On Oct 22, 2012, at 4:47 PM, was <skylog...@btconnect.com> wrote:
> As I'm not familiar with unix permissions, is there a way of changing the
> permissions for the App.AppName folder?
Yes: with the chmod(2) system call [0, 1]. (Insert rant about how C# actually
allows you to do things like this, while it's not easy in Java w/o using JNI).
> I looked at using permission: MODE_WORLD_READABLE and MODE_WORLD_WRITEABLE,
> but these aren't available in the MfA 4.2.6 Required Permissions list.
1. They're not permissions, they're integer constants for use with e.g.
Context.OpenFileOutput().
2. MODE_WORLD_READABLE is mapped to the
Android.Content.FileCreationMode.WorldReadable enum value [2].
> I'm also not sure they would fix the problem anyway.
Using FileCerationMode.WorldReadable would workaround the problem:
Context.OpenFileOutput() allows you to specify the FileCreationMode, which sets
the Unix mode for that specific file (at creation time, iirc):
using (var o = new StreamWriter(OpenFileOutput("foo.txt",
FileCreationMode.WorldReadable)))
o.WriteLine ("Hello, world!");
The file created in that fashion will be in a directory that by default can't
be listed:
$ adb shell ls -l /data/data/Scratch.PublicFiles/files
opendir failed, Permission denied
However, if you know the name of the file you can read it:
$ adb shell cat /data/data/Scratch.PublicFiles/files/foo.txt
Hello, world!
This may in fact be suitable for your purposes, and has an added "security"
benefit (obfuscation) that the names of the files aren't determined easily.
There is another interesting Context method that takes a FileCreationMode:
Context.GetDir(string, FileCreationMode) [3]. This will create a new directory,
but what's interesting is two things:
1. The directory it creates isn't a child of Context.FilesDir:
var d = GetDir ("foo", FileCreationMode.WorldReadable |
FileCreationMode.WorldWriteable);
Console.WriteLine ("Created: {0}", d.AbsolutePath);
// Created: /data/data/Scratch.PublicFiles/app_foo
Notice that the directory name gets an "app_" prefix.
2. The only way (that I've found) to create a file with a specific set of
permissions is Context.OpenFileOutput(), and Context.OpenFileOutput() doesn't
allow you to specify sub-directories. Consequently the only way to use the
above "app_foo" directory is via normal System.IO methods, which creates files
with the default process umask, which is no good here:
// C# code
var bar = Path.Combine (d.AbsolutePath, "bar.txt");
using (var o = File.AppendText (bar))
o.WriteLine ("managed foo/bar.txt contents");
# verification...
$ adb shell ls -l /data/data/Scratch.PublicFiles/app_foo
-rw------- u0_a62 u0_a62 58 2012-10-23 21:50 bar.txt
We can't do anything with that file; the "other" permissions are "---", aka
"nothing".
This makes Context.GetDir() + create-file rather worthless unless you
subsequently change the file's permissions:
int p666 = LinuxUtils.Syscall.S_IRUSR |
LinuxUtils.Syscall.S_IWUSR | \
LinuxUtils.Syscall.S_IRGRP | LinuxUtils.Syscall.S_IWGRP
| \
LinuxUtils.Syscall.S_IROTH | LinuxUtils.Syscall.S_IWOTH;
LinuxUtils.Syscall.chmod (bar, p666);
Given that the above is (1) ugly, and (2) requires a bit of support code ([0]),
the easiest path is to accept the inability to use `ls`, use
Context.OpenFileOutput(), and just "know" which files you can read or write.
- Jon
[0]
namespace LinuxUtils {
using System.Runtime.InteropServices;
static class Syscall {
public const int S_IRWXU = 0x1C0; // 00700
public const int S_IRUSR = 0x100; // 00400
public const int S_IWUSR = 0x080; // 00200
public const int S_IXUSR = 0x040; // 00100
public const int S_IRWXG = 0x038; // 00070
public const int S_IRGRP = 0x020; // 00040
public const int S_IWGRP = 0x010; // 00020
public const int S_IXGRP = 0x008; // 00010
public const int S_IRWXO = 0x007; // 00007
public const int S_IROTH = 0x004; // 00004
public const int S_IWOTH = 0x002; // 00002
public const int S_IXOTH = 0x001; // 00001
[DllImport ("c")]
public static extern int chmod (string path, int mode);
}
}
[1] This will change the permissions of /data/data/@PACKAGE_NAME@/files so that
it's world readable and world writable, using [0]:
LinuxUtils.Syscall.chmod (FilesDir.AbsolutePath,
LinuxUtils.Syscall.S_IRWXU | LinuxUtils.Syscall.S_IRWXG |
LinuxUtils.Syscall.S_IRWXO);
[2] http://androidapi.xamarin.com/?link=T:Android.Content.FileCreationMode
[3]
http://androidapi.xamarin.com/monodoc.ashx?link=M%3aAndroid.Content.Context.GetDir(System.String%2cAndroid.Content.FileCreationMode)
_______________________________________________
Monodroid mailing list
Monodroid@lists.ximian.com
UNSUBSCRIBE INFORMATION:
http://lists.ximian.com/mailman/listinfo/monodroid
