Test case for Radar 13167947.

write-file-by-merging.m

#import <Foundation/Foundation.h>

/*
 clang -fobjc-arc -O2 -Wall write-file-by-merging.m -o write-file-by-merging -framework Foundation
 
 echo qq > $HOME/Desktop/qq.txt
 open -e $HOME/Desktop/qq.txt
 
 then:
 
 date > /tmp/d; ./write-file-by-merging /tmp/d $HOME/Desktop/qq.txt
 
 TextEdit doesn't show the updated contents.
 
 This is *very* sensitive to timing or filesystem access in the _checkURL() function:
 
   * If either of the #if blocks in _pokeFile() are changed from #if 1 to #if 0, it works.
   * If the sleep(1) is uncommented right before the NSFileManager -replaceItemAtURL:... call (inside the coordinator block), it works.

 This happens on a variety of machines at Omni, but most are Retina MacBook Pro. System profile attached to Radar.
 
*/

BOOL _pokeFile(NSURL *fileURL, NSError **outError)
{
#if 1
    NSError *error = nil;
    NSDictionary *attributes = [[NSFileManager defaultManager] attributesOfItemAtPath:[fileURL path] error:outError];
    if (!attributes) {
        NSLog(@"Error getting attributes of %@: %@", fileURL, error);
        if (outError)
            *outError = error;
        return NO;
    }
#endif
    
#if 1
    NSData *fileData = [[NSData alloc] initWithContentsOfURL:fileURL options:NSDataReadingMappedIfSafe|NSDataReadingUncached error:outError];
    if (!fileData)
        abort();
#endif
    
    return YES;
}

static BOOL _checkURL(NSURL *localDocumentURL, NSFileCoordinator *coordinator, NSFileCoordinatorReadingOptions options)
{
    __block BOOL success;
    __block NSError *error;
    [coordinator coordinateReadingItemAtURL:localDocumentURL options:options error:&error byAccessor:
     ^(NSURL *newReadingURL) {
         // We don't actually check anything in this sample app.
         success = _pokeFile(newReadingURL, &error);
     }];
    
    return success;
}

static BOOL _writeFileByMerging(NSURL *sourceURL, NSURL *destURL, NSError **outError)
{
    // We treat 'sourceURL' as if it doesn't need file coordination (it is our private copy).
        
    NSFileCoordinator *coordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];
    __block NSError *error;
    __block BOOL success = NO;
    
    [coordinator prepareForReadingItemsAtURLs:nil options:0
                           writingItemsAtURLs:@[destURL] options:0/*don't know what we are going to do yet*/
                                        error:&error byAccessor:
     ^(void (^completionHandler)(void)){
         // Make cleanup easier...
         if (!completionHandler)
             completionHandler = ^{};
         
         // Do a read of the source to see if it has changed, w/o claiming we'll do any write above.
         __block BOOL validateSuccess = NO;
         [coordinator coordinateReadingItemAtURL:destURL options:0 error:&error byAccessor:^(NSURL *newURL) {
             validateSuccess = _checkURL(destURL, coordinator, 0);
         }];
         if (!validateSuccess) {
             NSLog(@"destination changed");
             completionHandler();
             return;
         }
         
         [coordinator coordinateWritingItemAtURL:destURL options:NSFileCoordinatorWritingForMerging error:&error byAccessor:^(NSURL *newURL) {
             //sleep(1);
             
             if (![[NSFileManager defaultManager] replaceItemAtURL:newURL withItemAtURL:sourceURL backupItemName:nil options:0 resultingItemURL:NULL error:&error])
                 return;
             success = YES;
         }];
         completionHandler();
         success = YES;
         
     }];
    
    if (!success && outError)
        *outError = error;
    return success;
}

int main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr, "usage: %s src dest\n", argv[0]);
        exit(1);
    }
    
    @autoreleasepool {
        NSURL *sourceURL = [NSURL fileURLWithPath:[NSString stringWithUTF8String:argv[1]]];
        NSURL *destURL = [NSURL fileURLWithPath:[NSString stringWithUTF8String:argv[2]]];
        
        NSError *error;
        if (!_writeFileByMerging(sourceURL, destURL, &error))
            NSLog(@"Error: %@", error);
    }
    
    return 0;
}