DEV Community: Alfie Torres

Are Singleton Patterns Bad?

Alfie Torres — Tue, 14 Jul 2020 06:15:05 +0000

Organising Cat Videos using Python

Alfie Torres — Fri, 10 Jul 2020 03:41:23 +0000

After learning Python yesterday, I thought that It would be best to solidify my learning by building something useful. One issue I had over the week involved compiling around 500+ videos for my kittens birthday celebration. After organising the first 10 videos by month, I was already fed up.

To my attention, I realised that I could actually make a script in python to go through these videos much faster. Using the GetFileInfo -d yourfile.mov, I realised that I could actually get the unique month and year that the file was created in.

Now, comes the part where I have to use Python


import os, shutil 
from datetime import datetime

filepath = "/Users/alfietorres/Downloads/"      #base file path 
for filename in os.listdir(filepath):           #iterate through each file in the directory

    r = os.stat(filepath+filename)              #look for the file path and the file name
    d = r.st_birthtime                          #look for the time created 
    date=datetime.fromtimestamp(d)              #assign the details to a date variable

    month_directory = filepath+str(date.month)+"-"+str(date.year)      #use the date variable to create a UNIQUE new directory 
    file_being_moved = filepath+filename        #file the path of the file being moved    

    if os.path.isdir(month_directory) :         #check if the directory is created
        print("directory found ... ")
        shutil.move(file_being_moved,month_directory)   #move the file we are iterating on to the directory
    else: 
        print("creating directory ... ")        
        os.mkdir(month_directory)                       #create new directory 
        shutil.move(file_being_moved,month_directory)   #move items in new directory

Essentially, we have a for each loop going through each file in the downloads directory.

Afterwards, we find the month-year of that file and check if has already been created.

If the new directory has already been created, then all we have to do is move the file.

If it has not been created then we will create a new directory and move the file into that directory.

After running the file, we get the following output (voila). Now you have an organised list of new directories. You can even add new videos in the Downloads directory and run the script again to reorganise the files.

The Memory Layout Explained

Alfie Torres — Sun, 05 Jul 2020 09:32:31 +0000

All programs are stored in memory, these are stored in virtual addresses that the OS/CPU map to physical addresses. The memory model has 5 segments and are responsible for holding memory

Stack Segment — function local variables, arguments, context

Heap Segment: dynamic program data (e.g., malloc)

Block Started by Symbol segment: uninitialized global and static variables

Data Segment: initialised global and static variables

Text Segment: program code and fixed program constants

On the third column of the diagram, we see examples of how these segments may actually look like.

Memory Allocation

Now that we know how the memory model looks like let’s see how memory is actually allocated.

Going back to our diagram, let’s look at what happens in runtime. During runtime, the stack segment and heap segment grow in opposite directions. The heap goes from lower addresses to higher addresses and the stack segment goes from high addresses to low addresses.

Ok I get what the stack segment stores, but how does memory get allocated in the stack ?

Stack

Alright, well in computer architecture, the stack is a hardware manifestation of the data structure (Last in, First Out Queue). The stack needs to

- Call a function — As such, we need to store data

- Return from a function — As such, we need to restore data

Working Example

Stack Layout

Given the code below we want access y and increment y by 1.

So in this example, we see that the arguments are arranged in the verse order, while the local variables are pushed in the same order they appear in the code.

Part 1: Call a Function

ESP

Every time, we push some data in the stack and the shrinks every time we pop something from stack. The

ESP is the Extended Stack Pointer and this register purpose is to let you know where on the stack you are. Thus, ESP always marks the top (highest point of the stack) of the stack.

EBP

In order to increment y, we need to know where y is stored in the stack. However, it’s difficult to know what y’s address is in compile time

For example, if y is stored in 0xbfff333, in the next time the function is called y can be stored in a totally different address (e.g. 0xbfff9F3).

Oh no, So how do we locate y?

Well luckily, we can use %ebp as an anchor point to find these variables. The EBP formally defined as the Extended Base Stack Pointer and its purpose is to point to the base address of the stack.

Based on the diagram above, let’s say that y is 8 bytes before EBP. So now the compiler will know that whenever this function is called, y will be 8 bytes before the EBP

Part 2: Return from a Function

So for example, when %esp has finally reached %ebp, we can

- push %ebp before local variables and

- then set %ebp to the current %esp and

- then set %ebp to the %ebp at return

In simple terms, we have saved the frame pointer in the stack.

Afterwards, we have updated the frame pointer to be the current stack pointer.

Now, when the func functions starts to run, it will push its local variables after the stack pointer.

How do we continue our operations in main?

Now that we have called the function and returned, how do make the sure the program continues to run? This is where EIP comes in handy.

EIP is formally defined as the Extended Instruction Pointer. It is a read-only register and it contains the address of the next instruction to read on the program, point always to the “Program Code” memory segment.

So, when main is running it moves the EIP up the main function. When it hits 0x*8048455, it calls func. When it goes to call it, the EIP goes to func at 0x*804840b. Let’s see how this looks like in the stack layout

So looking at the stack layout, we see that EIP is EBP+4. As such, when we are done we will just need to set the current frame pointer (EBP) to 4 from the callee (in the caller’s data).

