Configuration for Blazor WebAssembly

[danroth27]

We provide the config abstraction in the Blazor WebAssembly host, but we don't currently populate it with anything. We should consider what sort of out of the box support we want for configuration in Blazor WebAssembly apps.

[MarkFl12]

I have my WebAssembly project hosted in an ASP.NET core site that's running in docker. I'd like to be able to pass environment variables to the docker container and have them affect the configuration of the WebAssembly on the client.

[pranavkm]

// Blazor.Build
<!-- Do not publish the Development.json -->
<ItemGroup>
    <Content Update="wwwroot/appsettings.Development.json" CopyToPublishDirectory="Never" />
</ItemGroup>

Blazor.Boot.json will have an additional section that includes all available appsettings.* file. This helps avoid 404s

// boot.json
{
    "config": [
        "appSettings.Development.json",
        "appSettings.json"
    ]
}

// We have a middleware that adds a header for requests to blazor.boot.json

// Middleware - DevServer + Hosted template
if (app.IsDevelopment())
{
    app.Use(async (context, response) =>
    {
       response.Headers.Add("ComponentsWebAssemblyEnv", "Development"); 
    });
}

// Blazor.WebAssembly.ts

const response = await fetch('blazor.boot.json');
// Make it visible to user code?
const env = response.headers["ComponentsWebAssemblyEnv"] ?? 'Production';

if (boot.config) {
    // boot manifest contains filtered list
    boot.config.forEach(fetch);
    
    
    // boot manifest contains all files, but we filter on the client
    if (boot.config.contains("appsettings.json"))
        fetch('appsettings.json');
    
    if (env && boot.config.contains(`appsettings.${env}.json`)) {
        fetch(`appsettings.${env}.json`);
    
}

Open questions:

• Do we expose the environment via IWebAssemblyHost i.e. IWebAssemblyHost.IsDevelopment?

[knight1219]

I created this package because I needed access to the environment in a ASP.Net Core hosted situation. In a CDN/plain file hosted situation I'm not sure how you could get the client to understand the variables.