Develop Reference

emulator can't connect to Google App Engine dev server

In my Android emulator, I was able to contact the GAE dev server.
I use this url: "http://10.0.2.2:8080/myurl".
The server is listening on http://127.0.0.1:8080.
Then, after I've updated the emulator to the Nexus 5X version with Google Play(API 27), the connection fails and the server show this log:
ERROR 2018-01-11 11:17:05,463 wsgi_server.py:329] Request Host 10.0.2.2 not whitelisted. Enabled hosts are set(['127.0.0.1'])
I'm using the latest GAE python SDK with webapp2.
Any idea on how to solve the problem?

The more recent versions of the development server includes whitelisting checks of the source IP address of incoming requests.
You can use the --enable_host_checking=False command line option for the GAE devserver, which disables these checks. Not a good idea if you're running on an untrusted network.
You're probably seeing such errors even for accessing the devserver from the same machine. Another option for these requests would be to use the --host 10.0.2.2 devserver option (i.e. use your machine's external IP address instead of localhost/127.0.0.1, but that won't help with the emulator requests if you're running the emulator on some other machine.
Ideally the whitelist should IMHO be manageable independently from the server's IP address, but this is what is available presently.

Connect bluestack emulated hybrid app to localhost

I have created a hybrid mobile app using ionic 2. The app can connect to a Django-powered website on a localhost through Rest API when using "ionic serve" command (using web browser on my end device).
Now, I want to use the app using Bluestacks as emulator. The Django website and the API (running on the localhost) can be accessed through the browser app of the bluestacks. Here were the steps I performed to do this one:
Installed allow-control-allow-origin to enable cross origin information sharing on Google Chrome on my local device.
I have added ALLOWED_HOSTS = ['10.0.2.2'] in my django settings.
Access the django website through Bluestacks' browser using
http://10.0.2.2:8000/
However, the mobile app emulated in Bluestacks could not access the API. Any solution to this problem?

The django conf look's OK.
With this kind of problem, in general, i use tools like :
localtunnel (free)
ngrok
to acces to my localhost from everywhere
example with lt :
$ lt -p 8000 -s andynionic
your url is: https://andynionic.localtunnel.me
You must also add andynionic.localtunnel.me to the Django config
ALLOWED_HOSTS = ['10.0.2.2', 'andynionic.localtunnel.me']
with hibrid, you probably do CORS request, see also cors-django
hope it's help

Testing Java Endpoints on real device in Android Studio

I followed this tutorial to setup a cloud database for my Android App
https://github.com/GoogleCloudPlatform/gradle-appengine-templates/tree/master/HelloEndpoints
Everything compiled fine and the server is running at http://localhost:8080/
However I keep getting this error
failed to connect to /10.0.0.2(port 8080) after 20000ms
I tried replacing 10.0.0.2 with my local IP address but it didn't work and showed the same error.
I am using Android Studio and debugging the app on my Android phone. Kindly help. Thanks!

Couple of areas to check:
Make sure you can connect to your locally running server using local IP address. In in your computer browser go to :8080. If it doesn't work then make sure your Run/Debug Config in AS is calling 127.0.0.1 or 0.0.0.0 address.
your android app has to be calling your pc's local IP address.

You need to start the dev server listening on 0.0.0.0. By default, the dev server listens only on localhost which means requests from other devices will not work. Just edit your run configuration and set the server address.

First find the IP Address of your machine (e.g., 192.168.x.x), by using ifconfig.
Change your build.gradle file of the endpoints project by adding this code appengine.run.host='192.168.x.x' at the end of the file.
Change the address in your android code with .setRootUrl("http://192.168.x.x:8080/_ah/api")

Https connection, differences between Android 2.3 and 4

I'm working on a project that retrieves images from different servers (http and https).
I found this usefull Q/A to avoid the problem of No peer certificate error in Android 2.3, but i can't understand why in Android 4 (>3) this problem ("No peer certificate error") was not presenting.
Please, correct me if I'm wrong:
In Android 2.3 an HTTPS connection performs the whole certificate checks (and handshakes);
In Android > 3 the HTTPS connection is established even if the handshake fails (Ex: my app, as the peer, has not the certificate).
What are the differences between these version of Android?
Why I need to Trust all in Android 2.3 and not in Android 4?
Why in Android 2.3 I receive the following Exception: "javax.net.ssl.SSLPeerUnverifiedException: No peer certificate error"
while in Android 4 everything works fine and the connection is established?
Is everything related to SNI Server Name Indication, introduced in Android Honeycomb?

Your certifying authority probably is not listed in the 2.3.3 version of Android, but is in the 4.x version. To find out for sure check the keystore on both devices.
Using ADB from the command line you can dump out android's keystore to a file and check to see if that issuer is available in your keystore (may need to be root).
adb pull /system/etc/security/cacerts.bks cacerts.bks
Download and install Portecle (from: http://portecle.sourceforge.net/)
Select File / Open Keystore... and choose the cacerts.bks file.
Select Tools / Keystore Report and copy that information into a text editor to look for the CN specified in the certificate found from the web browser. In my case I couldn't find one from "Cybertrust Public SureServer SV CA".
Browse to the website you are interested in using https://example.website.com/ on your computer web browser and find out who the CN is. Compare that to the keystore as shown above. If it is not in the keystore you will need to add it.
NOTE: Android 4.0 phones have a different method for storing certificates and don't use the cacerts.bks file mentioned below. For them you should be able to open the desired https site in the web browser and add the desired certificates that way.
I had connection issues to facebook and redbox. To fix my problem and update my android 2.3.3 phone certificates I copied the one from the android 3.2 emulator and put that on my phone:
Create and start an android 3.2 virtual device.
Copy the cacerts.bks file from the emulator (make sure your other device is not connected).
adb pull /system/etc/security/cacerts.bks cacerts.bks
Disconnect the emulator.
Connect your device to be updated (must be root). You may need to remount the /system folder as rw for read/write capabilities. For mounting issues, see: this link
Save a copy of the old cert file from your device:
adb pull /system/etc/security/cacerts.bks cacerts.bks.old
Put the updated cert file on your device
adb push cacerts.bks /system/etc/security/
Reboot the device
Reconnect and verify the new cacert file was loaded.

Google App Engine conneced Android App Failure

I trying to deploy an android application connected to GAE. I run the online tutorial on google, I used the right configuration (as they write on the tutorial) but I can't communicate the Android Virtual Device with the web application running locally. The Web application shows me a "Server Error 500" and the android application on AVD shows me a "Failure:Connect to /192.168.56.1:8888 timed out" error.
I m running Eclipse Indigo and the virtual android device is with Google API Level 10.
Thank you.

Appengine dev server by default only accepts connections on localhost address (localhost and 127.0.0.1).
To make it accept connections on all ports add -bindAddress 0.0.0.0 to dev server parameters in Eclipse.