Android device connection refused in WebClient download request on localhost PC

Raymond Larkin 1

A VisualStudio 2019 project running on Windows 10 Home was taken from a tutorial that actually targeted Phone 8. It is a 'Book Store' app using data stored in an XML file which is loaded into the local host web page built with Asp.Net Core Web app. My Windows machine is wired to the router and the Android phone is USB tethered to the PC. The Android manifest has permissions for Internet and Network_State.

There is a call in the Mobile App using Xamarin.Forms that uses WebClient to down load the catalog from the server. The down load call has an event handler that is built to respond when the down load is complete.

With the firewall enabled the request times out. With the firewall off the request returns immediately with exception ConnectionFailure: Connection refused. It doesn't help to run VS as administrator.

The mobile app is using the Ip address of the PC and a number of ports have been tried yielding the same response.

As a note, I had to change the Api controller from using HttpResponseMessage to IActionResult because I believe target platforms may be different or changes in .Net versions pushed the issue.
As another note, I previously built a Xamarin.Android app that I could explore all the shared drives on my PC with. I'm not sure that has any bearing on this problem, but, I could access the PC through the wifi using the same Ip address of the PC.

Help in finding direction to resolve the issue would be appreciated.

Thanks

Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 42,746 Reputation points Microsoft Vendor

2022-06-13T02:58:13.443+00:00

Can you connect to the API using the browser on the device?

Would refer to this document Connect to local web services from iOS simulators and Android emulators to resolve your issue?
Raymond Larkin 1 Reputation point

2022-06-14T02:19:02.327+00:00

Thanks for the response.
I actually started with the link you suggested the: Connect to local services from Ios or Android...... Since posting my question I've also tried disabling anti-virus along with the firewall. In addition, I've also disabled synchronization with Chrome.
As for trying to connect with the api directly, all those attempts are refused as well. Postman will connect and read the catalog.
Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 42,746 Reputation points Microsoft Vendor

2022-06-14T08:03:26.563+00:00

As for trying to connect with the api directly, all those attempts are refused as well. Postman will connect and read the catalog.

Did you use the browser on your phone for connecting the API?

I noticed that you could use Postman to connect your API and My Windows machine is wired to the router and the Android phone is USB tethered to the PC.

The issue might be caused by your phone and your PC aren't on the same LAN.

Did you use localhost:port or 127.0.0.1:port for API testing?

If so, please make your phone and your PC are on the same LAN firstly, then you need to use ipconfig in cmd to get your LAN IP address of PC and make the host to 0.0.0.0:port.

After that, you could use your phone to connect your Web API by LAN IP:port/API_address.
Raymond Larkin 1 Reputation point

2022-06-14T23:49:53.74+00:00

Again, thanks for reply.
Sorry for confusion. I tried from phone using ip address of machine and localhost. Then I tried Postman.

Phone and PC go through same router so same LAN. As I mentioned in original post, I built a xamarin:android app that can browse all my shared drives, same ip address used.

Also I've tried switching to HttpClient so as to implement the insecurehandler from link you referenced. Same error.

So, I continue my web api education and poke this problem together. There seems a host of people that have battled this error for some time. Some get it when they get the port selection correct. Too many posts don't show resolution.
Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 42,746 Reputation points Microsoft Vendor

2022-06-15T05:44:29.903+00:00

Have you tried to use the Android Emulator in VS for testing? It might be helpful for resolving your issue.
Raymond Larkin 1 Reputation point

2022-06-15T12:33:09.027+00:00

Yes I have tried the emulator. I am going to try again and report back. With home version it takes quite a while for the program to come up. So I grow some coffee, pick it, grind it and brew it. Then go back to see if it's ready. Will be upgrading to pro. My PC won't take Win 11.

Here is what I ended up with from the emulator:

Http connection- TrustFailure, Authentication Failed;

Https connection- SecureChannelFailure, Authentication Failed because the remote party has closed the transport stream.
Since exception text is posted to the app I can select the error and see a new page that includes the inner exception. Return to the main page resends the request. That action resulted in TrustFailure.

I'll be researching this for what it's worth.

Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 42,746 Microsoft Vendor

Did you mean the following error occur when you test your app?

   {System.Net.WebException: Error: TrustFailure (Authentication failed, see inner exception.) ---> System.Security.Authentication.AuthenticationException: Authentication failed, see inner exception. ---> Mono.Btls.MonoBtlsException: Ssl error:1000007d:SSL routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED

If so, you could use ServerCertificateValidationCallback to resolve the issue.

   ServicePointManager.ServerCertificateValidationCallback = new  
       RemoteCertificateValidationCallback  
       (  
          delegate { return true; }  
       );

You could refer to ServicePointManager.ServerCertificateValidationCallback Property for more details.

Raymond Larkin 1 Reputation point

2022-06-16T13:43:55.01+00:00

Thanks @Yonglun Liu for persisting with this.

That is the error message although I can't get my client side code to break on the exception, yet. So the body of the inner exception I don't capture when the error data is returned.

I will try your suggestion.

Tried with several variations that I also found. Unfortunately, no difference.
Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 42,746 Reputation points Microsoft Vendor

2022-06-17T08:27:01.663+00:00

It's my pleasure for helping you.

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Android device connection refused in WebClient download request on localhost PC

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