What is WebAssembly and how to create a WebAssembly app?

Written on February 20, 2021

Preamble

The browsers only understand JavaScript, however with rise of stuff that we use on browsers e.g. Games, Virtual Reality, Augumented Reality, JavaScript hasn’t been able to catch up due to its inherent interpreted nature despite its powerful engines like V8.

Suppose you have a cool game or software developed in a low-level programming language e.g. C/C++ or a high-level programming language e.g. Java/C#/Rust/Go. With WebAssembly you can run these apps on a browser. Wihout re-writing them in JavaScript.

Wait, what?

What is WebAssembly?

WebAssembly (abbreviated Wasm) is a binary instruction format for a stack-based virtual machine. Wasm is designed as a portable compilation target for programming languages, enabling deployment on the web for client and server applications.

-https://webassembly.org/

WebAssembly, or wasm, is the most significant new technology to come to the web platform in a decade. Technically speaking, it is a new, low-level, assembly-like language that runs efficiently on the existing web platform and is backward-compatible with its precursor, asm.js. Most people, however, will use the wasm format as a compiler target, translating their applications into web-ready modules that can run in modern web browsers at near-native speeds.

-https://research.mozilla.org/webassembly

W A S M

Check out Milica Mihajlija’s awesome blog to know more.

Blazor

Blazor is an open-source framework from Microsoft to develop Component based UIs using language you already know and love, C#. I’ll be blunt and say:

It’s Microsoft’s response to Angular and React.

Because why not?

But it’s not why we’re talking about Blazor here. The reason is, one of the hosting models of Blazor is WebAssembly.

Blazor’s home page says:

Blazor can run your client-side C# code directly in the browser, using WebAssembly. Because it’s real .NET running on WebAssembly, you can re-use code and libraries from server-side parts of your application. -https://dotnet.microsoft.com/apps/aspnet/web-apps/blazor

Let’s Code a Webassemby App

Yeah, enough with the theory already. Let’s get down to the code.

Create a new Project

Open Visual Studio and create a new Blazor WebAssembly App
[Optional] Check Progressive Web Application. More on Progressive Web App in a later article.
Let’s have a look at the Code generated by the template:

The generated app uses WebAssebmlyHostBuilder, similar to WebHostBuilder in ASP.NET Core.

Run this shell application. A simple application with a Nav Bar saying Hello, world!
If you’ve checked the Progressive Web Application checkbox, you’ll see the standard Install icon, click on it.

The template had basic configuration setup for us to make this an installable PWA (Progressive Web App).
Add a new Blazor Component named Hash which will calculate SHA256 hash of a given input.

Copy the code into the Component. This will create an text input - where we’ll input our plain text, a button - on click of which we’ll calculate the hash, and label - where the hash would be shown.

  @page "/hash"
  <h1>Hash</h1>
  <p>Get SHA265 Hash via WebAssembly</p>
  <EditForm Model="@hashInput" OnSubmit="@CalculateHash">
      <div class="form-group">
          <InputText @bind-Value="hashInput" class="form-control" id="textInput" aria-describedby="emailHelp" placeholder="Enter text to calculate Hash" />
          <small id="hashHelp" class="form-text text-muted">@hashOutput</small>
      </div>
      <button type="submit" class="btn btn-primary">Submit</button>
  </EditForm>

  @code {
      private string hashInput = string.Empty;
      private string hashOutput;
      void CalculateHash()
      {
          hashOutput = GetSha256Hash(hashInput);
      }
      private static string GetSha256Hash(string plainText)
      {
          // Create a SHA256 hash from string   
          using var sha256Hash = System.Security.Cryptography.SHA256.Create();
          // Computing Hash - returns here byte array
          byte[] bytes = sha256Hash.ComputeHash(System.Text.Encoding.UTF8.GetBytes(plainText));

          // now convert byte array to a string   
          var stringbuilder = new System.Text.StringBuilder();
          for (int i = 0; i < bytes.Length; i++)
          {
              stringbuilder.Append(bytes[i].ToString("x2"));
          }
          return stringbuilder.ToString();
      }
  }

This is not using any trick to call JavaScript/interop to calculate hash. This is a real C# code running in Browser, powered by WebAssembly.

Run this application and enter a text in the input and press Submit!

