Object-Oriented Software Development

Thursday, October 19, 2023

Fido2.NetFramework

Just published a working code of a port of the fido2-net-lib library. The library is great, it works but there's a drawback - it targets .NET 6 (or higher) which means that creating Fido2/Webauthn compatible website in .NET 4.X using the library is impossible.

My ported library, called the Fido2.NetFramework is supposed to fill the gap. I downgraded the code so that it compiles using the old C# 4.8 compiler, I replaced all external references that targets APIs/libraries/frameworks that are not available in .NET 4.8. For example, the Nsec.Cryptography used in the source library, was replaced with BouncyCastle.

The code contains a working demo.

There's still some work to do, in particular, validate the port by porting unit tests and creating extra compatibility tests.

Monday, August 28, 2023

Rust/WebAssembly vs Javascript performance on Mandelbrot animation rendering

The pending question Is Rust/Wasm fast enough to even bother when comparing to Javascript? has now yet another biased benchmark. I've decided to take one of my Julia/Mandelbrot demos, benchmark it "as-is" and then, port to Rust and compare.

The HTML/Javascript source is short enough to post it here, the original demo code has some additional features (zooming) which are not present here

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Mandelbrot</title>
	<script type="text/javascript">
	        
        var cx = 0, cy = 0, kat1 = 0, kat2 = 1;           
        
        var WJulia = 1024;
        var HJulia = 1024;
        var frame  = 0;
        var startDate;
    
        var contextJulia;
        var contextSmall;
        var pixJulia;
        var imgdJulia;

        var iStart;
        var iEnd;
        var jStart;
        var jEnd;

        var iDelta;
        var jDelta;
        
        function setInitialScale()
        {
            iStart = -1.92;
            iEnd   = 1.92;
            jStart = -1.92;
            jEnd   = 1.92;

            iDelta = (iEnd-iStart)/1024;
            jDelta = (jEnd-jStart)/1024;

            startDate = new Date();
        }

        function SetupMandel()
        {	 
            var elemJulia = document.getElementById('JuliaCanvas');
            if (elemJulia && elemJulia.getContext)
            {
                contextJulia = elemJulia.getContext('2d');
                if (contextJulia)
                {
                    imgdJulia = contextJulia.createImageData(WJulia, HJulia);         
                    pixJulia = imgdJulia.data;
                }
            }

            setInitialScale();
          
            /* start */
            requestAnimationFrame( LoopMandel );
        }
                         
        function LoopMandel()
        {	 
            kat1 += 0.0021;
            kat2 += 0.0039;
            cx = .681 * Math.sin(kat1);
            cy = .626 * Math.cos(kat2);

            frame++;
            document.getElementById('fps').innerHTML = `FPS: ${1000*frame/(new Date()-startDate)}`;
			
            RysujMandel();	 
            
            requestAnimationFrame( LoopMandel );
        }
         
         
        /* tworzenie bitowego obrazu */
        function RysujMandel()
        {
            /* obliczenia */
            var wi, wj;
            var i, j;

            var iterations = 255;

            var px = 0;
            for (i = iStart, wi = 0; wi < 1024; i += iDelta, wi++)
            {
                var py = 0;
                for (j = jStart, wj = 0; wj < 1024; j += jDelta, wj++)
                {
                    var c = 0;

                    var x = cx;
                    var y = cy;
         
                    while (((x*x + y*y) < 4) && (c < iterations))
                    {
                        [x, y] = [x * x - y * y + i, 2 * x * y + j];
                        c++;
                    }

                    SetPixelColor( pixJulia, (py * WJulia + px) << 2, 255, 255-c, 255-c, 255 - (c/2) );
                                        
                    py++;
                }
         
                px++;
            }
            
            /* kopiowanie bitowego obrazu do context/canvas */
            contextJulia.putImageData(imgdJulia, 0, 0);		 
        }
         
        function SetPixelColor(pix,offs, a, r, g, b)
        {            
            pix[offs++] = r;
            pix[offs++] = g;
            pix[offs++] = b;
            pix[offs] = a;
        }
         
        window.addEventListener( 'load', SetupMandel );
        
        </script>    
</head>
<body>
    <span id="fps" style='display:block'></span>
    <canvas id="JuliaCanvas" width="1024" height="1024">
	</canvas>
</body>
</html>

When run on my machine and the Edge Browser, it makes ~10-11 frames per second. Not bad assuming 1024x1024 image and 255 iterations.

