Develop Reference

How to Post Data to Android App using Inbound Connection?

Is it possible to post data directly to an Android app from some URL on a local network using inbound connection?
Example: My Android device(Device 1) is running on local IP: xxx.xxx.x.146 and another Non-Android device(Device 2) is running on local IP: xxx.xxx.x.147. Device 2 only post data to URL. My requirement is to share Device 1 URL with Device 2, so that Device 2 can post data directly to Device 1 over same network. Any suggestions?
Thanks,
Gaurav Kapoor

I think you need to go with below way then it should be possible but rest cases not feasible please check below if it will help to you.
Option:1 with help firebase dynamic link to give data from url.
https://firebase.google.com/docs/dynamic-links/android/receive
Option:2 using some referral way for more details check below link
How to get Google Play referer in an Android application

Unable to validate issuer when trying to access API

so here's a quick explanation of my issue - my current setup is and IdentityServer4 implementation with ASP.NET Core Identity, an API resource protected by it and a Xamarin.Android application that is the client. My current issue is that the client(Android) cannot get anything from the API because of the following error(from the API logs):
"Bearer" was not authenticated. Failure message: "IDX10205: Issuer validation failed. Issuer: 'http://10.0.2.2:5000'. Did not match: validationParameters.ValidIssuer: 'null' or validationParameters.ValidIssuers: 'http://127.0.0.1:5000'."
Basically, since I'm using the Android emulator, in order to call something that's on localhost on my machine, I need to use the 10.0.2.2 URL for it. Then the problem pops up - the Identity Server is fine with authenticating, I can login fine, I get an access token, but after that I need to call the API. And that's where the error happens - it's expecting an issuer that is with the same authority(127.0.0.1:5000) but receives the 10.0.2.2:5000, which is the authority for the Android client.
So, my question is - is there a way to somehow specify that 10.0.2.2 is also a valid issuer, or do I have to start thinking about deploying both the API and the Identity Server just so I can test the client. I'd really like it if there was a way to have the whole solution running on my local machine rather than having to deploy for every little thing I want to try out.
Any help will be appreciated very much.

First: Given the standard, you manage just one Issuer.
Are you managing your own Identity / Token generation? It sounds like this isn't the case.
You could customize your API for creating your tokens explicitly. Then, you can indicate a global Issuer (like your project url) so anyone can validate against the same.
var token = new JwtSecurityToken(
issuer: "http://my-perfect-proj.net",
claims: ...,
notBefore: DateTime.Now,
expires: DateTime.Now.AddHours(1),
signingCredentials: ...)
);
After your token is created and sent, validate your incoming request based on your tastes (checking time, user's data, issuer).
ASP.NET Core JWT Bearer Token Custom Validation
Creating RESTful API with Authentication
EDIT: Using Xamarin and Visual Studio on the same machine, didn't gave me this kind of problems but in that case, I was using Visual Studio Emulator. You could give it a try and avoid doing other types of workarounds.

So, I managed to work around the issue by simply running the Web part of it so it's visible on my local network. What I did in more detail - in the Program.cs where I create the host, I use the .UseUrls("http://*:5001") method, and then I run the app with dotnet run.
In this way your app is accessible in your local network via the IP address of your machine and the port you've specified. Also, in order for this to work, you'd have to define a new Outbound Rule in your Firewall to allow traffic through that port you're using. Hope this helps someone else as well, this turned out to be the easiest way to get what I need to work, and that's after fighting with IIS for a while trying to get it to work through there as well.

Short answer: In IIS, don't leave the site binding host name set as blank.
Longer explenation:
I received a similar error, but could see that for some reason it was trying to match the issuer domain name vs IP (the domain does point to the IP, but I guess it tries to validate the two strings). I could see this error after allowing logging : IdentityModelEventSource.ShowPII = true.
Microsoft.IdentityModel.Tokens.SecurityTokenInvalidIssuerException:
IDX10205: Issuer validation failed. Issuer: 'http://ec2XXXXXom'. Did
not match: validationParameters.ValidIssuer: 'http://34.111.111.29' or
validationParameters.ValidIssuers: 'null'. at
Microsoft.IdentityModel.Tokens.Validators.ValidateIssuer(String
issuer, SecurityToken securityToken, TokenValidationParameters
validationParameters)
In IIS I previously had the host name set as blank (I am using the server name as domain name) - and therefore it set the issuer using the IP of the server. When I specifically set the site domain name, it worked.

Why is my Android phone sending data through an unknown server?

I've been creating an app to learn how Android works and just playing around with various features like the sensors, SMS listeners, phone listeners, wifi listeners, etc.
I recently added a bit of code from the Android Volley library to send a request to my website every time it connects to a wifi network (I don't have a cellular data plan).
It sends a GET request to a very sparse text file that returns back:
hello
The odd thing is that after connecting to open public wifi networks, oftentimes the response that the phone gets from this same request will be:
<html>
<title>Redirecting...</title>
<script language="javascript">
document.location.href="http://den-80202-7200.localdomain:8000/index.php?zone=pms&redurl=http://my-personal-server.com/hello
</script>
</html>
Which is really strange to me, as it will return this even the next day, connecting to other networks, connecting to my secured network at home, etc.
And I have no idea what this URL is:
http://den-80202-7200.localdomain:8000
It appears to me, (still learning about how this all works), that my phone is sending my GET request to my website, but somehow my website is returning back this possibly infected response, which, if I was in a browser may harm me. Maybe my website server is infected with something?
Or, my phone has malware that is sending all my requests through this unknown server?
Is that what is going on? How to prevent my phone from keep sending requests through this unknown server? I did a virus scan and it comes up clean. Is there a way to flush the phone's DNS cache or something similar?

