Add pathForGroup method

FS.common.js

@@ -190,6 +190,10 @@ var RNFS = {
     return RNFSManager.pathForBundle(bundleNamed);
   },
 
+  pathForGroup(groupName: string): Promise<string> {
+    return RNFSManager.pathForGroup(groupName);
+  },
+
   getFSInfo(): Promise<FSInfoResult> {
     return RNFSManager.getFSInfo();
   },

README.md

@@ -22,7 +22,7 @@ Native filesystem access for react-native
 
 First you need to install react-native-fs:
 
-```javascript
+```
 npm install react-native-fs --save
 ```
 
@@ -571,6 +571,17 @@ type FSInfoResult = {
 };
 ```
 
+### (iOS only) `pathForGroup(groupIdentifier: string): Promise<string>`
+
+`groupIdentifier` (`string`) Any value from the *com.apple.security.application-groups* entitlements list.
+
+Returns the absolute path to the directory shared for all applications with the same security group identifier. 
+This directory can be used to to share files between application of the same developer.
+
+Invalid group identifier will cause a rejection.
+
+For more information read the [Adding an App to an App Group](https://developer.apple.com/library/content/documentation/Miscellaneous/Reference/EntitlementKeyReference/Chapters/EnablingAppSandbox.html#//apple_ref/doc/uid/TP40011195-CH4-SW19) section. 
+
 ## Test / Demo app
 
 Test app to demostrate the use of the module. Useful for testing and developing the module:

RNFSManager.m

@@ -516,6 +516,19 @@ - (dispatch_queue_t)methodQueue
   }
 }
 
+RCT_EXPORT_METHOD(pathForGroup:(nonnull NSString *)groupId
+                  resolver:(RCTPromiseResolveBlock)resolve
+                  rejecter:(RCTPromiseRejectBlock)reject)
+{
+  NSURL *groupURL = [[NSFileManager defaultManager]containerURLForSecurityApplicationGroupIdentifier: groupId];
+
+  if (!groupURL) {
+    return reject(@"ENOENT", [NSString stringWithFormat:@"ENOENT: no directory for group '%@' found", groupId], nil);
+  } else {
+    resolve([groupURL path]);
+  }
+}
+
 RCT_EXPORT_METHOD(getFSInfo:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject)
 {
   unsigned long long totalSpace = 0;

android/src/main/java/com/rnfs/RNFSManager.java

@@ -587,7 +587,12 @@ public void stopDownload(int jobId) {
 
   @ReactMethod
   public void pathForBundle(String bundleNamed, Promise promise) {
-    // TODO: Not sure what equilivent would be?
+    // TODO: Not sure what equivalent would be?
+  }
+
+  @ReactMethod
+  public void pathForGroup(String bundleNamed, Promise promise) {
+    // TODO: Not sure what equivalent would be?
   }
 
   @ReactMethod