Afterwards, we can just return to the main function and continue where we left off.

References

Mercolino. (2014). Understanding Buffer Overflows Attacks. Retrieved from https://itandsecuritystuffs.wordpress.com/2014/03/18/understanding-buffer-overflows-attacks-part-1/

Google login authentication with Firebase in Android (2020)

Alfie Torres — Sun, 05 Jul 2020 09:26:39 +0000

Add the following dependencies in your build.gradle

implementation 'com.google.firebase:firebase-auth:19.3.1'  
implementation 'com.google.android.gms:play-services-auth:18.0.0'

Before starting, I am assuming that you already connected your Android app with firebase. In this case, I already connected week12lab with firebase

Afterwards, press the Android option and create a new app

The Android package name can be found in the build.gradle file under the applicationId name. Additionally we will have to create a SHA-1 certificate for debug signing

In order to generate the SHA-1 key type the following command in your terminal

keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android

Result of the command. I hid my SHA1 certificate fingerprints.

Add the google-services.json file to your app folder

Outline

A detailed explanation can be found in Google’s official documentation. This tutorial is simply made to explain each step as concisely as possible.

Configure Google Sign-in and GoogleSignInClient object
Check for existing signed-in use
Use Firebase Auth
Add What will happen if valid user logs in
Add a logout button
Play with user’s data
Update manifest

1 | Configure Google Sign-in and the GoogleSignInClient object

The following makes a sign in request to google

// Configure Google Sign In  
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT\_SIGN\_IN)  
        .requestIdToken(getString(R.string.default\_web\_client\_id))  
        .requestEmail()  
        .build();

Afterwards in onCreate we will need to add a Google sign in client

// Build a GoogleSignInClient with the options specified by gso.  
mGoogleSignInClient = GoogleSignIn.getClient(this, gso);

Line 15 and 27, show how we added a new GoogleSignInClient and instantiated it in the onCreate method.

2 | Create XML login button and Signin Method

Create Login Button

Create a new XML class called login.xml and add the Google sign in button.

Create a Sign In Method

We then need to make a sign in intent to Google. We will have to make a new method in the LoginActivity class.

private void signIn() {  
    Intent signInIntent = mGoogleSignInClient.getSignInIntent();  
    startActivityForResult(signInIntent, RC\_SIGN\_IN);  
}

RC_SIGN_IN can be any number. In this case, I assigned 1.

Create a new listener to use Sign In method

Create a new onclicklistener that makes use of the new signin() method we just created.

Find the button and set the onClickListener

Find the button that we create in our XML and assign the handleGoogleLogin listener to it.

3 | Use Firebase Auth

Now that we have made the intent, we can now check if the google account is a valid account.

Add onActivityResult


@Override  
public void onActivityResult(int requestCode, int resultCode, Intent data) {  
    super.onActivityResult(requestCode, resultCode, data);  


    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);  
    if (requestCode == _RC\_SIGN\_IN_) {  
        Task<GoogleSignInAccount> task = GoogleSignIn._getSignedInAccountFromIntent_(data);  
        try {  
            // Google Sign In was successful, authenticate with Firebase  
            GoogleSignInAccount account = task.getResult(ApiException.class);  
            firebaseAuthWithGoogle(account);  
        } catch (ApiException e) {  
            // Google Sign In failed, update UI appropriately  
            // ...  
            Toast._makeText_(this, e.getMessage(), Toast._LENGTH\_SHORT_).show();  
        }  
    }  
}

Add firebaseAuthWithGoogle(String idToken)

The credentials below will be the credential of the user logging in. If it is a success then we allow the user to sign in.

private void firebaseAuthWithGoogle(GoogleSignInAccount account) {  
    AuthCredential credential = GoogleAuthProvider._getCredential_(account.getIdToken(), null);  

    mAuth.signInWithCredential(credential)  
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {  
                @Override  
                public void onComplete(@NonNull Task<AuthResult> task) {  
                    if (task.isSuccessful()) {  
                        // Sign in success, update UI with the signed-in user's information  
                        FirebaseUser user = mAuth.getCurrentUser();  
                        Intent intent = new Intent(getApplicationContext(), MainActivity.class);  
                        startActivity(intent);  

                    } else {  
                        // If sign in fails, display a message to the user.  
                        Toast._makeText_(getApplicationContext(), "Sorry authentication failed ", Toast._LENGTH\_SHORT_).show();  

                    }  
                }  
            });  
}

Instantiate the FirebaseAuth in onCreate()

mAuth = FirebaseAuth.getInstance();

4 | Add What will happen if valid user logs in

On the onStart() lifecycle method add the following code in order to check if the current user is already signed in.

protected void onStart() {  

    super.onStart();  
    FirebaseUser currentUser = mAuth.getCurrentUser();  
    if(currentUser!=null){  
        Intent intent = new Intent(getApplicationContext(),MainActivity.class);  
        startActivity(intent);  
    }  
}

5 | Add a logout button

In my case, I have already had a drawer navigation layout. As such, I made a new id so that I can find the logout id and use it. However, whether or not you use a drawer navigation option to do this, the process will still be the same.

