Auto-populate ClientPlatform in Android Library

- Now works the same as the iOS Library

- Library users are not required to populate
  ClientPlatform, and we get consistent metrics
  across all clients

- Includes Android package name in ClientPlatform
  to capture app name

- Add PsiphonTunnel.setClientPlatformAffixes to add
  ClientPlatform prefix and suffix as required by
  Psiphon Android client

MobileLibrary/Android/PsiphonTunnel/PsiphonTunnel.java

@@ -103,6 +103,8 @@ public class PsiphonTunnel extends Psi.PsiphonProvider.Stub {
     private AtomicBoolean mRoutingThroughTunnel;
     private Thread mTun2SocksThread;
     private AtomicBoolean mIsWaitingForNetworkConnectivity;
+    private AtomicReference<String> mClientPlatformPrefix;
+    private AtomicReference<String> mClientPlatformSuffix;
 
     // mUsePacketTunnel specifies whether to use the packet
     // tunnel instead of tun2socks; currently this is for
@@ -130,6 +132,8 @@ public class PsiphonTunnel extends Psi.PsiphonProvider.Stub {
         mLocalSocksProxyPort = new AtomicInteger(0);
         mRoutingThroughTunnel = new AtomicBoolean(false);
         mIsWaitingForNetworkConnectivity = new AtomicBoolean(false);
+        mClientPlatformPrefix = new AtomicReference<String>("");
+        mClientPlatformSuffix = new AtomicReference<String>("");
     }
 
     public Object clone() throws CloneNotSupportedException {
@@ -185,6 +189,11 @@ public class PsiphonTunnel extends Psi.PsiphonProvider.Stub {
         startPsiphon("");
     }
 
+    public void setClientPlatformAffixes(String prefix, String suffix) {
+        mClientPlatformPrefix.set(prefix);
+        mClientPlatformSuffix.set(suffix);
+    }
+
     //----------------------------------------------------------------------------------------------
     // VPN Routing
     //----------------------------------------------------------------------------------------------
@@ -559,6 +568,25 @@ public class PsiphonTunnel extends Psi.PsiphonProvider.Stub {
             json.put("DisableLocalHTTPProxy", true);
         }
 
+        StringBuilder clientPlatform = new StringBuilder();
+
+        String prefix = mClientPlatformPrefix.get();
+        if (prefix.length() > 0) {
+            clientPlatform.append(prefix);
+        }
+
+        clientPlatform.append("Android_");
+        clientPlatform.append(Build.VERSION.RELEASE);
+        clientPlatform.append("_");
+        clientPlatform.append(mHostService.getContext().getPackageName());
+
+        String suffix = mClientPlatformSuffix.get();
+        if (suffix.length() > 0) {
+            clientPlatform.append(suffix);
+        }
+
+        json.put("ClientPlatform", clientPlatform.toString().replaceAll("[^\\w\\-\\.]", "_"));
+
         return json.toString();
     }