Fix crash under iOS 5.0.x due to attempt to use unavailable NSURLIsExcludedFromBackupKey symbol. fixes #1015

Code/CoreData/RKManagedObjectStore.m

@@ -147,18 +147,8 @@ static RKManagedObjectStore *defaultStore = nil;
     persistentStore = [self.persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nilOrConfigurationName URL:storeURL options:seedOptions error:error];
     if (! persistentStore) return nil;
     
-    /**
-     Exclude the SQLite database from iCloud Backups to conform to the iCloud Data Storage Guidelines
-     
-     See https://developer.apple.com/icloud/documentation/data-storage/
-     */
-    #if __IPHONE_OS_VERSION_MIN_REQUIRED
-    BOOL success = [storeURL setResourceValue:@(YES) forKey:NSURLIsExcludedFromBackupKey error:error];
-    if (!success) {
-        RKLogError(@"Failed to exclude SQLite store at path '%@' from iCloud Backup: %@", storePath, *error);
-        return nil;
-    }
-    #endif
+    // Exclude the SQLite database from iCloud Backups to conform to the iCloud Data Storage Guidelines
+    RKSetExcludeFromBackupAttributeForItemAtPath(storePath);
     
     return persistentStore;
 }

Code/Support/RKPathUtilities.h

@@ -55,3 +55,15 @@ NSString *RKPathFromPatternWithObject(NSString *pathPattern, id object);
  @return The expected MIME Type of the resource identified by the path or nil if unknown.
  */
 NSString *RKMIMETypeFromPathExtension(NSString *path);
+
+/**
+ Excludes the item at a given path from backup via iTunes and/or iCloud using the approaches detailed in "Apple Technical Q&A QA1719".
+ 
+ Excluding a path from backup can be necessary in order to conform to the iCloud Data Storage Guidelines. Please refer to the following links for more details:
+ 
+ 1. [iCloud Data Storage Guidelines](https://developer.apple.com/icloud/documentation/data-storage/)
+ 1. [Technical Q&A QA1719](http://developer.apple.com/library/ios/#qa/qa1719/_index.html)
+ 
+ @param path The path to the item that is to be excluded from backup.
+ */
+void RKSetExcludeFromBackupAttributeForItemAtPath(NSString *path);

Code/Support/RKPathUtilities.m

@@ -8,9 +8,12 @@
 
 #if TARGET_OS_IPHONE
 #import <MobileCoreServices/UTType.h>
+#import <UIKit/UIDevice.h>
 #else
 #import <CoreServices/CoreServices.h>
 #endif
+#import <Availability.h>
+#import <sys/xattr.h>
 #import "RKPathUtilities.h"
 #import "RKLog.h"
 #import "RKPathMatcher.h"
@@ -119,3 +122,40 @@ NSString *RKMIMETypeFromPathExtension(NSString *path)
     // Consult our internal dictionary of mappings if not found
     return [RKDictionaryOfFileExtensionsToMIMETypes() valueForKey:pathExtension];
 }
+
+void RKSetExcludeFromBackupAttributeForItemAtPath(NSString *path)
+{
+    NSCParameterAssert(path);
+    NSCAssert([[NSFileManager defaultManager] fileExistsAtPath:path], @"Cannot set Exclude from Backup attribute for non-existant item at path: '%@'", path);
+
+#if __IPHONE_OS_VERSION_MIN_REQUIRED
+    NSError *error = nil;
+    NSURL *URL = [NSURL fileURLWithPath:path];
+    
+    NSComparisonResult order = [[UIDevice currentDevice].systemVersion compare:@"5.1" options:NSNumericSearch];
+    if (order == NSOrderedSame || order == NSOrderedDescending) {
+        // On iOS >= 5.1, we can use the resource value API's. Note that we probe the iOS version number directly because the `setResourceValue:forKey:` symbol is defined in iOS 4.0 and greater, but performs no operation when invoked until iOS 5.1
+        BOOL success = [URL setResourceValue:@(YES) forKey:NSURLIsExcludedFromBackupKey error:&error];
+        if (!success) {
+            RKLogError(@"Failed to exclude item at path '%@' from Backup: %@", path, error);
+        }
+    } else {
+        order = [[UIDevice currentDevice].systemVersion compare:@"5.0.1" options: NSNumericSearch];
+        if (order == NSOrderedSame || order == NSOrderedDescending) {
+            // On iOS 5.0.1 we must use the extended attribute API's directly
+            const char* filePath = [[URL path] fileSystemRepresentation];
+            const char* attrName = "com.apple.MobileBackup";
+            u_int8_t attrValue = 1;
+            
+            int result = setxattr(filePath, attrName, &attrValue, sizeof(attrValue), 0, 0);
+            if (result != 0) {
+                RKLogError(@"Failed to exclude item at path '%@' from Backup. setxattr returned result code %d", path, result);
+            }
+        } else {
+            RKLogWarning(@"Unable to exclude item from backup: resource value and extended attribute APIs are only available on iOS 5.0.1 and up");
+        }
+    }
+#else
+    RKLogDebug(@"Not built for iOS -- excluding path from Backup is not possible.");
+#endif
+}