Same code ported to Rust and compiled with wasm-pack

// https://rustwasm.github.io/wasm-bindgen/examples/dom.html
use wasm_bindgen::prelude::*;
use wasm_bindgen::Clamped;
use web_sys::{CanvasRenderingContext2d, ImageData};

/* tworzenie bitowego obrazu */
#[wasm_bindgen]
pub fn mandel(
    ctx: &CanvasRenderingContext2d, 
    width: u32, height: u32,
    cx: f64, cy: f64) -> Result<(), JsValue> {

    let i_start = -1.92;
    let i_end   = 1.92;
    let j_start = -1.92;
    let j_end   = 1.92;

    let i_delta = (i_end-i_start)/width as f64;
    let j_delta = (j_end-j_start)/height as f64;

    /* obliczenia */    
    let iterations = 255;

    let mut pix_julia = Vec::with_capacity( usize::try_from(width * height).unwrap() );

    let mut j = j_start;
    for _wj in 0..height {

        let mut i = i_start;   
        for _wi in 0..width {
        
            let mut c: u8 = 0;

            let mut x = cx;
            let mut y = cy;
    
            while ( (x*x + y*y) < 4.0) && (c < iterations)
            {
                let _tx = x;
                x = x * x - y * y + i;
                y = 2.0 * _tx * y + j;
                c += 1;
            }

            pix_julia.push( 255-c );
            pix_julia.push( 255-c );
            pix_julia.push( 255-(c/2) );
            pix_julia.push( 255 );
            
            i  += i_delta;
        }
    
        j  += j_delta;
    }    

    let data = ImageData::new_with_u8_clamped_array_and_sh(Clamped(&pix_julia), width, height)?;
    ctx.put_image_data(&data, 0.0, 0.0)
}

The cargo.tomlwas

[package]
name = "hello-wasm"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[lib]
crate-type = ["cdylib"]

[dependencies]
wasm-bindgen = "0.2.87"

[dependencies.web-sys]
version = "0.3.4"
features = [
  'Document',
  'Element',
  'HtmlElement',
  'Node',
  'Window',
  'ImageData',
  'CanvasRenderingContext2d'  
]

[profile.release]
opt-level = 3
lto = true

[package.metadata.wasm-pack.profile.release]
wasm-opt = ["-O4", "--enable-mutable-globals"]

and the HTML

<!doctype html>
<html lang="en-US">
  <head>
    <meta charset="utf-8" />
    <title>Mandelbrot</title>
  </head>
  <body>
    <script type="module">
        import init, { mandel } from "./pkg/hello_wasm.js";
        
        (async function() {
		   await init();
           SetupMandel();    
        })();
	  
        var cx = 0, cy = 0, kat1 = 0, kat2 = 1;      
        var WJulia = 1024;
        var HJulia = 1024;        
        var frame  = 0;
		var startDate;
        
        var contextJulia;
        var contextSmall;
        var pixJulia;
        var imgdJulia;

        function SetupMandel()
        {	 
            var elemJulia = document.getElementById('JuliaCanvas');
            if (elemJulia && elemJulia.getContext)
            {
                contextJulia = elemJulia.getContext('2d');
                if (contextJulia)
                {
                    imgdJulia = contextJulia.createImageData(WJulia, HJulia);         
                    pixJulia = imgdJulia.data;
                }
            }
          
		    startDate = new Date();
			
