In today's world of NATs and firewalls, it's a problem for anyone but Skype and your phone company to establish a direct communication socket between two mobile devices. The Dyad Project solves this problem by combining GCM and ICE to create streaming peer-to-peer connections between apps running on Android devices.
It roughly works like this:
The Dyad Server keeps a database of pairs of GCM ids, called Dyads. The Dyad Client is an Android Library compiled into an app. When the Dyad Client contacts the Dyad Server, the server fires a GCM message to the correct device, which wakes up and also contacts the server. Through the server, both apps retrieve the information needed to connect directly through ICE. You can configure Dyad to fall back to a relayed (TURN) connection in case this fails. Both apps now possess a UDP communication socket that they can use to send streaming data directly to the other device.
The Dyad Project is completely open source and app developers can use it freely. Here's what you need to do to incorporate peer-to-peer-functionality into your own app:
Get the source code.
Install Dyad Server on a publicly accessible server somewhere.
Configure the Dyad Client Library and compile it into your app.
The Dyad Client is organized as an Android Library Project that you can import into your own projects.
The Dyad Client Android Library is located in the source
distribution in the subdirectoy client. To be able
to use it, you first need to install the Android SDK
from http://developer.android.com/sdk/.
After that, you have to configure the Dyad Client Android
Library by updating it with an Android target and, optionally,
with the Bump SDK if you
want to use Bump to perfom the bonding of dyads.
First, run the command android list targets and choose
the number that belongs the Android target you are
developing your app for. You can install new targets by
running just android. The minimum Android
version supported by Dyad is Android 2.2 (API 8).
Second, run the command android update lib-project --target
{target} --path {dir}/dyad/client where
{target} is the number you found in the previous step and {dir}
is the path to the directory where you placed the Dyad
source code.
If your app targets an Android version below 3.0, the Dyad
Client Library needs the
Android
support library. Copy
android-support-v4.jar
from the
directory android-sdk/extras/android/support/v4/
to dyad/client/libs/. If you're developing in Eclipse,
you can also right-click your project and select Android Tools > Add
Support Library.
If you want to use Bump for
bonding, sign up as a
developer for Bump and install the Bump SDK. Then, copy the
file BumpBonder.java from the
directory dyad/client/extras
to dyad/client/src/com/r2src/dyad. You can then use
the Bump Bonder like any other bonder.
Start new Android Project from existing source, use /dyad/client as the project directory. (the previous steps already configured this project as an Android Library Project) TODO: provide simple project.properties for both projects. Start new Android Project from existing source, use /dyad/client/test as the project directory. Don't start an Android Test Project, because a Test Project cannot test an Android Library Project. Start new Perl Project. Use dyad/server as the source directory.
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