如何使用“no-cors”将 JavaScript HTTP post 请求代码更改为 C#？

Question

I am trying to do the same thing that is done in the JavaScript code but in C#. The end result would be that I want to automate this task from a C# code where I will create these files manually. This code is being used for the web page in order to achieve its goal:

The First function is placing the file in a buffer a place.

        function FileIOU(file: File, backendUrl: string, dispatch: any) {
            return new Promise((resolve, reject) => {
                const reader = new FileReader();
                reader.onerror = reject;
                reader.onload = async () => {
                    await fetch(`${ backendUrl}/ www.FileIOU?filename =${file.name}`, {
                        method: 'POST',
                        body: reader.result,
                        mode: 'no-cors',
                    }).then(resolve).catch (err => {
                        console.log('FileIOU', err);
                        dispatch(consoleOutputAction('Failed to send file: ' + file.name, 'error'));
                        reject();
                    });
                };
         reader.readAsArrayBuffer(file);
        

The Second function is calling this file to be run on the site.

          fetch(`${props.configuration.backendUrl}/www.RunFile?name=${e.currentTarget.id}`); 
        

The way how I am mimicking this is by:

        public async static Task PostFile(string file)
    {
        byte[] byteArray = new byte[] { };
        File.WriteAllBytes(file, byteArray);
        var fileName = Path.GetFileName(file);
        var byteContent = new ByteArrayContent(byteArray);
        
        var response = await Client.PostAsync(
        "https://localhost/simulatorweb/www.FileIOU?filename="+$"{fileName}"
        , byteContent);
       
    }

and the second part is:

    public async static Task RunFile(string fileName)
    {
        var response = await Client.PostAsync(
            $"https://localhost/www.RunFile?name="+$"{fileName}", null);           
    }

Once I call this function I get the response 405 , though this possible looks like I need to set the 'no-cors' in C# as per the JavaScript, though I am not sure how to do this. But there could be other issues with this, which I am not seeing.

{StatusCode: 405, ReasonPhrase: 'Method Not Allowed', Version: 1.1, Content: System.Net.Http.HttpConnectionResponseContent, Headers:
{
  Date: Fri, 30 Oct 2020 06:15:42 GMT
  Connection: keep-alive
  Vary: Origin
  Accept-Ranges: bytes
  Content-Length: 0
  Allow: GET
  Allow: HEAD
  Allow: OPTIONS
}}

Answer 1

As John has outlined in the comments, no-cors is not a server side thing that you need to replicate. CORS is a browser feature whereby if JavaScript makes a request to download content from somewhere other than where the JavaScript file itself came from, then the browser (as a courtesy) checks with the destination server "for your url x, what places may a JavaScript have been downloaded from and be permitted to access x?" - this gives the server the opportunity to respond with "only JavaScript from these places a,b,c may request my file x" and the browser then makes a judgement as to whether the JavaScript currently running, may access x

You can turn this off if you can tolerate the restrictions that come with doing so, and that's what no-cors does; it changes the browser behavior

As such, you can hopefully see that no-cors is an instruction to the browser and with your c# you're effectively taking the browser out of the equation so it's unlikely that mimicking it will change the server behavior. It's theoretically possible; your server might be coded to refuse access to a url that it hasn't seen an OPTIONS request for recently(browsers in CORS mode send an options first), but it's actually more likely that the root cause is something simpler like you're Posting to an action that is coded to expect a Get