            /* start */
            requestAnimationFrame( LoopMandel );
        }
                         
        function LoopMandel()
        {	 
            kat1 += 0.0021;
            kat2 += 0.0039;
            cx = .681 * Math.sin(kat1);
            cy = .626 * Math.cos(kat2);

            frame++;
            document.getElementById('fps').innerHTML = `FPS: ${1000*frame/(new Date()-startDate)}`;
			
            mandel(contextJulia, WJulia, HJulia, cx, cy);	 
            
            requestAnimationFrame( LoopMandel );
        }	  
    </script>
    <span id="fps" style='display: block'></span>	
    <canvas id="JuliaCanvas" width="1024" height="1024">
	</canvas>	
  </body>
</html>

And the result? Similar, it also makes 10-11 frames per second. Additional tests (different resolution and number of iterations) and possible optimizations can be applied here.

Thursday, July 20, 2023

Background music for coding - playlist

It's only an hour or so at the moment but nonetheless - this is a collection of music I listen while coding. I hope to expand the list in future.

Link to the Spotify playlist

Rust binary tree with iterator

For few days I scratch my head over Rust. Never tried it before, not going to be a Rust developer but I feel I'm missing new challenges and this looks like one.

While the official docs are rather concise, there are good books, the Programming Rust: Fast, Safe Systems Development 2nd Edition by Blandy/Orendorff/Tindall is really good and it feels like it's written by folks who really like to help the reader. A lot of good examples and the background I missed in the official docs.

Anyway, my first successfull attempt at something not-that-obvious, a binary tree with an iterator. Doing this in C# would be a breeze, Rust had some surprises around every corner. I am lucky to have Łukasz who answers my questions, corrects my mistakes and gives critical hints on specific problems. Thanks!

The code below. For anyone wondering how much time did it take, starting from zero knowledge of the language to this point - few hours reading the book and then like 5-6 hours to get this result.

use std::fmt::Debug;

struct TreeNode<'a, T: 'a> {
    val  : &'a T,
    left : Option<Box<TreeNode<'a, T>>>,
    right: Option<Box<TreeNode<'a, T>>>
}

impl<'a, T> TreeNode<'a, T> {
    fn new(
        val: &'a T, 
        left: Option<Box<TreeNode<'a, T>>>, 
        right: Option<Box<TreeNode<'a, T>>>) -> Self {
        Self { val, left, right }
    }
}

/* C#'s IEnumerable on TreeNode - returns an iterator/enumerator */
impl<'a, T> IntoIterator for &'a TreeNode<'a, T> {
    type Item = &'a TreeNode<'a, T>;
    type IntoIter = TreeNodeIterator<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        TreeNodeIterator::init(&self)    
    }
}

/* C#'s IEnumerator */
struct TreeNodeIterator<'a, T: 'a> {
    stack: Vec<&'a TreeNode<'a, T>>
}

impl<'a, T> TreeNodeIterator<'a, T> {
    fn init(node: &'a TreeNode<'a, T>) -> Self {
        Self { stack: vec![node] }
    }
}

impl<'a, T> Iterator for TreeNodeIterator<'a, T> {
    type Item = &'a TreeNode<'a, T>;

    fn next(&mut self) -> Option<Self::Item> {
        
        if self.stack.len() > 0 {

            let curr = self.stack.pop()?;

            /* one way to tackle the child noe */
            if let Some(right) = &curr.right {
                self.stack.push( right.as_ref() );    
            }
            /* another way of doing the same */
            if curr.left.is_some() {
                self.stack.push(curr.left.as_ref().unwrap());
            }

            return Some(curr);
        }

        None
    }
}

/* auxiliary code to be able to test the enumerator */
struct TreeNodeUtility;
impl TreeNodeUtility  {
    fn do_work<'a, T> ( node: &'a TreeNode<'a, T> ) where &'a T: Debug {
        for n in node {
            println!("{:?}", n.val );
        }
    }
}

fn main() {

    let s1 = String::from("1");
    let s2 = String::from("2");
    let s3 = String::from("3");

    let root = Some( TreeNode::<String>::new(
        &s1, 
        
            Some(Box::new(TreeNode::<String>::new(
                &s2,
                None,
                None
            ))), 
        
