Allow overriding Metro server host with a system prop

Summary:
Allow a device to override the host to which to connect to for getting dev bundles, debugging etc.

This is read from a system prop so it can be shared across all React Native apps and persists between app installs.

Reviewed By: mdvacca

Differential Revision: D10842213

fbshipit-source-id: d15b7d0255130090744d60ffb239778cba15e49c

Author: stepanhruda

ReactAndroid/src/main/java/com/facebook/react/modules/systeminfo/AndroidInfoHelpers.java

@@ -5,19 +5,28 @@
 
 package com.facebook.react.modules.systeminfo;
 
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import java.util.Locale;
 
 import android.os.Build;
 
+import com.facebook.common.logging.FLog;
+
 public class AndroidInfoHelpers {
 
   public static final String EMULATOR_LOCALHOST = "10.0.2.2";
   public static final String GENYMOTION_LOCALHOST = "10.0.3.2";
   public static final String DEVICE_LOCALHOST = "localhost";
 
+  public static final String METRO_HOST_PROP_NAME = "metro.host";
+
   private static final int DEBUG_SERVER_HOST_PORT = 8081;
   private static final int INSPECTOR_PROXY_PORT = 8082;
 
+  private static final String TAG = AndroidInfoHelpers.class.getSimpleName();
+
   private static boolean isRunningOnGenymotion() {
     return Build.FINGERPRINT.contains("vbox");
   }
@@ -49,7 +58,10 @@ private static String getServerIpAddress(int port) {
     // We detect whether app runs on genymotion and replace js bundle server hostname accordingly
 
     String ipAddress;
-    if (isRunningOnGenymotion()) {
+    String metroHostProp = getMetroHostPropValue();
+    if (!metroHostProp.equals("")) {
+      ipAddress = metroHostProp;
+    } else if (isRunningOnGenymotion()) {
       ipAddress = GENYMOTION_LOCALHOST;
     } else if (isRunningOnStockEmulator()) {
       ipAddress = EMULATOR_LOCALHOST;
@@ -59,4 +71,41 @@ private static String getServerIpAddress(int port) {
 
     return String.format(Locale.US, "%s:%d", ipAddress, port);
   }
+
+  private static String metroHostPropValue = null;
+  private static synchronized String getMetroHostPropValue() {
+    if (metroHostPropValue != null) {
+      return metroHostPropValue;
+    }
+    Process process = null;
+    BufferedReader reader = null;
+    try {
+      process =
+          Runtime.getRuntime().exec(new String[] {"/system/bin/getprop", METRO_HOST_PROP_NAME});
+      reader =
+          new BufferedReader(
+              new InputStreamReader(process.getInputStream(), StandardCharsets.UTF_8));
+
+      String lastLine = "";
+      String line;
+      while ((line = reader.readLine()) != null) {
+        lastLine = line;
+      }
+      metroHostPropValue = lastLine;
+    } catch (Exception e) {
+      FLog.w(TAG, "Failed to query for metro.host prop:", e);
+      metroHostPropValue = "";
+    } finally {
+      try {
+        if (reader != null) {
+          reader.close();
+        }
+      } catch (Exception exc) {
+      }
+      if (process != null) {
+        process.destroy();
+      }
+    }
+    return metroHostPropValue;
+  }
 }

ReactAndroid/src/main/java/com/facebook/react/modules/systeminfo/BUCK

@@ -29,6 +29,7 @@ rn_android_library(
         "PUBLIC",
     ],
     deps = [
+        react_native_dep("libraries/fbcore/src/main/java/com/facebook/common/logging:logging"),
         react_native_dep("third-party/java/infer-annotations:infer-annotations"),
         react_native_dep("third-party/java/jsr-305:jsr-305"),
     ],