WgQuickBackend: Finish the implementation

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java

@@ -13,6 +13,8 @@ import com.wireguard.android.util.ToolsInstaller;
 import com.wireguard.config.Config;
 
 import java.io.File;
+import java.io.FileOutputStream;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -29,23 +31,45 @@ public final class WgQuickBackend implements Backend {
     private static final String TAG = "WireGuard/" + WgQuickBackend.class.getSimpleName();
 
     private final Context context;
+    private final File localTemporaryDir;
     private final RootShell rootShell;
     private final ToolsInstaller toolsInstaller;
 
     public WgQuickBackend(final Context context, final RootShell rootShell,
                           final ToolsInstaller toolsInstaller) {
         this.context = context;
+        localTemporaryDir = new File(context.getCacheDir(), "tmp");
         this.rootShell = rootShell;
         this.toolsInstaller = toolsInstaller;
     }
 
     @Override
-    public Config applyConfig(final Tunnel tunnel, final Config config) {
-        if (tunnel.getState() == State.UP)
-            throw new UnsupportedOperationException("Not implemented");
+    public Config applyConfig(final Tunnel tunnel, final Config config) throws Exception {
+        if (tunnel.getState() == State.UP) {
+            // Restart the tunnel to apply the new config.
+            setState(tunnel, State.DOWN);
+            try {
+                bringUpTunnel(tunnel, config);
+            } catch (final Exception e) {
+                // The new configuration didn't work, so try to go back to the old one.
+                bringUpTunnel(tunnel, tunnel.getConfig());
+                throw e;
+            }
+        }
         return config;
     }
 
+    private int bringUpTunnel(final Tunnel tunnel, final Config config) throws Exception {
+        final File tempFile = new File(localTemporaryDir, tunnel.getName() + ".conf");
+        try (FileOutputStream stream = new FileOutputStream(tempFile, false)) {
+            stream.write(config.toString().getBytes(StandardCharsets.UTF_8));
+        }
+        final int result = rootShell.run(null, "wg-quick up '" + tempFile.getAbsolutePath() + '\'');
+        if (!tempFile.delete())
+            Log.w(TAG, "Couldn't delete temporary file after bringing up " + tunnel.getName());
+        return result;
+    }
+
     @Override
     public Set<String> enumerate() {
         final List<String> output = new ArrayList<>();
@@ -85,11 +109,9 @@ public final class WgQuickBackend implements Backend {
         if (state == State.UP) {
             if (!new File("/sys/module/wireguard").exists())
                 throw new ErrnoException("WireGuard module not loaded", OsConstants.ENODEV);
-            // FIXME: Assumes file layout from FileConfigStore. Use a temporary file.
-            final File file = new File(context.getFilesDir(), tunnel.getName() + ".conf");
-            result = rootShell.run(null, String.format("wg-quick up '%s'", file.getAbsolutePath()));
+            result = bringUpTunnel(tunnel, tunnel.getConfig());
         } else {
-            result = rootShell.run(null, String.format("wg-quick down '%s'", tunnel.getName()));
+            result = rootShell.run(null, "wg-quick down '" + tunnel.getName() + '\'');
         }
         if (result != 0)
             throw new Exception("wg-quick failed");