If the code is running in the Browser, where are all the `DLLs`?

Behind the scene, Blazor generates a blazor.boot.json to determine which DLLs need to downloaded and then stores them into browser’s Cache. You can verify it by going to Dev Tools..
Here’s the full contents of the blazor.boot.json

{
  "cacheBootResources": true,
  "config": [ ],
  "debugBuild": true,
  "entryAssembly": "RunningWebAssemblyInBrowser",
  "icuDataMode": 0,
  "linkerEnabled": false,
  "resources": {
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      "System.Security.Claims.dll": "sha256-IrIAmM1U9wM7\/57wAYAiIxzYKVZQ4ZRFQkeX8EjxN20=",
      "System.Security.Cryptography.Algorithms.dll": "sha256-OOc3FJpuiC2EAeXLEH9jCpky7rNmCf2y4eI1hvIdGcc=",
      "System.Security.Cryptography.Cng.dll": "sha256-IDva\/1eexgejbrb2pd4tGvmb8RpRLFtPQdKOWIfg52M=",
      "System.Security.Cryptography.Csp.dll": "sha256-I0sStjWvyER\/g1UAcQVHxlGP8WYPnn44nZyV2H6QLAQ=",
      "System.Security.Cryptography.Encoding.dll": "sha256-+30slIRCLurv028FqLXHLM7zGwRhSzKPgkz4qkOXGU0=",
      "System.Security.Cryptography.OpenSsl.dll": "sha256-6+guWgFku742cEMRLSjakHewNpKUChOBogCJr1SQYlE=",
      "System.Security.Cryptography.Primitives.dll": "sha256-eufChtizf\/fju66cjq3xgVKCY0\/yC+vnIyxSRyCSZJ0=",
      "System.Security.Cryptography.X509Certificates.dll": "sha256-P6zBjvyTDbh1nsfDJvlGxhrbV4MOm9\/tqlS1wKnICLE=",
      "System.Security.Principal.Windows.dll": "sha256-qG\/e0zJYRbHyAuuSDIAVVT4zDYzK6dOelzJY9EHnEFQ=",
      "System.Security.Principal.dll": "sha256-rgrGJ7Jy1iC3hTuJ0NxjQI9arq++FcNDNCtPfBgm38g=",
      "System.Security.SecureString.dll": "sha256-u8wie2itS0QgYE8Z5V1cYURbwzekLHjH3ULeWLa7RQo=",
      "System.Security.dll": "sha256-+bMm1weerGqqoFU1O3tqnk6afz1pwdDWoQ3gh2F7NZw=",
      "System.ServiceModel.Web.dll": "sha256-CBVh+lyviXYUGahDypluY9Z0bxw5bsazhaZ67SZ\/m8I=",
      "System.ServiceProcess.dll": "sha256-ObrNFHgy2AFOupUAPhqdZiauSIc+HLthrcfwhMZ6mPg=",
      "System.Text.Encoding.CodePages.dll": "sha256-vFAYLW61g74CrF5JDtFryR3VDo3C601Id2xATX\/OG2g=",
      "System.Text.Encoding.Extensions.dll": "sha256-7DVVBgKA1h4kVYSWFKgA0ehwJw1Ch0zjTYqhLozwTO4=",
      "System.Text.Encoding.dll": "sha256-g0djnHxQwr\/8z3gt5036ltfeOCiukDB74ZtkCr9k3HE=",
      "System.Text.Encodings.Web.dll": "sha256-5PrzT8OUL8av4T0GE9Yv\/JADt9mH9PL55AIUfCpXbF4=",
      "System.Text.Json.dll": "sha256-I7fC8A1gTkp5IHCSLdYv8lBxVBcvgv\/qPynNjMGxwc8=",
      "System.Text.RegularExpressions.dll": "sha256-djYleXTr7Uamm+EzSkA9e3cVrb6UGavE8GFOTarGKBk=",
      "System.Threading.Channels.dll": "sha256-II1Z1hlKcL98K5KsaUrfQT2KnkBvubTk8yL5vM+XO90=",
      "System.Threading.Overlapped.dll": "sha256-aek5eBYcHGUBoi4vxLqi4fjLuW8TXNNwfTlDk2vJ5dQ=",