            Some(Box::new(TreeNode::<String>::new(
                &s3,
                None,
                None
            )))
    ) ) ;

    if root.is_some() {
        let rootc = root.unwrap();
        TreeNodeUtility::do_work( &rootc );
        TreeNodeUtility::do_work( &rootc );
    }
}

After consulting the clippy and trying to improve the code further, I came up with following changes:

changed the type of the iterator's item to &T from &TreeNode<T>
changed the TreeNodeIterator to a tupled struct (a struct with just a single field that doesn't even need a name)
dropped the init method of the iterator struct
changed the "if non empty stack - pop" code into a single liner
changed the "if option is some - do" code into a single liner

use std::fmt::Debug;

struct TreeNode<'a, T: 'a> {
    val  : &'a T,
    left : Option<Box<TreeNode<'a, T>>>,
    right: Option<Box<TreeNode<'a, T>>>
}

impl<'a, T> TreeNode<'a, T> {
    fn new(
        val: &'a T, 
        left: Option<Box<TreeNode<'a, T>>>, 
        right: Option<Box<TreeNode<'a, T>>>) -> Self {
        Self { val, left, right }
    }
}

/* C#'s IEnumerable on TreeNode - returns an iterator/enumerator */
impl<'a, T> IntoIterator for &'a TreeNode<'a, T> {
    type Item = &'a T;
    type IntoIter = TreeNodeIterator<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        TreeNodeIterator(vec![self])
    }
}

/* C#'s IEnumerator */
struct TreeNodeIterator<'a, T: 'a>(Vec<&'a TreeNode<'a, T>>);

impl<'a, T> Iterator for TreeNodeIterator<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        
        if let Some(curr) = self.0.pop() {

            /* one way to tackle the child node */
            if let Some(right) = &curr.right {
                self.0.push( right.as_ref() );    
            }
            /* another way of doing the same */
            if curr.left.is_some() {
                self.0.push(curr.left.as_ref()?);
            }

            return Some(curr.val);
        }

        None
    }
}

/* auxiliary code to be able to test the enumerator */
struct TreeNodeUtility;
impl TreeNodeUtility  {
    fn do_work<'a, T> ( node: &'a TreeNode<'a, T> ) where &'a T: Debug {
        for n in node {
            println!("{:?}", n );
        }
    }
}

fn main() {

    let s1 = String::from("1");
    let s2 = String::from("2");
    let s3 = String::from("3");

    let root = Some( TreeNode::<String>::new(
        &s1, 
        
            Some(Box::new(TreeNode::<String>::new(
                &s2,
                None,
                None
            ))), 
        
            Some(Box::new(TreeNode::<String>::new(
                &s3,
                None,
                None
            )))
    ) ) ;

    if let Some( rootc ) = root  {
        TreeNodeUtility::do_work( &rootc );
        TreeNodeUtility::do_work( &rootc );
    }
}

Wednesday, July 5, 2023

Notes to myself-from-the-future

The more code I write over the years, the more additional non-code information I tend to leave to myself from the future. The additional information, put in inline comments, comments in signatures, external markdown files, is intended to be targeted exactly to me from the future.

It usually starts when I look for something. Like for example - an ASP.NET application, something that looks like it works upon each request but there's no visible sign of a public http module registered in web.config. Since that's odd, I go to the global.asax and try to find a module registered programmatically (rather than declaratively). And then I remember - "wait a minute, I remember myself searching for the same information some time ago".

This is where I make a conclusion - if I search for something and I remember searching for it at least once before, I try to think like myself-from-the-future. Where would I search for this information next time? Well, I am in global.asax now, so there's a high probability that the future-me will also come to the global.asax.

I decide to use the global.asax then and I leave a note to myself-from-the-future - If you search for [....], this information is in [....]"

Looking for various information, I then am grateful to myself-from-the-past - I often just stumble upon these "If you search for ... this information is in ...." which means that at some point in the past I tried to think like the present-me and my prediction at that time was correct. And often, I have no memory of writing these notes, I just see them in the code, I belive I wrote them at some point, I can even check the source control and find the exact date. But I just don't remember writing it at all.

