security / viber by

In the age of instant communication, apps like Viber have become integral to our daily interactions. However, with the convenience of quick chats and video calls comes the risk of cyber threats. A recent security concern involves phishing links circulating on Viber, particularly those starting with “https://www.viber.com/activate_secondary/“. If you encounter such a link, exercise caution: clicking on it may compromise your account.

What Is a Phishing Link?

Phishing links are malicious URLs designed to steal personal information. Hackers craft these links to look legitimate, tricking users into handing over sensitive details like login credentials. Once clicked, these links can lead to unauthorized access to your accounts, financial loss, or identity theft.

The Viber Scam: What You Need to Know

On Viber, the scam link in question is part of a ploy to hack into accounts. The link prompts users to “activate” a secondary device, but in reality, it’s a method for a hacker to log in to your Viber account using their PC. The link is a disguised trap, and the consequences of clicking it are serious. The hacker can gain full access to your Viber account, allowing them to read your messages, access your contact list, and impersonate you.

How to Remove the access of a Hacker to your account

To deactivate Viber on your Desktop and Tablets from your mobile phone, you should follow these steps:

  1. Open the Viber app on your mobile device.
  2. Tap on More or the three lines in the bottom right corner to access the menu.
  3. Select Settings to open the settings menu.
  4. Go to the Account section.
  5. Tap on Desktop and Tablets. This will show a list of devices where your Viber account is active.
  6. From the list, select the device you want to deactivate.
  7. Confirm the deactivation when prompted.

This process will remove your Viber account from the selected devices, ensuring that no one can use it on those devices unless you activate them again​.

How to Protect Yourself

  • Don’t Click Suspicious Links: If you receive a link you weren’t expecting or that looks out of the ordinary, do not click on it.
  • Verify the Source: If a contact sends you a link, verify with them through a different communication method to confirm they intended to send it.
  • Use Official Channels: Always use the official Viber website or app for account-related actions.
  • Stay Informed: Keep up with the latest security updates from Viber and be aware of common phishing tactics.

Conclusion

Your digital safety is paramount. In the face of cunning cyber-attacks, staying informed and vigilant is your best defense. Remember, if you receive any link starting with “https://www.viber.com/activate_secondary/“, do not click on it. Protect yourself and your digital presence by being cautious and proactive about your online security.

Stay safe, stay connected.

Some technical information

As you will see in the following example, the link translates to a Viber command that prompts the device to accept the attacker’s device as a legitimate user device.

wget 'https://www.viber.com/activate_secondary/?u=bf63cd32389dcc342088c477a&k=u54BFqCQKGrL5-xPhV_Px82.&r=1&v=2'
--2023-11-02 16:21:36--  https://www.viber.com/activate_secondary/?u=bf63cd32389dcc342088c477a&k=u54BFqCQKGrL5-xPhV_Px82.&r=1&v=2
Resolving www.viber.com (www.viber.com)... 104.103.81.52, 2a02:26f0:9c00:395::24c5, 2a02:26f0:9c00:396::24c5
Connecting to www.viber.com (www.viber.com)|104.103.81.52|:443... connected.
HTTP request sent, awaiting response... 302 Moved Temporarily
Location: viber://auth?u=bf63cd32389dcc342088c477a&k=u54BFqCQKGrL5-xPhV_Px82.&r=1&v=2 [following]
viber://auth?u=bf63cd32389dcc342088c477a&k=u54BFqCQKGrL5-xPhV_Px82.&r=1&v=2: Unsupported scheme ‘viber’.