Cannot connect to localhost in windows store application

Question

As i read all over the internet microsoft block the option to listen and recieve traffic on localhost (127.0.0.1) for any port. I want for developing purposus to test my 2 s

Answer 1

My scenario: Developed an Windows Store App for internal use, ran fine on development machine, however when migrating to another machine any of the HttpClient calls failed. There are two issues I faced here:

1. HttpClient failure when communicating to IIS on the local machine

2. HttpClient failure When communicating to IIS on a remote machine on the local subnet

Problem 2 was an easy fix, in Visual Studio set the app to allow "Private Networks (Client & Server)" under the capabilities (Package.appxmanifest > Capabilities), redeploy and all is good.

Problem 1 was difficult to resolve. By default Visual Studio adds an exception in the NetIsolation which permits and denies local loopback/localhost access. You need to add your app as an exception in this list, however the information in the link provided in the OP doesn't work, I couldn't get the command to work at all, so here's how I did it:

(Note ensure the app is installed on the machine you are running this through)

1. Go to your registry, and CTRL+F to find your app (for example if it's called TESTApp1, then enter that in to the search box).
2. You should find a registry key that looks like a guid followed by a name, for example: ac2efce7-a15b-40d0-92db-3abde43a6778_1.0.1.15_neutral__025mzc78q1aqe

Once you have that name, in a command prompt (as administrator, just in case) run : CheckNetIsolation.exe LoopbackExempt -s

In the output, find your GUID. You will see the SID under it, make a note of this SID. 3) Run the following command, entering in your SID on the problem machine: CheckNetIsolation.exe LoopbackExempt -a -p=SIDHERE

Note: Alternative step 2: You can also find your SID under the following registry key (assuming you have installed the app):

HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\AppContainer\Mappings

Again, CTRL+F and find your app under there.