My OSX app is sandboxed and I am not able to read data from file by specifying the absolute path

Question

I am completely new to objective C and currently I am trying to advance the functionality of an already existing project. There is a finder extension in the project which on getting clicked performs an action inside (IBAction) Share(id) sender. Inside this action , I want to read a file from a particular location (the file contains the port number) and using that port I want to connect to the server. But what I found was when I click on this extension , nothing happens because it tries to go and read data from the file and is not able to read anything. I tried to debug this by printing out whatever it has read to some other file but all it printed was blank confirming that it is not able to read the data. Below is my code trying to read the port from a temporary location :

- (IBAction)privateShareAction:(id)sender {

  NSFileManager *filemgr;
  filemgr = [NSFileManager defaultManager];

  if ([filemgr fileExistsAtPath: @"/var/folders/y3/jv117_75505fnk8htdrs0qm40000gr/T/com.aprivacy.xmlCorePort.properties" ] == YES)
  {
    //create file handle
    NSFileHandle *file;
    file = [NSFileHandle fileHandleForReadingAtPath:@"/var/folders/y3/jv117_75505fnk8htdrs0qm40000gr/T/com.aprivacy.xmlCorePort.properties"];
    //read data into file in NSData format
    NSData *filedata;
    filedata = [file readDataToEndOfFile];
    NSLog(@"fileDATA = %@", filedata);

    //convert NSData to NSString
    NSString *string;
    string = [[NSString alloc] initWithData:filedata encoding:NSASCIIStringEncoding];

    NSMutableString *directoryPath1 = [NSMutableString stringWithString: @"share1>"];

    [directoryPath1 appendString: string];

    NSData *dataToWrite3 = [directoryPath1 dataUsingEncoding: NSUTF8StringEncoding];

    NSFileHandle* outputFile = [NSFileHandle fileHandleForWritingAtPath:@"/Users/yp/Downloads/a.txt"];

    [outputFile seekToEndOfFile];
    [outputFile writeData:dataToWrite3];

    //convert from string to array
    NSArray *lines = [string componentsSeparatedByString:@"="];
    NSLog(@"arrau = %@", lines);
    //take one of the string and store it in sword
    NSString *sword = [lines objectAtIndex:1];
    NSLog(@"port : %@", sword);
    int port1=[sword intValue];
    Communicator *c = [[Communicator alloc ]init];
    c.host=@"http:127.0.0.1";
    c.port=port1;
    [c setup];
  }

  else
  {
    NSAlert *alert = [[NSAlert alloc] init];
    [alert setMessageText:@"Error"];
    [alert setInformativeText:@"You are not logged in.Kindly login to start performing the operations"];
    [alert setAlertStyle:NSWarningAlertStyle];
    [alert runModal];
  }
}

The above code, on the action performed first tries to check if the file is present at the /var/folders/y3/jv117_75505fnk8htdrs0qm40000gr/T/com.aprivacy.xmlCorePort.properties location or not. This works perfectly fine , If the file is present , it shows a popup alert (which happens). But if the file is present , it goes inside the if condition and tries to read the file where it fails .It always prints a blank string showing that nothing is being read. So then I went and checked the entitlements in App Sandbox. I tried to add an entitlement named com.apple.security.temporary-exception.files.absolute-path.read-only with a string value set to /var/folders/y3/jv117_75505fnk8htdrs0qm40000gr/T/com.aprivacy.xmlCorePort.properties so that it gets the permission to read the file from this location but still it doesn't solve my problem. Could anyone please suggest how to get this file reading permission accessible in my app because the same code works completely fine in a newly created test project.

Following steps : Original client app running -login with user name and password Once logged in -it writes the port in a file At the same time ,once you are logged in with your application , if now you right click on any file in your system you will see certain extra extensions like share ,grant access etc. (This is because a finder project used to add extensions is merged with the original client) Now when I click on say share (on right clicking a file) , I want an action to be performed.The logic for action is written in (IBAction)Share (id) sender method This app used to add extensions is sandboxed because of which the permissions are restricted. So while I clicked on share , my logic was to read that file ,get the port and then connect to server using that port. I want to do everything inside action but I am unable to do so . It is not able to find the file data from /var/folder/y3/jv117_755fdlvfldsvgr/T/com.aprivacy.xmlcorePort.properties

Answer 1

Don't use absolute paths in sandboxed applications.

In OS X there is the NSTemporaryDirectory() function to have access to the temporary directory for this specific application in the container. Entitlements are not needed.

From the documentation

Some path-finding APIs (above the POSIX layer) refer to app-specific locations outside of the user’s home directory. In a sandboxed app, for example, the NSTemporaryDirectory function provides a path to a directory that is outside of the user’s home directory but specific to your app and within your sandbox; you have unrestricted read/write access to it for the current user. The behavior of these path-finding APIs is suitably adjusted for App Sandbox and no code change is needed.

Source: App Sandbox in Depth

Answer 2

Sandboxed apps (all in iOS) are only allowed access to specific directories. Use NSSearchPathForDirectoriesInDomainsto obtain paths to available directories.

Ex:

Objective-C:

NSArray *documentDirectoryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
NSString *filePath = [documentsDirectory stringByAppendingPathComponent:fileName];

NSError *error;
BOOL status = [string writeToFile:filePath atomically:YES encoding:NSUTF8StringEncoding error:&error];
if (status == NSError) {
    NSLog(@"error: %@", error)
}

Swift:

let filePath = "path/file.txt";
let documentDirectoryPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true).first as! String
let path = documentDirectoryPath + filePath

Note: Sandboxed paths is not consistent across clean builds.