The important part of this code is the logout id

Create a handleLogout method. This can also be rewritten as a onClickListener incase you are using buttons

The following invokes handleLogout when the logout case is chosen

6 | Play with user’s data

Now that a user has logged in, We can find some data about them to make the app more personalised to them. One way we can do this is by creating a toast if they logged back in the app. We can do this by adding the following in the MainActivity’s onCreate

//Google sign  
GoogleSignInAccount signInAccount= GoogleSignIn._getLastSignedInAccount_(this);  
if(signInAccount!=null){  
    Toast.makeText(this, "Welcome back "signInAccount.getDisplayName() , Toast._LENGTH\_SHORT_).show();  
}

7 | Update manifest

Make sure both LoginActivity and MainActivity are in the manifest

8 | Test

Top 10 IT Certifications To Take While You Are At University in 2020

Alfie Torres — Sun, 05 Jul 2020 09:17:04 +0000

Studying university courses are great, but up-skilling ourselves on industry used certifications can add a lot of value to our personal bag of skills once we graduate. Here are 10 certifications you should think about getting while you are still at university.

1 | Google Certified Professional Cloud Architect

Price: AUD 285.88

Career: Cloud Architecture

About: Ranked #1 top paying IT certification for 2019. Cloud computing is amongst one of the most popular technologies in 2019 because of its ability to make work practices more efficient and less costly. Google’s certification allows individuals to work with the Google Cloud Platform to:

Design and plan a cloud solution architecture

Manage and provision the cloud solution infrastructure

Learn More Here

2 | Certified ScrumMaster

Price:

Professional Scrum Master I (Fundamental) — AUD 214.41

Professional Scrum Master II (Advanced) — AUD 357.35

Professional Scrum Master III(Advanced) — AUD 714.71

Career: Project Management

About: Scrum is a methodology that allows a team to self-organize and make changes quickly, in accordance with agile principles. The scrum master manages the process for how information is exchanged. There are three levels

Learn More Here

3 | AWS Certified Solutions Architect — Associate

Price: AUD 214.41

Career: Software Design

About: AWS is certainly becoming an industry standard when it comes to cloud, infrastructure and automation technologies. This is why getting an AWS certificate is almost certainly going to help you later in your career path. By learning at least one AWS certificate you will be introduced to popular terms and techniques specially made in AWS rich ecosystem. One of the best certificates is AWS’ Certified Solutions Architect. This teaches you how to architect and deploy secure and robust applications on AWS technologies

Learn More Here

4| AWS Certified Developer — Associate

Price: AUD 214.41

Career: Software Development

About: In comparison to AWS’ Certified Solutions Architect, this certificate is specially made for developers who want to write code in serverless applications. This helps developers best practices when writing, maintaining and debugging code modules on AWS.

Learn More Here

5 | CEH — Certified Ethical Hacker

Price: AUD 1000+ Price varies depending on your course provider

Career: Cybersecurity

About: master an ethical hacking methodology that can be used in a penetration testing or ethical hacking situation. You walk out the door with ethical hacking skills that are highly in demand, as well as the globally recognised Certified Ethical Hacker certification

Learn More Here

Click Here to be directed to an Australian Course Provider

6 |Offensive Security Certified Professional (OSCP)

Price: AUD 1000 + Price includes Penetration Testing Training with Kali Linux

Career: Cybersecurity (Penetration Testing)

About: For hands-on experience, each student receives access to a virtual penetration testing lab where techniques learned within the course can be practiced The OSCP is among the most respected and sought-after designation within the information security space.

Learn More Here

7 | Project Management Professional

Price:

Member: AUD 578.92

Non-Member: AUD 793.33

Career: Project Management

About: This certification is meant for experienced project managers who want to go the extra mile in up-skilling themselves. This certificate signifies that you speak and understand the global language of project management and connects you to a community of professionals, organisations and experts worldwide.

Learn More Here

8 | Microsoft Exam 70–761

Price: AUD 235.85

Career: Database Administrator

About: This exam is intended for SQL Server database administrators, system engineers, and developers who are seeking to validate their skills and knowledge in writing queries. This would require individuals to learn technologies such as XML, JSON and temporal tables

Learn More Here

9 | ITIL v4 Foundation

Price: AUD 395 Price varies

Career: IT service management

About: Focuses on using the ITIL frameworks to provide the best practices for businesses to more effectively manage there IT services. This includes key concepts from Lean, Agile, DevOps, and why these are important to deliver business value

Learn More Here

10 | CISA: Certified Information Systems Auditor

Price:

Members — AUD 664.69

Non-Members — AUD 850.52

Career: Information Security Auditing

About: This certificate is highly valued by recruiters as it gives you an edge if you want to get in the world of IT auditing. However, this certificate is not something you would be getting in university. since this requires 5 years of work experience (or its equivalents).

Learn More Here