While in general it's good to be suspicious about hijacked or modified requests on open wifi networks, in this case it appears to be expected behavior for public wifi networks.
Specifically, many public wifi networks require authentication either for paid access or to accept terms of service. To accomplish this, they will often intercept HTTP requests from unauthenticated clients and return a response which redirects them to a captive portal.
Since .localdomain is not a valid TLD, this URL will not work outside a network without a local DNS entry for it. This appears similar to the use of .local as a reserved TLD for local-network only DNS entries. Again, this is indicative of public wifi networks using .localdomain URLs to redirect to a locally hosted captive portal.
Note also that the redirect URL has the parameter "redurl=http://my-personal-server.com/hello", this specifies the URL that you'll be redirected to after your authenticate. As expected, this was the original URL you requested.
NOTE: As for this showing up on your private wifi networks afterwards, I suspect this is a caching issue. Again, since .localdomain isn't a valid TLD the request to "http://den-80202-7200.localdomain:8000" will fail outside of the public wifi network with support for this specific DNS entry.

Maybe your system is infected with Malware or SpyBots.
Check out below link:
http://www.speedguide.net/port.php?port=8000

Fehler (error) 6 - the requested item could not be loaded

Currently I'm developing android application that needs to connect itself to REST API. It is crucial for my app to access API whenever connection is possible (mobile data/wifi).
But when testing my app something extremely weird happened. Application works as expected almost all the time, but when on VipMobile operator (Austria telekom group) I cannot connect to API.
At first I didn't get it, error was too unreadable. It says
j u fehler6 the requested item could not be loaded & wrong mime type
There are a lot of unprintable chars in that message too. When i figured out that it is operator fault i tried to copy link to my API and got this.
What could that possibly be? Can anyone point me in any direction, I cannot publish application as long as there are those ridickulous errors.

This happens when the user is on 3g connection. Some mobile operators intercept clients request and if the Content-Type is not good, or not defined they display page like this. This happens also to vipmobile operator in Serbia.
Try to add right content-type to response headers on your server side.
Try to put for example Content-Type:text/plain;charset=utf-8 to headers

How to debug http calls on Android devices?

I'm writing a Lovefilm client for Android, and it's not going too badly except I keep having problems with the remote calls to retrieve data from the API.
Does anyone have any tips for debugging remote calls like this? Can I tcpdump on Android or is there a native way of doing it?
For example, I'm using the Scribe-java library for OAuth to access the Lovefilm API, I can authenticate find and retrieve a list of films on the users account fine when the device is running Gingerbread, but trying to retrieve the accessToken on Froyo causes a blank response & and apparent response code of -1, I'd like to be able to see what's going on under the cvers their.
Another example I'd like to be able to the raw http for is trying to run a search, I get and IOError that says "Received authentication challenge is null"

I've used Fiddler (http-proxy for debugging http calls) with the android emulator in these cases. Just start the proxy, and start the emulator with the correct proxy address (-http-proxy ).

Fiddler is the most useful option. On the emulator #Scythe answer will work, but on a real device you will need to set the proxy in the Apache Http Client. The following code will do that:
HttpHost proxy = new HttpHost("youripaddr", 8888);
params.setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);
If you are using https, fiddler is not so useful. In that case can enable the build in logging support in Apache Http Client. The following code does that:
Headers only:
java.util.logging.Logger apacheHeaderLog = java.util.logging.Logger.getLogger("org.apache.http.headers");
apacheHeaderLog.setLevel(java.util.logging.Level.FINEST);
Headers & Wire:
java.util.logging.Logger apacheWireLog = java.util.logging.Logger.getLogger("org.apache.http.wire");
apacheWireLog.setLevel(java.util.logging.Level.FINEST);
Note that this will have to have a java.util.logging Handler configured at finest level and the default handler is configured to log to logcat, which will filter DEBUG (finest) entries by default.

If your system can share the wi-fi connection you should be able to route packets from any device through your system and then using wireshark you can get monitor your calls or get a tcpdump.
Also , and more importantly , it would be best if you log your network calls and responses as suggested by #Matthew
Windows 7 wi-fi connection sharing : http://www.winsupersite.com/article/faqtip/windows-7-tip-of-the-week-use-wireless-hosted-networking-to-share-an-internet-connection-wirelessly.aspx

Since I always run into similar troubles and it seems a lot of people having the same issues over and over again I wrote up a quick tutorial for debugging client-server communication by using netcat and cURL.
That of course only works for the simplified case that you always 'fake' on side of the connection.
For eavesdropping you can use tools like tcpdump or Wireshark. Which will definitely be easier if you're able to run the server instance directly on your local machine.

Stetho is a great tool from FB which helps in debugging android Apps. You can have access to local data and have a check on your network using this.
http://facebook.github.io/stetho/