plugin: add app.datadir API to get writable path

Adds app.datadir to the bridge to access a writable persistent path
from the nodejs-mobile runtime, which should be the FilesDir on
Android and the NSDocumentDirectory on iOS.
Also sets the os.tmpdir() to the CacheDir on Android.

install/nodejs-mobile-cordova-assets/builtin_modules/cordova-bridge/index.js

@@ -103,10 +103,24 @@ class EventChannel extends ChannelSuper {
  * Emit pause/resume events when the app goes to background/foreground.
  */
 class SystemChannel extends ChannelSuper {
+  constructor(name) {
+    super(name);
+    // datadir should not change during runtime, so we cache it.
+    this._cacheDataDir = null;
+  };
+
   processData(data) {
     // The data is the event.
     this.emitWrapper(data);
   };
+
+  // Get a writable data directory for persistent file storage.
+  datadir() {
+    if (this._cacheDataDir===null) {
+      this._cacheDataDir=NativeBridge.getDataDir();
+    }
+    return this._cacheDataDir;
+  };
 };
 
 /**

src/android/java/com/janeasystems/cdvnodejsmobile/NodeJS.java

@@ -19,6 +19,8 @@
 import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
 import android.content.SharedPreferences;
+import android.system.Os;
+import android.system.ErrnoException;
 
 import java.io.*;
 import java.lang.System;
@@ -66,6 +68,7 @@ public class NodeJS extends CordovaPlugin {
 
   public native Integer startNodeWithArguments(String[] arguments, String nodePath, boolean redirectOutputToLogcat);
   public native void sendMessageToNodeChannel(String channelName, String msg);
+  public native void registerNodeDataDirPath(String dataDir);
   public native String getCurrentABIName();
 
   @Override
@@ -76,7 +79,17 @@ public void pluginInitialize() {
     context = activity.getBaseContext();
     assetManager = activity.getBaseContext().getAssets();
 
+    // Sets the TMPDIR environment to the cacheDir, to be used in Node as os.tmpdir
+    try {
+      Os.setenv("TMPDIR", context.getCacheDir().getAbsolutePath(),true);
+    } catch (ErrnoException e) {
+      e.printStackTrace();
+    }
     filesDir = context.getFilesDir().getAbsolutePath();
+
+    // Register the filesDir as the Node data dir.
+    registerNodeDataDirPath(filesDir);
+
     nodeAppRootAbsolutePath = filesDir + "/" + PROJECT_ROOT;
     nodePath = nodeAppRootAbsolutePath + ":" + filesDir + "/" + BUILTIN_MODULES;
     trashDir = filesDir + "/" + TRASH_DIR;

src/android/jni/native-lib.cpp

@@ -37,6 +37,17 @@ Java_com_janeasystems_cdvnodejsmobile_NodeJS_sendMessageToNodeChannel(
   env->ReleaseStringUTFChars(msg, nativeMessage);
 }
 
+extern "C"
+JNIEXPORT void JNICALL
+Java_com_janeasystems_cdvnodejsmobile_NodeJS_registerNodeDataDirPath(
+    JNIEnv *env,
+    jobject /* this */,
+    jstring dataDir) {
+  const char* nativeDataDir = env->GetStringUTFChars(dataDir, 0);
+  RegisterNodeDataDirPath(nativeDataDir);
+  env->ReleaseStringUTFChars(dataDir, nativeDataDir);
+}
+
 extern "C" int callintoNode(int argc, char *argv[]){
   const int exit_code = node::Start(argc,argv);
   return exit_code;

src/common/cordova-bridge/cordova-bridge.cpp

@@ -96,6 +96,18 @@ void RegisterBridgeCallback(t_bridge_callback callback) {
   cordova_callback = callback;
 }
 
+char* datadir_path = NULL;
+/*
+ * Called by the Cordova plug-in to register the datadir,
+ * representing a writable path. Expected to be called once,
+ * while the plug-in initializes.
+ */
+void RegisterNodeDataDirPath(const char* path) {
+  size_t pathLength = strlen(path);
+  datadir_path = (char*)calloc(sizeof(char), pathLength + 1);
+  strncpy(datadir_path, path, pathLength);
+}
+
 /**
  * Channel class
  */
@@ -309,13 +321,25 @@ napi_value Method_RegisterChannel(napi_env env, napi_callback_info info) {
   return nullptr;
 }
 
+/**
+ * Get the registered datadir
+ */
+napi_value Method_GetDataDir(napi_env env, napi_callback_info info) {
+  NAPI_ASSERT(env, datadir_path!=NULL, "Data directory not set from native side.");
+  napi_value return_datadir;
+  size_t str_len = strlen(datadir_path);
+  NAPI_CALL(env, napi_create_string_utf8(env, datadir_path, str_len, &return_datadir));
+  return return_datadir;
+}
+
 #define DECLARE_NAPI_METHOD(name, func) { name, 0, func, 0, 0, 0, napi_default, 0 }
 
 napi_value Init(napi_env env, napi_value exports) {
   napi_status status;
   napi_property_descriptor properties[] = {
       DECLARE_NAPI_METHOD("sendMessage", Method_SendMessage),
       DECLARE_NAPI_METHOD("registerChannel", Method_RegisterChannel),
+      DECLARE_NAPI_METHOD("getDataDir", Method_GetDataDir),
   };
   NAPI_CALL(env, napi_define_properties(env, exports, sizeof(properties) / sizeof(*properties), properties));
   return exports;

src/common/cordova-bridge/cordova-bridge.h

@@ -10,5 +10,6 @@
 typedef void (*t_bridge_callback)(const char* channelName, const char* message);
 void RegisterBridgeCallback(t_bridge_callback);
 void SendMessageToNodeChannel(const char* channelName, const char* message);
+void RegisterNodeDataDirPath(const char* path);
 
 #endif

src/ios/CDVNodeJS.mm

@@ -62,6 +62,10 @@ - (void) pluginInitialize {
 
   RegisterBridgeCallback(sendMessageToCordova);
 
+  // Register the Documents Directory as the node dataDir.
+  NSString* nodeDataDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
+  RegisterNodeDataDirPath([nodeDataDir UTF8String]);
+
   NSString* nodePath = [[NSProcessInfo processInfo] environment][NODE_PATH];
   NSString* appPath = [[NSBundle mainBundle] bundlePath];
   NSString* builtinModulesPath = [appPath stringByAppendingString:BUILTIN_MODULES];