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I've been looking for a few days for a way of doing a post request synchronously from an azure web app and haven't been able to make it work. Here is how it should work:

  1. I have an azure web service (an aspx) that receives post requests.
  2. Upon receiveing a request, the code behind of the aspx gets data from an external server. Thus it needs to make an http post request to external server and wait for the response.
  3. Once the code behind receives the external server response, it uses the data received to populate the aspx that will be in the response.

Steps 1 and 2 (just having an asp and populating the response) are just fine but I've struggled a lot with step 2. I have tried many versions of the code, which right now looks like this (simplified version without logs and some other variables and stuff):

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace My_WebApp.EntryPoint
{
    public partial class MyEntryPoint : System.Web.UI.Page
    {
        private string uriWebRequest = "https://some.web.server";

        protected void Page_Load(object sender, EventArgs e)
        {
            // I only respond to post messages
            if (Page.Request.HttpMethod == "POST")
            {
                // I need to send a post request to a server to 
                // get data to populate my web
                var myTask = PostAsync(uriWebRequest, this.form1);
                var result = myTask.Result;
            }
        }

        static async Task<HttpResponseMessage> PostAsync(
                                string uriPeticion, HtmlForm form1)
        {
            try
            {
                using (var client = new HttpClient())
                {
                    // I make the post request to the other server 
                    // and wait for the response
                    HttpResponseMessage resp = 
                        await client.PostAsync(uriPeticion, null)
                                    .ConfigureAwait(false);

                    string respBody = 
                        await resp.Content
                                  .ReadAsStringAsync()
                                  .ConfigureAwait(false); // This always returns empty

                    string respuestaRecibidaString = "";
                    if (string.IsNullOrEmpty(respBody))
                    {
                        respuestaRecibidaString = "Empty response";
                    }
                    else
                    {
                        respuestaRecibidaString = respBody;
                    }

                    // Show the http post response in my web app response.
                    form1.InnerText = respuestaRecibidaString;

                    return resp;
                }
            }
            catch (HttpRequestException e)
            {
                System.Diagnostics.Trace.TraceInformation("(PostAsync) Error:");
                System.Diagnostics.Trace.TraceInformation(e.Message);
                return null;
            }
        }
    }
}

This code always returns empty response from the external server request. Not even errors or anything (I've tried with postman and the external server does return something, either actual value or error). And I don't know wether that's from the client.postAsync function or what.

I've googled around and found a couple of things like this and this but haven't been able to make it work. Do you guys know what I'm doing wrong?

Thanks

Kjartan
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Andrés Cuicui Studios
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  • If the external server is returning an empty response, then you'll need to find out why the external server is returning an empty response. There's nothing in `HttpClient` or `await` that will just return an empty string if something goes wrong; if it's returning an empty string, then that's because it *got* an empty response from the external server. – Stephen Cleary Jan 18 '22 at 14:14
  • @StephenCleary thanks for the comment. The thing is that I've been using the very same query in postman (basically to test that I'm sending the proper query) and I always get data when making the requests from postman. Therefore I must be doing something wrong with the post request I send by code. I don't know if it's the tas/sync part or just the request. – Andrés Cuicui Studios Jan 24 '22 at 10:36
  • I recommend using a tool like Fiddler to compare a working request from Postman and a nonworking request from your app. – Stephen Cleary Jan 24 '22 at 13:55
  • @StephenCleary thanks again for the comment. Yeah, I have used Fiddler to check the request from Postman, but how can I check the request send from my azure web app? – Andrés Cuicui Studios Jan 25 '22 at 11:48
  • You'd have to run it locally. – Stephen Cleary Jan 25 '22 at 11:50

1 Answers1

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Page_Load or any of the other web forms life cycle methods are not going to run asynchronously. They will return without waiting for the response.

The solution is to use RegisterAsyncTask which Mr. Hanselman describes here

Derek Gusoff
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