Develop Reference

Android SNI Issue on Devices below Android 7

I am trying to send a HTTP POST request (with images, but that should not matter) to a https-secured server using an AsyncHttpClient.
On Android 7+ everything seems to be working fine, the request finishes without errors.
However, on Android 5 and 6, I am getting the following error message:
javax.net.ssl.SSLException: hostname in certificate didn't match [...]
The server is using SNI, so I'm guessing that's the problem, but why would the connection work on Android 7+ with the same code?
What is the best way to fix this? I am not allowed to make any changes on the server, so I have to find a workaround for my app.

HTTP Server running within Android app

I'm working on a multilayer Android app where I have to intercept HTTP requests, modify one of the headers, execute and return responses. I can't change a way of creating requests, but I can change the API base URL used for requests. The approach I chose was writing a proxy listening on a specific port and doing a man-in-the-middle job:
taking requests,
applying required changes to HTTP requests,
executing it and
returning response.
I applied SparkJava as an HTTP server and OkHttpClient as an HTTP client. It worked like a charm until I found it works only on Android 8 and newer. There is a problem with missing ThreadLocal<S> ThreadLocal.withInitial (Supplier<? extends S> supplier) in API prior to 26 that SparkJava's backend - Jetty, uses).
I guess I will try to look for other HTTP server framework working fine in older API and reimplement my proxy.
In the meantime, does this approach seem to be ok? Or maybe there is another way of proxying HTTP requests in Android app that would allow modifying headers having only an option of changing base API URL?
All ideas much appreciated.
PS. I know that in a typical app this kind of proxying would make a security issue, but this is not a concern in this case.

Consuming .net rest api via android - 400 error

I have created REST service according to this: http://www.asp.net/web-api/overview/older-versions/creating-a-web-api-that-supports-crud-operations
tutorial and a android client according to this: http://www.techrepublic.com/blog/software-engineer/calling-restful-services-from-your-android-app/
I changed the service to receive the json messages, and the connection string to the same that works in the browser, with 10.0.2.2 instead of localhost(according to one of the advices in stackoverflow) - in the browser it works perfectly. When I try to test it on the emulator I get the 400 bad request error. Maybe this is totally wrong way of approaching this, I am confused - would you kindly show me the error in the implementation or the tutorial that could help me with consuming the rest api with android client?

Internet Connection Problems over Cellular

We have discovered a strange bug in on of our Android apps in that the app cannot connect to the internet over cellular on certain Android Models/Mobile Networks (connecting via WiFi works perfectly). The URL which the app is trying is to reach is however accessible using the device's normal browser, which rules out the URL being blocked upstream. Any ideas what could be causing this would be appreciated please.

which rules out the URL being blocked upstream
Not necessarily. As one of the commenters pointed out, you do not indicate how you are using this URL in your app. If this is an HTTP request, and it works in a browser but not your app, try changing the User-Agent HTTP header of your request to match the one from the browser.

You have provided no error log, but from experience I have run into a few inconsistencies when connecting to a server.
Using HttpsUrlConnection a SNI header is set on HoneyComb and above but not on previous versions, which can alter how the server responds. To add to this there are some general SSL handling inconsistencies between API levels, such as handling of wildcard domains in a certificate is buggy in some api levels.
Second some phones/api levels add a header to HttpUrlConnection requests that specifies time the request was sent like so:
X-Android-Sent-Millis=1353085024868
Some servers seem to use these headers to detect mobile traffic and alter the response.

I had problems when using a dual-simcard. Do you have more devices connected? Try to shut them down.

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/