      "System.Threading.Tasks.Dataflow.dll": "sha256-o4ntQJCPqewDh2YEkevZYtNL+aasZjjtk1wTpJpVGNU=",
      "System.Threading.Tasks.Extensions.dll": "sha256-XlTRz5WSLk9gN2uAfxD1EYJNvRrh0+6DzhkS8jDi+es=",
      "System.Threading.Tasks.Parallel.dll": "sha256-h0\/nVmiI7PVB2Tos17D\/74og+OmDu+JsCoXSHmr7O88=",
      "System.Threading.Tasks.dll": "sha256-FED4Gw+SuY8a75weI+V\/7NfCigOiBTM0GtX8MmeuaME=",
      "System.Threading.Thread.dll": "sha256-IwWzI0pRnUdmKGmAgI+p\/PrxA1wHcTK32p7K2SFKdak=",
      "System.Threading.ThreadPool.dll": "sha256-\/HMFOKLFhdin5KsvRIp7lZNSacXK5qeOEfV8V2UM+S0=",
      "System.Threading.Timer.dll": "sha256-3b\/gTvvFvw\/Lz4Sb5fCmUAoSvv9i4JPMdTwUxQX1bcU=",
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      "System.dll": "sha256-OOEghImLm2N7m3SVYkuSKqMFVoBDVnjZOMxQaiMVYEk=",
      "WindowsBase.dll": "sha256-HrFb5FWpXAvEO2lO5gi2rJPn9w4t71w3a0xEnrZdRiA=",
      "mscorlib.dll": "sha256-OoIy6q8Z4O5iSevqVXHfYC14mo\/kaxz74ydYX19CiAA=",
      "netstandard.dll": "sha256-FbW0xcZkySFb6B8yBpUE8XmaiMacDVdXdN9GeDH6xu4=",
      "System.Private.CoreLib.dll": "sha256-AQbVm+Z+NByScjRZWDWQnNUk5PBVgwCSWPLQN4YxxZs=",
      "RunningWebAssemblyInBrowser.dll": "sha256-ILu1dI7WEfCS42warORX3FWqhk3xQ6bIHHkKOl\/o41c="
    },
    "lazyAssembly": null,
    "pdb": {
      "RunningWebAssemblyInBrowser.pdb": "sha256-vfONhy33a3TutK1D+8w9Z0tPpet3tdhtpnTiLH8m7RA="
    },
    "runtime": {
      "dotnet.timezones.blat": "sha256-rFG55cwkAnfHzxmxwBL2tTwfj8X8cjcSEAlco4bc1eo=",
      "dotnet.wasm": "sha256-+NqBIg7FTMeA2q0mxzbehfuE2WPrnq53yqLsu47afbY=",
      "icudt.dat": "sha256-m7NyeXyxM+CL04jr9ui1Z6pVfMWwhHusuz5qNZWpAwA=",
      "icudt_CJK.dat": "sha256-91bygK5voY9lG5wxP0\/uj7uH5xljF9u7iWnSldT1Z\/g=",
      "icudt_EFIGS.dat": "sha256-DPfeOLph83b2rdx40cKxIBcfVZ8abTWAFq+RBQMxGw0=",
      "icudt_no_CJK.dat": "sha256-oM7Z6aN9jHmCYqDMCBwFgFAYAGgsH1jLC\/Z6DYeVmmk=",
      "dotnet.5.0.3.js": "sha256-sf1arnHfzSTa9MZNpdWBkQTecBMQBQRynOZ8+\/iLMUg="
    },
    "satelliteResources": null
  }
}

These assemblies are stored as follows:

Notice the WASM file dotnet.wasm. This is where the magic happens. It’s the CLR as a WASM module which runs our.NET Code on top of it.

Can I use Webassebly today?

Check out this interactive usage chart from https://caniuse.com.

Data on support for the wasm feature across the major browsers from caniuse.com

Live demo

Go to https://blog.satishyadav.com/RunningWebAssemblyInBrowser/hash a see the WASM in action. Go to Dev Tools are see for yourself.

What’s next?

https://webassembly.org/
https://dotnet.microsoft.com/learn/aspnet/blazor-tutorial/intro

Originally posted at: https://blog.satishyadav.com/What-is-Webassembly-and-how-do-I-create-a-Webassembly-application