Aspnetcore: Error when trying get data from real server

[Gyciauskas]

Hello,

I have issue with this code from demo:

@page "/fetchdata"
@inject HttpClient Http

@if (door == null)
{
    <p><em>Loading...</em></p>
}
else
{
    <table class='table'>
        <thead>
            <tr>
                <th>Id</th>
                <th>Name</th>
                <th>Version</th>
            </tr>
        </thead>
        <tbody>
            <tr>
                <td>@door.id</td>
                <td>@door.name</td>
                <td>@door.version</td>
            </tr>
        </tbody>
    </table>
}

@functions {
    Door door;

    protected override async Task OnInitAsync()
    {
        door = await Http.GetJsonAsync<Door>("http://localhost:58009/api/locations/1/doors/2");
    }

    class Door
    {
        public int id { get; set; }
        public int? locationId { get; set; }
        public string name { get; set; }
        public int strikeTime { get; set; }
        public int extendedAccessTime { get; set; }
        public int heldOpenTime { get; set; }
        public string version { get; set; }
    }
}

I'm getting error in browser console window:

SEC7120: Origin http://localhost:5375 not found in Access-Control-Allow-Origin header.

WASM: [System.Net.Http.HttpRequestException] TypeError: Failed to fetch

4 WASM: --- End of stack trace from previous location where exception was thrown ---

If I just simply request if in browser => "http://localhost:58009/api/locations/1/doors/2", I get this json response:
{
"id":2,
"locationId":1,
"name":"216office",
"strikeTime":3,
"extendedAccessTime":6,
"heldOpenTime":10,
"version":"AAAAAAAAKMw="
}

It is possible that need setup header content type to "application/json"?

[floreseken]

It's a CORS config problem

Add this to your startup.cs:

 public void ConfigureServices(IServiceCollection services)
        {

            services.AddCors(options =>
            {
                options.AddPolicy("CorsPolicy",
                    builder => builder.AllowAnyOrigin()
                    .AllowAnyMethod()
                    .AllowAnyHeader()
                    .AllowCredentials());
            });
...

And

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {

            app.UseCors("CorsPolicy");

On the server side

[Gyciauskas]

Ok, thanks!

But is Blazor app, service can't find such extension method...

Error CS1061 'IServiceCollection' does not contain a definition for 'AddCors' and no extension method 'AddCors' accepting a first argument of type 'IServiceCollection' could be found

using Microsoft.AspNetCore.Blazor.Browser.Rendering;
using Microsoft.AspNetCore.Blazor.Browser.Services;

namespace BlazerTesting
{
    class Program
    {
        static void Main(string[] args)
        {
            var serviceProvider = new BrowserServiceProvider(configure =>
            {
                configure.AddCors(options =>
                {
                    options.AddPolicy("CorsPolicy",
                        builder => builder.AllowAnyOrigin()
                        .AllowAnyMethod()
                        .AllowAnyHeader()
                        .AllowCredentials());
                });
            });

            new BrowserRenderer(serviceProvider).AddComponent<App>("app");
        }
    }
}

So I need this class: CorsMiddlewareExtensions. Which is in Microsoft.AspNetCore.Builder. Trying seach and add via nuget manager, but no success

[liamehenderson]

You need Microsoft.AspNetCore.Cors

https://www.nuget.org/packages/Microsoft.AspNetCore.Cors/

[floreseken]

The problem is server side.
It just surfaces as a client problem...

[danroth27]

@Gyciauskas To enable CORS you need to update the server project (not the client Blazor project). See https://docs.microsoft.com/en-us/aspnet/core/security/cors for details on how to enable CORS in ASP.NET Core.

[Gyciauskas]

Yes, it finally working! Thank you guys! Now the fun part begins

[danroth27]

🎉 🎆 :tada: :smile:

[Pat28]

@Gyciauskas how did you solve the issue?
I am struggling with the same thing, did the stuff in Blazor to AddCors() and AddPolicy etc...
But were to tell to use that policy?
Or is it still a server side issue?
I am using IISExpress from Visual Studio and even that won't let me do a request to any website/page.

[tusharparik]

Same Issue with me post hosting it on IIS the data in table is not fetched and Console says

blazor.webassembly.js:1 GET http://...:99/api/Employee/Index 500 (Internal Server Error)

blazor.webassembly.js:1 WASM: at BlazorAppHosted.Client.Pages.FetchEmployee.OnInitAsync () <0x1c99308 + 0x000d0> in :0

[jbarrineau06]

I'm having the same issue, but I can't call UseCors() in the Startup.Configure method because it takes an IBlazorApplicationBuilderand not an IApplicationBuilder.

[Suchiman]

@jbarrineau06 as mentioned previously, CORS need to be enabled on the server side, not in blazor (CORS is about security so the server must permit the browser to call it)

[jbarrineau06]

@Suchiman I'm using the Blazor project template, not the Blazor (ASP.NET Core hosted) project template, how would I do this there where I don't have the separate Client and Server projects?

[Suchiman]

@jbarrineau06 who is providing the Service you're trying to call? The provider of the service must enable CORS

[jbarrineau06]

@Suchiman This is just a localhost project

[Suchiman]

@jbarrineau06 that localhost project needs to enable CORS
Http.GetAsync("http://localhost:12345")
this-----------------------^^^^^^^^^^
project needs to enable CORS

[wcolorless]

Is it not possible to include Cors in an application template without a server? Then he is not so interesting. This is a big problem.