allow fetching any resource under js folder via packager

Summary: This is a simple hook to allow native side to fetch any file under the js root folder via packager. Historically, only the `main.jsbundle` is fetched via the packager. This then allows fetching local file like a json file that lives under the same root js folder

Reviewed By: yungsters

Differential Revision: D4037730

fbshipit-source-id: a2d6eb5e30d148fee573d413fc4036d0189f4938

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevServerHelper.java

@@ -53,6 +53,7 @@ public class DevServerHelper {
 
   private static final String BUNDLE_URL_FORMAT =
       "http://%s/%s.bundle?platform=android&dev=%s&hot=%s&minify=%s";
+  private static final String RESOURCE_URL_FORMAT = "http://%s/%s";
   private static final String SOURCE_MAP_URL_FORMAT =
       BUNDLE_URL_FORMAT.replaceFirst("\\.bundle", ".map");
   private static final String LAUNCH_JS_DEVTOOLS_COMMAND_URL_FORMAT =
@@ -217,11 +218,20 @@ public class DevServerHelper {
     return String.format(Locale.US, BUNDLE_URL_FORMAT, host, jsModulePath, devMode, hmr, jsMinify);
   }
 
+  private static String createResourceURL(String host, String resourcePath) {
+    return String.format(Locale.US, RESOURCE_URL_FORMAT, host, resourcePath);
+  }
+
   public void downloadBundleFromURL(
       final BundleDownloadCallback callback,
       final String jsModulePath,
       final File outputFile) {
-    final String bundleURL = createBundleURL(getDebugServerHost(), jsModulePath, getDevMode(), getHMR(), getJSMinifyMode());
+    final String bundleURL = createBundleURL(
+        getDebugServerHost(),
+        jsModulePath,
+        getDevMode(),
+        getHMR(),
+        getJSMinifyMode());
     final Request request = new Request.Builder()
         .url(bundleURL)
         .build();
@@ -449,4 +459,46 @@ public class DevServerHelper {
     // host itself.
     return createBundleURL(getHostForJSProxy(), mainModuleName, getDevMode(), getHMR(), getJSMinifyMode());
   }
+
+  /**
+   * This is a debug-only utility to allow fetching a file via packager.
+   * It's made synchronous for simplicity, but should only be used if it's absolutely
+   * necessary.
+   * @return the file with the fetched content, or null if there's any failure.
+   */
+  public @Nullable File downloadBundleResourceFromUrlSync(
+      final String resourcePath,
+      final File outputFile) {
+    final String resourceURL = createResourceURL(getDebugServerHost(), resourcePath);
+    final Request request = new Request.Builder()
+        .url(resourceURL)
+        .build();
+
+    try {
+      Response response = mClient.newCall(request).execute();
+      if (!response.isSuccessful()) {
+        return null;
+      }
+      Sink output = null;
+
+      try {
+        output = Okio.sink(outputFile);
+        Okio.buffer(response.body().source()).readAll(output);
+      } finally {
+        if (output != null) {
+          output.close();
+        }
+      }
+
+      return outputFile;
+    } catch (Exception ex) {
+      FLog.e(
+          ReactConstants.TAG,
+          "Failed to fetch resource synchronously - resourcePath: \"%s\", outputFile: \"%s\"",
+          resourcePath,
+          outputFile.getAbsolutePath(),
+          ex);
+      return null;
+    }
+  }
 }

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevSupportManager.java

@@ -11,6 +11,8 @@ package com.facebook.react.devsupport;
 
 import javax.annotation.Nullable;
 
+import java.io.File;
+
 import com.facebook.react.bridge.NativeModuleCallExceptionHandler;
 import com.facebook.react.bridge.ReactContext;
 import com.facebook.react.bridge.ReadableArray;
@@ -44,6 +46,9 @@ public interface DevSupportManager extends NativeModuleCallExceptionHandler {
   void reloadSettings();
   void handleReloadJS();
   void isPackagerRunning(DevServerHelper.PackagerStatusCallback callback);
+  @Nullable File downloadBundleResourceFromUrlSync(
+      final String resourceURL,
+      final File outputFile);
   @Nullable String getLastErrorTitle();
   @Nullable StackFrame[] getLastErrorStack();
 }

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevSupportManagerImpl.java

@@ -655,6 +655,13 @@ public class DevSupportManagerImpl implements DevSupportManager, PackagerCommand
     mDevServerHelper.isPackagerRunning(callback);
   }
 
+  @Override
+  public @Nullable File downloadBundleResourceFromUrlSync(
+      final String resourceURL,
+      final File outputFile) {
+    return mDevServerHelper.downloadBundleResourceFromUrlSync(resourceURL, outputFile);
+  }
+
   @Override
   public @Nullable String getLastErrorTitle() {
     return mLastErrorTitle;

ReactAndroid/src/main/java/com/facebook/react/devsupport/DisabledDevSupportManager.java

@@ -11,6 +11,8 @@ package com.facebook.react.devsupport;
 
 import javax.annotation.Nullable;
 
+import java.io.File;
+
 import com.facebook.react.bridge.DefaultNativeModuleCallExceptionHandler;
 import com.facebook.react.bridge.ReactContext;
 import com.facebook.react.bridge.ReadableArray;
@@ -129,6 +131,13 @@ public class DisabledDevSupportManager implements DevSupportManager {
 
   }
 
+  @Override
+  public @Nullable File downloadBundleResourceFromUrlSync(
+      final String resourceURL,
+      final File outputFile) {
+    return null;
+  }
+
   @Override
   public @Nullable String getLastErrorTitle() {
     return null;