All these notes I send to myself, from the past to the future, are nice and useful and somehow let me feel like the past-me and the present-me is for sure the very same me, despite the time that passes. Things change but the way I think about myself is solid.

Today was the day I tried to find something in the code. The code is an old desktop utility app that registers some HTTP listeners at start. There are multiple places listeners can be added, in the Main function, in the main form's constructor, in the main form's load event etc. At first I've assumed the myself-from-the-past would possibly leave a note to the present me somewhere.

I've checked few obvious places. Is there a global markdown file for such notes? Nope. Is there a comment in the main *.cs file? Nope. Is there a comment in the form constructor? Nope. Is there a comment above the form class definition? Yes, there is but the summary section doesn't seem to contain any information about registration of HTTP listeners.

So I've spent like 3 minutes to track down the registration. Found a method that does it. Found a reference to the method. Tracked the reference, until I've ended up in form's Load method.

Just leave a note to myself-from-the-future - I thought. Next time I will try to search for it, I will probably go to main form class and a comment above it. The place that already contains the summary section but lacks the information about listener registrations.

So I go there, go to the very bottom of the summary section, since it spans a dozen of lines I carefully navigate to its ending to put a new line with the new information about the registration of HTTP listeners.

And guess what. The summary section ends, the remarks section starts there, a section I obviously missed few minutes eariler (I just haven't noticed it's there, I thought the whole green block of comment lines was the summary section)!

And the only line in the remarks section is: If you search for registration of HTTP listeners, it's in frmMain_Load

I swear it was not there few minutes ago ... But the fact that I've spent few minutes doing something I thought I hadn't done before but ultimately looks like I had, is kind of reassuring.

Thursday, June 1, 2023

C# Puzzle No.25 (intermediate)

Let's have list of references to objects of a custom type that have a state. Let's loop through the list and alter the internal state of each object on the list.

Will the change of the internal state be preserved after the loop ends?

A first answer should of course be yes.

Take a look at this then:

var elements =
    Enumerable.Range(0, 10)
        .Select( i => new Foo() { Bar = i });

foreach ( var e in elements )
{
    // yields 0,1,2,3,4,5,6,7,8,9 which is correct
    Console.WriteLine( e.Bar );
}

foreach ( var e in elements )
{
    e.Bar += 10;

    // yields 10, 11, ...., 19
    Console.WriteLine( e.Bar ); 
}

foreach ( var e in elements )
{
    // yields 0,1,2,3,4,5,6,7,8,9 which doesn't seem correct 
    // (original values restored)!
    Console.WriteLine( e.Bar );
    
    // expected: 10, 11, ..., 19!
}


public class Foo
{
    public int Bar { get; set; }
}

First we create a list of elements. Then we loop it to check if it's correct. Then we loop it to alter the internal state of objects.

Then we loop again and, oddly, it seems like original values are restored.

Not that obvious to spot what's wrong here, a similar issue was caught on production code. The goal is to find a simplest fix.

Monday, May 22, 2023

Unable to generate an explicit migration because the following explicit migrations are pending

There's an old SO question about this, the dreadful Unable to generate an explicit migration because the following explicit migrations are pending.

Not sure if SO answers cover this scenario but this is issue can occur in following setup:

you have a parameterless DbContext's constructor and also a connection-string parameter constructor
you generate migrations by adding the -ConnectionString and -ConnectionProviderName parameters of add-migration
there's no default connection string in the configuration file

The first migration is created correctly but the second one cannot find the migration already applied to the database. Seems it's a bug.

A simple solution is to add a default connection string to the configuration file and drop -ConnectionString and -ConnecitonProviderName from the invocation of add-migration. This picks the default connection string and further checks all new migration against the default database. Still, the other constructor can be used in production code.

public class FooDbContext : DbContext
{
  public FooDbContext() { } // this constructor is used by migration generator
  
  public FooDbContext( string connectionString ) : base( connectionString ) { } // you could be using this from your code
}