Files Copied to Clipboard are empty and "Missing Sandbox Extension" When Pasted - objective-c

Question

I have an application that is copying files to the clipboard. Here is the relevant code (arguments is an array of NSStrings containing file paths):
NSMutableArray *filesToCopy = [[NSMutableArray alloc] init];
int i;
for (i=1; i < [arguments count]; i++) {
NSString* pathToFile = [arguments objectAtIndex:i];
NSURL* fileURL = [[NSURL alloc] initFileURLWithPath:pathToFile];
[filesToCopy addObject:fileURL];
}
NSPasteboard *pasteboard = [NSPasteboard generalPasteboard];
NSInteger changeCount = [pasteboard clearContents];
BOOL OK = [pasteboard writeObjects:filesToCopy];
However, in testing when trying to paste a file copied to the clipboard by the program into an empty email in Mail, often the file shows up as zero bytes and the following error appears on the console:
11/13/13 6:27:12.173 AM Mail[627]: Failed to obtain a valid sandbox extension for item: [789514] of flavor: [public.file-url] from the pasteboard.
11/13/13 6:27:12.174 AM Mail[627]: Failed to get a sandbox extensions for itemIdentifier (789514). The data for the sandbox extension was NULL
and then that is followed by the following error on the console:
11/13/13 8:24:41.947 AM sandboxd[172]: ([627]) Mail(627) deny file-read-xattr [full path of file]
What is strange is that if I copy the file from Finder then it pastes just fine with no errors every time. In other words, somehow Finder copies the file to the clipboard with different information than the way I am doing it. To verify this, I did a simple AppleScript to return clipboard info. After I copy a file to the clipboard that returns the following:
{{«class furl», 115}, {«class utf8», 115}, {«class ut16», 232}, {string, 115}, {Unicode text, 230}}
After I copy the same file to the clipboard using Finder, the Applescript returns the following:
{{«class furl», 33}, {«class icns», 795020}, {«class ut16», 112}, {«class utf8», 55}, {«class 8BPS», 1630436}, {«class BMP », 4194358}, {«class TPIC», 1059291}, {TIFF picture, 4197954}, {«class PNGf», 392648}, {«class jp2 », 213480}, {GIF picture, 121307}, {JPEG picture, 116181}, {Unicode text, 110}, {string, 55}}
So Finder is putting more information about the file on the clipboard and different information. For example, the furl class has a different length. This extra information is obviously what is cause Mail to successfully past a file copied from Finder while it has an error pasting a file copied by my program.
Any clues to what information I'm missing when I put the file on the clipboard or what extra information I should be adding to the paste? I'm guessing that Finder is pasting not just an array of NSURL's, but an array of Dictionary Keys that includes other file information. It also seems to be creating the furl class differently than I am. I've spent time pouring over documentation and I'm stuck on this one.

Answer 1

I believe I found the problem. It seems like when command line applications copy to the pasteboard, there is a permission related to sandboxing that is not transferred. The files copied could be pasted fine into any non-sandboxed app, but not into a sandboxed application. The solution in this case was to just create a regular Cocoa based .app program. I'm still not sure how, but it copies the files in a way that the permissions are properly transferred and the file can be pasted in both non-sandboxed and sandboxed applications.

Answer 2

There is is lot written out there about avoiding triggering the Sandboxing mechanism in Sandboxed Apps.
But all answers lack the most obvious trouble that can trigger Sandboxing.
When you make a copy of a NSURL (which is still based on NSString) into NSPasteboard without properly escaped characters still containing non-valid signs and spaces before transforming into 'NSURL'.
This is one of the ways URLs can become malicious, so it is only a little bit annoying that the Error Message you get while trying to expose the link to pasteboard is not telling you what the obvious reason was in detail. But maybe this is also because, "never give too much informations how to circumvent the safety barriers".
It just says:
[sandbox] CreateSandboxExtensionData failed: urlData: 0x0000000000XYZ length: 0 (-1 means null)
then you have to properly escape the string with
NSString *encodedStringForURL = [yourString stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
this will exchange special characters that should not be part of n URL.
After that you can transform to NSURL as usually.
or
Failed to obtain a valid sandbox extension
then you also used a wrong NSPasteboardType that exposes a URL without proper type. In example when you exposed a String that poses as Link because you tried to avoid the [sandbox] trigger by being clever and telling the pasteboard this is only a random string. The Sandbox is still more clever when you prepend the string with file://.
Then the solution is to use NSPasteboardTypeFileURL and/or NSPasteboardTypeURL. This will inform the sandbox that you exposed links on purpose with proper type.
There are more pitfalls, but also remember you have to use YourURL.absoluteString when you paste to Pasteboard.